Answer / k.prakashchandra

Gen side means usually 11 KV.The generator current at full
load will be very high for 60 MW( 52.5 x MVA A)for an
indoor breaker .Therefore , synchronization and tripping on
fault are done at EHT breaker which is of above 110 KV.For
any fault between the breaker and gen ,the master trip is
employed ,which trips the field breaker ,CB and the governor.

Answer / kunal singh dabi

Due to following points
1)Transient Recovery Voltage (TRV)
2)Higher X/R value
3) Delayed current Zero
circuit breakers was not used after above 60 MW generators.

However please note that now full line of IEEE C37.013
qualified medium-voltage vacuum generator circuit breakers
for voltages up to 24 kV and generators up to 200 MW for
both indoor and outdoor applications are available in
market.

Please note that Circuit breakers applied to generator
switching applications are subject to conditions quite
different than those of a normal distribution circuit
breaker used in industrial, commerical and utility systems.
Distribution circuit breakers, whether of the outdoor
substation type or of the drawout type for use in metal-
clad switchgear, conform to IEEE C37.04 (basis of ratings),
IEEE C37.06 (preferred ratings), IEEE C37.09 (testing) and
IEEE C37.10 (application.)

What is the need of earthing transformer for delta side of a transformer. (Think of a line section between a star/delta transformer at a grid substation and delta/star transformer at a village. An earthing transformer is there at the delta side of the star/delta transformer at grid substation). As there are no ground reference there will not be fault current if a one phase is grounded. Further L-L phase will be sensed by the primary side of star/delta transformer as a L-G fault. So why an earthing transformer is required at delta side

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