If there are large system transformers connected to the high-voltage bus at the generator
switching station, switching of these transformers may be of concern. Such switching should
not affect the generator differential protection, but the de offset associated with the transient
current may saturate the generator CT's. This reinforces the concept that the CT's be of
identical design so they will saturate together and uniformly. We conclude that no harmonic
restraint is required in the GSU transformers, but some engineers still provide this feature as
a safeguard against unnecessary tripping of the generator.