NEUTRLA GROUNDING RESISTOR PERMANENT CURRENT 1

[tszpun]

Hello Experts,

We are specifying Neutral Grounding Resistor for our industrial distribution system.
We already know the fault current level, which is 1000 amp for 5 sec.
However, I do not know how to specify the permanent current value.
Does any body know, how I can find / calculate the permanent current value for neutral grounding resistors ?

Regards,
tszpun

 

[davidbeach]

It depends.

If all you feed are high-side delta windings it will be pretty darned low. If you feed wye-wye transformers with single phase loads it could be most anything. Nobody here can come up with a better number than you can.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[RRaghunath]

Per IEEE 32, there is no continuous rating assigned for neutral grounding resistors.
In case of Inductive devices (neutral grounding transformers etc.), a 10s rated device will have continuous rating of 3% (of 10s rating).
Since there is no 5s rating mentioned in the standard, we may use the same 3% formula.
However, you are free to specify required continous current rating while ordering.