NGR sizing

[swiminelectricity]

I am conducting a system study for 6.6KV system. NGR=152

I am trying to figure out current setting of G-F relay. The formula I have is V(L-N)/152,which is 25A. I don't have a lot of experince. Is my calculation right?

 

[alehman]

If NGR means 'neutral grounding resistor' and 152 is the resistance in ohms, 25A would be the theortical GF current, neglecting system capacitances. In reality, capacitances will influence the GF current depending on where the fault occrus.

To minimize transient voltages on the system, the grounding resistor should be selected so that it is roughly equal or less than the system phase-ground capacitive reactance.