Distribution Transformer Main Handbook

Distribution Transformer HANDBOOK

Copyright © 2009 International Copper Association Southeast Asia Ltd

All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or

retrieval system, without the prior written permission of the publisher.

Foreword|

t is hard to expect that energy prices will not continue to increase in the next few decades. Climate change mitigation

will play an increasingly important role in the development of power sector favouring renewable energy systems, energy conservation and energy efficiency. Thus more and more attention should be paid to energy losses. According to our studies (“Global energy savings potential from high efficiency distribution transformers”, ECI 2004) technical energy losses in all of the world’s electrical distribution networks are at the level of one thousand TWh. About 30% of these losses occur in distribution transformers which are one of the two largest loss making components in electricity networks. Although typical distribution transformers seem very efficient, the reduction of losses in transformers may have almost no limits. However there is a certain technological and economical optimum at which existing losses in distribution transformers may be roughly halved reaching life cycle cost minimum at the same time. Replacing distribution transformers is relatively easy compared to lines or cables and in the event, of highly inefficient units it is worthwhile to do it even before they reach their technical lifetime. In the purchase decision process relating to newer equipment, it is imperative to include the cost of losses in the investment calculation. As already stated, distribution transformers can bring economic benefits to users but also environmental benefits for the society. The economic benefits will not always remain in the investors’ hands as energy regulators may try to interfere in the balance of capital and operating cost of distribution companies in order to protect customers against rapid price increases. The customers will pay the cost of losses for the entire transformer life, but will not see any rapid change in their electricity bill.

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A good practice, in the purchase decision criteria, is to perform a lifetime cost analysis based on the capitalization formula. The relative data for this formula is: energy prices projections, interest rates, transformer lifetime, transformer loading and anticipated change in future loading. The other side of the equation presents the transformer price and its dependence on the level of rated losses. The analysis is not extremely difficult but may be sensitive to a number of parameters, the most relevant of which may be interest rates, and lifetime but also changes in commodity prices. Planning on a broad scale is a key component to optimization. Large distribution companies quite often use procurement efficiency standards to specify transformers. Such practices help manufacturers so that they have prior knowledge of requirements and thus they know what they can expect from buyers. In this case, a well prepared procurement procedure may prove useful and will help to avoid misunderstandings between a buyer and a seller and should lead to optimum purchasing decision with losses kept sufficiently in focus. We think the rationale of this Handbook was to facilitate such a process.

Hans de Keulenaer Roman Targosz Electrical Programme Manager Project Manager European Copper Institute European Copper Institute

Introduction| The Lower Mekong Subregion (LMS) Harmonisation Programme

ambodia, Lao People’s Democratic Republic (Lao PDR), Thailand and Vietnam have achieved different levels of

economic development. These countries in the Lower Mekong Subregion (LMS) have strong economic inter-dependence. Being developing countries, their power distribution systems, an essential infrastructure, play a significant role in the economic development. Energy end-users are dependent on the availability, reliability, and quality of electricity from the power distribution systems. The level of development and advancement of power distribution systems has direct impact on the developmental potential and economic growth, especially in urban cities. The power distribution systems in the urban areas of these LMS countries, however, do not have the same level of development. It is widely acknowledged that harmonisation in the development of power distribution systems can benefit these countries and accelerate their economic growth. In 2005, six power partners entered into a Memorandum of Understanding (MOU) to share the intent of working together towards harmonisation of power distribution systems in the following four LMS countries: Cambodia, Lao PDR, Thailand and Vietnam. The founding partners are: • Electricité du Cambodge (EDC), Cambodia • Electricité du Laos (EDL), Lao PDR • Ho Chi Minh City Power Company (HCMC PC), Vietnam • Hanoi Power Company (HNPC), Vietnam • Metropolitan Electricity Authority (MEA), Thailand • International Copper Association Southeast Asia (ICASEA) [formerly known

as Copper Development Centre • Southeast Asia]

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This led to a study of power distribution systems of the power partners in Cambodia, Lao PDR and Vietnam; and the preparation of a regional cooperation roadmap and action plan. Building on the success of the first MOU, ICASEA and MEA inked a second MOU to continue their strategic partnership in conducting further studies and facilitating programmes as outlined in phase 2 of the road map and action plan. This impetus is to enable the LMS countries to make further progress towards harmonisation and the realisation of the objectives as set out in the MOU with all the power partners. The study of power distribution systems in the LMS countries under the first MOU had revealed that there are many differences in the power distribution systems in this region. The objective of this second MOU was to narrow down the differences in six key areas and enable the LMS countries to move towards greater harmonization of their power distribution systems.

Preface| Loss in the Power Distribution System is a common and pressing concern expressed by Utilities in the LMS. Reducing loss is the priority given the energy shortage arising from rapid economic growth and high oil prices. A Regional Loss Reduction Workshop for LMS Utilities was held in Phnom Penh, Cambodia on 18 & 19 March 2008. It concluded with a consensus to, amongst other areas of collaboration, reduce losses in the Power Distribution Systems of EDC, EDL, HCMC PC and HNPC by harmonising technical specifications and developing a best practices handbook for energy efficient equipment based on international standards. The views of and input from participating Utilities were crucial in the development of technical specifications for the harmonisation of power equipment in the LMS. Only with acceptance and implementation of the technical specifications can LMS Utilities reduce losses associated with inefficient power equipment. Hence, a 6-member Technical Working Group (TWG) comprising a senior technical representative from each Utility and ICASEA was formed to participate and contribute in discussions and meetings. The objective of the TWG was to start with the development of technical specifications to harmonise low loss power transformers in the LMS. This step-by-step approach was to enable the participating Utilities to review and evaluate the result of this Technical Working Group before collectively moving to the next step of harmonising other equipment. This handbook was developed to help LMS Utilities implement low loss transformers. Reduction will only come when the minimum performance guidelines are followed and implemented by all associated with the design of the electricity grid, specifying the standards of equipment for procurement and subsequently operating or maintaining them. Members of the Technical Working Group: Chairman

Mr.Surapon Soponkanaporn Director of Research and Development Department, MEA

Electricite Du Cambodge (EDC), Cambodia

Mr. Lim Sisophuon Deputy Chief, Dispatching Control Centre

Electricite Du Laos (EDL), Lao People’s Democratic Republic Mr. Xanaphone Phonekeo Deputy Manager, Technical Standards Office

Ho Chi Minh City Power Company (HCMC PC), Vietnam

Mr. Nguyen Duy Hoang Electrical Engineer, Technical Department

Hanoi Power Company (HNPC), Vietnam

Mr. Vu Quang Hung / Mr Trinh Xuan Nguyen Vice Director, Technical / Manager, Technical Department

Metropolitan Electricity Authority (MEA), Thailand

Mr. Werawat Buathong Deputy Director, Power System Planning Division Mr. Somchai Homklinkaew Senior Electrical Engineer Mr. Sompong Sittichaiyanan Electrical Engineer

International Copper Association Southeast Asia (ICASEA)

Mr. Louis Koh Project Leader, Power Distribution Mr. Piyadith Lamaisathien Country Manager, Thailand

MEA Project Support Team

Ms. Sutida Sindhvananda, Director of Int’l Services, Business Div. Ms. Sasianong Vacharasikorn, Electrical Engineer Ms. Suthiluck Wannadit, Executive Secretary

Acknowledgements|

he harmonisation of power distribution systems in the LMS will contribute to the expansion of the ASEAN

Power Grid. However, harmonisation requires a robust partnership and sustained effort over many years. The harmonisation of technical specifications together with the development of this handbook is taking the process a step closer towards the realisation of the objectives as set out in the strategic roadmap for the harmonisation of power distribution systems in the LMS. Strengthening regional cooperation to build the capacity of both technical and functional staff would not have been possible without the endorsement and support of: Electricité du Cambodge, Cambodia

Mr. Keo Rottanak, Managing Director Mr. Chan Sodavath, Deputy Managing Director

Electricité du Laos, Lao People’s Democratic Republic Mr. Khammany Inthirath, Managing Director Mr. Sisavath Thiravong, Deputy Managing Director Mr. Boun Oum Syvanpheng, Deputy Managing Director

Ho Chi Minh City Power Company, Vietnam

Mr. Le Van Phuoc, Director Mr. Tran Khiem Tuan, Deputy Director

Hanoi Power Company, Vietnam Mr. Tran Duc Hung, Director Mr. Vu Quang Hung, Vice Director, Technical Mr. Nguyen Anh Tuan, Vice Director, Business

Metropolitan Electricity Authority, Thailand

Mr. Pornthape Thunyapongchai, Governor Mr. Surapon Soponkanaporn, Director, Research & Development Department

International Copper Association Southeast Asia

Mr. Steven Sim, Chief Executive Officer

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Contents| Chapter 1 Preparation of National Normative Technical Specification of Distribution Transformer 1. Introduction 2. Objective 3. Principle specification 4. Electricité du Cambodge - Additional Specification 5. Electricité du Laos - Additional Specifications 6. Ho Chi Minh City Power Company - Additional Specification 7. Hanoi Power Company - Additional Specification 8. References Chapter 2 Bidding Evaluation 1. Introduction 2. Objective 3. Formula Analysis 4. How to Evaluate The Best Choice 5. Excess Losses and Penalty 6. The Low Loss Limitation Table 7. Conclusion 8. Appendices Chapter 3 Transformer Production Inspection 1. Introduction 2. Objective 3. Inspection committee management 4. Inspection Process 5. Conclusion Chapter 4 Contract Acceptance 1. Introduction 2. Objective 3. Acceptance Committee Management 4. Acceptance Process 5. Conclusion Chapter 5 Installation and Operation 1. Introduction 2. Objective 3. Construction Standard 4. Loading Guide

5. Conclusion Chapter 6 Maintenance and Asset Management 1. Introduction 2. Transformer Load Monitoring (TLM) 3. Maintenance and Inspection 4. Conclusion Figures Figure 1: Expenses generated by transformer price and cost of electricity losses Figure 2: Calculation of the present value of no-load loss Figure 3: Calculation of the present value of no-load loss in actual costs Figure 4: Calculation of the present value of load loss Figure 5: Calculation of the present value of load loss in actual costs Figure 6: Evaluation formula analysis Figure 7: Production Process Flow Figure 8: Silicon Steel Core Loss Curve Figure 9: Test circuit & Apparatus Configuration for No-load Loss Measurement Figure 10: Test Circuit & Apparatus Configuration for Load Loss Measurement Figure 11: Punch List Form Figure 12: List of approval drawings Figure 13: Sample Drawing of Technical and Guaranteed Data Figure 14: Supplier’s routine test report Figure 15: Acceptance routine test report Figure 16: Penalty Calculation without raising the Guarantee Value Figure 17: Penalty Calculation with Raising the Guarantee Values Figure 18: Construction drawing for transformer installation (single concrete pole) Figure 19: Bill of material for transformer installation (single concrete pole) Figure 20: Construction drawing for transformer installation (platform) Figure 21: Bill of material for transformer installation (platform) Figure 22: Transformer load monitoring (TLM) system configuration Tables Table 1: The low loss limitation of no-load & load loss for each transformer rating Table 2: Table of power efficiency for low losses transformer Table 3: Example of standard loss transformers Table 4: Temperature condition of transformer Table 5: Minimum permissible insulation resistance measurement

Chapter 1

Preparation of National Normative Technical Specification of Distribution Transformer 1. Introduction This is the first normative specification for distribution transformers. It is prepared for the Lower Mekong Sub-region (LMS) utilities which are: Electricité du Cambodge (EDC) Cambodia, Electricité du Laos (EDL), Lao People’s Democratic Republic, Hanoi Power Company (HNPC), Ho Chi Minh City Power Company (HCMCPC) Vietnam, and the Metropolitan Electricity Authority (MEA), Thailand. The specifications refer to the latest edition of international and national standards. Single-phase, three-phase and oil-immersed transformers are covered in the discussion. The scope also includes transformers with maximum voltages of 36 kV, off-circuit tap changing, frequency of 50 Hz and those of neutral solidly grounded at the distribution substation and as well as outdoor application.

2. Objective The Primary goal is to help to reduce losses caused by the ineffective use of transformers, and minimize the need for new investment, through teaching the utilities' about loss reduction programs and minimizing negative environmental impact on our tomorrow. The secondary goals are to: encourage greater energy efficiency in low loss energy consuming transformers, create new national standards, start cost effective savings programs in both utilities and customers, reduce losses from utility-owned transformers and minimize life cycle costs. In addition, this will provide not only more energy, but also decrease the investment cost of constructing new distribution substations, while meeting the customers demand.

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3. Principle Specification

Scope: This specification is created for power utility companies in LMS. Transformers shall be connected to the system with neutral solidly grounded at the distribution substations and fault level values in normal distribution status between 20kA and 25kA.

