Internship Report

Internship Report on KAPCO

Internship ReportOn KAPCOFrom July 08th, 2014 to August 21st, 2014

OPENING

In the name of ALLAH, The Most Benevolent, ever Merciful, All Praise be to ALLAH, Lord of the whole world. Most Beneficent, ever Merciful, King of the Day of Judgment, You Alone we worship for, and to You Alone we turn for Help. O GOD, Guide us to the Path that is straight. The Path of those, who are blessed by you, neither of those, who have earned Your Anger, nor of those who have gone to astray.

PREFACE

Concepts we build by studying theory in classroom, & dimensions while observing & analyzing the activities in real world. Practical internship and research work on Technical studies is an integral part of Engineering program. To become an expert to understand all concerning issues concerning Ethics, only theoretical knowledge does not provide a concrete base. Research work, report writing, internship reports also considered a significant task along with theoretical knowledge therefore I was assigned a internship report on Kot Addu Power Company (KAPCO), so that I gain a clear insight of the real world.

Acknowledgement

I am indebted to most respected Principal Engineer of BLOCK-III Engr. Atta ur Rehman, for his able guidance, motivation and cooperation that he expended to me during the internship program. In addition, I wish to express my deep and sincere appreciation and thankfulness to Mr.Faiz Ul Hassan (Foreman) & Mr. Muhammad Rafique (Test Inspector) for their able guidance Whenever I needed them, they were ready to help me by any means, indeed very kind and wonderful human. Without their continuous help and encouragement, this internship & this report would surely not be able to take this present shape.

OPENING1PREFACE2ACKNOWLEDGEMENT3List of Contents4introduction6

quantitative engineering activities7categories of numerical methods & applications8linearization 8solving systems of equations10optimization14

numerical integration and differentiation16references20

Table of contents

1. Acknowledgement

2

2. Abstract

3

3. Contents

4

4. Introduction

5

5. Vision and Mission

6

6. Plant General Characteristics

77. Generator

9

8. Parts of Generator

11

9. Generator cooling system

14

10. Generator Protection

15

11. Power factor

1612. Transformer

1913. Types of Transformer

20

14. Transformer Protection

24

15. Battery rooms

26

16. Switch yard

2717. Black Start

30

18. Neutral and Grounding

31Gas Turbine Power Station, KAPCO Kot AdduIntroduction to the ProjectThe need for electricity is increasing day-by-day in the developing countries. Energy plays a basic role in the developing plans. To meet the targets of economic development and social growth the development in energy sector is the main requirement. In order to get this target WAPDA played an important role and then the project of Gas Turbine Power Station in Kot Addu started.KAPCO is Pakistan's largest Independent Power Producer (IPP) with a name plate capacity of 1600 MW. KotAddu Power Plant (the "Power Plant") was built by the Pakistan Water and Power Development Authority ("WAPDA") in five phases between 1985 and 1996 at its present location in KotAddu, District Muzaffargarh, Punjab. In April 1996, KotAddu Power Company Limited ("KAPCO") was incorporated as a public limited company under the Companies Ordinance, 1984 with the objective of acquiring the Power Plant from WAPDA. The principal activities of KAPCO include the ownership, operation and maintenance of the Power Plant.

The Power Plant is a multi-fuel gas-turbine power plant with the capability of using 3 different fuels to generate electricity, namely: Natural Gas, Low Sulphur Furnace Oil and High Speed Diesel to generate electricity. The Power Plant is also the only major plant in Pakistan with the ability to self-start in case of a country wide blackout.On June 27, 1996, following international competitive bidding by the Privatization Commission Government of Pakistan (the "Privatization Commission"), the management of KAPCO was transferred to National Power (now International Power) of the United Kingdom, which acting through its subsidiary National Power KotAddu Limited (NPKAL), bought shares representing a 26% stake in KAPCO. Later, NPKAL bought a further 10% shareholding in KAPCO increasing its total shareholding to 36%.The other majority shareholder in KAPCO is WAPDA with a present shareholding of 46%.

