According to the contract, we are obliged to provide earth fault protection for an emergency diesel generator. Also, according to the diesel generator manufacturer’s documents, overcurrent and earth fault protection is provided, however, the employer’s consultant claims that the anticipated earth fault protection is not able to protect the earth faults that occur on the generator winding and the earth fault relay must be connected through the allocated neutral ring type current transformer. Given that such a current transformer is not available, is there a solution for this issue?

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[محمد سعید جعفرپورKeymaster]

In the existing TNS grounding system, there is no solution to this issue other than installing a toroidal current transformer. But if the employer accepts the TNC-S plan, this problem can be solved by moving the ground point to a new location as illustrated below. In the new conditions, the earth fault protection provided for the generator will act as a restricted earth fault protection system and will protect the entire winding of the generator.

Reference IEEE C37.101

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