2014

Electrical Substations

Project Report,132 KV Substation,Purukul, Dehradun

Power Transmission Corporation of

Uttarakhand Limited

Submitted By:Girish GuptaId no. 42206,

4th Year,Electrical Engineering,College of Technology,

Govind Ballabh Pant University of Agriculture & Technology,

Pantnagar

Sl.No.

Topic PageNo.

1. Training Order 2

2. Certificate 4

3. Acknowledgement 5

4. Power Transmission Corporation of Uttarakhand Limited 6

5. 132 KV S/s Purukul, Dehradun 8

6. Substation 10

7. Transformer 16

8. Power Line Carrier Communication 19

9. Bus Bars 22

10. Circuit Breakers 23

11. Isolators 27

12. Insulators 28

13. Relays 30

14. Capacitor Bank 33

15. Protection of Substation 34

16. Conclusion 38

17. Bibliography 39

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INDEX

CERTIFICATEThis is to certify that Mr. Girish Gupta, student of 4th year, Electrical Engineering, Bachelor of Technology, College of Technology, Govind Ballabh University of Agriculture & Technology, Pantnagar has undergone summer training at 132KV Substation, Purukul, Dehradun under Power Transmission Corporation of Uttarakhand Limited (PTCUL) from 7th July, 2014 to 7th August, 2014 under the overall guidance of Mr. Prabhash Dabral, S.D.O., Purukul, Dehradun.

Mr. Girish Gupta has successfully completed his training and submitted the training project report. During the period of training he was found sincere, punctual and regular. His conduct and behavior was very good.

Mr. Prabhash Dabral

Sub Division Officer

132 KV Substation

PTCUL

Purukul, Dehradun

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ACKNOWLEDGEMENT

I am very thankful to Mr. Ravindra Kumar, Executive Engineer, Power Transmission Corporation of Uttarakhand Limited who gave me an opportunity to undergo training at 132KV Substation, Purukul, Dehradun under Power Transmission Corporation of Uttarakhand Limited (PTCUL).

I am also thankful to Mr. Prabhash Dabral, Sub Division Officer, 132 KV Substation, PTCUL who organized the training in a systematic manner and guided me through the whole training programme.

I would also like to thank all officer/officials who guided and helped me at each and every step in the training programme.

Girish Gupta

Id no. 42206

4th year,

Electrical Engineering

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4. POWER TRANSMISSION CORPORATION OF UTTRAKHAND LIMITED (PTCUL)

Power Transmission Corporation of Uttarakhand Ltd. is the power transmission utility of the state of Uttarakhand formerly known as Uttaranchal. On 9 November 2000, this 27th state of the Republic of India was carved out of the Himalayan and adjoining northwestern districts of Uttar Pradesh per the Uttar Pradesh State Re-organization Act, 2000.

The State of Uttaranchal in exercise of the power granted to it under Section 63(4) of the State Re-organization Act, 2000, formed two separate companies in power sector - Uttaranchal Jal Vidyut Nigam Ltd. for generation of hydro-electricity in the state and Uttaranchal Power Corporation Ltd. for transmission & distribution of electricity in the state.

Enactment of the Electricity Act, 2003, a distinct watershed in the Indian power sector, as it introduced innovative concepts like power trading, Open Access, Appellate Tribunal, etc., and special provisions for the rural areas, made it mandatory for all the States to restructure their SEBs.

As per the provisions of Electricity Act, 2003, the state government separated power transmission business from UPCL which was left only with distribution of electricity. A new company by the name & style of Power Transmission Corporation of Uttaranchal Ltd. was created to handle power transmission business and registered as a Government Company under Section 617 of Companies Act, 1956 on 27th May, 2004. It started functioning w.e.f. 1st June, 2004.

100% shares of the Company is held by the Government of Uttarakhand either directly or through its nominees. Authorized capital of the Company at the time of incorporation was Rs. 10 crores divided into one lac equity shares of Rs. 1000 each. At present the authorized capital of the company is rupees one hundred crores. The Company is managed by the Board of Directors who meet frequently at least once in every quarter. The day to day management of the Company is looked after by the Managing Director and other full time Directors of the Company along with other senior officers. The Corporate and Registered Office of the company is at Vidyut Bhawan, Near ISBT Crossing, Saharanpur Road, Majra, Dehradun.