Following the successful completion of the offer for sale by the Privatization Commission (on behalf of WAPDA) in February 2005, 20% of KAPCOs shareholding is now held by the General Public. On April 18, 2005 KAPCO was formally listed on all three Stock Exchanges of Pakistan.The Power Plant is situated in District Muzaffargarh, Punjab, 100 KM. north east of Multan on the left bank of the River Indus at a distance of 16 K.M. from Taunsa Barrage. The area is surrounded by agricultural land on the north and west side of KotAddu.VISION AND MISSIONVISION STATEMENT:

To be a leading power generation company, driven to exceed our shareholders expectations and meet our customers requirementsMISSION STATEMENT: To be a responsible corporate citizen

To maximize shareholders' return

To provide reliable and economic power for our customer

To excel in all aspects relating to safety, quality and environment

To create a work environment which fosters pride, job satisfaction and equal opportunity for career growth for the employees

General Plant data Gas Turbines

10

HRSGs

10

Steam Turbines

05

Total Installed Capacity

1600MW

Max. Load Generation

1510MW

Load According to IDC Test (1996)

1345MW

Load According to ADC Test (2010)

1355MW

No. of Circuits

6 x220KV; 6 x132KV

Max. Generation in one day

35,667Mwh

Combination of Gas Turbines (GT) & Steam Turbines (STG) at KAPCO

INTRODUCTION TO ALL BLOCKSThere are total three blocks in KAPCO. The details of these three is given below.

Block-I:

Block-I is equipped with six turbines in total. In which four are Gas Turbine (GT1, GT2, GT3 and GT4) and other two are Steam Turbines (STG 9, STG10). The whole system is based on combined cycle.GT1 and GT2 are German made and are manufactured by Siemens Engineering Company Limited. They have overall thermal efficiency 28% and having rated capacity of 100MW. Rated speed is 3000rpm. GT3 and GT4 are Italian made and are manufactured by Fiat Engineering Company Limited. They have overall thermal efficiency 28% and having rated capacity of 100MW. Rated speed is 3000rpm.

Steam Turbines (STG 9, STG 10) are manufactured by ABB. As there is not any kind of compressor which uses about 60% energy of GT, so its efficiency is increased up to 48%.

Block-II:

GT5 and GT6 are France made and are manufactured by ALSTHOM Engineering Company Limited. They have overall thermal efficiency 28% and having rated capacity of 100MW. Rated speed is 3000rpm. GT7 and GT8 are also France made and are manufactured by ALSTHOM Engineering Company Limited. They have overall thermal efficiency 28% and having rated capacity of 100MW. Rated speed is 3000rpm. All these machines are synchronized directly with the bus bar i.e. at 220 KV to attach with bus bar.

Block-III:Block-III is equipped with three turbines in total. In which two are Gas Turbine (GT13, GT14) and other one is Steam Turbine (STG 15). Gas Turbines GT13, GT14 and STG 15 are German made and are manufactured by Siemens engineering co. ltd. They have overall thermal efficiency 45% in combine cycle mode.

Connection with Switch YardBlock-I is connected to 132KV bus bar by using Unit transformer and then with the help of autotransformers, these voltages stepped up to 220 KV to attach it with the main bus bar.From the 132 KV bus bar, direct lines are going to different areas. Two of them are going to KOT ADDU. The output of Block-III is stepped up to 220KV and then transmitted.The detail of each circuit will be discussed later.

The Generator:

Synchronous generator is used to convert mechanical energy into electrical energy. Basic Working principle:

According to Faradays law of electromagnetic induction:If there is a relative motion between conductor and magnetic field, then an EMF will be induced into the conductor.

To create this relative movement, it does not matter whether the magnet is rotating and the conductor is stationary or the conductor is moving and magnet is stationary.

The magnitude of the induced EMF is directly proportional to the No of conductors (N) and the rate of change of magnetic flux crossing the conductors.

E = N (d/dt)

Difference between AC generator and DC generatorThere is one main difference between an AC and DC generator. In DC Generator, the armature rotates but the field system remains stationary but in AC generator, the case is reverse because here armature remains stationary but field winding rotates.

The general thing to keep in mind in this reference is that armature is a thing, which produces alternating magnetic field. Therefore, in DC, this magnetic field is being produced by rotor, which is called the armature, and in AC, this remains stationary and here it is called the stator.

The stator consists of a cast iron frame, which supports the armature core having slots on its inner periphery for housing the armature conductors. In a slip ring induction machine the rotor, winding terminals are coming out and then they are supplied with a DC supply to produce the stationary magnetic field, which is converted into the rotating magnetic field by rotating the rotor by an external source, which is called the prime mover.

