Final Project

JIS COLLEGE OF ENGINEERING

Block-a, Phase-III, Kalyani, Nadia-741235

(Approved by AICTE & affiliated to WBUT)

Vocational training report

Under

AE, Kalyani Trans.(O&M) Sub-Division, W.B.S.E.T.C.L

Dated-27th December 2010 to 8th January 2011

At Kalyani 132 kV Substation

Report Submitted By:-

Debojyoti Roy

Department of Electrical Engineering

3rd Year EE/08/62

4TH Semester

JIS College Of Engineering, Kalyani

Signature of training in-charge

AE, Kalyani Trans. (O&M) Sub-Division, W.B.S.E.T.C.L

Signature of trainee

ACKNOWLEDGEMENT

I am very much thankful to the HR&A department of W.B.S.E.T.C.L Bidyut Bhavan, Salt Lake and Kalyani sub station for providing me the opportunity of vocational training at their substation. I am especially thankful to Sir S. Ghosh, asst. engineer for his kind attention. I am equally thankful to Mr. Ghosh, Mr. Ganguly, Mr. Bhattacharyya, Mr. Mayti and other officers for sharing their valuable experiences at the yard and in control room by making me acquainted with the practical phenomenon happening over there.

INTRODUCTION

Sub-station as the source of energy of local area of distribution in which these are located. The main function of a substation is to receive energy, transmit at high voltage from the generating station, to reduce the voltage to a value appropriate for distribution and to provide the facilities of switching. Substation has some additional functions. They provide points where the safety devices are to be installed to disconnect equipments or circuits when faults occur. Voltage on the outgoing distribution feeders can be regulated at the substation. A substation is a convenient place for installing synchronous condensers at the end of the transmission line for the purpose of improving power factor and make measurements to check the various parts power system. We got the opportunity to visualize all the phenomena written above at the Kalyani substation of 132 KV of W.B.S.E.B. from 26.12.2006 to 12.01.2007 and our experiences of the actions of different parts of the sub stations are summarized in the following section as much as possible.

According to the voltage level substation is divided into following:

1) RECEIVING SUB-STATION:- The power generating stations generally produce 11 KV powers which is stepped up by 132 KV for distribution to reduce loss. Now the receiving substation collects 132 KV and step down it to 33KV and then feed it again into the distribution line.

2) INTERMEDIATE SUB-STATION :- These types of sub stations are located at the center of the city, which steps down 33 KV to 11 KV. From here bulk consumers like factories, railways etc get power. So, from intermediate substation is short

3) DISTRIBUTION SUB-STATION :- It collects 11 KV, 3 phase, 3 lines power and then steps down it into 415 V or 230 V, 3 phases 4 wire system for giving the power supply to the domestic consumers at the different areas of the cities.

The network has various voltage levels for generation, transmission, distribution, utilization, control and protection.

~ Generation is at the voltage level up to 30 KV A.C.(R.M.S.)this is due to design limitation of ac generators.

~ Long distance power transmission by EHV lines rated 220 KV, 400 KV, 760 KV, ac for long distance and high power higher voltages are economical and essential.

~ Backbone of transmission network is by EHV ac transmission line 400 KV ac.

Utilization is at low voltage up to 33 KV and step down it to 400 V ac larger factories power at 132 KV and have internal distribution at 3.3 KV to 400 V ac.

Generating unit:

In the generating unit mechanical power is converted into electrical power and the power is transmitted through transmission line and conductors and towers. Usually it is done at high voltage to the generating station in which the switching operation and stepping down operation is done.

In our Kalyani substation the main power is coming from BTPS generating unit and DHARAMPUR substation .in case of fault occurring in DHARAMPUR substation, KALYANI SUBSTAION can transmit power to DHARAMPUR substation. The power is transmitted through various types of conductors which are suspended from various types of towers.

TOWERS:

The supporting structures for line conductors are called towers.

In general towers have the following properties:

1) High mechanical strength to withstand the weight of conductors and wind loads.

2) Light in weight without the loss of mechanical strength3) Cheap in cost 4) Longer life 5) Easy accessibility of conductors for maintenance.

For transmission purpose we only use steel towers.

Various types of steel towers:1) A TYPE tower : it’s a suspension type tower and it has angle of deviation of

0-2 degree between the conductors2) B TYPE tower : these are tension towers having an angle of deviation of 2

-15 degree

3) C TYPE tower : : these are tension towers having an angle of deviation of 15 -30 degree

4) D TYPE tower: these are also tension type tower having angle of deviation of 30-60 degree.

