Difference between High Resistance Grounding vs. High Impedance Grounding in Generation?

[BTC]

I am working on a project that has existing high resistance grounding (HRG) in the form of neutral grounding resistor. It is my understanding from discussing with a colleague that there is a different means of doing this via high impedance grounding. I'm not 100% sure what the differences are, design considerations, etc.

Any information that can be provided would be much appreciated.

 

[GoldDigger]

It seems to me that grounding via an inductive reactance could make it easier to withstand fault clearing current for a longer period of time without having to provide for as much heat dissipation. Whether that is a practical deciding factor, I don't know.

 

[kwired]

It seems to me that grounding via an inductive reactance could make it easier to withstand fault clearing current for a longer period of time without having to provide for as much heat dissipation. Whether that is a practical deciding factor, I don't know.

But wouldn't that also typically mean a high inrush current when the fault first occurs similar to what you have when first energizing a motor or transformer?

 

[paulengr]

High inductance in practice works similar but does not save money. Low resistance can keep the resistor size down but you have to trip quickly. So for instance with a high resistance system usually you can easily get an infinite time resistor where low resistance (400 A or 100 A) systems are typically 10 second resistors and trip times are a couple seconds. This is more useful above 10 kV where which resistance becomes impractical.

 

[synchro]

But wouldn't that also typically mean a high inrush current when the fault first occurs similar to what you have when first energizing a motor or transformer?

The large inrush on energizing a motor or transformer happens when the iron core saturates due to excessive magnetic flux during the initial transient before the voltage and flux can achieve quadrature under steady state conditions. To avoid saturation air core inductors must be used but they are physically large. A problem is that the inductive reactance often cannot be high enough to significantly limit the fault current because the inductance will resonate with the shunt capacitance on the lines and cause overvoltages to occur.