When the rotor rotates, the stator conductors are cut by magnetic flux, hence they have an induced EMF produced in them. As magnetic poles are alternately N and S, they induce an EMF and hence current starts flowing in armature conductors, which first flows in one direction and then in the other. Hence, alternating EMF is produced in the stator conductors whose frequency depends on the No of N and S poles moving past a conductor in one second and its direction is given by Flemings right hand rule:

First fingerMagnetic field

Second fingerDirection of current

ThumbMotion of the conductor

Different Parts of Generator:

The two-pole generator uses directly air-cooling for the rotor winding and indirect air-cooling for the stator winding. All types of losses (iron, friction, windage, stray and etc) are also dissipated through air. Generally a generator consists of following parts:

Stator

Rotor

Excitation system

Carbon brushes and Slip rings

Retaining rings

Bearing

Rotor grounding system

Cooling system

Stator:

It is a stationary part of the generator. The stator has two main components:

Stator frame,Magneticcore,Statorwinding,Stator End shields

Stator frame:

The frame is for to support the laminated core and winding and also for to increase the mechanical strength of the machine. It is the heaviest part of the generator. Air ducts are provided for the rigidity of stator frame. End shields are also bolted to this frame. For the foundation purposes feet are provided. Electrical connection of bars and Phase connectors:

Electrical connection between the top and bottom bars is made by brazing. One top bar strand being brazed to one strand of associated bottom bar, so that the beginning of each strand is connected without having any electrical contact with the remaining strands. This connection offers the advantage that circulating current losses in the stator bars are kept small.

The phase connectors consists of flat copper sections, the cross section of which results in a low specific current loading. The ends of each phase are attached to the circular phase connector, which leads from winding ends to the top of the frame. The phase connectors are mounted on the winding support, using clamping pieces and glass fabric tape.

Rotor:It is the rotating part of the generator. It is driven by the turbine and it creates rotating magnetic field. There are two types of rotor:

Cylindrical type

Salient-pole type

The cylindrical type rotor is used in turbo alternators and a having a uniform air gap. Normally it is used in all types of thermal power stations where the rotating speed of rotor is high like 3000 rpm in PAKISTAN. For 3000 rpm, it has two poles. The field winding is accumulated in slots on the solid rotor.

Salient pole rotors are used for low speed operation like about 167 rpm for 50 Hz. For this arrangement, we use 36 poles of the rotor.

Rotor has the following main components:

Rotor shaft:

The rotor shaft is made of single gorging whose ingot is made in an electric furnace and then vacuum cast. The rotor consists of an electrically active portion and the two shaft ends. A forged coupling is used to couple the rotor to the turbine. The longitudinal slots hold the field winding. Slot pitch is selected so that two solid poles are displaced by 180 electrical. In these slots field coils are milled into shaft body and is arranged so as to generate magnetomotive force wave approaching a sine wave.Rotor teeth are provided with axial and radial ducts enabling the cooling air to be discharged into the air gap for intensive cooling of the end winding.

Rotor winding:Rotor winding has also two distinct parts:

The shaft contained in shaft body.

The part outside the shaft body.

The rotor winding consists of several coils, which are inserted into the slots, and series connected such that two coil groups form one pole. Each coil consists of several series connected turns, each of which consists of two half turns which are connected by brazing in the end section.

Strips of laminated glass fabric insulate the insulated turns from each other. The edges of slots are made up of high conductivity material and they are there to act as damper winding. At the ends, the clots are short-circuited by retaining rings.

Rotor fan:

The generator cooling air is circulated by two axial flow fan located at the end of the shaft. To argument the cooling of the rotor winding, the pressure established by the fan in conjunction with the air expelled from the discharge port along the rotor. The moving of the fan have threaded roots for being screwed into the rotor shaft. Threaded roots fastening permits the blade angle to the required level.

Excitation system:The excitation system is to supply the direct current to rotor which allows the generator to maintain a controlled voltage between its terminals when connected to the network. A voltage regulator drives the excitation system. The excitation power for the generator is supplied by an exciter with rotating diodes that are fitted at the end of main generator shaft.

The excitation voltage is developed by rotating DiodeBridge that supplies the rotor winding. These rectifying diodes are given supply by an excitation transformer of which the primary winding is supplied by the main generator. Then a three-phase thyrister bridge rectifies the secondary winding.

Generator cooling system

The heat losses arising in the generator interior are dissipated to the secondary coolant (cooling water) through air. Direct cooling of rotor removes hot spots and differential temperature between the adjacent components. Indirect cooling is used for stator winding.Air and hydrogen are two cooling media for the generator cooling. The field and armature copper losses are evacuated by air/ hydrogen gas flowing inside the generator. The axial fans circulate the air. In KAPCO all generators are air cooled.

Advantages of Air-cooling:

Lower cost price Easy maintenance Short inspection

Air cooling circuit:Cooling air is circulated in the generator by two axial-flow fans on the rotor shaft. Cold air is drawn by fans from cooler and then divided into three parts:

Flow path 1:Itis directed into the rotor end winding and cools the rotor winding. Along this path heat of the rotor winding is directly transferred to the cooling air.Flow path 2:Itis directed over the stator end winding to the cold air ducts and in the stator frame space between the generator housing and the stator core.