INSULATOR:-

The insulators are used for to purpose. They support the conductors and provide necessary insulation between line conductors and supports. The most commonly used material for manufacturing insulators are

Porcelain

Glass Synthetic Resin

Among them Porcelain are hugely used.

The porcelain is basically glazed.

There are several types of insulators used in a substation which are used depending upon the service requirement. Post insulators are used for bus-bars. A post insulator consists of a porcelain body, cast iron cap and flanged cast iron base. The hole in the cap is threaded so that the bus bar can be directly bolted to the cap. When the line is subjected to greater tension, strain insulators are used. For low voltage lines shackle type insulator is used. For high voltage lines suspension type insulators are used. When tension in the line is exceedingly high, two or more strings are used in parallel. At the dead end tension type insulators are used also where the line has any bend tension type insulators are used. The insulators are shown in the figure beside.

PROFORMA FOR USING INSULATOR

Area where the insulator be used Specification of insulator

Rail Crossing Both end tension type

High Way crossing (N.H. or Large Road) At least one type tension and double string suspension type

Small Road crossing Double string suspension type

PILOT DISC: - When there is a bend near about 90° movement in transmission line then the inside jumper can be get in touch with the tower earthed body by wind pressure. To prevent this one more insulator string is to be attached with the tower this is called pilot disc.

DIAGRAM OF DIFFERENT TYPES OF INSULATORS

OVERHEAD LINES :-

An overhead line may be used to transmit or distribute electric power. The successful operation of an overhead line depends to a great extent upon the mechanical design of the line. In general, the main components of an overhead line are:1) Conductors2) Supports3) Insulators4) cross-arms

CONDUCTOR MATERIALS: The conductor is one of the important items as most of the capital outlet is invested for it. Therefore proper choice of material and size of the conductor is considerable importance. The

conductor material used for transmission and distribution of electric power should have the following properties:1) High electric conductivity2) High tensile strength3) Low cost so that it can be used for long distances4) Low specific gravity so that weight/volume is small.

The most commonly used conductor materials are copper, aluminium, steel core aluminium and galvanized steel.

Due to low tensile strength aluminium conductors’ produces great sag. These prohibits their use for larger spans and makes them unsuitable for long distance transmission in order to increase the tensile strength the aluminium conductor is reinforced with a core of galvanized steel wires. The composite conductors thus obtained are known as steel cored aluminium and is abbreviated as A.C.S.R. It is an acronym of Aluminium conductor steel reinforced.

According to I.E rules the conductors are distinguished by their common names by different names of animals for easy identification of workers such as ACSR PANTHER, ACSR ZEBRA, ACSR DEER, ACSR DOG, and ACSR MOOSE.

The specification of ACSR PANTHER: - for 132 Kv transmissions it is used.

It consists of central core of galvanised steel wires surrounded by a number of aluminium strands usually diameter of both steel and aluminium wires is the same. The cross section of ACSR PANTHER is 21 mm having 7 steel conductors at centre and 30 aluminium conductor at the periphery each of 3 mm. The current carrying capacity of ACSR PANTHER is 520 A at 40 degree ambient temperature.

The result of these composite conductors is that steel core takes greater percentage of mechanical strength while aluminium strands carry the bulk of current. The steel cored aluminium conductors have the following advantages:-

1) The reinforcement with steel increases the tensile strength but at the same time keeps the composite conductor light. Therefore the steel

A.C.S.R

cored aluminium conductors will produce smaller sag and hence longer span can be used.

2) Due to smaller sag steel cored aluminium conductors, towers of smaller heights can be used.

GANTTI TOWER: - To give horizontal displacement to vertically displaced transmission line at the entrance in substation the towers basically used is called gantti tower. It has a small base area. The conductors coming from transmission lines fall upon this tower structure. From the gantti tower Power line carrier communication (PLCC) used for telecommunication, tele-protection and tele-monitoring between electrical substations through power lines at high voltages is suspended.

Diagram of a Gantii tower

Wave trap: - Power line carrier communication (PLCC) is also called "Wave trap". It is connected in series with the power (transmission) line. It blocks the high frequency carrier waves (24 kHz to 500 kHz) and let power waves (50 Hz - 60 Hz) to pass through. It is basically an inductor of rating in milli henry.

We have audible frequency between 20 Hz- 20,000 Hz.In a PLCC system the communication is established through the power line. The audio frequency is carried by a carrier frequency and the range of carrier frequency is from 50 kHz to 500 kHz. The modulation generally used in this system is amplitude modulation. The carrier frequency range is allocated to

include the audio signal, protection and the pilot frequency. The pilot frequency is a signal in the audio range that is transmitted continuously for failure detection.

