Neutral Grounding Resistor

Neutral Grounding Resistors are used for resistance grounding of industrial power system. They are generally connected between ground and neutral of transformers, generators and grounding transformers. Neutral Grounding Resistors are used in order to limit maximum fault current to a value which will not damage the equipment in the power system, yet allow sufficient flow of fault current to operate protective relays to clear the fault. Although it is possible to limit fault currents with high resistance Neutral Grounding Resistors, earth short circuit currents can be extremely reduced. As a result of this fact, protection devices may not sense the fault. Therefore, it is the most common application to limit single phase fault currents with low resistance Neutral Grounding Resistors to approximately rated current of transformer and / or generator.

Neutral Grounding (or some time name Earthing) resistor systems protect power transformers and generators from damaging fault currents. Earthing of the neutral limits the ground fault current to a high level (typically 50 amps or more) in order to operate protective fault clearing relays and current transformers. These devices are then able to quickly clear the fault, usually within a few seconds. The importance of this fast response time is that it:

  • Limits damage to equipment
  • Prevents additional faults from occurring
  • Provides safety for personnel
  • Localizes the fault
  • UL Listed
  • CSA approved up to 7200v
  • Seismic Zone 4 Certifications and type tests also available

The limited fault current and fast response time also prevent over-heating and mechanical stress on conductors. Please note that, like the solidly earthed neutral system, the circuit must be shut down after the first ground fault. Neutral Earthing Resistors are typically rated 400 amps for 10 seconds, and are commonly found on medium and high voltage systems.

Features & Capabilities:

  • Neutral Earthing Resistors protect power transformers and generators from damaging fault currents
  • Available for systems rated 240v to 72kv line-line (CSA approved up to 7200v)
  • Stamped stainless steel grid or edgewound design
  • Current ratings up to 5000 amps
  • All Neutral Earthing Resistors designed and tested per IEEE32
  • Certified test reports and installation/maintenance instructions accompany each Neutral Earthing Resistor
  • Standard ventilated enclosures are painted or mill-galvanized, with stainless steel, hot-dipped galvanized, and aluminum as options
  • PGR will gladly package CTs, PTs, disconnect switches, earthing transformers, and heaters in the Neutral Earthing Resistor cubicle
  • Seismic zone 4 certifications and type tests also available
  • Technical papers on the theories of Resistance Earthing readily available