Flow path 3:It is directed into the air gap via the rotor retaining rings. This path mainly cools the rotor retaining rings, the end of the rotor body and end portion of the stator frame.Then this flow of air is mixed up in air gap from where it goes for the cooling of the other remaining portion of the stator core and the stator winding. The hot air is returned to the cooler via hot air ducts re-cooling and draws again by the fans.

GENERATOR PROTECTION:

There are different types of fault can occur on to the generators so the protection of these faults to the generators we used some protections. These are giving below.

Negative phase sequence protection.

Rotor earth fault protection.

Loss of excitation.

Reverse power protection.

Differential protection.

Under frequency/over frequency relay.

Stator over current protection.

Stator over voltage protection.

Different Loads and their Power FactorLoad TypesDistribution systems are typically made up of a combination various resistive, inductive, and capacitive loads.Resistive LoadsResistive loads include devices such as heating elements andincandescent lighting. In a purely resistive circuit, current and voltage rise and fall at the same time. They are said to be in phase.True Power

All the power drawn by a resistive circuit is converted to usefulwork. This is also known as true power in a resistive circuit. True power is measured in watts (W), kilowatts (kW), or megawatts (MW).Inductive Loads

Inductive loads include motors, transformers, and solenoids. Ina purely inductive circuit, current lags behind voltage by 90. Current and voltage are said to be out of phase. Inductive circuits, however, have some amount of resistance. Depending on the amount of resistance and inductance, AC current will lag somewhere between a purely resistive circuit (0) and a purely inductive circuit (90). Capacitive Loads

Capacitive loads include power factor correction capacitors and filtering capacitors. In a purely capacitive circuit, current leads voltage by 90. Capacitive circuits, however, have some amount of resistance.

Reactive LoadsCircuits with inductive or capacitive components are said to bereactive. Most distribution systems have various resistive and reactive circuits. The amount of resistance and reactance varies, depending on the connected loads.Reactive Power

Power in an AC circuit is made up of three parts; true power, reactive power, and apparent power. We have already discussed true power. Reactive power is measured in volt-amps reactive (VAR). Reactive power represents the energy alternately stored and returned to the system by capacitors and/or inductors. Apparent Power

Apparent power is the vector sum of true power, which represents a purely resistive load, and reactive power, which represents a purely reactive load. A vector diagram can be used to show this relationship. . Larger values can be stated in kilovolt amps (kVA) or megavolt amps (MVA).Power Factor

Power factor (PF) is the ratio of true power (PT) to apparent power (PA), or a measurement of how much power is consumed and how much power is returned to the source. Power factor is equal to the cosine of the angle theta in the above diagram. Power factor can be calculated with the following formulas.

Solutions

As we have learned, there are a number of things that can affect power quality. The following table provides some basic guidelines to solve these problems. It should be remembered that the primary cause and resulting effects on the load and system should be considered when considering solutions.Problem Effect Solution

SagComputer shutdown resulting in lost data, lamp flicker, electronic clock reset, false alarm.Voltage regulator, power line conditioner, proper wiring.

SwellShorten equipment life and increase failure due to heat.Voltage regulator, power line conditioner.

UndervoltageComputer shutdown resulting in lost data, lamp flicker, electronic clock reset, false alarm.Voltage regulator, power line conditioner, proper wiring.

OvervoltageLife expectency of motor and other insulation resulting in equipment failure or fire hazard. Shorten life of light bulbsVoltage regulator, power line conditioner.

MomentaryPowerInterruptionComputer shutdown resulting in lost data, lamp flicker, electronic clock reset, false alarm, motor circuits trip.Voltage regulator, power line conditioner, UPS system.

NoiseErractic behavior of electronic equipment, incorrect data communication between computer equipment and field devices.Line filters and conditioners, proper wiring and grounding.

TransientsPremature equipment failure, computer shutdown resulting in lost data.Surge suppressor, line conditioner, isolation transformers, proper wiring, grounding.

HarmonicsOverheated neutrals, wires, connectors, transformers, equipment. Data communication errors.Harmonic filters, K-rated transformers, proper wiring and grounding.

Power FactorIncreased equipment and power costsPower factor correction capacitors.

