29-06-2012, 01:12 PM
BRIEF VIEW OF CHYANDRYANAGUTTA SUBSTATION
BRIEF VIEW OF CHYANDRYANAGUTTA SUBSTATION.doc (Size: 7.79 MB / Downloads: 211)
Typical outdoor Sub-station:-
In any outdoor substation, transformer is the heart. A transformer is supplied with power duly providing the protection and controlling equipment like circuit breakers, current transformers, air break isolators, lightning arresters both on HV and LV side which are exposed to air
1.1 Lightning arresters
Lightning arresters are also known as surge diverters or surge arresters. The alternative name surge diverters is based on the fact that the function of the device is to divert to earth the heavy current and voltage surge on an over head line resulting from a lightning stroke.
Lightning arresters are connected between line and ground at the sub station and always act in shunt with the equipment to be protected and perform their protective function by providing a low impedance path for the surge current so that the surge arresters protective level is less than the surge voltage withstanding the capacity of the insulation of equipment being protected.
1.2 WAVE TRAP:
Wave trap is an inductive device, which offers high impedance to high frequency signals. Hence it will not allow communication signals towards substation equipment. Wave trap offers negligible impedance to power frequencies hence power flow will be unaffected. Because of wave trap even if the line is earthed with the line earth switch (located behind wave trap) communication will not be affected.
1.3 INSTRUMENTAL TRANSFORMERS:
Instrument transformers are used to protect apparatus from high voltage and permit use of reasonable insulation level and carrying current capacity in relays and meters the standard instrument transformers, relays and meters are rated for 5 amps and 1amp and 110 volts, 50cycles on secondary side the transformers can be arranged in front or behind the outgoing feeder isolator or on the bus bar.
They are two types:
1. Current transformer(CT)
2. Voltage transformer (VT)
a) Current transformer:
The instrument current transformer (CT) steps down the current of a circuit to a lower value and is used in the same types of equipment as a potential transformer. This is done by constructing the secondary coil consisting of many turns of wire, around the primary coil, which contains only a 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 current when under load, this large increase in magnetizing current will build up a large flux in the magnetic circuit and cause the transformer to act as a step-up transformer, inducing an excessively high voltage in the secondary when under no load.
These transformers are basically used to get the incoming current on the incoming feeders. It steps down the incoming 800 amps to 1 amp.
132 KV CT front view
b.Potential transformers:
There are 2 types of potential transformers
1) Potential Transformer----PT
2) Capacitor voltage Transformer CVT
The instrument potential transformer (PT) steps down voltage of a circuit to a low value that can be effectively and safely used for operation of instruments such as ammeters, voltmeters, watt meters, and relays used for various protective purposes.
There are two potential transformers used in the bus connected both side of the bus. The potential transformer uses a bus isolator to protect itself. The main use of this transformer is to measure the voltage through the bus. This is done so as to get the detail information of the voltage passing through the bus to the instrument.
There are two main parts in it
(a) Measurement
(b) Protection.
c) Communication (for CVT)
Potential transformer ratings:
High voltage side: 245 V
Rated insulation voltage: 395/ 900
Voltage rating: 220/√3 kV/ 110/ √3 V-110v