The voice signal is converted/compressed into the 300 Hz to 4000 Hz range, and this audio frequency is mixed with the carrier frequency. The carrier frequency is again filtered, amplified and transmitted. The transmission of these HF carrier frequencies will be in the range of 0 to +32db. This range is set according to the distance between substations.

There are two types of PLCC:-

1) C.C :- Coupling capacitor wave trap2) C.V.T :- Capacitor Voltage Transformer Wave trap

ISOLATOR :-

In

HORIZONTAL ISOLATOR

substations, it is often desired to disconnect a part of the system for general maintenance and repairing. This is accomplished by an isolator.

An isolator is a knife switch and is design to open a circuit under no load. If an isolator is open carelessly when carrying a heavy current the resulting arc easily causes a flashover to the earth. This may disrupt the supporting insulators and may even cause a fatal accident to the operator, particularly in high voltage circuit.

The operating mechanism is manual plus one of the following:

Electrical motor mechanism Pneumatic mechanism

Isolators cannot be opened unless circuit breaker is opened. Circuit breaker cannot be closed unless isolator is closed.

Isolators are of two types:

Horizontal isolator

Vertical isolator

MAIN BUS: - Main bus is the prime portion from which power is transmitted to power transformer for step down operation. It receives power through the isolator and then transmits to the power transformer. Main bus is a three phase line where ACSR DEER is used. (AS PER I.E. RULES). But 132 KV ACSR panther can also be used. Since as per strong recommendation of I.E RULES ACSR DEER is used in KALYANI SUBSTATION.

BUSBARS: - When a number of lines operating at the same voltage have to be directly connected electrically, bus bars are used as the common electrical component. Bus bars are of copper or aluminium bars and operate at constant voltage. The incoming and outgoing lines in a substation are connected to the bus-bars. The most commonly used bus-bars arrangements in sub-stations are

1) Single bus bar arrangement2) Single bus bar system with sectionalisation3) Double bus bar arrangement

Spare bus bar: - In case of repair of main bus bar or fault occurring on it the continuity of supply can be maintained by transferring it through the spare bus bar to the power transformer.

BUS COUPLER: - The interlocking function blocks the possibility to operate high voltage switching devices, for instance when a disconnector is under load, in order to prevent material damage and accidental human injury.

Each control terminal has interlocking functions for different switch yard arrangements, each handling interlocking of one bay. The function is distributed to each control terminal and not dependent on any central function. For the station wide interlocking, the control

Figure 1

Figure : BUS COUPLER

Figure 1

Figure : BUS COUPLER

terminals communicate via the system wide interbay bus or by using hard wired binary input-output.

The interlocking conditions depend on the circuit configuration and status of the installation at any given time.

COMMUNICATION ROOM:-The work of PLCC is controlled and manipulated in communication room.

As human voice frequency is low so it is amplified to high level by amplifier, also there are various types of filters, capacitors and rectifiers to get crystal communication.

MAJOR ELECTRICAL EQUIPMENTS USED IN SUB STATION

POWER TRANSFORMERS: - The transformers are a stationary apparatus by which electrical power is transformed from one circuit to another circuit without change in frequency. It can rise or lower the voltage with a corresponding increase or decrease in current. Two circuits primary and secondary are linked by common magnetic flux through mutual induction. The two circuits are electrically isolated but magnetically linked through a path of low reluctance. If one coil is connected to an ac supply, an alternating flux is set up in which links both the circuits and thus self inductance and mutually induced EMFs are set up in both circuits. This helps to transfer voltage from one side to another. We have observed 3 power transformers in the Kalyani substation along with a stationary auxiliary transformer. These transformers are step down transformers (132/33kv) connected in Y-D mode and the remaining transformers are in the D-Y mode and stepping down the voltage 33/11 KV.

ACCESSORIES OF POWER TRANSFORMER

CORE AND WINDING:- The core of the transformer may be of various shapes i.e. core, shell. It is made by cold-rolled grain oriented silicon-steel lamination. Laminated sheets are insulated from each other by applying a thick layer of varnish insulation on the lamination. The core is laminated to reduce eddy current losses. The laminations are made in steps and try to give circular cross section. Bolts and nuts secure the lamination. The core is placed at the bottom of the tank. The tanks are constructed from welded sheet steel for small tanks and boiler sheet steel for large tanks. There are thermometer pockets, radiators tubes for increasing cooling surface. A three phase transformer has six separate windings- three primary and three secondary wounded on iron core. Enameled copper with insulation is used for winding. Insulated papers are used for inter layer insulation. Paper in the form of tape may be used for taping winding leads and other parts. Press boards are used as insulation between windings and cores. Press boards are also used to separate H.V. windings from L.V. windings input nearer the core.