Site and Service Condition: LMS utilities operate in a tropical climate. The altitude ranges from 0 meters to 1,800 meters above sea level, ambient temperature ranges from 30°C to 45°C and relative humidity measures mostly 100%. Reference Standard: International Electrotechnical Commission (IEC) is the common reference standard for all LMS utilities and a majority of countries around the world. For transformers, IEC 60076 series is the key reference. Some utilities also refer to their National standards which correspond to IEC except special requirements such as temperature, installation, etc. Test, Inspection and Test Report: There will be two main test reports, specifically Type Test and Routine Test reports. Because the transformer is a very critical and expensive piece of equipment, the type test report is a key source of information for purchase assessment and decision. Type Test contains data that validate factors such as design, raw material, workmanship and quality control during the manufacturing process are well within standard limits. The Routine Test certifies that all units pass limited values according to the reference standards before installation for service. The Utility reserves the right to send representatives to invigilate all required tests on the manufacturer’s site. Thus, sampling of the first batch of the transformers lies in the responsibility of the Utility’s representatives. Drawings and Instructions: The supplier shall furnish six copies of all significant details of the transformer to the Utility for response in approval within a stipulated timeframe. To protect mutual interest in cases of delayed or late submission, compensation terms shall be specified in the contract. Special installation instructions, characteristic curves, installation instructions and instruction manuals with the contract number marked thereon, in the metric system, shall be machine printed or typed and delivered prior to the first shipment. Ratings and Features: The major characteristic of the transformer must be properly specified, such as suggested in the following:

Type Overhead, outdoor type, three phase, mineral-oil-filled

Frequency 50 Hz

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Cooling method ONAN

kVA ratings To be specified during bid

Temperature rise (winding, Top oil) 60 degree (winding), 55 degree (oil)

High-voltage rating 6 kV, 10 kV, 22 kV or 35 kV

Low-voltage rating 400 V

Tap ±2 x 2.5 % or +4x2.5%

Vector group Dyn11 or Dyn1

Insulation level

Voltage Rating 400V, 6kV, 10kV 15kV 22kV 35kV

BIL Full Wave (kV crest) N/A 50 70 125 170

Power Frequency Test Voltage (kV) N/A 28 38 50 70

Impedance voltage

kVA Range from 50 to 3200

Nominal value Range from 4% to 7%

General Requirements The transformer shall be self-cooled and/or designed with sealed-tank to ensure that forced cooling is not required. The transformer installation methods such as single concrete pole or platform concrete pole shall also be included. To protect the transformer from damage caused by lightning, it will be the most efficient and practical to install three lightning arresters on the transformer tank cover. The lightning arrester shall be of the distribution class with a ground lead disconnector, gapless or gapped with metal oxide as main elements. The gaskets shall be specified to withstand hot oil of extremely high temperatures and have a life span of more than 20 years. One of the plans included to reduce system losses, is to up-rate the distribution voltage; the dual voltage switch type shall be required such as 12/24 kV,

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The kVA rating value should be visibly specified and easy to locate for field workers. The information regarding the centre of gravity (CG) of the transformer is essential for the installation and to improve safety for the field workers. The concrete poles need to be designed to withstand the bending moment which is calculated by accounting for the weight of the transformer, associated equipment, cables, and wind speed. Hence, all transformers are recommended to have weight limits. Transformers installed in close proximity to public facilities such as hospitals, schools, etc shall also be designed to keep noise level within 58 to 68 decibels. Transformers installed near hospitals, schools and important places should also be designed to generate audible noise within the limit of 58 to 68 decibels. Tank and Cover The material for fabricating the tank side walls and bottom shall be corrosion resistant. Rust-preventive finishing shall be strongly recommended for units with more than 20 years of service life. The paint coat shall depend on utilities’ requirement in preferred colours. Core It is necessary to mention the quality of the core material, such as high permeability silicon steel, because no-load loss is mainly caused by the core material. The core construction shall be firmly fixed in the tank and designed to avoid the occurrence of loosened core strips due to vibration from road traffic. Adequate cooling facilities shall also be provided at the oil ducts. The magnetic circuit shall be grounded in accordance with practices mentioned in the specification. The different maximum flux density is designed to meet 1.55 to 1.65 Tesla to prevent harmonic behaviour. Windings The winding or coil shall be made of copper for better performance based on technical and economic comparisons. To cater to the physical characteristic, the winding shall be designed to withstand thermal and mechanical effects caused by external short circuits. The coil clamping arrangement and clamping rings shall be designed to withstand force due to short circuit. To cater to the electrical characteristic, the winding shall be designed and assembled to handle temperature increase specified in the tender specification. The insulation of winding and connections shall not be likely to soften, loose, shrink or collapse during service. Insulating Oil As mineral oil is used as the insulation and cooling mechanism; it should be well filtered and tested to meet the dielectric strength (which is not less than 30kV) before filling in the transformer tank. The insulating oil dielectric taken from a new transformer shall not be less than 26 kV as tested by the method specified by ASTM D877.

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Bushings and Terminals The requirements for bushings and terminals should be specified for different applications such as platform transformer or pole mounted transformer to facilitate installation, monitoring and maintenance. To maintain the current integrity throughout the equipment’s useful lifecycle, the connectors shall be made with solderless tin-plated copper; two belleville spring washer, coned-disk types shall be supplied to provide adequate pressure on the conductor during thermal-cycling. The size of the terminals or connectors, both high voltage and low voltage, shall be subjected to the transformer capacity. The bushing cover shall be made of ultra-violet radiation resistant and track resistant plastic or rubber to protect equipment from impairments caused by animals such as birds, squirrels and snakes, etc. Accessory Equipment The transformers will be equipped with standard accessories, at least with lifting lugs, tap changer, manual pressure relief fitting, nameplate, tank grounding pad or stud, etc. Other accessories will be also specified depending on the size and application.

3.1. Transformer Evaluated Cost

Typically, the transformer price depends on core and winding loss i.e. high loss transformers have a lower cost, and the low loss transformer a higher one. Thus, Utilities work out an “evaluation formula” which takes into consideration many factors such as: transformer service life, load factor, operation and maintenance cost, interest rate and inflation rate, etc. Each utility should compute the cost estimate based on updated data. This shall eventually be used in the bid comparison for the evaluation of unit costs and losses. The following is an example of cost evaluation.

A = B + XC + YD

Where A = Evaluated cost of transformer in any currency B = Unit cost of transformer converted into US Dollars according to the

evaluation clause specified in the bid condition C = No-load loss at room temperature not more than 30°C in kW D = Load loss in kW X = Constant value for No-load condition Y = Constant value for Loading condition

Excess Losses and Penalty The excess loss and penalty will concentrate on transformer losses which are higher than guaranteed no-load and load losses including allowable tolerances stated in the reference standards. It will be divided into the following two cases:

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a. The individual transformer loss is higher than tolerance: Individual transformer with losses beyond the limits will be rejected unless the supplier agrees to increase the guaranteed value of average losses of all transformers, compensated at 1.5 times (arbitrary value) of the evaluation formula.

b. The total number of transformers: In the event that the supplier’s report shows

that the no-load and load loss values conform to the guaranteed values within the tolerance limit, the utility shall conduct sampling on the transformers for their individual loss measurement (i.e. the number of transformers depends on utilities’ facility, but normally 5% of the contracted quantity or at least one unit for small quantity order).

If the average values of no-load loss and load losses are higher than average losses from the manufacturer test report by 2.5% (arbitrary value), the manufacturer measured value will be adjusted by the ratio of difference between both sets of measurements, and use the adjusted losses for the calculation of loss compensation. Otherwise the losses from the manufacturer’s report will be used.

Additional Requirements for Marking and Packing Consideration shall be given to facilitate convenient clearing from the port customs. The transformers shall be shipped oil-ed with the serial number properly indicated in the invoice. All spare parts shall be delivered with the first shipment to ensure that spares are available in the event of need. . Equipment or instruments packed in the cartons shall be firmly attached on pallets for easy handling. Additional Requirements for Responsibility In the event of breakdown within the period of warranty, the manufacturer shall promptly investigate, repair or replace the unit. All replacement shall be made with 60 days from the first notice, or risk forfeiting equipment performance and security.

4. Electricité du Cambodge - Additional Specification

This section discusses about the additional specifications specially collated for Electricité du Cambodge of Cambodia (EDC). 4.1. For Reliable Performance of the Transformer

EDC should consider adding technical information as follows: a. Short circuit test reports that prove that the design, raw materials and

workmanship of the manufactures are adequate, and that they possess a high level of quality control management.

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b. The lightning arresters should be specified to be installed on the transformer tank’s cover to effectively protect the transformer itself. The lightning arrester ground lead isolator operation test is required to be submitted with the quotation.

c. The transformers shall not produce audible noise exceeding the specified limits due to environmental disturbance, especially when installed near hospitals, temples and schools, etc.

4.2. For Loss Reduction:

It has been reported that the EDC’s total losses are approximately of 10% of those in the year 2007. The utility has begun many activities to aid in reducing losses, including hosting conferences which invited papers and research from different experienced utilities. EDC plans to reduce the loss to 7% by the year 2012. One of the programs suggested in this Handbook is to acquire and/or increase the use of low loss transformers in EDC’s system.

It is better to start by using an evaluation formula for a specific time period, for example 5 years. After this period, the EDC will have learned about the advanced transformer technology efficiency improvement by compiling records of the best values of no-load loss and load loss for each rating and applying it to the guaranteed low loss transformer table, included in the transformer specification for implementation. a. In the basic loss evaluation process, three transformer figures are:

purchase price, no-load loss and load loss. For the purposes of bid comparison, the transformer unit cost and losses shall be evaluated to obtain the evaluated transformer’s cost according to the formula below: A = B +7,121C +2,939D Where A = Evaluated cost of transformer in US Dollars. B = Unit cost of transformer converted into US Dollars according to the evaluation clause specified in the bid condition. C = No-load loss at room temperature not more than 30°C in kW.

b. No-load Loss: Typically, it is called core loss or iron loss. The no-load loss is a constant value varying for each designed transformer rating and is present no matter if the load is connected or not. There are two types of core losses: hysteresis loss and eddy current loss. The core material development progressed from hot-rolled steel to the cold-rolled grain oriented silicon steels (CGO) to reduce the core losses. It has since advanced to the new technology of high permeability grain oriented steel (HiB) that controls the domains of the iron crystals by laser etching.

Finally, another technology of amorphous iron has been gradually applied in some countries. Its deployment is limited because of the limited

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number of manufacturers and sophisticated production lines which need highly skilled workers and non-typical instruments. Nowadays, the low loss transformers are more often used in large cities in order to reduce the total system losses and to avoid construction of new substations in expensive locations in attractive city centres. HiB grain oriented steels together with experienced design, advanced core cutting and slitting machine, high skilled fabrication and assembly, may exhibit transformer efficiencies of up to 99.7%.

c. Load Loss: When the load is connected, the transformer will supply the

power to that load and produce resistive losses in windings as well as eddy current losses in windings, structural steelwork and tank. These load losses increase proportionally to the square of the load current. To reduce the load losses, the designer may increase the cross section of the windings. The designer must keep in mind, however, how it will affect flux density and core losses.

Most of the transformer windings will be made of copper due to its high conductivity and subsequent effect on energy efficiency, size reduction and energy saving. The technology of the copper windings is remarkably developed to withstand the short circuit strength, to prolong the service life and safety by using copper foil instead of windings which can also reduce eddy current loss from non-linear loads. There is another solution to improve the load loss reduction by upgrading the copper windings to super-conducting windings, but unfortunately, this new technology of super-conducting transformers is not ready for market deployment due to a number of technical obstacles and high construction cost.

d. Extra losses due to harmonics: Harmonics can be caused by the source and the loads. The transformer is a component with a magnetizing circuit which is sensitive to the harmonic distortion when it is designed to perform near to the yield point of the steel characteristics. Some components of the transformer’s non-linear loads are: TV sets, computers, UPS systems, variable speed drives, inverters and other instruments which convert alternating current (AC) to direct current (DC) supply. Harmonics not only present an extra load loss, but also de-rate the transformer capacity and affect the transformers’ service life. To prevent this harmonic effect, the utility must set harmonic restrictions both voltage and current generated to the industries which are the major contributors to power distortion in the distribution system.

4.3. Transformer Loss Reduction Benefits Transformer losses are one of the main losses in the distribution system. However, more research is necessary to predict and design a typical model that takes into account items such as: the detailed loading patterns, types of transformer, operation, and loading guides. When achieved, this will aid in achieving: energy cost savings, greenhouse gas reduction, CO2 reduction and increased ability for emissions trading. Nowadays, the trend of both the

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manufacturers and the utilities is to try to meet high efficiency transformer performance while maximizing production capability and minimizing investment costs.

• Reduce total energy loss:

Eloss[kWh] = (P0 + Pk * I ² ) * 8,760 Where: Eloss is total energy loss P0 is the no-load loss [kW]. Pk is the load loss [kW]. I is the rms-average load of the transformer. 8,760 is the number of hours in a year

• Increase power efficiency of a transformer:

EP = Load power/ [Load power + Power loss] = PL / [PL + PC + PW] Where: The real power delivered to the load is: PL watts The No-load core loss is: PC watts The Load Loss is: PW watts

• Increase life cycle cost

TCCloss = Eloss * C * (1 + r) ⁿ - 1/ r * (1 + r) ⁿ Where: TCCloss = Total Capitalized Cost of the losses C = the estimated average electricity cost per kWh r = the cost of capital n = the life time of the transformer in years ELoss = Total energy loss

• Environmental and Health Costs

These environmental and health costs originate from the various types of emissions resulting from the combustion of fossil fuels. Apart from CO2, the main offenders are SO2 and NOx which contribute to the acidification of the environment. According to the Kyoto Protocol, the use of low loss energy transformers can show a positive effect on carbon credits and can balance the global warming effect. This will support the country’s policy of the installation of more clean energy systems such as solar energy, wind turbines, energy from waste energy, etc.