Following given is the power line map of Uttarakhand which shows various installed substations of different capacities and transmission lines in Uttarakhand. It also indicates the position of the new upcoming substations in the different regions.

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Power and Transmission Line Map of Uttarakhand

5. 132 KV SUBSTATION, PURUKUL, DEHRADUN

The 132 KV substation was commissioned in the year 27th March, 1983.There are two main 132 KV bus incoming for the substation. These buses are:-1. 132 KV Purukul-Dhalipur Line2. 132 KV Purukul-Majra Line

Now the transmission line first parallel connected with lightning arrester to diverge surge, followed by CVT connected parallel. CVT measures voltage and steeps down from 132KV to 63.5 Volts A.C. for control panel, at the location a wave trap is connected to carrier communication at higher frequencies. A current transformer is connected in series with line which measure current and step down current at ratio 800:400:200:1 for control panel.Switchgear equipment is provided, which is the combination of a circuit breaker having an isolator at each end. Two transformers are connected to main bus. The main bus has total capability of 60 MVA for 132 KV, which is subdivided into two transformer capacity of 60 MVA (40MVA + 20MVA) parallel connected for 132KV. In addition to the Main bus, Transfer Bus is also provided in the substation in case any maintenance work is to be carried out on the main bus or there is a glitch in the main bus.After the Main bus, lightning arresters, current transformers, isolators and circuit breakers before the transformers are provided. Current Transformers steps down current at ratio 400:200:1 for control panel. Then Transformer step downs voltage from 132KV to 33KV. The main bus is then again provided with switchgear equipment & a current transformer. This gives way to six feeders transmitting power to various places. The main bus is connected to jack bus or transfer bus through a bus coupler & 33KV is provided with switchgear equipment. This gives way to feeders transmitting power to

1. Opto Electronics2. Anarwala I3. Anarwala II4. Mussoorie I5. Mussoorie II6. I.T. Park7. GEMES

A step down transformer of 33KV/440V is connected to control panel to provide supply to the equipments of the substation. Capacitor bank is connected to main bus of 33KV. It is provided to improve power factor & voltage profile. Capacitor Bank comprises of two units of 5 MVAR making total capacity of 10 MVAR.

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At present, an extra 20 MVA transformer is being currently installed at the substation.

Also an additional 132 KV Purukul-Bindal Line is now being connected to the substation.

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6. SUBSTATIONS

A substation is a part of an electrical generation, transmission and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. Substations may be owned and operated by an electrical utility, or may be owned by a large industrial or commercial customer. Generally substations are unattended, relying on SCADA for remote supervision and control. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages.Substations are classified by two broad categories:- 1. According to the service requirement:

Transformer substation

Switch substation

Power factor correction substation

Frequency change substation

Converting substation

Industrial substation

Collector Substation

Convertor Substation

Switching Substation

2. According to the constructional features:

Indoor substation

Outdoor substation

Underground substation

Pole mounted substation

TRANSFORMER SUBSTATION

They are known as transformer substations as because transformer is the main component employed to

change the voltage level, depending upon the purposed served transformer substations may be

classified into:

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a) STEP UP SUBSTATIONThe generation voltage is steeped up to high voltage to affect economy in transmission of electric power. These are generally located in the power houses and are of outdoor type.

b) PRIMARY GRID SUBSTATIONHere, electric power is received by primary substation which reduces the voltage level to 33KV for secondary transmission. The primary grid substation is generally of outdoor type.

c) SECONDARY SUBSTATIONSAt a secondary substation, the voltage is further steeped down to 11KV. The 11KV lines runs along the important road of the city. The secondary substations are also of outdoor type.

d) DISTRIBUTION SUBSTATIONThese substations are located near the consumer’s localities and step down to 400V, 3-phase, 4-wire for supplying to the consumers. The voltage between any two phases is 400V & between any phase and neutral it is 230V.

SUBSTATION CHARACTERISTICS1. Each circuit is protected by its own circuit breaker and hence plant outage does not

necessarily result in loss of supply. 2. A fault on the feeder or transformer circuit breaker causes loss of the transformer and

feeder circuit, one of which may be restored after isolating the faulty circuit breaker. 3. A fault on the bus section circuit breaker causes complete shutdown of the substation.

