High Resistance Grounding: Neutral conductor contribution to 3-phase charging current?

[brainsalad]

Greetings:

The generator neutral conductor of a HR grounded system is rated 5kV, 1/C, #2/0, 100'. In totaling the system capacitance, how can it reasoned to include the shunt capacitance of the neutral conductor? Under balanced operation, the voltage across the neutral should be zero, which shouldn't permit the shunt capacitance to charge (Vng=0). During the fault this becomes Vng = Vln, providing a charging current. Can the shunt capacitance (a zero-sequence neutral to ground) be added in parallel with those in the unfaulted phases? Thanks for your thoughts.

 

[brainsalad]

Hello, to refresh and add a new thought: when the generator is first powered, couldn't the neutral conductor shunt capacitance become charged before the Vng becomes zero? Thanks for your thoughts.

 

[pwrtran]

If the system is effectively grounded system, which means Z0/Z1<=3 the shunt capacitance can be negligible. Also the fault current mostly will return from the neutral conductor. However, if your system is ungrounded 3-wire system, you need consider the charging current.

 

[brainsalad]

pwrtran: thanks for your response.

The generator is neutral grounded through a high resistance scheme (through a distribution transformer, 10 kVA, 4160/240V, with 4.2ohm on the secondary.).

My main question was: given that the components which determine Xco (the 3-phase capacitive reactance) are coming from the 3-phase system, how can I add in the contribution from the neutral conductor (a 5kV, 1/C, #2/0, 100' cable, which would create a shunt capacitance to ground, even though Vng = 0 under normal balanced conditions), when this is a "neutral to ground" quantity and shouldn't be lumped with the "3-phase" shunt capacitive quantities?

Thanks for your thoughts.

 

[pwrtran]

I wouldn't bother by the shunt reactance out from a 100 ft cable for the normal operation conditions, even for the phase conductor cable.
During a fault, the return current will go through the neutral grounding resistance then back to the winding X0 point and your neutral and the earth bond together so they are at the same potential.