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5. Electricité du Laos - Additional Specifications This section discusses about the additional specifications specially collated for Electricité du Laos of Lao PDR (EDL). 5.1. For Reliable Performance of the Transformer:

EDL should consider adding technical information as follows: • Short circuit test reports to prove that the design, raw material and

workmanship of the manufactures are adequate experienced and represent high level of quality control management.

• The lightning arresters should be specified to be installed on the transformer tank’s cover to effectively protect the transformer itself. The lightning arrester ground lead isolator operation test is required to be submitted with the quotation.

• The transformers shall not produce audible noise exceeding the specified limits due to environment disturbance especially, when installed near hospitals, temples and schools, etc.


It has been reported that the EDL’s total losses are approximately 17.5% of those in the year 2007. The utility has begun many activities to aid in reducing losses, including hosting conferences which invited papers and research from different experienced utilities. EDL plans to reduce the total system losses. One of the programs suggested in this Handbook is to acquire and/or increase the use of low loss transformers in EDL’s system. It is better to start by using an evaluation formula for a specific time period, for example 5 years. After this period, EDC will have learned about the advanced transformer technology efficiency improvement by compiling records of the best values of no-load loss and load loss for each rating and applying it to the guaranteed low loss transformer table, included in the transformer specification for implementation.

a. In the basic loss evaluation process, three transformer figures are:

purchase price, no-load loss and load loss. For the purpose of bid comparison, the transformer unit cost and losses shall be evaluated to obtain the evaluated transformer cost according to the formula below: A = B +5,000C +3,500D Where A = Evaluated cost of transformer in US Dollars. B = Unit cost of transformer converted to US Dollars according to the evaluation clause specified in the bid condition. C = No-load loss at room temperature not more than 30°C in kW.

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b. No-load Loss: Typically, it is called core loss or iron loss. The no-load loss is a constant value varying for each designed transformer rating and is present no matter if the load is connected or not. There are two types of core losses: hysteresis loss and eddy current loss. The core material development progressed from hot-rolled steel to the cold-rolled grain oriented silicon steels (CGO) to reduce the core losses. It has advanced to the new technology of high permeability grain oriented steel (HiB) that controls the domains of the iron crystals by laser etching. Finally, another technology of amorphous iron has been gradually applied in some countries. Its deployment is limited because of the limited number of manufacturers and sophisticated production lines which need highly skilled workers and non-typical instruments. Nowadays, the low loss transformers are more often used in the capital or large cities in order to reduce the total system losses and to avoid construction of new substations in expensive locations in attractive city centres. HiB grain oriented steels together with experienced design, advanced core cutting and slitting machine, high skilled fabrication and assembly, may exhibit transformer efficiencies of up to 99.7%.

c. Load Loss: When the load is connected, the transformer will supply the

power to that load and produce resistive losses in windings as well as eddy current losses in windings, structural steelwork and tank. These load losses increase proportionally to the square of the load current. To reduce the load losses, the designer may increase the cross section of the windings. He must keep in mind, however, how it will affect flux density and core losses. Most of the transformer windings will be made of copper due to its high conductivity and subsequent effect on energy efficiency, size reduction and energy savings. The technology of the copper windings is remarkably developed to withstand the short circuit strength, to prolong the service life and safety by using copper foil instead of windings which can also reduce eddy current loss from non-linear loads. There is another solution to improve the load loss reduction by upgrading the copper windings to super-conducting windings, but unfortunately, this new technology of super-conducting transformers is not ready for market deployment due to a number of technical obstacles and high construction cost.

d. Extra losses due to harmonics: Harmonics can be caused by the source and the loads. The transformer is a component of the magnetizing circuit which is sensitive to the harmonic distortion when it is designed to perform near to the yield point of the steel characteristics. Some components of the transformer’s non-linear loads are: TV sets, computers, UPS systems, variable speed drives, inverters and other instruments which convert alternating current (AC) to direct current (DC) supply. Harmonics not only present an extra load loss, but also de-rate the transformer capacity and affect the transformers’ service life. To prevent this

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harmonic effect, the utility must set harmonic restrictions both voltage and current generated to the industries which are the major contributors to power distortion in the distribution system.

5.3. Transformer Loss Reduction Benefits

Transformer losses are one of the main losses in the distribution system. However, more research is necessary to predict and design a typical model that takes into account items such as: the detailed loading patterns, types of transformer, operation, and loading guides. When obtained, this will aid in achieving: energy cost savings, greenhouse gas reduction, CO2 reduction and increased ability for emissions trading. Nowadays, the trend of both the manufacturers and the utilities is to try to meet high efficiency transformer performance while maximizing production capability and minimizing investment costs.


Eloss[kWh] = (P0 + Pk * I ² ) * 8,760 Where: Eloss is total energy loss P0 is the no-load loss [kW]. Pk is the load loss [kW]. I is the rms-average load of the transformer 8,760 is the number of hours in a year

• Increase power efficiency of a transformer:



TCCloss = Eloss * C * (1 + r) ⁿ - 1/ r * (1 + r) ⁿ Where: TCCloss = Total Capitalized Cost of the losses C = the estimated average cost per kWh r = the cost of capital n = the life time of the transformer in years ELoss = Total energy loss

• Environmental and Health Costs These environmental and health costs originate from the various types of emissions resulting from the combustion of fossil fuels. Apart from CO2,

12

the main offenders are SO2 and NOx which contribute to the acidification of the environment. According to the Kyoto Protocol, the use of low loss energy transformers can show positive effect on carbon credits and can balance the global warming effect. This will support the country’s policy of the installation of more clean energy systems such as solar energy, wind turbines, energy from waste energy, etc.

6. Ho Chi Minh City Power Company - Additional Specification

This section discusses about the additional specifications specially collated for Ho Chi Minh City Power Company (HCMCPC). 6.1. For Reliable Performance of the Transformer

HCMC PC should consider adding the following technical information: • Short circuit test reports to prove that the design, raw material and

workmanship of the manufactures are adequate and represent a high level of quality control management.


• The transformers shall not produce audible noise exceeding the specified limits due to environment disturbance especially, when installed near hospitals, temples and schools, etc.


It has been reported that the HCMC PC’s total losses are approximately 7.07% of those in 2007. The utility has begun many activities to aid in reducing losses, including hosting conferences which invited papers and research from different experienced utilities. HCMCPC plans to reduce the total system losses. One of the programs suggested in this Handbook is to acquire and/or increase the use of low loss transformers in HCMC PC’s system. It is better to start by using an evaluation formula for a specific time period, for example 5 years. After this period, EDC will have learned about the advanced transformer technology efficiency improvement by compiling records of the best values of no-load loss and load loss for each rating and applying it to the guaranteed low loss transformer table, included in the transformer specification for implementation.

a. In the basic loss evaluation process, three transformer figures are:

13

purchase price, no-load loss and load loss. For the purpose of bid comparison, the transformer unit cost and losses shall be evaluated to obtain the evaluated transformer cost according to the formula below:

A = B +4,080C +2,220D Where A = Evaluated cost of transformer in US Dollars. B = Unit cost of transformer converted in US Dollars according to the evaluation clause specified in the bid condition. C = No-load loss at room temperature not more than 30°C in kW.

b. No-load Loss: Typically, it is called core loss or iron loss. The no-load loss is a constant value varying for each designed transformer rating and is present no matter if the load is connected or not. There are two types of core losses: hysteresis loss and eddy current loss. The core material development progressed from hot-rolled steel to the cold-rolled grain oriented silicon steels (CGO) to reduce the core losses. It has advanced to the new technology of high permeability grain oriented steel (HiB) that controls the domains of the iron crystals by laser etching. Finally, another technology of amorphous iron has been gradually applied in some countries. Its deployment is limited because of the limited number of manufacturers and sophisticated production lines which need highly skilled workers and non-typical instruments. Nowadays, the low loss transformers are more often used in the capital or large cities in order to reduce the total system losses and to avoid construction of new substations in expensive locations in attractive city centres. HiB grain oriented steels together with experienced design, advanced core cutting and slitting machine, high skilled fabrication and assembly, may exhibit transformer efficiencies of up to 99.7%.

c. Load Loss: When the load is connected, the transformer will supply the power to that load and produce resistive losses in windings as well as eddy current losses in windings, structural steelwork and tank. These load losses increase proportionally to the square of the load current. To reduce the load losses, the designer may increase the cross section of the windings. He must keep in mind, however, how it will affect flux density and core losses. Most of the transformer windings will be made of copper due to its high conductivity and subsequent effect on energy efficiency, size reduction and energy saving. The technology of the copper windings is remarkably developed to withstand the short circuit strength, to prolong the service life and safety by using copper foil instead of windings which can also reduce eddy current loss from non-linear loads. There is another solution to improve the load loss reduction by upgrading the copper windings to super-conducting windings, but unfortunately, this new technology of super-conducting transformers is not ready for market deployment due to

14

a number of technical obstacles and high construction cost.

d. Extra losses due to harmonics: Harmonics can be caused by the source and the loads. The transformer is a component of the magnetizing circuit which is sensitive to the harmonic distortion when it is designed to perform near to the yield point of the steel characteristics. Some components of the transformer’s non-linear loads are: TV sets, computers, UPS systems, variable speed drives, inverters and other instruments which convert alternating current (AC) to direct current (DC) supply. Harmonics not only present an extra load loss, but also de-rate the transformer capacity and affect the transformers’ service life. To prevent this harmonic effect, the utility must set harmonic restrictions both voltage and current generated to the industries which are the major contributors to power distortion in the distribution system.

6.3. Transformer Loss Reduction Benefits Transformer losses are one of the main losses in the distribution system. However, more cases or research to predict and design a typical model taking into account the detailed loading patterns, types of transformer, operation, and loading guides are needed. This will result in energy cost savings, greenhouse gas reduction, CO2 reduction and emission trading. Nowadays, the trend of both the manufacturer and the utility is to try to meet high efficiency transformer performance while maximizing production capability and the minimizing the investment cost.



• Increase power efficiency of a transformer



TCCloss = Eloss * C * (1 + r) ⁿ - 1/ r * (1 + r) ⁿ Where:

15

TCCloss = Total Capitalized Cost of the losses C = the estimated average cost per kWh r = the cost of capital n = the life time of the transformer in years ELoss = Total energy loss

• Environmental and Health Costs

These environmental and health costs originate from the various types of emissions resulting from the combustion of fossil fuels. Apart from CO2, the main offenders are SO2 and NOx which contribute to the acidification of the environment. According to the Kyoto Protocol, the use of low loss energy transformers can show positive effect on carbon credits and can balance the global warming effect. This will support the country’s policy of the installation of more clean energy systems such as solar energy, wind turbines, energy from waste energy, etc.

7. Hanoi Power Company - Additional Specification

This section discusses the additional specifications specially collated for Hanoi Power Company, Vietnam (HNPC). 7.1. For reliable performance of the transformer:

HNPC should consider adding technical information as follows: • Short circuit test reports to prove that the design, raw materials and

workmanship of the manufactures are adequate and they have a high level of quality control management.


• The transformers shall not produce audible noise exceeding the specified limits due to environmental disturbance, especially when installed near hospitals, temples and schools, etc.

7.2. For Loss Reduction: It has been reported that the HNPC’s total losses are approximately of 8.85% of those in the year 2007. The utility has begun many activities to aid in reducing losses, including hosting conferences which invited papers and research from different experienced utilities. HNPC plans to reduce the loss to 7% by the year 2012. One of the programs suggested in this Handbook is to

16

acquire and/or increase the use of low loss transformers in HNPC’s s system.

It is better to start by using an evaluation formula for a specific time period, for example 5 years. After this period, the HNPC’s will have learned about the advanced transformer technology efficiency improvement by compiling records of the best values of no-load loss and load loss for each rating and applying it to the guaranteed low loss transformer table, included in the transformer specification for implementation a. In the basic loss evaluation process, three transformer figures are purchase

price, no-load loss and load loss. For the purpose of bid comparison, the transformer unit cost and losses shall be evaluated to get the transformer evaluated cost according to the formula below: A = B +6,300C +1,300D Where A = Evaluated cost of transformer in US Dollars. B = Unit cost of transformer converted in US Dollars according to the evaluation clause specified in the bid condition. C = No-load loss at room temperature not more than 30°C in kW.

b. No-load Loss: Typically, it is called core loss or iron loss. The no-load

loss is a constant value varying for each designed transformer rating and is present no matter if the load is connected or not. There are two types of core losses: hysteresis loss and eddy current loss. The core material development progressed from hot-rolled steel to the cold-rolled grain oriented silicon steels (CGO) to reduce the core losses. It has advanced to the new technology of high permeability grain oriented steel (HiB) that controls the domains of the iron crystals by laser etching. Finally, another technology of amorphous iron has been gradually applied in some countries. Its deployment is limited because of the limited number of manufacturers and sophisticated production lines which need highly skilled workers and non-typical instruments. Nowadays, the low loss transformers are more often used in the capital or large cities in order to reduce the total system losses and to avoid construction of new substations in expensive locations in attractive city centres. HiB grain oriented steels together with experienced design, advanced core cutting and slitting machine, high skilled fabrication and assembly, may exhibit transformer efficiencies of up to 99.7%

c. Load Loss: When the load is connected, the transformer will supply the power to that load and produce resistive losses in windings as well as eddy current losses in windings, structural steelwork and tank. These load losses increase proportionally to the square of the load current. To reduce the load losses, the designer may increase the cross section of the windings. He must keep in mind, however, how it will affect flux density and core losses.