Transformer

Transformer is a device that transfers electrical energy from one circuit to another by magnetic coupling without requiring relative motion between its parts. It usually comprises two or more coupled windings, and, in most cases, a core to concentrate magnetic flux. An alternating voltage applied to one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings. Varying the relative number of turns between primary and secondary windings determines the ratio of the input and output voltages, thus transforming the voltage by stepping it up or down between circuits. It has effect on voltage, current and phase angle.A transformer makes use of Faraday's law and the ferromagnetic properties of an iron core to efficiently raise or lower AC voltages. It of course cannot increase power so that if the voltage is raised the current is proportionally lowered and vice versa. Classification:The many uses to which transformers are put leads them to be classified in a number of different ways by:

Power level:It converts from a fraction of a volt-ampere (VA) to over a thousand MVA;

Voltage class:It converts from a few volts to hundreds of kilovolts;

Cooling types: Air cooled

Oil filled

Fan cooled

Water cooledApplication function: such as power supply, impedance matching, or circuit isolation;

End purpose:distribution, rectifier, arc furnace, amplifier output;

Winding turns ratio: step-up, step-down, isolating (near equal ratio), variable

Frequency range:power-, audio-, or radio frequency;

TYPES OF TRANSFORMER:Transformers are constructed so that their characteristics match the application for which theyare intended. The differences in construction may involve the size of the windings or therelationship between the primary and secondary windings. Transformer types are also designatedby the function the transformer serves in a circuit, such as

DistributionTransformer Start-up Transformer

Auxiliary Transformer

Auto Transformer Matching Transformer

IsolationTransformer Instrument potentialTransformer isolation transformer.

Instrument current TransformerAccording to cooling mediam:They are classified as,

1. Dry (Air-cooled):

These are used according to the environment temperature and heat dissipation. They are less expensive and they require less maintenance. Its main disadvantage is that its output rating decreases by 1amp with an increase of one C temperature.

Oil type:

These transformers have following types, having oil as a cooling media.Unit Transformer:Unit transformers are used in many different types andapplications. Unit transformers are used oil cooled. Here unit transformers are used for very heavy duty. Block-2 Unit transformers have ability to convert 11kv into 220kv.Unit Transformers take voltage from auxiliary transformers and then pass it to the switchyard. Block-2 has Alsthom CGEE transformer made of Itlay. Start-up Transformer: KAPCO has the ability of self-start. There are two start-up transformers. Start-up transformer are used to step-down the voltage. Here in KAPCO they are used to step-down 132KV to 11KV and energize 11KV bus bar.

First transformer is connected with unit 1 and 2 while 2nd transformer is connected with unit 3 and 4. All units of KAPCO are interconnected start-up transformer of unit 1and 2 can provide supply to unit 5and 6 similarly start-up transformer of unit 3 and 4 is connected with unit 7 and 8.

Block 3 units can get supply from units 5 to 8.

Auxiliary Transformer:

They are very used to make supply of unit stable they take 11kv from unit and transformer it to unit transformer and as well 11kv bus bar. The output voltage of unit can different from exact 11kv, which can be 10.8kv or something so these transformers are used to stable this value.Auto Transformer:

Autotransformer is generally used in low power applications where a variable voltage is required. The autotransformer is a special type of power transformer. It consists of only one winding. By tapping or connecting at certain points along the winding, different voltages can be obtained. Only switchyard of 132kv has four autotransformers, which has ability to convert 132kv into 220kv they also convert, 220kv into 132kv .They are like interconnection between 132kv and 220kv.

Matching Transformer:It is used for CT to make the voltage equal on both sides of transformer. They have small size.

Isolation Transformer:Isolation transformers are normally low power transformers used to isolate noise from or toground electronic circuits. Since a transformer cannot pass DC voltage from primary tosecondary, any DC voltage (such as noise) cannot be passed, and the transformer acts to isolatethis noise.

Instrument Potential Transformer(PT):

The instrument potential transformer (PT) steps down voltage of a circuit to a low value that canbe effectively and safely used for operation of instruments such as ammeters, voltmeters, wattmeters, and relays used for various protective purposes. They are used for Measuring ,Control ,Protection.Instrument Current Transformer (CT):

The instrument current transformer (CT) steps down the current of a circuit to a lower value andis used in the same types of equipment as a potential transformer. This is done by constructingthe secondary coil consisting of many turns of wire, around the primary coil, which contains onlya few turns of wire. In this manner, measurements of high values of current can be obtained.A current transformer should always be short-circuited when not connected to an external load.Because the magnetic circuit of a current transformer is designed for low magnetizing currentwhen under load, this large increase in magnetizing current will build up a large flux in themagnetic circuit and cause the transformer to act as a step-up transformer, inducing anexcessively high voltage in the secondary when under no load.

