REACTANCE GROUNDING OF POWER SYSTEM BASIC INFORMATION

What is reactance grounding? How reactance grounding is beneficial?

The term reactance grounding describes the case in which a reactor is connected between the system neutral and ground.

Since the ground-fault that may flow in a reactance-grounded system is a function of the neutral reactance, the magnitude of the ground-fault current is often used as a criterion for describing the degree of grounding.

In a reactance-grounded system, the available ground-fault current should be at least 25% and preferably 60% of the threephase fault current to prevent serious transient overvoltages (X0 </=X1).

This is considerably higher than the level of fault current desirable in a resistance-grounded system, and therefore reactance grounding is usually not considered an alternative to resistance grounding.

In most generators, solid grounding, that is, grounding without external impedance, may permit the maximum ground fault current from the generator to exceed the maximum three-phase fault current that the generator can deliver and for which its windings are braced.

Consequently, neutral-grounded generators should be grounded through a low-value reactor that will limit the ground-fault current to a value no greater than the generator three-phase fault current.

In the case of three-phase four-wire systems, the limitation of ground-fault current to 100% of the three-phase fault current is usually practical without interfering with normal four-wire operation.

In practice, reactance grounding is generally used only in this case and to ground substation transformers with similar characteristics.