17

Most of the transformer windings will be made of copper due to its high conductivity and subsequent effect on energy efficiency, size reduction and energy saving. The technology of the copper windings is remarkably developed to withstand the short circuit strength, to prolong the service life and safety by using copper foil instead of windings which can also reduce eddy current loss from non-linear loads. There is another solution to improve the load loss reduction by upgrading the copper windings to super-conducting windings, but unfortunately, this new technology of super-conducting transformers is not ready for market deployment due to a number of technical obstacles and high construction cost.

d. Extra losses due to harmonics: Harmonics can be caused by the source and the loads. The transformer is a component of the magnetizing circuit which is sensitive to the harmonic distortion when it is designed to perform near to the yield point of the steel characteristics. Some components of the transformer’s non-linear loads are: TV sets, computers, UPS systems, variable speed drives, inverters and other instruments which convert alternating current (AC) to direct current (DC) supply. Harmonics not only present an extra load loss, but also de-rate the transformer capacity and affect the transformers’ service life. To prevent this harmonic effect, the utility must set harmonic restrictions both voltage and current generated to the industries which are the major contributors to power distortion in the distribution system.

7.3. Transformer Loss Reduction Benefits Transformer losses are one of the main losses in the distribution system. However, more cases or research to predict and design a typical model taking into account the detailed loading patterns, types of transformer, operation, and loading guides are needed. This will result in energy cost savings, greenhouse gas reduction, CO2 reduction and emission trading. Nowadays, the trend of both the manufacturer and the utility is to try to meet high efficiency transformer performance while maximizing production capability and the minimizing the investment cost. • Reduce total energy loss:


• Increase power efficiency of a transformer: EP = Load power/ [Load power + Power loss] = PL / [PL + PC + PW] Where:

18

The real power delivered to the load is: PL watts The No-load core loss is: PC watts The Load Loss is: PW watts

• Increase life cycle cost TCCloss = Eloss * C * (1 + r) ⁿ - 1/ r * (1 + r) ⁿ Where: TCCloss = Total Capitalized Cost of the losses C = the estimated average cost per kWh r = the cost of capital n = the life time of the transformer in years ELoss = Total energy loss

• Environmental and Health Costs These environmental and health costs originate from the various types of emissions resulting from the combustion of fossil fuels. Apart from CO2, the main offenders are SO2 and NOx which contribute to the acidification of the environment. According to the Kyoto Protocol, the use of low loss energy transformers can show positive effect on carbon credits and can balance the global warming effect. This will support the country’s policy of the installation of more clean energy systems such as solar energy, wind turbines, energy from waste energy, etc.

19

8. References

• Energy saving in industrial distribution transformers transformer losses, May 2002, W.T.J. Hulshorst and J.F. Groeman (KEMA)

• The Potential for Global Energy Savings from High Efficiency Distribution Transformers, February, 2005, (Roman Targosz, editor ; Main authors and reviewers: Ronnie Belmans, Jan Declercq, Hans de Keulenaer, Katsuaki Furuya, Mayur Karmarkar, Manuel Martinez, Mike McDermott, Ivo Pinkiewicz)

• Technical Report, Distribution Transformers : Proposal to Increase MEPS Levels, October 2007, T R Blackburn

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Chapter 2 Bidding Evaluation

1. Introduction

This chapter is to guide and assist the utility to learn about the solution, and from what criteria it is derived. Only distribution transformers will be discussed in this handbook. Therefore, there will three factors: purchase price of the transformer, load losses and no-load losses which shall be considered. The lowest evaluated cost including losses will be the criteria utilized to choose the initial proposal that the utility will study before making a contract. It will affect the utility investment cost, paying a little more for low loss transformers, but in return it can save more money than the cumulated value of losses during transformer operation. The penalty values should be specified as well in the bid documents.

2. Objective

The trade off between the transformer’s price and the losses of the transformer is simplified in the tender specification. It is accomplished by adding the evaluation formula where the purchase cost minus the loss, which reflects the utilities’ true investment cost. The manufacturers should offer their best design capability and highest quality of raw materials and workmanship in order to convince the utilities to invest in energy efficient transformers.

3. Formula Analysis

There are many factors to be taken into account in the evaluation formula which are: no-load loss, load loss, interest rate, inflation rate, electricity unit cost, operation & maintenance cost and transformer service life. All these values differ due to fluctuations in the economy and government policies which each utility operates in.

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3.1. Interest Rate

Interest rates are an important part of a loan; they help determine its total cost. Each utility has to apply for a loan in both local and foreign countries. It is typical that the local loan will be less advantageous in terms of interest rate, grace period and repayment terms than a foreign one. It is recommended that one ask for all of this information, from the Finance Department or the Department which responds to the loan application.

3.2. Inflation Rate The purpose of this factor is to show the effect of the inflation rate on the real value of the money. In fact, a substantial increase in the price of transformers is related to an increase in the inflation rate which means a decrease in the value of money. As inflation rate increases, the price of goods increases. As with the interest rate analysis, the finance department will analyze and provide the real figures. These figures will differ from country to country.

3.3. Electricity Price Purchased Some countries have divided the generation utility and distribution utility; in this case it is common for distribution utility to get the average electricity unit purchased from the generation utility. But some countries have an organization who owns both power generation and distribution. In this case, the electricity unit purchase will be calculated on the basis of the investment cost of electricity unit production at the point of the terminal station where electricity is sold to customers.

3.4. Operation and Maintenance (O&M) Expenses in Distribution System

This cost (USD/kW/Year) must be calculated from the accumulated actual expenses as follows:

- Transformer and distribution cost - Customs accounting and collections cost - Administrative and general costs - Depreciation cost

As shown, this figure is obtained and calculated from information from many disparate groups and/or different departments, the more realistic the expenses, the more accurate the operating & maintenance costs.

3.5. Distribution Transformer Life

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This is understood as the average service life of the transformer in number of years. Some transformers may still be in service after 25 years, while others may only reach the age of 15. After discussions with reputable transformer manufacturers, all confirm that the recommend service life of the transformers is typically to be 20 years for regular loading according to the international standards. The evaluation formula analysis starts from the no-load loss calculation. Once the transformer is energized, the utility has to pay both the transformer cost and the cost of electricity losses or energy losses consists of no-load loss (core loss) and load loss (winding loss) throughout the life of the transformer as shown in Figure 1.

Price ofTransformer

Cost ofElectricity Losses

Year 0 Year 1 Year 2 Year 3 Year 4 Year N Figure 1: Expenses generated by transformer price and cost of electricity losses

a. Criteria for calculation of no-load loss used in this case

• Distribution transformer life = 20 years • Interest rate = 6.26% • Inflation rate = 1.56% • Electricity unit purchased = 0.0597 $/kWh • O&M expenses in distribution system = 29.29 $/kW/Year The cost of no-load loss will be generated by the transformer core which means that once the transformer is energized, this loss is present throughout the transformers life and calculated back to present value as shown in Figure 2.

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Cost ofNo-Load Losses

Year 1 Year 2 Year 3 Year 4 Year N

Year 0

Computation ofPresent Value

Figure 2: Calculation of the present value of no-load loss

The result is calculated from the values of criteria as shown in clause a., using the formula of present value and is shown in Figure 3.

No-load expenses = (0.0597 x 8,760) + 29.29 = 552.3 $/kW/Year

Present Value calculation result = 552.3 (1-(1.0156/1.0626)20) (1.0156) / (1+0.0626) (1-(1.0156/1.0626)) = 7,109.29 $/kW (see Figure 3)

$552.30/kW/year


Year 0


$7,109.29/kW

Figure 3: Calculation of the present value of no-load loss in actual costs

b. Criteria for calculation of load loss used in this case.

• Distribution transformer life 20 years

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• Interest rate = 6.26% • Inflation rate = 1.56% • Electricity unit purchased = 0.0597 $/kWh • O&M expenses in distribution system = 29.29 $/kW/Year • Loss factor 0.3803 (see more detailed below)

Loss factor = 0.84(Load factor)2 + 0.16(Load factor) = 0.84(0.5843)2 + 0.16(0.5843) = 0.3803 Remark: Load factor (distribution system) = 0.5843

(Formula from REA Bulletin 160-1)

The cost of load loss will reflect resistive losses in the windings and leads, and losses generated by eddy currents in the windings, the structural steelwork, and the tank, throughout the transformer life and calculated back to present value as shown in Figure 4.

Cost ofLoad Losses


Year 0


Figure 4: Calculation of the present value of load loss

The result is calculated from the values of criteria as shown in clause b., using the formula of present value and is shown in Figure 5. Load loss expenses = (0.0597 x 8,760 x 0.3803) + 29.29

= 228.18 $/kW/Year

Present value of Load loss expense = 2,936.95 $/kW (20 years) (see Figure 5)

25

$228.18/kW/year


Year 0


$2,936.95/kW

Figure 5: Calculation of the present value of load loss in actual costs

A = B + 7,109C + 2,936D (see Figure 6) Where A = Evaluated cost in USD B = Transformer price in USD C = No-load loss of transformer in kW D = Load loss of transformer in kW The evaluation formula analysis is shown in Figure 6 consisting of the components: the price of transformer, the no-load loss and the load loss at the present values calculated for the entire 20 year service life of transformer.

Price ofTransformer ($)

Year 0 Year 1 Year 2

2,936D

7,109C

Figure 6: Evaluation formula analysis

4. How to Evaluate The Best Choice Often, engineers are asked to choose the best transformer with a suitable price (as low as possible). Best choice means utilizing many factors from which to decide upon the best transformer for the money. As discussed, engineers will not only analyze the price or cost of the transformer, but will also consider quality which

26

leads to loss issues as well. In this case that typically means total losses of the transformer. Of course, its characteristics must conform to the reference standards. The following example will show the Least Cost Analysis for the two transformers having ratings of 24 kV 3-phase 500 kVA capacity and conform to the same reference standards or specification, but the transformer price, no load loss and load loss are different as shown below. After applying the evaluation formula A = B + 7,109C + 2,936D, it can be seen that in this case, the transformer with the price of UDS 24,533.- will be selected because its evaluated cost is cheaper which means it will return more profit in the future within 20 years. In fact, it can be less than 20 years if there is an increase in the cost of raw materials, workmanship, interest rates and/or cost of living. The benefit will be realized earlier than shown in the formula. Transformer X

[Low Loss] Transformer Y

[Standard Loss] kVA 500 500 Price($) 24,533 15,758 No load(kW) 0.67 0.97 Load loss(kW) 3.030 5.500 Evaluated cost($) 38,192 38,801 Preferred Selection

5. Excess Losses and Penalty Transformers will always have losses. It cannot be avoided. The amount of the loss depends on the quality of workmanship of each crew and the factory’s experience. Therefore, international standards limit the tolerances which the utilities will refer to in accepting a transformer. The process to deal with the acceptance of the transformers which are in excess of the guaranteed values will be explained, including a discussion of the penalty clause which has been used for over twenty years. After the supplier delivers the transformers to the utility together with the routine test report, all units of the transformers technical information will be reported, according to the contract. The testing values of no-load loss and load loss will be calculated and declared for each unit with its separate serial number. The acceptance process is explained as follows: a. Limits of tolerance:-

No-load loss: not more than +10% No-load loss + Load loss: not more than +6%

b. The individual transformer having losses beyond the limits of tolerance will be

rejected immediately

27

c. If average losses of all transformers of the same kVA rating exceeds the guaranteed value but remains within the limits of tolerance, the penalty will be:

No-load loss at USD 10,697 / kW x N. Load loss at USD 4,424 / kW x N. Where N = Number of transformers.

In the event of negotiation and/or dispute over loss tolerance, the maximum value of the transformer shall be used to compute tolerance limits relating to higher guaranteed values. In this case, the supplier shall bear all penalties rightful of total purchase made.

6. The Low Loss Limitation Table Some utilities have applied the evaluation formula for more than 20 years. Finally, the low loss values of the transformer will be reached to maximize profits to the utility. These low loss values will be adjusted and arranged in the table for each rating. The transformers losses in the table are the lowest losses that most of the reputable manufacturers can design and keep to meet the contract values which all transformers shall not exceed.

Transformer Rating Transformer Loss (Watt) (kVA) No Load Loss Load Loss

15 70 160 45 160 360 75 220 580 112.5 255 840 150 300 1,000 225 420 1,530 300 480 1,860 500 670 3,030 750 840 4,370 1,000 1,000 6,400 1,500 1,200 10,000

Table 1: The low loss limitation of no-load & load loss for each transformer rating

• All transformer losses shall be within the limits without any tolerance. For each transformer rating, and each lot of shipment, the utility will sample the transformers for their own loss measurement purposes, at quantity specified by the contract. The transformers will be accepted if the measured losses for the sample are within the limits.

