Core and windings:
The core of the transformer is made up of thin laminated (insulated) metal sheets of soft iron pressed together. The 3ph primary and secondary is wound over the core. In the transformer used here in 33 KV Duliajan power station switchyard is delta connected at the LV side and star connected at the HV side.
Conservator:
The conservator is a tank containing the oil used for cooling and proper insulation of the core. A level gauge is attached with the conservator to indicate the oil level. There are two types of level gauges 1) Prismatic gauge and, 2) Magnetic gauge
Radiator:
The radiators are made up of metal sheets projected outside the transformer enclosure to release the heat generated inside the core to the atmosphere.
Silica Gel Dehydrating Breather:
The breather is a container like thing containing silica gel in it. The purpose of a breather is to remove the moisture from the cooling oil and the core.
Bushings: Bushings are the insulated leads via which the output of the transformer is taken. They are made up of ceramic, procelain or epoxy insulating materials. They penetrate inside the enclosure of the transformer and are connected to the R, Y and B phases.
Bucholz Relay: Bucholz relay is a protecting relay mounted at the top of the transformer enclosure. A bucholz relay can detect the rise in gaseous pressure inside the core. Whenever some electrical fault occurs in the core of the transformer the temperature rises in the core and consequently the gas pressure rises, which is detected by the relay.
Lightning arrestor:
Lightning arrestors are connected to each of the phases coming out of the trasformer.Whenever lightning occurs the lightning arrestors act as low resistance path and high voltage charge available in the conductors due to lighting is grounded . Thus it protects the transformer windings from the high current produced due to lightning.
Current Transformers (CT):
Current transformers are used for both protection and metering purpose. The high current flowing through 11kV or 220 kV conductors can't be directly measured by any Ammeter nor this can be fed to any relay. That’s why the high current is reduced to some lower value by using CTs.The circuit symbol of a CT is shown below:
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Potential Transformers (PT): Potential transformer is nothing but a step down transformer which steps down the High voltage to some lower value so that it can be used for some metering purpose as well as to feed into relays.
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ISOLATORS:
They are mechanical devices which break or isolate the circuit under no load condition. They are manually operated devices made into use whenever some repairing work is to be done.
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Centre break type Isolator Isolators
LIGHTENING ARRESTER:
Lightening arrester provides a means by which lightening current may enter or leave the earth without passing through the circuitry to be protected. Lightening arresters are installed in equipment behaves as if it is absent so that the normal operation of the equipment is not at all affected. During lightening event if the voltage in the installed circuit goes up beyond a value due to lightening energy, the arrester becomes active due to the high voltage leading to short circuit of the lightening energy to earth. The time taken for the arrester becomes active due to the high voltage leading to a short circuit of the lightening energy to earth. The time taken for the arrester to become active is of the order of 1/109 second. Hence the arrester prevents the lightening energy from entering the equipment.
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