in transformers for ex. 100mva and 400kv the secondary current is about 420 am

in transformers for ex. 100mva and 400kv the secondary
current is about 420 amps but for selection of bushing the
capacity of selected bushing is 2000A why there is such
big difference ?

Question Posted / nasrolahtaheri

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in transformers for ex. 100mva and 400kv the secondary current is about 420 amps but for selection..

Answer / k.prakashchandra

The insulated leads of secondary from the Tr windings are
taken through hollow rods inside the bushing and connected
at the top.As the rod has to bear the all the mechanical
forces like torsion and strain, the wall has to be thick enough.

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in transformers for ex. 100mva and 400kv the secondary current is about 420 amps but for selection..

Answer / k.prakashchandra

I must have used the word 'pipe' instead of rod.Further,in
the condenser type bushing the oil inside is locked and
isolated from the oil in the tank.Hence it is deprived of
cooling. The pipe should be of much higher capacity to avoid
heating up due to the current flowing through it.

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