We have two grounding transformers (wye- broken delta) directly connected to MV switchgear (Main-Tie-Main) Bus A and Bus B with resistor connected in broken delta respectively. Only one grounding transformer is ON when the bus tie is closed.
The spec says that, "Where medium voltage neutral grounding switchgear is provided, interlocks shall be provided that prevent access to the switchgear neutral grounding resistor unless all of the main generator breakers are open and isolated."
What is the meaning of this sentence from the spec? Don't the isolation of MV fused vacuum contactor which is feeding the grounding transformer is not enough? Why all the main generator breakers need to be isolated?
The spec says that, "Where medium voltage neutral grounding switchgear is provided, interlocks shall be provided that prevent access to the switchgear neutral grounding resistor unless all of the main generator breakers are open and isolated."
What is the meaning of this sentence from the spec? Don't the isolation of MV fused vacuum contactor which is feeding the grounding transformer is not enough? Why all the main generator breakers need to be isolated?