28

In the event that one of the samples has loss(es) higher than the limits in Table 1, the Utility will resample the transformers from the same lot in the same quantity as the first sampling. All transformers in that lot will be rejected, if one of the second sample of transformers has loss(es) higher than the limits. In case the quantity of the sample is equal to the total number of the purchase, no second test will be performed. The utility will reject only the transformer(s) which loss(es) is (are) over the limit. Based on the above conditions, the supplier shall repair and replace ALL failed units. No penalty shall be negotiated. The supplier must design and assemble transformers with care and accuracy without further provision of tolerances.

7. Conclusion The evaluation formula in this chapter has been well proven to be the best practice for distribution system of the capital city with lowest loss. Many factors such as O&M expenses, electricity unit cost, interest rate, inflation rate, etc are part of the evaluation process though some utilities may decide to use balance emphasis on different factors, e.g. in USA, they will use the cost of installation for generation and transmission system; while in some European countries, only electricity unit cost is applied for loss evaluation. The illustrated evaluation was an example of a standard procurement practice. The users should exercise judgment in the evaluation. Finally, the utilities are recommended to develop their own evaluation formula by harnessing the information in the course of making a purchase decision. The evaluation method also reinstates the need for manufacturers to design and deliver the most economic transformer with ideal quality standards.

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Chapter 3 Transformer Production Inspection

1. Introduction After the procurement contract for transformers is signed, there are several processes to verify that the equipment fulfils the specifications and conditions specified in the agreement. Approval drawings shall be provided for the benefit of common understanding of specification between both the utility and the supplier. Representatives from the utilities, who are likely appointed based on experience in various aspects such as specification handling, installation, testing, maintenance and purchasing, shall inspect the manufacturing of the equipment on site. Acceptance is another process to ensure quality compliance to the contract and specification before actual installation, and delivery of electricity to end-users. The contract will be fulfilled once the utility receives all goods purchased in operational condition and payment is transferred to the seller. After which, the service guarantee for a period of one year (standard practice) will commence. In this chapter, only the manufacturing inspection will be discussed with reference to a real-life example as illustration.

2. Objective This production inspection is very important because if any process or raw material is found non-conforming to the specification, the inspection committee shall reserve the right to suspend the production line and resolve all issues before restarting the production line.

This chapter details low loss verification which includes no-load loss and load loss. A careful production inspection is fundamental to a transformer of satisfactory quality that is operational for at least 20 years.

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3. Inspection Committee Management Each utility may have different practices and regulations depending on governmental policies. This practice is used in the utility which distributes electricity in the capital city and has a proven track record of success in the lowest loss transformer selection and also suits this country’s economic background. The inspection committee should be approved by the top management who is responsible for the technical knowledge, after the contract is signed. The inspection members will be selected from the related department which verifies the transformer specifications at a minimum, as follows:

i. Electrical engineering department which takes care of the specification or term of reference (TOR)

ii. District service department which maintains records of the transformer’s data characteristics and performance monitoring.

iii. Testing division or Maintenance department which is experienced in testing and preventive maintenance on the transformers which aids in prolonging the service life.

iv. Purchasing or Contract department which controls the related document starting from the quotation, technical and commercial condition agreement and the approval drawings.

All engineers and technicians who are represented in the production inspection committee will be given the approval drawings and related correspondence for their references when witnessing the transformer production line and testing. The supplier shall provide free access to the facilities where the transformers are being manufactured and shall satisfy the representatives that the raw material and finished transformers are in accordance with this specification and the purchase contract. In the event of disagreement or dispute, either the contract’s details are not clear or the supplier would like that an exception be made (for example, the value of the guaranteed loss), these issues should be presented at a meeting with the top management. The meeting should discuss the disadvantages and advantages to the utility as the main focus. This convention should remain and be considered the standard practice.

4. Inspection Process There will be two main issues to discuss in this clause, the production process flow of the transformer manufacturing which shows each step of production line and inspection, and the second part which will explain some principal practical inspection trips. In Figure 7, the production process flow shows the process of manufacturing,

31

beginning from the incoming raw material, thru each step of production line and inspection activities, testing facility, until packing and delivery to the customers.

There will be 11 processes of production line which are: • In-coming materials • Silicon steel cutting • Core stacking process • HV, LV Coil Winding • Insulation preparation • Tank, Cover, Equipment and Accessory Preparation • Core & coil assembly , Tap changer installation , Wire connection • Drying, Vacuum and Oil Filling • Accessory assembly, colour paint • Packing • Customer delivery

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Figure 7: Production Process Flow

For the purpose of low loss transformer verification, the production inspection committee should scrutinize some main process concerns. Let’s start with the in-coming material process which primarily is the silicon steel as most of the low loss transformers shall be manufactured from high permeability grain oriented steel.

33

Figure 8: Silicon Steel Core Loss Curve As can be seen from Figure 8: core loss can be reduced in two ways: firstly, the standard technology of silicone steel can be upgraded to a silicone steel core which is called the Laser –Irradiated Hi B silicone steel. Secondly, it can be achieved via a thickness decrease, utilizing a less thick piece of silicon steel. This will also have a lower no load loss. In the factory, the inspectors can clearly identify Laser Hi-B silicone steel because its surface has a dotted line where the Cold Grain Oriented silicone steel is plainly visible. The load loss is generated from the copper windings in both high voltage and low voltage sides. For low load loss transformers, the copper winding having a ‘high temperature class’ shall be selected in order to avoid the risk of deformation of the enamel coat on the copper material. Secondly, the core stacking process requires more skilled workers with many years of experience. In this process there usually are two workers, one will insert the silicon steel sheet while the other will compactly assemble. The fact is that lower no loss is obtained by decreasing the gaps in each layer of the steel sheet.

34

Thirdly, the welding of winding to make tapping and connections is also important. Here, care must be taken in the welding quality and highest working area cleanliness and orderliness is of utmost importance. The utility’s report always shows the extra loss of the transformer and the failure records of short circuit caused by the scrap in the welding process Fourthly, there will be testing prior to the production of the core staking and winding process. Samples of core staking with some designed turns of copper winding assembly will be taken to be tested to verify the no load loss value. If the value is over the guaranteed no load loss the core shall be investigated and redesigned to meet the contract agreement. This will be done in order to convince the inspection committees that the low loss transformers will be able to meet the contract guarantee values. Finally, the finished transformer is ready to undergo routine, and other special tests required by the utility or customers. The inspection committee will randomly test some transformers by themselves to run no-load loss and load loss tests during routine testing. The testing circuit and apparatus configuration for no-load loss and load loss measurement has shown in Figure 9 and 10 respectively.

Figure 9: Test circuit & Apparatus Configuration for No-load Loss Measurement

Figure 10: Test Circuit & Apparatus Configuration for Load Loss Measurement

4.1. Measurement of No-Load Loss

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a. Purpose and Test Method

No-load losses (also referred to as excitation losses, core losses and iron losses) are a very small part of the power rating of the transformer, usually less than 1%. Since these losses are essentially constant over the lifetime of the transformer (do not vary with load), they generally represent a sizable operating expense especially when energy costs are high. Therefore, accurate measurements are essential in order to evaluate individual transformer performance.

Requirements, as stated in IEEE Std.C57.12.90-1993 and C57.12.91-1979, for reporting no-load loss/excitation current measurements, are: • Voltage is equal to rated voltage unless specified otherwise. • Frequency is equal to the rated frequency. • Measurements are reported at the reference temperature. • The voltage applied to the voltmeters is proportional to that

across the energized winding. • Whenever applied waveform is distorted, measurement must be

corrected to a sinusoidal voltage waveform.

The no-load loss and current can be measured on one of the winding at rated frequency and voltage on principle tapping. The remaining winding shall be left open-circuited. Measuring no-load losses of a transformer when subjected to a sinusoidal voltage wave form can be achieved simply as per Figure 9. Transformers may be subjected to a distorted sine-wave voltage. In order to achieve the required measuring accuracy, the instrumentation used should accurately respond to the power frequency harmonics encountered in these measurements. Also, measured values need to be corrected to account for the effect of the voltage harmonics on the magnetic flux in the core and hence on both the hysteresis and eddy current loss components of iron losses. The hysteresis loss component is a function of the maximum flux density in the core, practically independent of the waveform of the flux. The maximum flux density corresponds to the average value of the voltage (not the rms value), and, therefore, if the test voltage is adjusted to be the same as the average value of the desired sine wave of the voltage the hysteresis loss component will be equal to the desired sine wave value. The eddy-current loss component of the core loss varies approximately with the square of the rms value of the core flux. When the test voltage is held at rated voltage with the average-voltage voltmeter, the actual rms value of the test voltage is generally not equal to the rated value. The eddy-current loss in this case will be related to the correct eddy-current loss at rated voltage by a factor k given in Equation 8.2, Clause 8 of the IEEE Std. C57.12.90-1993and

36

C57.12.91-1979 Standard. This is only correct for a reasonably distorted voltage wave.

b. Reference standard

IEC publication 60076-1: Power transformer Part 1: General ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers: Sub-Clause 8

c. List of equipment and instrument

Current transformer refers to IEC standard, Accuracy 1% Potential transformer refers to IEC standard, Accuracy 1% Power meter refers to IEC standard, Accuracy 0.5%

d. Acceptance Criterion

The acceptance of transformer no-load loss and current shall be lower than guarantee values or within tolerance of +15% of no-load loss guarantee values and +30% of no-load current guarantee values.

4.2. Measurement of Load Loss

a. Purpose and Test Method Transformer load losses, often called copper losses, include I2R losses in windings due to load current, stray losses due to stray fluxes in the windings, core clamps, magnetic shields, tank wall, etc. and losses due to circulating current in parallel windings and parallel conductors within windings.

Load losses are normally measured by short circuiting one winding of a transformer, usually the low voltage winding, and impressing sufficient voltage (referred to as impedance voltage) on the high voltage winding to cause rated current to circulate in the high voltage winding. Input voltage, current, and power are then measured.

The short-circuit impedance and load loss of winding shall be measured at rated frequency and relevant rated current (tapping current) not less than 50% with approximately sinusoidal voltage applied to one winding. The temperature of the winding shall be record to rated current and reference temperature of 75°C or 85°C.

Special precautions i. Measurement at a lower than rated current: According to IEEE Std

C57.12.90-1993, load losses should be measured at a load current equal to the rated current for the corresponding tapping position. However, if it is not exactly equal to the rated current, the measured load loss value will need to be corrected by the square of the ratio of the rated current to the test current (average of the measured phase current in three-phase transformers).

ii. Duration of the load loss measurement test:

37

During load loss measurement, the current in the winding increases winding temperature and hence increases winding I2R losses. To minimize the magnitude of this effect, it is the manufacturer’s responsibility to keep the test time as short as possible.

iii. Optimizations of measuring range of instrumentation: Transformer manufacturers are encouraged to use the instruments at their optimum operating range to minimize the errors. Phase angle corrections of voltage instrument transformers and current instrument transformers that have magnetic core materials are generally significantly higher when they are operated at lower than about 70% of their rated operating voltage/current. Also, these corrections can vary significantly with the turns-ratio setting of the instrument transformer.

iv. Other precautions with the use of instrument transformers: Using the proper burden, clean connections, and demagnetizing the current transformer after every use are measures that would help achieve a better measuring accuracy.

b. Reference standard

IEC publication 60076-1: Power transformer Part 1: General ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers: Sub-Clause 9

c. List of equipment and instrument

Current transformer refers to IEC standard, Accuracy 1% Potential transformer refers to IEC standard, Accuracy 1% Power meter refers to IEC standard, Accuracy 0.5%

d. Acceptance criteria

The acceptance of transformer load loss shall be lower than the guarantee values or within tolerance of +15% of guarantee values and voltage impedance shall be ±10% of guarantee values.

4.3. Traceability and Calibration A measurement possesses traceability if it can be compared, directly or indirectly, through a series of calibrations to the value established by higher level standards, national or international. Obtaining direct traceability for transformers is generally difficult because of the large physical size of the test object and the large voltage and power requirements. An alternative is to have a “portable” loss measuring system that can be used for on-site calibration. Indirect traceability is obtained by calibrating this loss measuring system on a regular basis using a standard measuring system. Calibration of a multi-component measuring system requires calibration of each of the components as well as the total system. In a loss measuring system, it is necessary to calibrate both the magnitudes and phase angle.

38

5. Conclusion Some utilities may have their own inspection form or special document to process the comments and some corrections during the inspection such as witness tests, discussion, dimension and facilities, etc. One of the most practical forms used in the production process inspection is called “Punch List” and shown in Figure 11. Punch List. The inspection committee can give the notices and make pictures to compare the status before and after modification or corrections are made on it.

Figure 11: Punch List Form

39

Chapter 4 Contract Acceptance 1. Introduction The commercial and technical conditions are all specified in the purchasing contract. It is commonplace for utilities to make special requests in order to assure the quality of the transformers fulfil the contract requirements. This step is also important in that the utility must manage the delivery of the transformers as it can delay the installation plans. This step is also important for the utility to manage the delivery time of the transformers to avoid the delaying installation plans such as to install the transformers before the contract can be completely settled to reach both the utilities and supplier’ satisfaction. The contract acceptance is difficult when the delivered transformers do not conform to the contract specification which has many classifications such as: physical characteristic, exceeding the guaranteed loss, etc. It is the intention of this chapter to guide the utilities to learn and share experiences in solving these problems by sample analysis and conclusion.