All circuits may be restored after isolating the faulty circuit breaker. 4. Maintenance of a feeder or transformer circuit breaker involves loss of the circuit. 5. Introduction of bypass isolators between bus bar and circuit isolator allows circuit

breaker maintenance facilities without loss of that circuit.

STEPS IN DESIGNING SUBSTATION

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The First Step in designing a Substation is to design an Earthing and Bonding System.

Earthing and BondingThe function of an earthing and bonding system is to provide an earthing system connection to which transformer neutrals or earthing impedances may be connected in order to pass the maximum fault current. The earthing system also ensures that no thermal or mechanical damage occurs on the equipment within the substation, thereby resulting in safety to operation and maintenance personnel. The earthing system also guarantees equipotent bonding such that there are no dangerous potential gradients developed in the substation. In designing the substation, three voltages have to be considered these are:

1. Touch VoltageThis is the difference in potential between the surface potential and the potential at earthed equipment whilst a man is standing and touching the earthed structure.

2. Step VoltageThis is the potential difference developed when a man bridges a distance of 1m with his feet while not touching any other earthed equipment.

3. Mesh VoltageThis is the maximum touch voltage that is developed in the mesh of the earthing grid.

Substation Earthing Calculation Methodology

Calculations for earth impedances, touch and step potentials are based on site measurements of ground resistivity and system fault levels. A grid layout with particular conductors is then analyzed to determine the effective substation earthing resistance, from which the earthing voltage is calculated. In practice, it is normal to take the highest fault level for substation earth grid calculation purposes. Additionally, it is necessary to ensure a sufficient margin such that expansion of the system is catered for. To determine the earth resistivity, probe tests are carried out on the site. These tests are best performed in dry weather such that conservative resistivity readings are obtained.

Earthing Materials

1. ConductorsBare copper conductor is usually used for the substation earthing grid. The copper bars themselves usually have a cross-sectional area of 95 square millimeters, and they are laid at a

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shallow depth of 0.25-0.5m, in 3-7m squares. In addition to the buried potential earth grid, a separate above ground earthing ring is usually provided, to which all metallic substation plant is bonded.

2. ConnectionsConnections to the grid and other earthing joints should not be soldered because the heat generated during fault conditions could cause a soldered joint to fail. Joints are usually bolted.

3. Earthing RodsThe earthing grid must be supplemented by earthing rods to assist in the dissipation of earth fault currents and further reduce the overall substation earthing resistance. These rods are usually made of solid copper, or copper clad steel.

Switchyard Fence Earthing

The switchyard fence earthing practices are possible and are used by different utilities. These are:

a) Extend the substation earth grid 0.5m-1.5m beyond the fence perimeter. The fence is then bonded to the grid at regular intervals.

b) Place the fence beyond the perimeter of the switchyard earthing grid and bond the fence to its own earthing rod system. This earthing rod system is not coupled to the main substation earthing grid.

CONDUCTORS USED IN SUBSTATION DESIGN

An ideal conductor should fulfill the following requirements:

a) Should be capable of carrying the specified load currents and short time currents. b) Should be able to withstand forces on it due to its situation. These forces comprise self-

weight, and weight of other conductors and equipment, short circuit forces and atmospheric forces such as wind and ice loading.

c) Should be corona free at rated voltage. d) Should have the minimum number of joints. e) Should need the minimum number of supporting insulators. f) Should be economical.

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The most suitable material for the conductor system is copper or aluminums. Steel may be used but has limitations of poor conductivity and high susceptibility to corrosion. In an effort to make the conductor ideal, three different types have been utilized, and these include: Flat surfaced Conductors, Stranded Conductors, and Tubular Conductors.

OVERHEAD LINE TERMINATIONS

Two methods are used to terminate overhead lines at a substation.

a) Tensioning conductors to substation structures or buildings

b) Tensioning conductors to ground winches.

