Visit on substation Report

Contents 1) Introduction…………………………………………………………………… 1 2) Equipment details……………………………………………………………. 4 3) Padmanabah nagar sub-station (66/11 KV)……………………………….6 4) Single line layout of the substation…………………………………………6 5) Earthing mat……………………………………………………………………7 6) Lighting arrester……………………………………………………………….7 7) Isolators………………………………………………………………………....8 8) SF6 circuit breaker…………………………………………………………….9 9) Transformer……………………………………………………………………10 10) CTR fire protection system………………………………………………….12 11) Auxiliary transformer………………………………………………………...13 12) Control room………………………………………………………………….13

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Introduction Substation The substation consists of the following essential equipments: Incoming lines Outgoing lines Control room (control and protection panels) Transformers (main power transformer and auxiliary transformer) Circuit breaker, isolators, relay and metering panels CT’s, PT’s, power cables and control cables Station service equipment such as lighting arresters, auxiliary battery supply Compressed air system Station earthing system Communication equipment such as carrier equipment telephone system etc Classification of types of substation depends on various factors in which the major factor is

Based on voltage level: A substation is named in accordance with its higher voltage level. Example: a 66/11 KV A.C substation higher voltage level of 66 KV. Standard Indian voltages Refer to normal power frequency phase to phase A.C voltages. Types of substation for voltages more than 66 KV and above

Conventional outdoor: Substations (open terminal air insulated type) in which busbars and live parts can be seen with the naked eye.

Gas insulated metal enclosed substation: Substation in which various equipments are with alluminium enclosures filled with internal insulation, such substations can be generally indoor.

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Electrical substation has several indoor and outdoor equipment Each equipment has a certain functional requirements. The choice of the equipment depends on technical considerations, rated voltage, rated MVA and the type of substation.

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Various Equipment Details:

Equipment Bus bars

Surge arrestor (lightning arrestor)

Isolators (disconnecting switches)

Function Various incoming and outgoing circuits are connected to bus bars. They receive power from incoming circuits and deliver power to the outgoing circuits. Surge arrestors discharge the over voltage surges to earth and protect the equipment insulation from switching surges and lightning surges. (The word surge refers to impulse in transmission and distribution.) To provide isolation from the live parts for the purpose of maintenance.

Earth switch

Discharge the voltage on the circuit to earth for safety.

Current transformer

Stepping down the current measurement ,protection and control.

Voltage transformer

Stepping down voltage for measurements, protection and control.

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Remarks Flexible ACSR or all alluminium stranded bus bars supported from the two ends by strain insulators.

Connected generally between phase conductors and ground Located as the first equipment as seen from the incoming over head line and also near transformer terminals phase to ground.

Located at each side of circuit breaker. Does not have any rating for current breaking or current making. Mounted on the frame of the isolators. Located generally for each incomer and each bus section. Protective CT Measuring CT Location decided by protective zone measurement requirements. Types

Electro magnetic Capacitive VT (CVT) Location on feeder side of circuit breaker.

OBSERVATION OF PART OF SUBSTATION

RAIN SHEDH LIGHTNING ARRESTER ARCING HORN

ISOLATOR CABLE (XLPE) SF6CIRCUITBREAKER CT

AL.PIPES

LATTICS STRUCTURE POLE

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Padmanabah nagar sub-station (66/11 KV) The 66/11 KV padmanabah nagar sub-station is located opposite one of the famous landmarks of Bengaluru namely Devegowda (India’s former prime minister) petrol station.The sub-station is one of the several 66/11 KV sub-station in Bengaluru. There are total 40 nos. 66/11 KV sub-station in Bengaluru catering a load of 2000 MW which is 1/3rd of power supply in Bengaluru. There are 10 nos. of 220/66 KV sub-station in Bengaluru. Bengaluru follows’ a ring structure around the city which is one of its kind in India from which several 66/11 KV supply is taken, this ring structure terminates at the same point where it started. All equipment and system is earthed properly through GI strips of 25X6 mm and 150X6 mm via earth electrode which in turn is connected to earth-mat. The sub-station is having two 66 KV incoming supply. These two incoming supply is coming from Subramanyapura- 1 & 2 sub-station through XLPE ( Cross Linked Polyi-Ethylene) cable’s. These cables are 660sq.mm, 3-phase single core copper cable. These cables are designed according to required voltage, creapage and rain .At present the station bay (area under an over head structure) is being extended to provide another 66 KV line to serve as another alternate 66 KV source since both the present feeders are from the same station. The present two incoming feeders are used alternatively (one at a time). The station peak load is 24 mega watts and handle about 3,25000 units every day.

Single line diagram of 66 / 11 KV substation :

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Earthing Mat The earth mat is designed after the procurement of land area. The land is excavated by 1m deep. After the excavation the galvanized iron rods are laid in latitudinaly and longitudinally. In this sub-station the earthing mat design is done by KPTCL using software. During construction of the earth-mat charcoal and sand with water is added to lower the resistivity of soil. The dimension of GI material is 25X2 mm and 150X6 mm. The main criterion to design the earth-mat is to find soil resistivity. The soil resistivity varies widely and depends on the nature of soil. The main purpose of designing earthing system is to protect both human and electrical system from electric hazards. Humans are very vulnerable to the effects of electric currents. Even a current of 0.1 A is lethal at power frequency. The purpose of earthing is to provide:To provide low impedance path to current. To ensure living beings in the vicinity of sub-station are not expose to unsafe potentials. To retain system voltages at reasonable limits. To provide an alternating path for induced currents there by minimize electric noise.

