13-05-2011, 06:08 PM
110KV SUB-STATION PARUTHIPARA
IV REPORT
IV REPORT
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INTRODUCTION
The hydel power development in Kerala began with the commissioning of Pallivasal hydro electric project in 1940. Next few decades saw the progressive developments of various schemes. The Paruthipara substation is the oldest substation in Trivandrum. There are 4 main feeders into this substation .it consists of a upper yard and a lower yard. The upper yard has the 2 feeders from Pothencode substation. These are 110kv feeders. The power basically comes from the Sabarigiri power project via Edamon and Pothencode. The substation supplies power in 2 ratings -66kv and 11kv. The 66kv supply feeds the following:TVT1,TVT2,Veli,terls. The 11kv supply feeds the following :Attingal,TVM East, Engineeringcollege, Vydyuthibhavan, Medicalcollege, Pattoor(Ulloor), Nedumangad, Kilimanoor, Aruvikkara, Peroorkada, Kowdiar. From the station 2 feeders of 110kv capacities are directed to medical college substation and are called TMC lines .
COMPONENTS OF THE SUBSTATION The power transformers are used to step down the voltage. The transformer core is made of high grade non-ageing cold rolled grain oriented steel laminations. the cooling is provided by means of ONAN(Oil Natural Air Natural)and ONAF(Oil Natural Air Forced). There are fans rotating at very high speed near to fins (used to increase the surface area).
Tap changing mechanism is provided for maintaining the secondary voltage constant with varying primary voltage. Tap changing causes change in leakage reactance, core loss, I2R loss etc. the tap changing means changing the turns ratio. The tapings are provided on the HV side so that it carries minimum current.
Tank is welded construction. It is stiffened by structured steel. It is provided with 2F earth terminals. HV and LV bushings are transported in crates.
Conservator is a cylindrical tank divided into 2 chambers –one for the main tank and other for OLTC. The function of the main conservator is to keep the main tank completely filled with oil. OLTC is fitted with an oil sight window. Explosion vent has a bursting plate and is used as a safety device. When the internal pressure of transformer increases by abnormal phenomenon the diaphragm bursts. In latest models this is replaced by a pressure release valve.
Breather: When transformer becomes warm, the oil and gas expands. The gases at the top of the oil expel out and air is drawn into the transformer. This process is called breathing. The air entering is made moisture free by letting it to pass through the breather. It consists of a small container with silica gel crystal. The material is blue when dry and whitish when damp. At the bottom of the container some oil is present along with aluminum silicate in order to absorb dust particles. There are 2 breathers, one for the main conservator tank and the other for OLTC.
Two gauges keep track of the temperature of the oil and winding and an alarm goes off when the temperature rises beyond the limited value. The gauges are fixed on the mounting plate of the transformer. The 2 types of indicators are –Oil Temperature Indicators (OTI)-Winding Temperature Indicators (WTI)
There is provision for the control of fan motor by sensing the oil temperature.
Specifications And Ratings
63MVA, 110/66kV Autotransformer
• Volts at no load HV : 11000
LV : 66000
• Ampere HV : 220/331
LV : 367/551
• Phase HV : 3
LV : 3
• Type of cooling : ONAN/ONAF
• Frequency : 50HZ
• Impedance voltage : 14.02%
• Weight of Core and windings : 26200kg
• Weight of oil : 18740kg
• Volume of oil : 20829 litres
• Guaranteed maximum
Temperature rise in oil : 450C
• Number of working taps : 9
10 MVA, 110/11kV Transformer
• kVA HV : 10000
LV : 10000
• Volts on no load HV : 110,000
LV : 11,000
• Amperes HV : 52.48
LV : 524.86
• Phase HV : 3
LV : 3
• Type of cooling : ONAN
• Frequency : 50Hz
• Impedance voltage : 9.65%
• Untanking mass : 11500kg
• Mass of oil : 7920kg
• Total mass : 26200kg
• Volume of oil : 8800 litre
• Guaranteed maximum
temperature rise in oil : 450C
ISOLATORS In order to disconnect a part of system for maintenance and repair isolators are used. It is a knife switch designed to open a circuit under no load. If isolators are to be opened, the CB connected must be opened first. Otherwise there is a possibility of occurrence of a spark at the isolator contacts. After repair, first isolators are closed and then CB. There are two types of isolators- line isolators and bus isolators. For bus isolators, there is no earth switch. During maintenance works the line isolator contacts are opened, so that the three phases trip simultaneously. For the ease of earthing, dead weights are provided at the end of earthing arms.
Ratings
• Current : 800A
• Max design voltage : 125kV
• Impulse withstand voltage : 550kV
CIRCUIT BREAKERS A circuit breaker is an equipment which can open or close a circuit under normal as well as fault conditions. It can be operated manually from the yard as well as from control room using a pulse trigger under normal condition and automatically under fault condition. For latter relay circuits are used.
It consists of a moving and fixed contacts enclosed in strong metal tank. Under normal conditions contacts remain closed and the CT senses full load current. When fault occurs, the over-current in the CT primary winding increases the secondary emf thus energizing the trip coil and moving contacts are pulled down, thus opening the contacts and hence the circuit. The arc produced is quenched by SF (6outdoor CB) and vacuum(indoor CB)
SF6 Circuit Breaker
Its closing is by spring action and tripping is in air. Each CB has an air tank in which pressure is maintained at 15kg/cm2. If pressure goes below this a rotary compressor is automatically activated. Pressure of SF6 is continuously monitored. SF6 being costly, is filled separately in each CB. The gas can be reconditioned after each operation. Operation mechanism is through air, which is being stored in a closed tank. Other CBs are interconnected through tubes. Gang operation is initiated while tripping.
Ratings
• Rated voltage : 145kV
• Normal current : 1250 A
• Frequency : 50Hz
• Lightning impulse withstand voltage: 650kV(peak)
• First pole to clear factor : 1.5
• Short time withstand current : 31.5kA
• Duration of SC current : 5 sec
• SC breaking current
Symmetrical : 31.5kA
Asymmetrical : 32.7kA
• SC making current : 80kA
• Out of phase breaking current : 7.9kA
• SF g6as pressure at 300C : 6.3bar
• Total mass of SF6 gas : 8.7kg
• Total mass of circuit breaker : 1300kg
BATTERY AND BATTERY CHARGER
The station DC source is facilitated through battery of 400 Ah capacity and 200 Ah capacity. The 400 Ah battery bank no 1 is fed through the battery charger from the main control room. This is of 110kV, 50 A capacity. The second 400Ah battery bank has the same capacity. 200 Ah bank is fed through the battery charger located in the old control room. This is of 110kV, 15 A capacity. This feeds only 11kV cubicles located in the old control room. 110 volt supply is always provided as a standby as there is possibility of power failure in station. At this time also the tripping in case of fault should continue; for this the 80V DC supply is very essential. 55 batteries each of 2 volt are provided giving a total of 110 V. In some area the required voltage is less, in such cases the batteries used also should be less. The batteries are lead acid cells and have sulphuric acid as its electrolyte with lead electrode along with spongy lead in between. They have 400 Ah capacity i.e. they can supply a current of 400 A for a time of 1 hour. So it can be used to supply 200 A at intervals of 2 hours. This voltage always provided in parallel with the AC supply. It can be used in case the AC fails. The batteries can be charged in 2 modes, float charging and boost charging. Float charging is used when AC is present and Boost charging is used when the battery is in the back up mode. Battery is regularly checked in the substation to check the acidity of electrolyte. A hydrometer is used to measure the same. To measure the voltage there is the centre zero voltmeter.