The choice is influenced by the height of towers and the proximity to the substation. The

following clearances should be observed:

VOLTAGE LEVEL MINIMUM GROUND CLEARANCE

less than 11kV 6.1m

11kV - 20kV 6.4m

20kV - 30kV 6.7m

greater than 30kV 7.0m

STANDARD SIZES OF CONDUCTOR FOR LINES OF VARIOUS VOLTAGES

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Clearance in accordance with voltage value

The following sizes have now been standardized by CEA for transmission lines of different voltages:-

1. For 440 KV LinesTwin 'Moose' ACSR having 7-Strands of steel of dia 3.53 mm and 54-Strands of Aluminum of dia 3.53 mm.

2. For 220 KV Lines'Zebra' ACSR having 7-strand of steel of dia 3.18 mm and 54-Strands of Aluminum of dia 3.18 mm.

3. For 132 KV Lines'Panther' ACSR having 7-strands of steel of dia 3.00 mm and 30-Strands of Aluminum of dia 3.00 mm.

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7. TRANSFORMERS

Transformer is a static machine, which transforms the potential of alternating current at same frequency. It means the transformer transforms the low voltage into high voltage & high voltage to low voltage at same frequency. It works on the principle of static induction principle.

When the energy is transformed into a higher voltage, the transformer is called step up transformer but in case of other is known as step down transformer.

TYPES OF TRANSFORMERS

1. Power TransformerIt is used for the transmission purpose at heavy load, high voltage greater than 33 KV & 100% efficiency. It also having a big in size as compare to distribution transformer, it used in generating station and Transmission substation at high insulation level. They can be of two types: Single Phase Transformers and Multi Phase Transformers.

2. Instrument TransformersThese transformers are used for the measurement purposes at that points where standard voltmeters and ammeters cannot be used. They are of two types:-

a) CURRENT TRANSFORMER A current transformer (CT) is used for measurement of alternating electric currents. When current in a circuit is too high to apply directly to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer isolates the

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measuring instruments from what may be very high voltage in the monitored circuit.

b) POTENTIAL OR VOLTAGE TRANSFORMER Voltage transformers (VT) (also called potential transformers (PT)) are a parallel connected type of instrument transformer, used for metering and protection in high-voltage circuits or phasor phase shift isolation. They are designed to present negligible load to the supply being measured and to have an accurate voltage ratio to enable accurate metering. A potential transformer may have several secondary windings on the same core as a primary winding, for use in different metering or protection circuits.

3. Auto TransformersAn autotransformer is an electrical transformer with only one winding. The "auto" prefix refers to the single coil acting on itself and not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer. The winding has at least three taps where electrical connections are made. Autotransformers have the

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advantages of often being smaller, lighter, and cheaper than typical dual-winding transformers, but the disadvantage of not providing electrical isolation.

4. On the basis of workingOn the above basis, transformers are of two types: Step up Transformer and Step down Transformer.

5. Distribution TransformersA distribution transformer is a transformer that provides the final voltage transmission in the electrical power distribution system, stepping down voltage to the level used by customers.

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8. POWER LINE CARRIER COMMUNICATION (PLCC)

Reliable & fast communication is necessary for safe efficient & economic power supply. To reduce the power failure in extent & time, to maintain the interconnected grid system in optimum working condition; to coordinate the operation of various generating unit communication network is indispensable for state electricity board.In state electricity boards, the generating & distribution stations are generally located at a far distance from cities where P & T communication provided through long overhead lines in neither reliable nor quick.Power-line communication (PLC) carries data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. By using the existing AC power lines as a medium to transfer the information, it becomes easy to connect the houses with a high speed network access point without installing new wirings. This technology has been in wide use since 1950 and was mainly used by the grid stations to transmit information at high speed.

PRINCIPLE OF PLCCPower-line communications systems operate by adding a modulated carrier signal to the wiring system. All type of information is modulated on carried wave at frequency 50Hz to 500 KHz. The modulated HF carrier fed into the power line conductor at the sending end and filtered out again at the respective stations. Long earlier system double side band amplitude modulation was more common but the present amplitude modulated system. Since high voltage power lines are designed to carry large quantities of energy on the high voltage and the communication system at low voltage, they cannot be directly connected to high voltage lines. Suitably designed coupling equipments have therefore to be employed which will permit the injection of high frequency carrier signal without undue loss and with absolute protection of communication equipments or operating personal from high voltage hazard.

