Why restricted earth fault protection is needed? Why can’t
differential
Protection is sufficient?
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Answer Posted / bandarawy
Due to the fact that current transformers always have a
certain error, the differential current always differs from
zero as soon as there is a load current flowing. Especially
during a through-fault condition with high short circuit
current , the differential current may be very high due to
the error of the current transformers. Depending on the
sensitivity of the setting value of the overcurrent
protection relay, when it is used as a simple differential
protection relay, unwanted tripping may occur.
For this reason, it is necessary to stabilize the
differential protection by means of a so called bias
current. For the restricted earth-fault protection using
the biased differential protection principle
| Is This Answer Correct ? | 3 Yes | 8 No |
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