Control Transformer:Control transformers are generally used in electronic circuits that require constant voltage or constant current with a low power or volt-amp rating. Various filtering devices, such as capacitors, are used to minimize the variations in the output. This results in a more constant voltage or current.DistributionTransformer:They are generallyusedin electrical power distribution and transmissionsystems. This class of transformer has the highest power, or volt-ampere ratings, and the highestcontinuous voltagerating. Thepowerratingis normally determined by the type of coolingmethods the transformer may use. Some commonly used methods of cooling are by using oilor some other heat-conducting material. Ampere rating is increased in a distribution transformerby increasing the size of the primary and secondary windings; voltage ratings are increased byincreasing the voltage rating of the insulation used in making the transformer.

Energy losses in TransformerAn ideal transformer would have no energy losses, and would therefore be 100% efficient. Despite the transformer being amongst the most efficient of electrical machines, with experimental models using superconducting windings achieving efficiencies of 99.85% energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 95%. A small transformer such as a plug-in "power brick" used for low-power consumer electronics may be less than 85% efficient.

Losses in the transformer arise from;

Winding resistance: Current flowing through the windings causes resistive heating of the conductors. At higher frequencies, skin effect and proximity effect create additional winding resistance and losses.Hysteresis losses:Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the frequency, and is a function of the peak flux density to which it is subjected.

Eddy currents:Ferromagnetic materials are also good conductors, and a solid core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.

Mechanical losses:In addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise, and consuming a small amount of power.

Transformer Protections:

Protections are very important for electric devices, which protect them from destroying and make them more safe to use. They also has importance for workers safety. Larger things has more protections than smaller things.

For safety purpose there are two main Operations;

Alarm, Tripping

Alarm:

Alarm shows the critical situation of component. Alarm will ring when a device reaches its critical value. It also shows indication in CCR.Tripping:

Tripping is the next step of alarm. When machine or device dont operate on its standard functioning then after reasonable time breaker make the faulty component isolate and safe the transformer.

Protection of transformer

There are basically two types of protection of transformer.

Electrical

Non-Electrical

Non-Electrical Protections:

Thermal Protection

Pressure Protection

Level Protection

Thermal Protection:Heat can be produced due to spark ,hot weather and high voltage in heavy duty transformer. Mercury is used to ring alarm and for tripping. When transformer is heated, mercury is moved from Pocket and operates protection.To safe the transformer we have two most important operation alarm and tripping.

Pressure Protection:Pressure Relief value is for body protection. In case of sparking oil is heated-up and can damage the body of transformer . The value release the pressure that is built inside the body.

Level Protection:

Oil level decreases with the increase of temperature. On decrease of oil Alarm will ring but oil level protection has no tripping option. As oil has basi purpose of cooling so it is very important to maintain the oil level .

Buchholz Relay Protection:

It is used for protection of oil filled transformer having low level of oil. This relay is installed between transformer tank and conservator. The minor faults in transformer tank below oil level actuate Buchholz relay so as to give an alarm. The arc due to fault causes decomposition of transformer oil. Buchholz relay is fitted in the pipe leading to the conservator. The gas is collected in the upper part of the Buchholz relay, therefore oil level in the Buchholz relay drops down. The float in the oil level in realy tilts down with lowering oil level. While doing so the mercury switch attached to the float is closed and mercury switch closes the alarm circuit. The transformer is disconnected and gas is tested.

Electrical Protections:

High Voltage Protection

Over-Fluxing Protection

Earth Fault Protection

Differential Protection

Restricted Earth Fault Protection

1)High Voltage Protection:High voltage can distort the insulation of transformer winding. A relay is connected in parallel detect this fault and indication after reasonable time.

2)Over-Fluxing Protection:Heat is produced due to over-fluxing due to increase of eddy current losses. The relay measures the average voltage/frequency ration and ring the alarm if fault is not removed during alarm then tripping operation will occur.

3) Earth Fault Protection:

In this case a relay which is connected with neutral point is used and safe the transformer from over-heating.

4) Restricted Earth Fault Protection:

This is also an earth relay (only in unit transformer) it is in function when fault is near the neutral point.

5)Differential Protection:

The differential protection operates on vector difference between two quantities. For transformer protection, CTS are used on both sides of transformer.The out of phase currents flows through the relay operating coil and make the transformer safe.

THE BATTERY ROOMS

PURPOSE:

The purpose of the battery room is to provide dc supply needed for the relay action(mostly for protection purposes).

They are also source of excitation in case of blackout thud have vital use as dc backup supply.

THE BATTERIES:They are of the two types with respect to output voltage.

