MV Switchgear - NGR Logic

[Charz]

In our system, the grounding transformer (wye‑grounded / broken‑delta with resistor) is directly connected to the MV switchgear bus.
During generator start‑up, the generator is essentially operating in an ungrounded condition.
My question is:
Should the breaker feeding the grounding transformer be closed before energizing the corresponding incomer, so that grounding is established first? Or is it acceptable to energize the incomer first and only then close the grounding transformer breaker?

 

[ron]

I don't design with this type of grounding often, but I generally want the grounding to be in place before the source so there is stability.

Preferred sequence: close the grounding transformer breaker first, then close the incomer.

Less preferred but sometimes tolerated: close the incomer first and then the grounding transformer breaker only if the system is explicitly designed and procedurally approved to accept a brief ungrounded interval during startup, with protection, surge arresters, and operating procedures all checked for that condition. If you energize the incomer first and only afterward close the grounding transformer breaker, the bus is temporarily ungrounded. Ungrounded operation allows the system to float with respect to earth and is more susceptible to transient overvoltages.