Therefore, the coupling equipment essentially comprises the following:

1. Wave Trap or Line TrapWave trap is connected in series with power line between the point of connection of coupling capacitor and S/S. Wave trap offers negligible impedance to HF carrier. Wave trap stands electromechanically and thermally for short circuit current in the event of fault on the line. On the basis of blocking frequency bank, the wave trap can be following type:

a) All wave

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b) Single Frequencyc) Double Frequency’d) Broad Band

2. Coupling CapacitorThe modulated carrier is let into power line through coupling capacitor specially designed to with stand line voltage under all-weather condition. The upper end of the coupling capacitor is connected directly to the line and the lower end is connected to the ground through a carrier frequency chock coil or drain coil. Thus coupling capacitor forms the link between the PLCC equipment and power line. The coupling capacitor used in UPSEB is 2200pf capacitance.The coupling capacitor are designed for outdoor use and hence to withstand normal atmospheric phenomenon such as temperature & humidity changes, rain, snow, anticipated wind load, nominal wire tension etc. at full rated voltage. In some case capacitive voltage transformers (CVT) used as a source of line voltage for metering and protection as also used coupling capacitor for PLCC.

3. Protective Device of Coarse Voltage ArrestorThis is connected across the primary of the coupling filter i.e. one end is connected to the bottom of the coupling capacitor and other end is earthed. This is provided to protect the coupling filter against line surges. An air gap is provided, where voltage of the order of 1.8 to 2KV as observed across due to lighting etc. on line.

4. Coupling of FilterThe coupling filter is inserted between the low voltage terminal of the coupling capacitor and the carrier frequency connection of the carrier terminal. Sometime an earth switch is also provided with this unit. This unit mainly performs two functions; firstly it isolates the connection of equipment from the power line. Secondly it serves to match characteristic impedance of the power line to that of the H.F. cable to connection equipments.

5. H. F. CableH.F. cable normally used to connect the coupling filter to another coupling terminal. The cable is insulated to withstand the test voltage of 4KV. The impedance of this H.F. cable is so as to match with the output of the PLCC terminal and secondary impedance of coupling filter.

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PLCC technology can be deployed into different types of applications in order to provide

economic networking solutions. Hence merging with other technologies it proves useful in

different areas. These are few key areas where PLC communications are utilized:

a. Transmission & Distribution Network: PLCC was first adopted in the electrical transmission and distribution system to transmit information at a fast rate.b. Home control and Automation: PLCC technology is used in home control and automation. This technology can reduce the resources as well as efforts for activities like power management, energy conservation, etc.c. Entertainment: PLCC is used to distribute the multimedia content throughout the home.d. Telecommunication: Data transmission for different types of communications like telephonic communication, audio, video communication can be made with the use of PLCC technology.e. Security Systems: In monitoring houses or businesses through surveillance cameras, PLCC technology is far useful.f. Automatic Meter Reading – Automatic Meter reading applications use the PLCC technology to send the data from home meters to Host Central Station.

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Wave Trap

9. BUSBARS

When numbers of generators or feeders operating at the same voltage have to be directly connected electrically, bus bar is used as the common electrical component. Bus bars are made up of copper rods operate at constant voltage. The following are the important bus bars arrangements used at substations:

Single bus bar system Single bus bar system with section alisation. Duplicate bus bar system

In large stations it is important that break downs and maintenance should interfere as little as possible with continuity of supply to achieve this, duplicate bus bar system is used. Such a system consists of two bus bars, a main bus bar and a spare bus bar with the help of bus coupler, which consist of the circuit breaker and isolator.In substations, it is often desired to disconnect a part of the system for general maintenance and repairs. An isolating switch or isolator accomplishes this. Isolator operates under no load condition. It does not have any specified current breaking capacity or current making capacity. In some cases isolators are used to breaking charging currents or transmission lines.While opening a circuit, the circuit breaker is opened first then isolator while closing a circuit the isolator is closed first, then circuit breakers. Isolators are necessary on supply side of circuit breakers, in order to ensure isolation of the circuit breaker from live parts for the purpose of maintenance.A transfer isolator is used to transfer main supply from main bus to transfer bus by using bus coupler (combination of a circuit breaker with two isolators), if repairing or maintenance of any section is required.