Output voltage of 48V Output voltage of 220V.

They are of led acid type having sulfuric acid (H2SO4) as the electrolyte.

Ring System:In Pakistan all Power station are interconnected through ring system NPCC is the main head, which control all the power Stations, and tells control the process of demand and supply. Mr. Ghulam Ishaq Khan, President of Pakistan on 20 January 1990, inaugurated the National Power Control Centre Islamabad. This is first phase of the giant project. It envisages implementation of the modern computerized load dispatch facilities for operating WAPDA's power system, by setting up of one NationalPowerControl Centre (NPCC) at Islamabad and two Regional Control Centers at Islamabad and Jamshoro for northern and southern parts of the network respectively. The main functions of these PowerControl Centers areNational Power Control Centre system ensures supply of energy to every consumer at all times at rated voltage, frequency and specified waveform, at lowest cost and minimum environmental degradation. The switchgear, protection and network automation are integral parts of the modern energy management system and national economy.The modern 3-ph, 50 Hz, AC interconnected system has several conventional and non-conventional power plants, EHV AC and HVDC Transmission system, Back to Back HVDC coupling stations, HV Transmission network, substations, MV and LV Distribution systems and connected electrical loads. The energy in electrical form is supplied to various consumers located in vast geographical area, instantly, automatically, and safely with required quality at all times. The service continuity and high quality of power supply have become very important.

For fulfilling the foresaid purpose, a state of the art, scientifically and technologically advanced SUBSTATION is required. Sub-Station is the load control center of the thermal plant where power at rated voltage, frequency and waveform is exported/imported as per requirements.

SWITCHYARD

Switchyard is a place to import/export electricity. KAPCO has two switchyard of 132 KV and 220 KV.

Switchyard of 132 KV:

First feeder goes to INDUSTRIAL ESTATE MULTAN.

Second feeder goes to MUZAFFARGARH-1

Third feeder goes to GUJRAT SOUTH

Forth feeder goes to D.I.KHAN-1

Fifth feeder goes to D.I.KHAN-2

Sixth feeder goes to KOT ADDUThis switchyard has single transmission scheme. This scheme is not very effective in case of trouble because it can completely dead the line and we dont have standby path. It contains 2 bus bar of 132 kv and BAYs from 4 to 22. From switchyard of 132 KV 6 transmission lines go to different part of country. BAY 18 and 20 are connected with autotransformer which convert 132 KV into 220 KV.BAY 6 and 17 are connected with startup transformer they convert 132KV into 11KV GT 1,2,3 and 4 are connected with BAY 4,5,16 and 19 respectively. While ST-9 and ST-10 are connected with BAY 7 and 15 respectively.

Switchyard of 22o KV:

It contains two bus bar and BAYS from 1 to 14. This yard has one and half scheme of breakers in which we have standby path to continue our transmission without any difficulty.

Total 12 feeders go out from the KAPCO six feeders are 220KV and six are 132KVA.

The detail of six feeders of 220KV is given below.

From bay 1 feeder goes to MUZAFFAR GARH

From bay 2 feeder goes to AES PAKGEN

From bay 6 feeder goes to VEHARI

From bay 7 feeder goes to NEW MULTAN 6

From bay 13 feeder goes to NEWMULTAN 3

From bay 14 feeder goes to NEWMULTAN 4

After step up, the 220 KV output from the generator transformer is fed to either of the two bus bars through relays and circuit breakers and these are connected to various feeders through various equipments.

Different Types of Equipment used in Switchyard:

1. BUS-BARS: -

Bus bar is a term used for main bar of conductor carrying an electric current to which many connections may be made. These are mainly convenient means of connecting switches and other equipments into various arrangements.

Every switchyard have two bus bars. Mostly are made of aluminum and all the incoming and outgoing supplies are connected through the bus bars.

2. LIGHTENING ARRESTORS: -

These are equipments designed to protect insulators of power lines and electrical installations from lightening surges by diverting the surge to earth and instantly restoring the circuit insulation to its normal strength with respect to earth.

3. CURRENT TRANSFORMERS: -

The main purpose of current transformer is to step down the current to a level that the indicating and monitoring instruments can read. When rated current flows through its primary winding, a current of nearly 1 amp will appear in its secondary winding.The primary is so connected that the current being passes through it and secondary winding is connected to an ammeter. The CT steps down the current to the level of the ammeter.

4. POTENTIAL TRANSFORMER: -

These are used to step do the voltage to a level that the potential coils of indicating and monitoring instruments can read. These are also used to feed the potential coils of relays. The primary winding is connected to the voltage being measured and the secondary winding to a voltmeter. The PT steps down the voltage to the level of the voltmeter.

