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Neutral Earthing Resistor

Neutral Earth Resistors (NER) protect equipment from damage in the event of earth faults. They do this by limiting the current that flows through the neutral point of a transformer to a safe level so as prevent damage to equipment but still operate protection devices. Neutral Earth Resistors can be used to protect critical equipment including switchgear, generators and transformers.

When is earth fault limiting right for you? Do I need an NER?

  1. Electrical faults and damage to equipment due to high earth return currents
  2. Risk of electrical shock and arc flash hazards to personnel and equipment
  3. Interference in telecommunications equipment due to high earth return currents
  4. Production losses due to unplanned downtime
  5. High maintenance requirements and expenses due to ageing equipment

How does an NER work?

Neutral Earthing Resistors (NERs) are used in an AC distribution networks to limit transient overvoltages that flow through the neutral point of a transformer or generator to a safe value during a fault event such as a phase to phase, phase to neutral or phase to earth fault.

Generally connected between ground and neutral of a transformer or generator, NERs reduce the fault current to a pre-determined maximum level such that damage to equipment or network shutdown is avoided while allowing a sufficient amount of fault current to activate protection devices. A fast response time allows protection relays and current transformers to operate and quickly identify, isolate and clear the fault.  Subsequent faults are also avoided. Damage to equipment is therefore minimised and the risk of hazardous arc flash is reduced or eliminated.

Given that an NER must absorb and dissipate a huge amount of energy during a fault without exceeding temperature limitations, the design and selection of an NER is critical to ensure equipment and personnel safety as well as continuity of supply.

NER 850px 72dpi2

What we offer

Captech offer a range of high performance NER solutions.

Available as a standard or customised unit, Captech neutral earthing resistors can be supplied as individual units, packaged with a transformer or integrated into a power distribution system.

NERs are available with roof mounted or side mounted HV bushings. Lower voltage units may have the connection point underneath.

Captech utilise Powerohm resistors as the base technology of our neutral earthing resistors used in mining, utility network and industrial electrical systems. Captech are exclusive Australian and New Zealand distributors of Powerohm resistors.

Related documents

Neutral Earthing Resistor Fact Sheet

 

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