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Bus Bars

10. CIRCUIT BREAKERS

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. There are different types of circuit breakers which are:-

1. Low-voltage circuit breakersLow-voltage (less than 1,000 VAC) types are common in domestic, commercial and industrial application, and include Miniature Circuit Breaker (MCB) and Molded Case Circuit Breaker (MCCB).

2. Magnetic circuit breakersMagnetic circuit breakers use a solenoid (electromagnet) whose pulling force increases with the current. Certain designs utilize electromagnetic forces in addition to those of the solenoid.

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3. Thermal magnetic circuit breakersThermal magnetic circuit breakers, which are the type found in most distribution boards, incorporate both techniques with the electromagnet responding instantaneously to large surges in current (short circuits) and the bimetallic strip responding to less extreme but longer-term over-current conditions. The thermal portion of the circuit breaker provides an "inverse time" response feature, which trips the circuit breaker sooner for larger over currents.

4. Common trip breakersThree-pole common trip breaker for supplying a three-phase device. This breaker has a 2A rating. When supplying a branch circuit with more than one live conductor, each live conductor must be protected by a breaker pole. To ensure that all live conductors are interrupted when any pole trips, a "common trip" breaker must be used. These may either contain two or three tripping mechanisms within one case, or for small breakers, may externally tie the poles together via their operating handles.

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5. Air circuit breakersRated current up to 6,300 A and higher for generator circuit breakers. Trip characteristics are often fully adjustable including configurable trip thresholds and delays. Usually electronically controlled, though some models are microprocessor controlled via an integral electronic trip unit. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance.

6. Vacuum circuit breakersWith rated current up to 6,300 A, and higher for generator circuit breakers. These breakers interrupt the current by creating and extinguishing the arc in a vacuum container.

7. Oil circuit breakersA high-voltage circuit breaker in which the arc is drawn in oil to dissipate the heat and extinguish the arc; the intense heat of the arc decomposes the oil, generating a gas whose high pressure produces a flow of fresh fluid through the arc that furnishes the necessary insulation to prevent a restrike of the arc.The arc is then extinguished, both because of its elongation upon parting of contacts and because of intensive cooling by the gases and oil vapor. They are further of two

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types: Bulk Oil Circuit Breaker (BOCB) and Minimum Oil Circuit Breaker (MOCB).

8. Sulfur hexafluoride (Sf6) high-voltage circuit breakersA sulfur hexafluoride circuit breaker uses contacts surrounded by sulfur hexafluoride gas to quench the arc. They are most often used for transmission-level voltages and may be incorporated into compact gas-insulated switchgear.

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11. ISOLATERS

In electrical engineering, a disconnector, disconnect switch or isolator switch is used to ensure that an electrical circuit is completely de-energized for service or maintenance. Such switches are often found in electrical distribution and industrial applications, where machinery must have its source of driving power removed for adjustment or repair. High-voltage isolation switches are used in electrical substations to allow isolation of apparatus such as circuit breakers, transformers, and transmission lines, for maintenance. The disconnector is usually not intended for normal control of the circuit, but only for safety isolation. Disconnector can be operated either manually or automatically (motorized disconnector).

Unlike load break switches and circuit breakers, disconnectors lack a mechanism for suppression of electric arc, which occurs when conductors carrying high currents are electrically interrupted. Thus, they are off-load devices, intended to be opened only after current has been interrupted by some other control device. Safety regulations of the utility must prevent any attempt to open the disconnector while it supplies a circuit. Standards in some countries for safety may require either local motor isolators or lockable overloads (which can be padlocked).

Disconnectors have provisions for a padlock so that inadvertent operation is not possible (lockout-tag out). In high-voltage or complex systems, these padlocks may be part of a trapped-key interlock system to ensure proper sequence of operation. In some designs, the isolator switch has the additional ability to earth the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits which inter-connect power distribution systems where both ends of the circuit need to be isolated.