5. POWER TRANSFORMER: -These are used to step up down the voltage from one a.c voltage to another AC voltage level at the same frequency. Unit transformer takes supply from auxiliary transformer and transfers it to switchyard bus bar.

6. WAVE TRAP: -

Wave trap is used to prevent high frequency signals from entering other zones. NPCC is connected with all power station through telephone line which put their signal on line and separated from wave trap.

7. INDICATING AND METERING INSTRUMENTS: -

Ammeters, voltmeters, wattmeters, KWH meters, KVAR meters are installed in sub-station to watch over the currents flowing in the circuit and the voltages and the power loads.

8. ISOLATORS: -One of the cardinal measures for ensuring full safety in carrying out work on equipment in electrical installations is to disconnect reliably the unit or the section on which the work is to be done from all other live parts of the installation. To guard against mistakes, it is necessary that apparatus, which makes a visible break in the circuit such as isolators, should do this.Isolators do not have arc control devices therefore cannot be used to interrupt currents at which the arc will be drawn across the contacts. The open arc in these is very dangerous, in that it will not only damage the isolator or the equipment surrounding it but will also cause the flashover between the phase in other words, it will result in short circuit in the installation i.e. why isolators are used only for disconnecting parts after de-energizing them by opening their respective circuits by use of their circuit breakers.

9. EARTHING SWITCHES: -Earthing switch is used to discharge the voltage on deadlines to earth. An auxiliary switch to provide interlock always accomplishes it.

10. CIRCUIT BREAKERS: -

Circuit breakers are mechanical devices designed to close an open contact or electrical circuit under normal or abnormal conditions. CB is equipped with a strip coil directly attached to relay or other means to operate in abnormal conditions such as over power etc. In here, two types of CB are used. SF6 CB is used to control 220 KV in switchyard. Which has 6 bar pressure and air is used to operate breaker which has a pressure of 19bar In block-3 switchyard portion breaker are hydraulic operated and air is used for cooling.

Breaker:

It is an on load device which is used for safety purpose. It make the different electric component separate in case of fault.Trip Supervision:

To check the healthiness of breakers trip supervision is used which is in parallel to breaker and in case of failure of breaker it give command the other one and operate related breakers.DUPLICATE BUS BAR ARRANGEMENT:

The duplicate bus bar system provides additional flexibility, continuity of supply and permits periodic maintenance without total shut down. In the event of fault o n one bus the other bus can be used.

While transferring the power to the reserve bus, the following steps may be performed:

1. Close tie circuit breaker, i.e. bus coupler. The two buses are now at the same potential. 2. Close isolators on reserve bus starting from far end. 3. Open isolators o9n main bus starting from far end.

Each pole of the circuit breaker comprises one or more interrupts or arc extinguishing chambers. The interrupts are mounted on support insulators. The interrupts enclose a set of fixed and moving contact. The moving contacts can be drawn apart by means of the operating links of the operating mechanism. The operating mechanism of the circuit breaker gives necessary energy for opening and closing of contacts of the circuit breaker.

GENERAL ELECTRICAL SUPPLIES IN THE PLANTElectrical Auxiliary System

AC Auxiliary supply system DC supply system

AC auxiliary supply system is used to feed all the AC auxiliaries installed in the plant.The DC supply system, which consists of 220 V DC, 110 V DC, +/- 24 V DC, 48 V DC etc., is used for control supplies as required for system control and protection equipment.

Black Start

Emergency Function:

KAPCO is the very valuable power station of PAKISTAN because it has the facility of self-start. In case of complete black, it can run its self for this there is a Black start where diesel generator produce electricity energizes the excitation bus bars of GTS.

Bus Bar:Black start bus bar is energized my dc batteries of 220V and help the diesel generator to start functioning

Diesel Generator:

Mostly it is not used but in case of complete blackout, it is very help to put power station into action. It provide 11 KV and energize the common bus bar.

Neutral and Ground

Neutral:

A reference connection in a power distribution system .

Ground:

A connection to the earth or to a conductive object such as an equipment chassis.There are two objectives to the intentional grounding of electrical equipment: Keep potential voltage differentials between different parts of a system at a minimum to reduce the shock hazard.

Keep impedance of the ground path to a minimum. The lower the impedance, the greater the current is in the event of a fault. The greater the current, the faster an over current device will open.

Presented By

Muhammad Ikram

2K11-EPE-354

Electrical Engineering Department

NFC Institute of Engineering & Technology

Multan