The purpose of a neutral grounding resistor is to limit the ground fault current to a safe level so that all the electrical equipment in the power system is protected. The resistor should be the only current path between the neutral of power transformers or power generators and ground.

When the neutral of a system is not grounded it is possible for destructive transient overvoltages to appear from line to ground during normal switching of a circuit having a line-to-ground fault. Experience has proved that these overvoltages cause aging and failure of insulation at locations on the system other than at the point of fault. In this way, a relatively unimportant line-to-ground fault on one circuit may result in considerable damage to equipment and interruption of service on other circuits, not to mention the increased difficulty in finding the original location of the problem.

A neutral grounding resistor is designed to limit the ground fault current to asafe valuewhile at the same time letting enough current to flow to operate the protective relays that will alarm or clear the fault. While the disturbance lasts the resistor must be capable of absorbing and dissipating the energy generated without exceeding the temperature limits established by IEEE-32 Standards. In this way the fault is safely limited, isolated, and the power system is protected against over-voltages.

Advantages of using Neutral Grounding Resistors:

• Reduced operation and maintenance expenses.
• Fast isolation of the original fault.
• Reduced transient over-voltages.
• Reduced physical damage on the equipment at fault.
• Simplification of ground fault location.
• Increased life and protection of transformers, generators and related equipment.
• Reduced frequency of faults.
• Improved service reliability.
• Increased protection in the use of lightning arresters.
• Increased safety for personnel.