2. Objective Experience shows that there are three main factors to discuss in the process of transformer contract acceptance. One is a detailed specification with approval drawings, the second is routine test reports with guaranteed loss verification and the third is the final sampling test of the transformers before energizing and put in service. Various scenarios are given and explained to be used as a problem solving guide. It shows the process from top management’s policy viewpoint regarding practical standards in the procurement system.

3. Acceptance Committee Management This follows the same procedure as mentioned above in the production inspection committee. The acceptance committees should be approved by upper management after the contract is signed. The acceptance committee members who cover the

40

technical information will be selected from the related department which is knowledgeable about transformer specification and testing at a minimum, as follows:

i. Research and development department which takes care of the transformer failure analysis

ii. Distribution equipment department which maintains records of the transformer’s data characteristic and performance evaluation.

iii. Testing division which has experience in transformer testing procedures. iv. Purchasing or Contract department which controls the relevant

documentation starting from the quotation, technical and commercial condition agreement and the approval drawings.

All engineers and technicians who are represented as the contract acceptance committee will be given the approval drawings as shown in Figure 12: List of approval drawings and related accessories for their reference during sampling of the delivered transformers for testing. Samples of technical and guaranteed data of the transformer are shown in Figure 13. The supplier shall submit the routine test report of all the transformers together with the transformers apart from the commercial document. In the event of disagreement or dispute, either the contract’s details are not clear or the supplier would like that an exception be made (for example, the value of the guaranteed loss) these issues should be presented at a meeting with the upper management. The meeting should discuss the disadvantages and advantages to the utility as the main focus. This convention should remain and be considered the standard practice.

4. Acceptance Process The acceptance committee will make a visual inspection for the quantity of the delivered transformers according to the invoice of the supplier, after scrutinizing all transformers and documents such as the instruction manual, spare parts, etc. The acceptance committee will then randomly select a quantity of transformers per that which is stated in the contract. This amount typically does not exceed 10 sets due to the expense and time. It is recommended that even though the supplier performs the entire routine test for all transformers as shown in Figure 14: Supplier’s routine test report, the utility should perform sampling for its own re-verification before installation on site. The utility should implement a detailed step by step, pre-verification laboratory in order to assure that the transformers conform to the specification, especially with respect to guaranteed losses; otherwise, the supplier may try to deliver cheap transformers with high losses. In the event that the utility has budgetary constraints, it is strongly recommended

41

that a third party be employed to witness the tests and approve all contract documents at the factory. This may require a monetary investment, but the value outweighs the cost due to the high cost of equipment. At a minimum, the following acceptance tests should be done at the utility’s laboratory: 4.1. Routine Test

• Insulation Resistance Test • Winding Resistance Measurement • Oil Dielectric Test • Applied Voltage Test • Induced Voltage Test • Ratio And Vector Group Test • No-load Loss Test • Load Loss Test

4.2. Type Test

• Temperature Rise Test - The sample of the utility’s acceptance test report is shown in Figure 15: Acceptance routine test report: as can be seen, the no-load loss and load loss are measured and calculated to verify that the sampling transformers’ losses conform to the guarantee values per the contract. The payment shall then occur and the file will close and include a guarantee of performance for one year after delivery.

4.3. Excess Loss Management

4.3.1. Case No. 1 - Utility randomly selects some transformers to compare with the supplier’s report.

i. If the utility’s values are greater than the supplier’s report by

2.5%, the utility will increase the supplier’s values of all transformers with the following consecutive procedures.

ii. The utility has to investigate which transformer’s values exceed the guaranteed values including the tolerance limits, the transformer(s) should be rejected and the remainder are considered for penalty by calculating the average values of the total number of transformers.

iii. The compensation penalty is calculated by using penalty values which are 2.0 times of the formula constants x values of loss exceeding x Total number of transformers, as shown in Figure 16 Penalty Calculation Without Raising the Guarantee Values.

iv. Some suppliers may ask the utility to accept the rejected transformer(s) considering clause 3 above, provided the average value of that transformer is: • Guarantee load loss = 5,600 W • The different average value between the utility and supplier =

5.61%

42

• Average supplier’s report value = 5,481.33 W • New guarantee load loss is raised to = 5,481x1.0561 =

5,788.83 W • The penalty is calculated to = (5,788.83 – 5,600)x penalty

values (normally is 2.0 times of the formula constant) x Total number of transformers

This is illustrated in Figure 17 Penalty Calculation with Raising the Guarantee Values

4.3.2. Case No. 2 - Utility does not have the requisite facility for making

acceptance tests and is dependent on the routine test report of all transformers in computing excess losses. The process will be the same as mentioned in case no. 1 above, by using tolerance limit instead of the different values between the utility and supplier.

i. In case of increased no-load loss, provided the supplier’s routine test report shows the following values: • Guarantee no-load loss = 5,000 kW. • Tolerance limit specified in the contract = 15 % • Supplier report shows no-load loss = 6,000 kW > 5,000+15

% • Increased no-load loss guarantee = 6,000/1.15 = 5,217.39 kW • The penalty is calculated to = (5,217.39 – 5,000) x penalty


ii. In case of total loss exceeds the tolerance but with no-load loss within the limit, the increase in load loss to the new guarantee value is equal to (total loss)/( 1+%tolerance/100) – no-load as shown below: • Guarantee no-load loss = 5,000 kW • Guarantee load loss = 10,000 kW • Tolerance of no-load loss = 15 % • Tolerance of total loss = 10 % • Supplier report shows no-load loss = 4,500 kW < 5,000 kW • Supplier report shows load loss = 13,000 kW • Supplier report shows total loss = 13,000+5,000 = 18,000 >

(5,000+10,000)+10% kW • Raised load loss guarantee = (18,000/1.10) – 5,000 =

11,363.64 kW • The penalty is calculated to = (11,363.64 – 10,000) x penalty


• Check again if the average supplier’s load loss is lower than the new guaranteed load loss value

43

NO.

1 OUTLINE DRAWING Tr. 6300 kVA, 3 Ph. Dyn 11 11000 - 6900/3984 V.

TYPE : CONSERVATOR

2 TRANSFORMER BASE

3 CABLE BOX TYPE 1

4 HV. LV. BUSHING WITH EXTENSION BAR

5 NAMEPLATE WITH CONNECTION DIAGRAM CONNECTION Dyn11

6 NAMEPLATE BUSHING CURRENT TRANSFORMER SPECIFICATION

7 NAMEPLATE TAG. NO.

8 CONTROL BOX

9 WIRING DIAGRAM OF INSTRUMENT

NO.

1 HIGH AND LOW VOLTAGE BUSHING DT 10 Nf 630 DIN 42532

2 HV. TERMINAL CONNECTOR 630 A.

3 LV. TERMINAL CONNECTOR 630 A.

4 OIL LEVEL INDICATION SO-HE-6

5 LIQUID FILLED THERMOMETER 1187/S

6 TAP CHANGER NO. 3

7 DEHYDRATING BREATHER SILICAGEL SIZE 3 KG.

8 GROUNDING PAD For cable 50 sq.mm.

GLOBE VALVE, oil sampling and drain valve

9 Upper f ilter valve

Oil sampling valve 1/2"

10 BUTTERFLY VALVE FOR RADIATOR FIN EE-W80

11 BUTTERFLY VALVE (For buchholz relay) DN 50

12 PRESSURE RELIEF DEVICE WITH CONTACTS COMEM/80T

13 BUCHHOLZ RELAY BR50

14 WINDING TEMPERATURE INDICATOR Messko (MT-ST160W)

15 RUBBER AIR CELL AIR CELL

NAME TITLE EFF. DATE :

DRN. BY

CHK. BY SCALE : PAGE 2

APP. BY DWG. NO. REV. 0

Symbol ISODimension in millimetres

LIST OF DRWAING

N.T.S.

A4NAM E OF M ANUFACTURER

14

LIST OF ACCESSORIES

DESCRIPTION MODEL/TYPE CATALOGUE NO.

2"

8

9

10

11

12

13

LIST OF DRAWING

DESCRIPTION PAGE

3-6

7

Figure 12: List of approval drawings

44

kVA FREQUENCY Hz.

% TAPPING

CONNECTION

V. SEC. VOLT. V.

A. SEC. AMP. A.

NO LOAD LOSS W.

LOAD LOSS AT 75 °C W.

IMPEDANCE AT 75 °C %

TOTAL LOSS W.

OIL TEMP. RISE K

WINDING TEMP. RISE K

TITLE

DESIGN NO.

SCALE: PAGE 1

A 4 DWG. NO. 0

FOR APPROVAL DRAWING

APP. BYCHK. BYDRN. BYEFF. DATE REMARK

REV.NAME OF MANUFACTURER

Tr. 6300 kVA, 3 Ph. Dyn11

OUTLINE DRAWINGS

11000 - 6900 / 3984 V.

TYPE: CONSERVATION

51463011101

DRAWING FOR S/O 51320093

In order to keep the product's delivery schedule,

IEEE C57.12.00 IEEE C57.12.90 OTHER

+ 15 %

+ 15 %

± 10 %

+ 10 %

+ 10 %

-

55

60

± 7.5 %

+ 6 %

IEC 60076GUARANTEED

54000

11.00

60400

TOLERANCE

3

ONAN

11000

330.66

CAPACITY

PHASE

COOLING TYPE

527.15

please return the approval drawing before ……………………

Logo and Name of the manufacturer

N.T.S.

6400

50

± 2 x 2.5

Dyn11

6900 / 3984PRI. VOLT.

PRI. AMP.

GUARANTEED DATA

TECHNICAL DATA

6300

45

Figure 13: Sample Drawing of Technical and Guaranteed Data

S/N W/OCustomer Design No.Object Distribution Transformer Doc No.Type Oil-immersed BIL (HV) 125 kVRated Power 100 kVA BIL (LV) - kVRated HV 22000 V I - HV 2.62 ARated LV 400 V I - HL 144.34 AFrequency 50 Hz Tapping ± 2 x 2.5%Phase 3 Vector group Dyn11Cooling ONAN Standard IEC 60076VOLTAGE RATIO & VECTOR (DEV.) CALCULATION 30.3 °C 75 °C

Tap. 1 2 3 4 5Voltage 23100 22550 22000 21450 20900 % No-load current 0.43 - %

Ratio 100.03 97.64 95.26 92.88 90.5 % Load test current 99.49 - %A - B +0.15 +0.15 +0.08 +0.1 +0.12 RH (Average) 103.415 120.8392 OhmB - C +0.15 +0.15 +0.08 +0.1 +0.12 RL (Average) 8.6444 10.1009 mOhmC - A +0.15 +0.15 +0.08 +0.1 +0.12 I2RH 712 832 W

RESISTANCE RH (Ohm) Test tap : 3 30.3 °C I2RL 540 631 WTap. 1 2 3 4 5 TOTAL I2R 1253 1464 W

A - B 72.680 70.690 68.760 66.830 64.770 Stray loss 34 29 WB - C 72.760 70.940 68.980 67.020 65.020 Load loss 1286 1492 WC - A 72.990 71.050 69.090 67.290 65.120 Impedance voltage 3.80 3.87 %

RESISTANCE RL (mOhm) 30.4 °C Total loss (TL) - 1722 Wa - b 17.2870 RPL 30 °C RPH 30 °C Eff. 100% PF = 1 - 98.31 %b - c 17.2280 8.6346 103.298 Reg. 100% PF = 1 - 1.56 %c - a 17.3710 Correction factor (% deviation) -0.100 - %

NO-LOAD LOSS (NLL) 30.3 °C(Vrms) (Vmean) (A) (W) (V) (A) APPROVAL400.4 400 0.617 229.7 831.5 2.611

SEPEARATE VOLTAGEHV 50 kVLV 3 kV Checked By DateINDUCTED VOLTAGEHV 44 kVMEGGERHV - LV 13400 Mohm Approved By DateHV - G 14000 MohmLV - G 4900 Mohm Quality Assurance ManagerOIL BREAKDOWNGap 2.5 mm. 59 kVTANK LEAKAGE3 psi - 1 Hr.TEST RESULT

Declared Min. Max. TestedNLL 250 - 250 229.5LL 1550 - 1550 1492TL 1800 - 1800 1722%Imp 4.00 3.60 4.40 3.87

ROUTINE TEST REPORT

MANUFACTURER NAME AND LOGO

Status Passed andConcern Signature

PassedPassedPassedPassed

Dyn11

Test Supervisor

Passed(Hemetically seal type / Corrugate)

2500 V- 1 min. Passed

IEC 60156 Passed

400 Hz - 15 sec. Passed

LOAD LOSS (LL)(W)

1273.050 Hz - 1 min. Passed

Figure 14: Supplier’s routine test report

46

Customer: Standard: IEC 60076Contract No.: Manufacturer: Serial No.: MEA No.:

TECHNICAL DATACapacity: 50 kVA HT. Voltage: 24000 V. LT. Voltage: 480 / 240 V.

Phase: 1 Phase HT. Current: 2.1 A. LT. Current: A.Frequency: 50 Hz Tap: -4 x 2.5 Impedance at: 75.0 °C %

Insulation Class: - Vector Group: Subtractive NO Load Loss - W.Type: Cooling: ONAN Load Loss at: 75.0 °C - W.