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12. INSULATORS

An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it very hard to conduct an electric current under the influence of an electric field. The insulator serves two purposes. They support the conductors (bus bar) and confine the current to the conductors. The most common used material for the manufacture of insulator is porcelain. There are several types of insulators (e.g. pin type, suspension type, post insulator etc.) and their use in substation will depend upon the service requirement.Different types of insulator are:-

Pin type insulator As the name suggests, the pin type insulator is mounted on a pin on the cross-arm on the pole. There is a groove on the upper end of the insulator. The conductor passes through this groove and is tied to the insulator with annealed wire of the same material as the conductor. Pin type insulators are used for transmission and distribution of electric power at voltages up to 33 kV. Beyond operating voltage of 33 kV, the pin type insulators become too bulky and hence uneconomical.

Suspension insulator For voltages greater than 33 kV, it is a usual practice to use suspension type insulators shown in Figure. Consist of a number of porcelain discs connected in series by metal links in the form of a string. The conductor is suspended at the bottom end of this string while the other end of the string is secured to the cross-arm of the tower. The number of disc units used depends on the voltage.

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Strain insulator A dead end or anchor pole or tower is used where a straight section of line ends, or angles off in another direction. These poles must withstand the lateral (horizontal) tension of the long straight section of wire. In order to support this lateral load, strain insulators are used. For low voltage lines (less than 11 kV), shackle insulators are used as strain insulators. However, for high voltage transmission lines, strings of cap-and-pin (disc) insulators are used, attached to the crossarm in a horizontal direction. When the tension load in lines is exceedingly high, such as at long river spans, two or more strings are used in parallel.

Shackle insulator In early days, the shackle insulators were used as strain insulators. But now a day, they are frequently used for low voltage distribution lines. Such insulators can be used either in a horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt or to the cross arm.

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13. RELAYS

In a power system it is inevitable that immediately or later some failure does occur somewhere in the system. When a failure occurs on any part of the system, it must be quickly detected and disconnected from the system. Rapid disconnection of faulted apparatus limits the amount of damage to it and prevents the effects of fault from spreading into the system. For high voltage circuits relays are employed to serve the desired function of automatic protective gear. The relays detect the fault and supply the information to the circuit breaker.

The electrical quantities which may change under fault condition are voltage, frequency, current, phase angle. When a short circuit occurs at any point on the transmission line the current flowing in the line increases to the enormous value. This result in a heavy current flow through the relay coil, causing the relay to operate by closing its contacts. This in turn closes the trip circuit of the breaker making the circuit breaker open and isolating the faulty section from the rest of the system. In this way, the relay ensures the safety of the circuit equipment from the damage and normal working of the healthy portion of the system.

Relay works on two main operating principles:-

Electromagnetic Attraction Electromagnetic Induction

RELAY USED IN CONTROLLING PANEL OF SUBSTATION

Differential Relay A differential relay is one that operates when vector difference of the two or more electrical quantities exceeds a predetermined value. If this differential quantity is equal or greater than the pickup value, the relay will operate and open the circuit breaker to isolate the faulty section.

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Over Current Relay This type of relay works when current in the circuit exceeds the predetermined value. The actuating source is the current in the circuit supplied to the relay from a current transformer. These relay are used on A.C. circuit only and can operate for fault flow in the either direction. This relay operates when phase to phase fault occurs.

Earth Fault Relay This type of relay sense the fault between the lines and the earth. It checks the vector sum of all the line currents. If it is not equal to zero, it trips.

Tripping Relay This type of relay is in the conjunction with main relay. When main relay sense any fault in the system, it immediately operates the trip relay to disconnect the faulty section from the section.

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Auxiliary Relay An auxiliary relay is used to indicate the fault by glowing bulb or showing various flags.

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14. CAPACITOR BANK

The load on the power system is varying being high during morning and evening which increases the magnetization current. This result in the decreased power factor. The low power factor is mainly due to the fact most of the power loads are inductive and therefore take lagging currents. The low power factor is highly undesirable as it causes increases in current, resulting in additional losses. So in order to ensure most favorable conditions for a supply system from engineering and economic stand point it is important to have power factor as close to unity as possible. In order to improve the power factor come device taking leading power should be connected in parallel with the load. One of such device can be capacitor bank. The capacitors draw a leading current and partly or completely neutralize the lagging reactive component of load current.

Main functions of Capacitor Bank are:- Supply Reactive Power Improve Terminal Voltage Improve Power Factor

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15. PROTECTION OF SUBSTATION

LIGHTNING ARRESTORSA lightning arrestor is a device used in power systems and telecommunications systems to protect the insulation and conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high-voltage terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth.