TRANSFORMER OIL:- The tank filled with transformer oil and tank is sealed. It is a mineral oil obtained by refining crude petroleum. It serves the following purposes:

Provides additional insulation. Carries away the heat generated in the core and oils.

A Good transformer oil should have:

High dielectric strength. Low viscosity to provide good heat transformer. Good resistance to emulsion. High flash/fire point. Free form inorganic acid, alkali and corrosive sulphur. Free form slugging under normal operating conditions.It is necessary to check the

oil in regular intervals.

DIVERTER TANK: - It is drum like structure, mounted on a transformer wall and filled with transformer oil and connected to a conservator. It reduces arcing during tap changing processes.

RADIATOR: - It is of small thickness and large diameter plates and used for heat dissipation of oil during operation. Larger diameter means larger surface area and better cooling.

CONSERVATOR: - The conservator consists of an air-tight metal drum fixed above the level of the top of the tank and connection with the tank is completely filled with oil. The conservator is partially filled with oil. The function of a conservator is to take up construction and expansion of oil without allowing it to come in contact with outside air. (Transformer oil will expand due to the heat generated because of the losses taking place in the transformer.)

BREATHER: - When the temperature changes, the oil expands or contracts and there is a displacement of air. When the transformer cools down, the oil level goes down and air is drawn in. The oil should not be allowed to come in contact with atmospheric air as it may take up moisture which may spoil its insulation properties.

Air may cause acidity and slugging of oil; so the air, coming in, is passed through an apparatus called breather for the purpose of extracting the moisture. The breather consists of a small vessel, which contains a drying agent called silica gel crystals.

TEMPERATURE INDICATOR: - There are two temperature indicators on the transformer tank, one for the oil temperature measurement and other for the core temperature measurement. In 31.5 MVA transformers, when oil temperature reaches 65 degree c cooling fans start automatically. But when the oil temperature rises

CONSERVATOR TANK

s

75 degree c or winding temperature rises at 85 degree c the alarm circuit will be closed. Further increase in oil or winding temperature the circuit will be trip automatically. Cooling fans are placed beside the radiator tube, which are used for oil cooling. Generally the cooling fans start automatically, but when needed it can be start manually.

BUSHING: - Bushing is fixed on the transformer tank and through those connections are made to the external circuit. Ordinary Porcelain insulators can be used as bushing up to a voltage of 33 KV. Above 33kv, oil filled type of bushing are used. In oil filled bushing, the conductor is passed through the hollow porcelain insulator filled with oil.

BUCCHOLZ RELAY: - It is a gas activated relay inside in oil immersed transformers for protection against all types of fault. Any fault produces heat and in course the evaluation of gases. It mainly consists of two float switches and placed in the connecting pipe between he main tank and the conservator. Under normal condition the main tank and the Bucholz relay is completely filled up with oil and the conservator tank is half full. When the fault occurs, it produces gas which is collected in the container. So the oil level falls and closing the alarm circuit. If no attention is paid to it the gas collection will be more and close another circuit, which will cut out the transformer from the line.

BUSHING

ADVANTAGES:

1. It is the simplest form of transformer protection2. It detects the slow developing faults at a stage much earlier than other forms

of protection.

EXPLOSION VENT/PRESSURE RELEASE VENT: - When the gas pressure on the container is heavy, explosion vent is released. Alarm and the trip circuit are closed by the Bucholz relay, before opening the explosion vent.

TAP CHANGING: - Mainly 132/33 KV transformer used on load tap changing and 33/11 KV transformer use off load tap changing. The tap changing is mainly done on the H.V. side because current flow is less than he L.V. side, which reduces flashing during tap changing. Here tap is changed in 132/133 KV transformer.

SWITCH POSITION NUMBER

H.V. SIDE VOLYTAGE SWITCH CONNECT LEAD NUMBER

1 145200 NTO 12 143550 NTO 23 141900 NTO 34 140250 NTO 45 138600 NTO 5 6 136550 NTO 67 135300 NTO 78 133650 NTO 89 132000 NTO 910 130350 NTO 1011 128700 NTO 11 12 127050 NTO 1213 125400 NTO 1314 123750 NTO 1415 122100 NTO 1516 120450 NTO 16

17 118800 NTO 17