Neutral-Grounding-Resistor System

Neutral-Grounding-Resistor System

Neutral-Grounding Resistors (NGRs) are used to ground power systems by inserting a resistor between the system neutral and ground. This lowers the prospective ground-fault current to a predetermined value.

A properly designed resistance-grounded system provides benefits over both ungrounded and solidly grounded systems. Because the system is grounded, transient over voltages do not occur and ground fault current can flow, allowing it to be detected and measured. Also, because a resistor is used to ground the system, the very large and destructive ground-fault currents of solidly grounded systems are absent. Ground-fault relays (such as the SE-701) can be used on feeders to provide selective coordination and the ability to quickly locate or isolate the fault.

 neutral ground resistor

Applications

Resistance grounding is typically applied on transformers and generators where safety and continuity of service are important. A faulted feeder may remain in operation until it is safe to repair the fault, where allowed by the local electrical code.

Benefits

1. Eliminate phase-to-ground arc-flash incidents

2. Eliminate transient over voltages

3. Reduced point-of-fault damage

4. Can provide continuity of service during a ground fault

Features

1. ER-series Sensing Resistor and Current Transformer required for NGR monitoring come pre-installed inside the enclosure

2. Can be packaged with a zigzag transformer to resistance ground an ungrounded delta system, or a system with an inaccessible neutral

3. SE-325 or SE-330 NGR Monitor can provide continuous NGR monitoring and ground-fault protection; NGR failure will render current-sensing ground-fault protection inoperative

4. Stainless steel resistor elements prevent corrosion

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