INSULATION RESISTANCE TEST at: 1000 V.DC Amb. Temp. 28.0 °C Humidity: 77 %H.T.-L.T.: 69.00 G-Ohms H.T. Ground: 43.00 G-Ohms L.T. Ground: 27.60 G-Ohms

DIELECTRIC TEST

Applied voltage test: 75% Amb. Temp. 28.0 °C Humidity: 76 %H.T.-L.T.+Ground: 30.0 kV Frequency: 50 Hz Time: 60 Sec.L.T.-H.T.+Ground: 7.5 kV Frequency: 50 Hz Time: 60 Sec.

Inducted voltage test: 75% Amb. Temp. 28.0 °C Humidity: 76 %Supply: kV Frequency: 200 Hz Time: 30 Sec.

MEASUREMENT OF OIL DIELECTRIC STRENGHT Amb. Temp. 28.0 °C Humidity: 77 %Standard: ASTM D877 Oil breakdown voltage: 31.2 kV Breakdown voltage not less than 26 kV

MEASUREMENT OF WINDING RESISTANCE Amb. Temp. 27.0 °C Humidity: 66 %

Tap1

MEASUREMENT OF VOLTAGE RATIO AND VECTOR GROUP Amb. Temp. 28 °C Humidity: 76 %

100.00 50.00 97.50 48.75 95.00 47.50 92.50 46.25 90.00 45.00

0.05 N/A 0.06 N/A 0.07 N/A 0.10 N/A 0.12 N/A0.05 N/A 0.06 N/A 0.07 N/A 0.10 N/A 0.12 N/A

Polarity test:

MEASUREMENT OF NOLOAD LOSS And EXCITING CURRENT Amb. Temp. 27.5 °C Humidity: 67 %Voltage test: 240.0 V. Current: 8.7 A. No-load loss : W. at reference temp. 20 °C

MEASUREMENT OF LOAD LOSS AND IMPEDANCE VOLTAGE Humidity: 69 %LT. Short circuit ; Apply HT. at: Tap 1 Voltage: V. Current: A.

At temp.: 29.0 °C Impedance: 1.86 % Load loss : W.At temp.: 75.0 °C Impedance: 1.89 % Load loss : W. Total loss: W.

Efficiency: 98.96 % Voltage regulation: 0.70 % (at PF = 1.0)

Complied

36.000

Complied

Complied

HT. Winding resistance (Ohm)H1-H2

33.1760

LT. Winding resistance (Ohm)X1-X2

13.2470

Complied

1 2 3 4 5

24 kV System 446.3 2.1

Tap positionStandard ratio

Ratio error 1-3 (% )Ratio error 2-4 (% )

Subtractive

184.2

Complied

293.9343.9 528.1

TEST REPORT

DISTRIBUTION TRANSFORMER

Conventional

104.21.53

960932 4D-2044

Figure 15: Acceptance routine test report

47

MA4-7552-AGA

12/24 kV 750 kVA THREE PHASE

NO LOAD LOSS 880.00 WLOAD LOSS 4300.00 WTOTAL LOSSES 5180.00 W

* Total 1 set REP.NO. 01-31DATE: SEP. 3, 2001

Supplier's Report MEA's Report

NO Serial NO LOAD LOAD TOTAL NO Serial NO LOAD LOAD TOTALNumber LOSS (W.) LOSS (W.) LOSS (W.) Number LOSS (W.) LOSS (W.) LOSS (W.)

1 10108 864.00 4197.00 5061.00 1 10108 861.00 4383.30 5244.30

No load Loss -0.35% %Load Loss 4.44% %Total Loss 3.62% %

SUMMARY :

The above table shows that no load loss from MEA's report is not over the guarantee value but the load loss from MEA's report isgreater than that from supplier's report more than 2.5% and over the guarantee value. Therefore, results from MEA's report areused in calculating compensation as follows:

penalty compensation of load loss = (load loss-guarantee load load) x (106.5 baht / W) x (total set)

= (43.83.3-4300) x (106.5) x 1

= 8871.45 Baht

Percent Deviation of Losses between both results

GUARANTEE VALUE

Figure 16: Penalty Calculation without raising the Guarantee Value

48

MA4-7553-AGA12/24 kV 750 kVA THREE PHASE

DISTRIBUTION TRANSFORMER CONVENTIONAL TYPE

NO LOAD LOSS 1060.00 WLOAD LOSS 5600.00 WTOTAL LOSSES 6660.00 W

* Total 3 sets REP.NO. 01-32DATE: SEP. 3, 2001

Supplier's Report


1 10109 1008.00 5484.00 6492.00 3 10111 1017.00 5540.00 6557.002 10110 1018.00 5420.00 6438.00

1014.33 5481.33 6495.67

Samples from Supplier's Report Samples from MEA's Report


1 10109 1008.00 5484.00 6492.00 1 10109 1008.00 5821.20 6829.202 10111 1017.00 5540.00 6557.00 2 10111 1019.00 5821.50 6840.50

1012.50 5512.00 6524.50 1013.50 5821.35 6834.85

No load Loss 0.10% %Load Loss 5.61% %Total Loss 4.76% %

SUMMARY :

The above table shows that load loss from MEA's report is greater than that from supplier's report more than 2.5% and over theguarantee value. Therefore, load loss from supplier's report will be raised up 5.61% to used in calculating compensation as follows:

average load loss = 5481.33 W.

raised up = 5.61 %

adjusted average load loss = (5481.33) x (1.0561) x 1

= 5788.83 W.

penalty compensation of load loss = (adj. average load loss-guarantee load load) x (106.5 baht / W) x (total set)

= (5788.83-5600) x (106.5) x 3

= 60331.19 Baht

Percent Deviation of Losses between both results

Average

AverageAverage

GUARANTEE VALUE

Figure 17: Penalty Calculation with Raising the Guarantee Values

49

5. Conclusion

As mentioned earlier, the purpose of this chapter is to explain the practical acceptance test process and exceeding transformer losses management which have been utilized for more than 40 years and have been approved by the Asian Development Bank (ADB) and World Bank (WB). In reality, there may be many different opinions or arguments due to various political or customary practices. The aforementioned, does solve typical problems, however, based on the mutual benefits between the utility and the suppliers. The penalty values, while appearing to be high in nominal amounts, represent fairness in the evaluation of all suppliers and are beneficial for implementation by the utilities.

50

Chapter 5 Installation and Operation 1. Introduction As the utility accepts the transformers delivered by the supplier, some transformers shall be installed at the destination, but the balance will be kept in the warehouse as stock. The suppliers’ transformer manual will be submitted with the transformer for utility’s field workers to perform installation and operation. Therefore, all instruction and caution will be completely utilized in order to assure quality for at least twenty years. The information provided in this transformer handbook on the proper installation and operation of oil filled transformers, is provided as a guide. This is a brief outline for the proper procedures and requirements for the general and required care that must be followed. Neglect of these fundamental requirements may lead to serious problems, if not the loss of the transformer or other vital equipment. The installation and operation in this chapter will be explained based on application from well known utility having at least 50 years experience in the installation and operation of the low losses transformers.

2. Objective The transformers having low losses or standard transformers shall utilize the same process of installation and operation. There are two main installation configurations which are installed at the station: concrete or wooden pole type, and pad-mount type. The construction standards will be shown to guide the utility to set up the transformers and also other equipment in order to facilitate installation by the field workers. The loading guide will be discussed to keep the high efficiency for the low losses transformers.

51

3. Construction Standard Firstly, the characteristics of the transformer have to be obtained from the nameplate which shall be affixed to the transformer tank as per the requirement of the relevant standards. The nameplate shall provide the necessary information for transformer energizing, installation and operation. The nameplate shall include all relevant information. Secondly, the transformers will be separated, and warehoused for future extension power distribution planning. Various recommendations will be briefly discussed, and an explanation of the other transformers will be clarified in detail, according to the utility’s construction standards. 3.1. Name Plate

a. Serial number: To identify each and every transformer manufactured by

the manufacturer, the utility has to refer to this serial number when service is required. For the utility’s transformer management’s utilization, items such as: rated capacity monitoring, maintenance services, etc. should be noted and utilized. The utility should mention in the contract that they wish to obtain another running serial number which belongs to the utility’s references.

b. kVA: To signify transformer capacity or kilovolt ampere capacity.

c. Phase: This is the phase at which transformers are designed to operate.

d. Frequency: This is the design of the transformer to meet the frequency of the electricity supply.

e. Voltage & Ampere: To signify the primary and secondary voltages, whereas the displayed ampere is the rated normal electricity current on primary and secondary side.

f. Type: This is the method of cooling system used to cool the system from the heat generated during the transformer operation.

g. Insulation class: This is the classification of the insulated materials at which the transformers can withstand either the electricity current or the temperature rise.

h. Temperature rise: This is the average of oil temperature rise and winding temperature rise above ambient temperature at the rated kVA.

i. Percentage of impedance: The real figure is obtained from testing which will affect the transformer losses.

j. Oil quantity: To signify the quantity of transformer oil to be used in each unit of the transformer.

52

k. The total weight (kg): This is the total weight of the complete set of transformer.

l. Winding connection diagram: This is provided to show the relevant location of bushings and internal terminals. The winding connection diagram will be designed to meet the utility’s system configuration.

m. Vector group: Follows the international standard per the specification

mentioned by the utilities’ system designer. 3.2. Storage Management

It is recommended that if the transformer is not to be put into service immediately, the unit be placed in its permanent location and be filled with oil. The foundation should include: that it be placed on a solid level foundation in the storage area (as soon as possible), it should be dry and protected from the effects of weather, or preferably stored indoors. This will contribute to keeping transformer dry and the paint in good condition.

If the event that two or more transformers are stored together, there must be sufficient space between the transformers to prevent collision on any projecting attachments and also allow space for routine visual inspection.

If the transformer is stored longer than twelve months, it should be checked before installation. Check the condition of all the safety gauges; manually turn the tap changer to all positions till smooth turning occurs. An oil sample should be taken for analysis; the result should not be lower than 30kV/2.5mm. The tests results should be verified with the original results from the factory to assure they are still within acceptable limits.

3.3. Installation Management

a. Transportation

The Transformer must be properly secured to prevent shifting and movement during transportation and handling. Jolting and vibration should be avoided. No pressure should be exerted on the radiator or corrugated fin. The transformer must be handled in the normal upright position and lifting from the lifting lugs on the tank (if provided) or lifting on the cover in the event that no lifting lug can be utilized. Likewise, the jacking pads are to be used for jacking purposes. Note: Do not attempt to lift/jack the transformer other than the fitting parts provided for this purpose.

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The liquid immersed transformers, hermetically sealed type, are suitable for indoor and outdoor installation. It can be moved to the designated position utilizing wheels, roller, crowbar or pulley and must be levelled when installed at the designated location.

b. Indoor Installation

Transformers with natural cooling depend on the surrounding air to dissipate its heat. There must be sufficient ventilation for the transformer. Warm air will rise to the top and cool air flows down. A good ventilation transformer room should have an opening on top to dissipate the warm air and a bottom air inlet to intake the cool air. Both must locate diagonally across the room. As a guide, losses of 1 kW require an air flow of 5.2 m3/min, with air intake temperature at 30°C and air temperature rise of 10°C. The noise level measurement should be monitored according to the reference standards. For the air to circulate freely around the transformer and access maintenance facilities there must be a distance of at least 0.5 meter between the transformer and the wall of partition, the same precaution must be taken should there be several transformers in a room.

c. Outdoor Installation

It is recommended that transformers to be utilized for for outdoor installation, be installed on a solid plinth. However, if plinth is not available, the base shall be strong enough to support the transformer. The weight of the transformer is stated on the transformer rating plate. The samples of the construction standards has shown the single concrete pole installation and the two concrete pole or plat-form type in Figure 18 & 19 in Figure 20 & 21 respectively.

d. Cabling

The cables connected to the transformer must be properly supported and clamped to prevent unnecessary strain on the HV bushings and LV bus bars. If the cable boxes are supplied, the cable gland plate and cable must be properly tightened.

e. Bolt Tightening Torque

• Torque Setting for various bushing and bolt sizes. Bushing Bolt Size Tightening Torque (Nm)

1/250 M12 14 1/630 M20 24

1/1000 M30 36 1/2000 M42 70

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1/3150 M48 70

• Torque Setting for various bolt sizes used in bus bar Connections - Steel

Bolt Size Tightening Torque (Nm) M6 6-9 M8 15-22

M10 35-44 M12 70-75 M16 120-150

f. Energizing the transformer

When the voltage is first applied to the transformer, if possible, it should be brought up slowly to its full value so that any incorrect connection or other problem may be diagnosed before damage can occur. If this is not possible, then energize without load. It is recommended, especially if the excitation is through cables or fuses, that the output voltage be measured to ensure that all three phases are energized. After full voltage has been applied, the transformer should remain energized at full voltage for a few hours without load. It should be kept under observation during this time and also during the first hours that it delivers electricity to the loads.

g. Check the transformer after energizing The transformer should be checked after energizing to ensure that it is in normal operating condition before loading as follows: • Check the LV voltage. If the voltage is insufficient, then de-

energize the transformer to reset the tap changer to the correct voltage level.

• Check the phase sequence. If the phase sequence is incorrect, then de-energize the transformer to re arrange the cable connection.

