Various type of transformers have been provided at 220& 132 kv Substation. Capacity and voltage ratio wise 100 MVA, 40MVA & 12.5 MVA and 220/132/11 kV. 132/66 kV, These transformers are of TELK, BHEL, GEC, NGEF, C & G, Hitachi and Bharat Bijlee make and have most of the features common except few accessories which may be different. These transformers have following main components.
Main Core & Winding
Bushing :-
- 220 kV High voltage bushings :
Condenser type bushings with insulating body and central conducting tube-backelised with paper wound capacitor have been provided. Innermost of the capacitor layer is electrically connected to the tube and outermost to the mounting flange on insulating body. The central tube insulating body and mounting flange are oil filled assembled. High dielectric Strength oil is filled between central tube and insulating body. Oil level indicators are provided on the bushing.
- 132 kV Medium voltage bushing :
These bushing are also of condenser type and are of similar construction as in the case of 220 kV bushing in 200 MVA transformers.
In 40 & 20 MVA transformers 132 kV bushings are also of oil filled type in which oil is filled up when the transformer tank is topped up. Necessary air vent screws are provided on top of the bushings for release of trapped air at the top of oil fitting.
- 66 kV. 33 kV. & 11 kV. Bushings :
These are oil filled bushing and simpler in construction.
Tap Changer :-
The transformers have been provided with on load tap changer, which consists of diverter switch installed in an oil compartment separated from transformer oil and the tap selector mounted below it. The tap changer is attached to the transformer cover by means of tap changer head, which also serves for connecting the driving shaft and the oil conservator.
Protective Relays :
Generally there are two protective bucholz relays, one for main transformer tank and other for tap changer.
In 40MVA GEC transformers oil surge relay has also been provided in tap changer.
In 20 & 12.5 MVA transformers no separate bucholz - really has been provided for tap changer.
Pressure Relief Valve :
40 MVA GEC make transformers have been provided with pressure relief valve which operates in case of sudden pressure formation in side the transformer.
Cooling System :
100 MVA transformers have been provided with cooling bank installed on separate structures. These cooling banks have provided with to groups of fans and 2 nos. pumps. These fans and pumps automatically operate, depending upon the settings of winding temperature Indicator.
40, 20, 12.5 MVA transformers have been provided with tank mounted radiator bank and two groups of cooling fans-operating automatically with the setting of winding temperature indicator.
Tertiary Bushing :
100 MVA transformers have been provided with tertiary bushing connected with 11 kv capacitor and lighting arrestor t absorb switching surges.
Electrical Protection :
The following electrical protection have been provided on the transformers :-
- Differential Protection
- Restricted Earth Fault
- Winding temp high
- Oil temp high
- Pressure relief valve
- Oil surge relay
- Over current relay
- Local Breaker Back up protection
- Surge arrestors on HV, MV & LV sides.