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why neutral of 6.6 kv star connected sq. cage induction
motor does not get earthed, though for earth fault
protection it is must.
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Answer Posted / engr. l. o. osuji
Hi Pratikjain,
The answer in #4 is partly correct. Your question is on the
motor and not on the feeder. Provide appropriate cts and
wire correctly using an over-current earth fault relay.
Note, this relay has three operating elements known as red,
yellow and blue-phase elements. The yellow-phase element is
for earth fault. This relay works on the principle that Ir
+ Iy + Ib = 0 for a balanced load. This summation is
algebraic. In times of an earth fault the above equation is
no longer equal to zero hence the residual current flows
through the yellow-phase element as an earth fault provided
your cts and relay are properly connected. In this way the
cb for the motor is tripped by the yellow-phase element as
an earth fault if the relay is properly set.
| Is This Answer Correct ? | 2 Yes | 4 No |
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