Question

A magnetisation transient  can occur when a transformer is energised.

The protection scheme must not unecessarily trip the transformer by mistaking the inrush for a fault. For a large transformer the better approaches are:

Select one:

a. Block the protection scheme for a few seconds when the transformer is energised.

b. Use a even harmonic or minimum gap time scheme.

c. Time the breaker closing to reduce the inrush transient.

d. Set the differential protection levels high enough so that a trip does not occur.

Answer 1

Since magnetic current contains second order harmonics.

If we use even harmonic for  protection for transformer.

Then transformer circuit will not trip.

Hence answer is option b.