• Check the transformer noise. If the humming sound is abnormal, then de-energize the transformer and notify the manufacturers.

4. Loading Guide 4.1. Loading in Normal Operation

Transformers are suitable for full-load operation at rated temperature rise without loss of life, providing the following conditions are met:

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• Ambient temperature does not exceed 40°C; or average more than 30°C; in one 24 hour period, the transformer may be used in over 40°C ambient for very short intervals. Unless it is a specially designed unit with the properly upgraded insulation level which can be operated at a higher temperature rating.

• Installed elevation does not exceed 3,300 feet (1,000 meters) above sea level, otherwise the transformer capacity will be de-rating due to the air density and the cooling efficiency of the transformer is reduced, the factors that can be calculated refer to ANSI standard C57.

• Overloading should be in accordance with ANSI standard C57 Loading Guide or IEC standards.

• A schedule should be made for periodic checks of the load applied to the

transformer to verify that an excessive load is not being applied to the unit.

4.2. Loading According to Optimization of Power Efficiency of The

Transformer As noted in Chapter 1, the most important consideration for low losses transformers, when high investment of the low losses transformers concerned, is the power efficiency of the transformer operation as can be seen in Table 2 Power efficiency of transformer loading. Maximum efficiency will occur at a load when the no-load loss and load loss of transformer are equal.

Transformer

rating (kVA)

Transformer Loss (Watt) % Load Factor - Highest Efficiency No-load Loss Load Loss

15 70 160 66.14% 45 160 360 66.67% 75 220 580 61.59%

112.5 255 840 55.10% 150 300 1000 54.77% 225 420 1530 52.39% 300 480 1860 50.80% 500 670 3030 47.02% 750 840 4370 43.84% 1000 1,000 6400 39.53% 1500 1200 10000 34.64%

Table 2: Table of power efficiency for low losses transformer

The power efficiency of the transformer is the best method of specifying the lowest losses during operation or loading the transformer as designed approximately 40% of the transformer capacity. In fact the power efficiency of

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transformers serviced in rural areas are s skewed by the continual presence of no-load losses so that the transformer represents an energy drain on the system when unloaded and when loaded at light loads (below about 15%), the efficiency is very poor. In contrast, in transformers which are serviced in the urban area or large cities, it was found that the loading capacity is approximately 50%, which is still defined as low loss energy.

4.3. The Timeline of the Differing Sizes in Transformers First stage, 40 years ago, Metropolitan Electricity Authority (MEA) started using many sizes ranging from 5 kVA, 20 kVA, 50 kVA to 500 kVA. At least 20 ranges. Most of the transformers were single phase. The energy supplies to the loads were located in different places with a small increase in customers.

When a transformer reached full capacity due to the increasing customers’ demands, the utility would either replace the transformer with a larger one, or would bank three single phase transformers into a three phase system to increase the power capacity.

Second stage, 10 years later MEA started to buy three phase and single phase transformers with the same sizes and many ranges in capacity, to accommodate the increase in customers. MEA made a decision to utilize the transformers as efficiently as possible by considering the load curve of each type of customers, load growth per annum and five year expansion consumption plan. The result was that the need to replace transformers due to overcapacity was not reached as frequently as had previously been the case.

Final stage. Currently, with the advanced power distribution designed software, MEA is trying to reduce costs concerning the transformer management such as inventory cost, warehouse’s facilities, low loss transformers, also, they decided to minimize the sizes of transformers. They are only considering 8 ranges or sizes which are 75 kVA, 150 kVA, 225 kVA, 500 kVA, 750 kVA, 1,000 kVA, 1,500 kVA and 2,000 kVA.

MEA had reduced costs considerably after the above mentioned changes. They have also realized avoidance of heavy traffic, and lessened environmental impact.

For other LMS utilities, the sizing of the transformers shall be considered by using power distribution software and load forecasting, in some cases, it is recommended to separate the urban and rural area’s sizing transformer solutions due to different load characteristics, inventory cost, heavy traffic impact, etc.

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Figure 18: Construction drawing for transformer installation (single concrete pole)

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Figure 19: Bill of material for transformer installation (single concrete pole)

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Figure 20: Construction drawing for transformer installation (platform)

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Figure 21: Bill of material for transformer installation (platform)

5. Conclusion As stated, low cost - high losses transformers but high cost - low losses transformer are both available. The recommendation is to reach and optimal financial decision between the cost and the low losses of the transformer. Both the standard loss transformers and the low loss transformers should be implemented for rural usage

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and urban area respectively. The example of the standard loss transformer table has shown in Table 3.

The loading guide of those types of transformers which are standard loss and low loss applications should be carefully studied and practiced to reach the most efficiency of transformer utilization.

Table 3: Example of standard loss transformers

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Chapter 6 Maintenance and Asset Management 1. Introduction The information provided in this chapter on maintenance and asset management of oil filled transformers, is provided as a guide. This is a brief outline for the proper procedures and requirements for the general and required practices that must be followed. This is an addition to the international standard ANSI and IEC requirements for the maintenance and asset management for low losses transformers. Best practices should be followed to lead to the best solution for the utility to prolong the transformer‘s service life and maximize its operating efficiency.

2. Transformer Load Monitoring (TLM) The power distribution system in large cities which services a large supply system, consists of a variety of electrical equipment, the transformers is one of the main pieces of electrical equipment having installed at the pole more than 40,000 sets. Each district office or branch that has to manage the units individually, will send field workers or technicians to inspect general characteristics and measure or update the load capacity of each transformer periodically, this is time consuming and a waste of manpower. Measurement of transformer loading by the Utility can take a few years to complete. This data is therefore not current compared to real time monitoring which is explained in another chapter. The Transformer Load Monitoring (TLM) system is designed to obtain basic data from the transformer. It includes information such as: voltage, current, etc. It then sends the data remotely to the control centre so that they may monitor the results and send it to the operators for transformer management. Thanks to the TLM system, the transformer management operator can make use of this data for preventive maintenance, up-rated transformer replacement, and electrical system planning and emergency mal-function management.

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2.1 The TLM system consists of three main parts as follows:

a. Remote terminal units (RTU) b. Master Station c. Communication protocol

2.2 Principal Concept

The Transformer Load Monitoring project will be first designed as a trial project having the objective of developing and building up operator units or sections to manage via remote control and metering for 5 sets with one master station and the communication protocol having system configuration shown in Figure 22 below.

Figure 22: Transformer load monitoring (TLM) system configuration

a) Master station This is a computer server which will be installed at each district office or branch as the centre for collecting all transformer data from Remote Terminal Unit (RTU) and convert to the data base having three main functions which are: i) Database Server: It serves as a data collector of the transformers

from RTU and keeps this data for investigation; the facilities are briefly explained as follows:

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• Acquire the transformer data, using the Protocol given in the specification or TOR of the project

• Database capacity should be large enough to keep the electrical data such as voltage, current , etc. of all transformers in each district office at least one year having three values (maximum, minimum and average) a day including the system event of fault or mal-function.

• Searching criteria favour to the utility such as Transformer manufacturer name, date-month-year of the malfunction.

ii) Human-machine interface (HMI) station: HMI is a modification of

the original term MMI (Man-Machine Interface) which allows the users to manipulate a system and allow the system to indicate the effects of the users' manipulation, showing the status and transformer data in different patterns such as graphs, tables and reports detailed as follows: • To assess the preliminary data such as voltage, current, resistive

power, reactive power, power factor, etc. • To display the characteristic data in form of graphic mode, table

mode with designed specific criteria • To display all transformers installed in the system showing all

status of ampere, voltages, etc. having full options of searching facility.

NOTE: Special options for the advanced program which shows the transformers in the form of a single line diagram of the distribution system located in different district offices. The monitor displays an alarm when any event occurs, and also displays the communication between master station and each RTU.

It is capable to increase/decrease or relocate the transformer locations and setting of each RTU, the report can be managed in various formats such as loading report of each transformer, loading report of transformer each day, each transformer electrical data and error message, etc.

iii) Historical Database Server: Storing all transformers characteristics in electronic format for searching, displaying, retrieval and data comparison

b. Remote Terminal Unit (RTU)

RTU is an instrument installed near or at each transformer to gather and deliver all transformer data such as current, voltages, etc. to the Master Station through wireless communication or fiber optic to alert when malfunction occurs, this includes the following capabilities: • Measuring electrical characteristic of transformer such as voltages,

current, etc.

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• Calculating the power factor of the transformers • Transferring the data in form of Protocol as specified in the

specification • Warning message to alert users in case of sudden abnormal situation • Withstanding to outdoor application such as Ultra violet (UV), direct

sunlight, pollution, etc.

c. Communication The communication between Master Station and RTU should be via high speed internet fiber optic communication wireless communication.

d. Protocol

Protocol for communication between the Master Station and RTU is capable of: • Sending important information such as RTU ID, electrical

characteristics and emergency case. • Support for extension of installation of RTU more than 5,000 sets • Verify the accuracy of information • Support transmitting of data of “Polling” form • Support transmitting of data in the form of Message (once an

emergency is found)

3 Maintenance and Inspection

3.1 Remarks on Making Maintenance and Inspection • While working adjacent to live parts: Be sure to check that the apparatus

is disconnected from the live circuit. The work should begin only after ascertaining that the apparatus is not live.

• In case of regularly maintenance and inspection: Try to identify any abnormal conditions or problems with the transformer as early as possible by comparing such indication with the operation records carefully.

3.2 Regularly Inspection

• Check the top oil temperature of the transformer: The top oil temperature

of transformer is specified to be not more than in Table 4. Make certain that oil temperature rise is not more than Table 4. The Dial thermometer is set to close the supervisory contacts at the temperature specified in Table 4. (See column Alarm) for alarm status and Table 4. (See column Tripping) for tripping purpose.

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Temperature of transformer (°C)

At 40°C ambient temp. Dial thermometer

Contacts closed at (°C) Oil Temperature

Rise Top Oil

Temperature Alarm Tripping

50 55 60

90 95 100

85 90 95

95 100 105

Table 4: Temperature condition of transformer

• Looseness on locking or binding points: In case of any looseness being found on various binding bolts along the outside surface, please tighten all the loose parts as necessary.

• Oil leakage: Carefully check the parts to which gaskets are applied. Note: While operating, transformer will generate heat and will effectively remove condensation and moisture on the transformer.

3.3. Periodical Maintenance and Inspection

The transformer should be properly installed and maintained. Maintenance should be performed regularly and when there is an indication of irregularities or problems. Inspection should typically be performed when the transformer is out of operation. The inspection should be done as follows: • Check the protective devices such as dial thermometer and oil level for

proper functioning. If it is out of order, replace it with a new one. The replacement of dial thermometer does not require draining the oil out, because the thermo-scope is inserted in the thermometer pocket which is separated from the oil.

• Check all bushings if the following damages have occurred: - Dirty spots, cracks and traces of discharge on porcelain insulator. - Loosened bolts, nuts and irregular tightness on fixing terminals or studs.

• Measurement of insulation resistance for each winding and ground, and between windings. Insulation resistance is subjected to wide variation with temperature, humidity and cleanliness of insulators. When the insulation resistance falls below the minimum permissible value, it can, in most cases of good design and where no defects exist, be brought up to the required standard by cleaning and drying the transformer. A tentative minimum value for operation is shown in Table 5 below:

Temperature °C 20 30 50 60 Insulation resistance MΩ 800 400 100 50

Table 5: Minimum permissible insulation resistance measurement

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3.4. Recommended Maintenance Schedule

Description One month after initial energizing

Once a year after energizing

Gauge readings Tank leakage Control wiring & circuits Point finish Liquid dielectric test Bushing terminal Insulator cleanliness inspection

Note: indicator the applicable one

4. Conclusion

The asset management of the transformer begins with the specification preparation. Reference standard design, raw materials and workmanship are used to manufacture the transformer. The lifetime of transformers is determined by the lifetime of the electrical insulation which is mainly organic in its chemical nature (being composed of mineral oil, impregnated paper, cellulose materials, etc.) and the stability of such materials is very susceptible to the operational temperature. Thus, the operating temperature must be very closely specified and controlled in operation. If the maximum temperature is exceeded for any length of time, the insulation lifetime may be reduced from the nominal level. Any overloading of the transformer, harmonic influences, faults by treeing and animals are present, will affect the insulation temperature above its permissible level as designed or mentioned in the nameplate and will reduce the life of the transformer. The usual rule of thumb is that continuous operation above the rated temperature by only 6°C will halve the effective life of the insulation: this is the life reduction factor used in most international Standards such as the Australian Transformer loading Standard AS2374.7 [11]. Finally, the main purpose of this Handbook is to encourage the utilities to begin using the low loss transformer by implementing the evaluation formula. Then it will lead to the specified values of low loss figures for each rating of transformers which are suitable for their own system. It will result in the electrical reduction of losses by improved transformer efficiency and will thus extend the life of transformers and is an additional justification for the introduction of new high efficiency levels for transformers.

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Applying the new technology of the transformer load monitoring (TLM) will aid the utility to keep the service transformer’s capacity to be in the limit of the loading guide, and to reach the generated lowest loss energy. Another key is that the insulation need be maintained within the appropriate temperature limits to reach and surpass the service life at least twenty years as mentioned in the evaluation formula.

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Notes

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Notes

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Notes

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Documents

Distribution Transformer Main Handbook