Lightening Arrester The lightening or surge arresters (L.A) used in the sub-station is rod gap type. These are used for the protection of power system equipments. The surge arrester used here is of 45 KV. The XLPE cable coming from Subramanyapura sub-station terminates here through L&T-type clamps. The surge arresters are mounted on the platform which is earthed by GI strip and through the earthed electrode it is connected to earthing-mat. The XLPE cables terminating on these arresters are earthed by another single core cable on to the GI strip. The conductor used from LA’s to line bus is ACSR wolf conductor. The working Formula to find the rating of surge arrestor is:Rating :( 66/√3) = 38 KV

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Isolators The isolator is 66 KV incoming line Gang Operating Switch (GOS). The main purpose of the isolator is to carry out maintenance work after line clearance. The isolators are mounted on the lattice structures and are earthed by GI strips to earth electrode which in turn is connected to earthing mat. The first line isolators are always provided with the earth or grounding switch. This grounding switch is provided to carry out maintenance work. Whenever there is any work required to carry out in the system we put operate the earth switch so that the whole system will be at ground potential. This earth switch is provided in both of the sub-stations i.e padmanabah and Subramanyapura. In some isolators there is mechanical interlocking provided so that the earth switch cannot be operated when the system is in line. If this is done than the whole system will be at high risk and havoc is created. There are two types of isolator:-

Single Break Isolator: This isolator is used where the line current is less than 200 A.

Double Break Isolator: This isolator is used when the line current is more than 200 A. The isolators are always designed on fault current.

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SF6 Circuit Breaker The 66 KV SF6 circuit breaker comes after the isolator. In this breaker SF6 (Sulphur Hexafluoride) gas is used. In this breaker the arc quenching is done by SF6 gas whereas the air is used for tripping and spring loading purpose. SF6 gas is considered to be very good arc quenching property. The pressure maintained in SF6 cylinder is 6 kg/cm 2 and in air cylinder is 15 kg/cm2. There is one compressor installed inside the breaker cabin whenever the pressure of air drops below 15 kg/cm2 it starts automatically. There are two types of SF6 breaker:Single break This is used for 66 and above. In this the female contact is fixed and male contact is movable and is non-electric conductor. Double break This is used for 220 KV and above. In this the live part is kept at ground potential. The tripping time in this breaker is 10-20 ms and charging time is 100 ms. The top most part used for connection and central portion hold conductor called interrupter. The pressure inside interrupter is around 6kg/cm2.There are two DC coils present one is for tripping and other is for back protection (in case the first one fails to operate). One of the several advantages of using SF6 is that the loss of gas is very minimum and it can go upto 2 years without stopping. Some of the safety features of this breaker are as follows:a) DC failure safety (breaker trips itself whenever dc fails and fails to obey any command. b) Air pressure below 12 kg/cm2 cylinder automatically starts. c) Interrupter is designed at 6 kg/cm2. d) Tripping and charging is done by quick action spring.

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Transformer There are two one of 16\20MVA and another of 31.5 MVA Dyn11 vector group 66/11kv class transformers. Feeding supply through double circuit of ring main

Observation

Transformer rating Vector group Cooling system Bushing Cooling fans Conservator tank On load tap changer Breather

16/20 MVA (66/11 KV) 19/31.5 MVA(66/11 KV) DYn11 16 MVA – ONAN TYPE 20 MVA – ONAF TYPE Oil impregnated condenser bushing (66 KV) 4 nos 2 nos For active part For OLTC MR type 33 rev = 1 tap Silica gel breather

Protection of Transformer The type of a protective gear for a Transformer depends upon several factors such as: Type of Transformer Size of Transformer One of the Common Protection is Buchholz Protection

Buchholz Protection Buchholz Relay is installed between the Transformer and the Conservator tank and is used to give warning in case of less severe internal faults in oil immersed Transformer and to disconnect the Transformer from the main supply in case of severe Internal faults. It is practically used on all oil immersed Transformer having rating more than 750kva.It is used in conjunction with some form of electrically operated protective gears because it provides protection against Transformer Internal faults and does not respond to external bushing or cable connection faults.

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CTR Fire Protection system Transformer is also protected from fire during any abnormal fault condition. Well adequate clearance is maintained between the two transformers in the substation. Main equipment used for this is the water emulsified fire extinguisher which takes care of the abnormal conditions. During these fault conditions CTR has equipment which does not allow the oil passage from the top portion of the conservator tank when it senses any abnormal temperature difference.

Various monitoring conditions employed in CTR fire protection scheme Differential relay trip Pressure relief valve trip Buchholz Protection Fire detector trip Transformer trip Line fault differential trip Line fault PRV Lamp test

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Auxiliary transformer Back up transformer is also maintained in the substation through which supply is fed to the control panel equipments and for lighting purpose. Specifications of the auxiliary transformer: 410/55-0-55 V/ 500 VA

Control room Monitoring of the entire substation can made from the control room. In this all the preliminary actions for the improvement or for any fault clearing conditions can be monitored.

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