TRANSFORMER PROTECTIONTransformers are totally enclosed static devices and generally oil immersed. Therefore chances of fault occurring on them are very easy rare, however the consequences of even a rare fault may be very serious unless the transformer is quickly disconnected from the system. This provides adequate automatic protection for transformers against possible faults. Various protection methods used for transformers are:-

Buchholz Relay Buchholz relay is a safety device mounted on some oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is used as a protective device sensitive to the effects of dielectric failure inside the equipment. Depending on the model, the relay has multiple methods to detect a failing transformer. On a slow accumulation of gas, due perhaps to slight overload, gas produced by decomposition of insulating oil accumulates in the top of the relay and forces the oil level down. A float switch in the relay is used to initiate an alarm signal. Depending on design, a second float may also serve to detect slow oil leaks. If an arc forms, gas accumulation is rapid, and oil flows rapidly into the conservator. This flow of oil operates a switch attached to a vane located in the path of the moving oil. This switch normally will operate a circuit breaker to isolate the apparatus before the fault causes additional damage.

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Conservator and Breather

When the oil expands or contacts by the change in the temperature, the oil level goes either up or down in main tank. A conservator is used to maintain the oil level up to predetermined value in the transformer main tank by placing it above the level of the top of the tank. Breather is connected to conservator tank for the purpose of extracting moisture as it spoils the insulating properties of the oil. During the contraction and expansion of oil air is drawn in or out through breather silica gel crystals impregnated with cobalt chloride. Silica gel is checked regularly and dried and replaced when necessary.

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Marshalling box

It has two meter which indicate the temperature of the oil and winding of main tank. If temperature of oil or winding exceeds than specified value, relay operates to sound an alarm. If there is further increase in temperature then relay completes the trip circuit to open the circuit breaker controlling the transformer.

Transformer cooling

When the transformer is in operation heat is generated due to iron losses the removal of heat is called cooling.There are several types of cooling methods, they are as follows:

1. Air natural coolingIn a dry type of self-cooled transformers, the natural circulation of surrounding air is used for its cooling. This type of cooling is satisfactory for low voltage small transformers.

2. Air blast coolingIt is similar to that of dry type self-cooled transformers with to addition that continuous blast of filtered cool air is forced through the core and winding for better cooling. A fan produces the blast.

3. Oil natural coolingMedium and large rating transformers have their winding and core immersed in oil, which act both as a cooling medium and an insulating medium. The heat produce in the cores and winding is passed to the oil becomes lighter and rises to the top and place is taken by cool oil from the bottom of the cooling tank.

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4. Oil blast coolingIn this type of cooling, forced air is directed over cooling elements of transformers immersed in oil.

5. Forced oil and forced air flow (OFB) coolingOil is circulated from the top of the transformers tank to a cooling tank to a cooling plant. Oil is then returned to the bottom of the tank.

6. Forced oil and water (OWF) coolingIn this type of cooling oil flow with water cooling of the oil in external water heat exchanger takes place. The water is circulated in cooling tubes in the heat exchanger.

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16. CONCLUSION

Now from this report one can conclude that electricity plays an important role in our life. At the end of the training, I came to know about the various parts of substations and how they are operated. Also I learnt about how transmission is done in various parts of Uttarakhand.

As evident from the report, a substation plays a very important role in the transmission system. That’s why various protective measures are taken to protect the substations from various faults and its smooth functioning. Power Transmission Corporation of Uttarakhand Limited takes such steps so that a uniform and stable supply of electricity can reach in every part of this state.

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17. BIBLIOGRAPHY

1. Energy efficiency in electrical utilities, Guide book for National certification examination for energy managers and energy auditors, Bureau of energy efficiency, Ministry of Power, Govt. of India, 2003.

2. General aspect of energy management and energy audit, Guide book for National certification examination for energy managers and energy auditors, Bureau of energy efficiency, Ministry of Power, Govt. of India, 2003.

3. www.wikepedia.com

4. www.slideshare.com

5. www.electrical-installation.org

6. www.home-energy-metering.com

7. www.enspecpower.com

8. www.allaboutcircuits.com

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