Neutral Grounding Resistor And Anti-Islanding Methods

Good afternoon,

I am both electrcial engineer in water treatment system and a student for master program in university.

I have been investigating NGR for 1 years.

Now I am writting an article for embedded generator protection during phase to ground fault.

I asked this question to you because your experiences are very important for me.

In addition to this I want to ask a new question to you that;

I think during phase to ground fault ; the phase –to –phase voltage remains the same and the phase to ground voltage in two healthy phases increases.

Do you agree with me?

In addition to this, I want to ask a question to you that;

A 5MVA load on 22kV system corresponds to 131A, whilst at 11kV this is 262A. From the sequence network we know that the 3I0 circulating current is proportional to the load (the load current shares between the unbalance impedance Z, the negative sequence and zero sequence networks), so one would expect more circulating current at lower voltages (for the same load).

When going from 22kV to 11kV, that both the negative and zero sequence network impedances drop significantly. The unbalance impedance Z stays the same.

Does it mean that for the same load ıf we use 11 kV instead of 22 or 34,5 kV maximum phase to ground current will drop significantly? And Why?

In my opinion in three phase-three wire radial network system, during phase to ground fault voltage of faulty phase drops zero and phase to ground fault of healthy phase increases.

But if we want to prevent embedded generator operating in island mode because of an earth fault of anywhere in network we must provide selective current protection.

We can't provide this protection with overvoltage or undervoltage protection?

What is your opinion and suggest?

Best Regards,

Musa UÇAN