Neutral Earthing Resistors
Neutral Earthing Resistors (NERs) - sometimes called Neutral Grounding Resistors - are employed in AC distribution networks to limit the current that would flow through the neutral point of a transformer or generator in the event of an earth fault.
NERs limit fault currents to a value that does not cause any further damage to switchgear, generators or transformers beyond what has already been caused by the fault itself, and in some cases limit touch and step potentials to safer values than a solidly grounded systems. In addition, consideration is given to operation of protection relays within the required time.
Why use Fortress NER’s?
The Fortress Difference
Fortress has a history of successfully managing large projects and provides value to customers by ensuring we understand the customer’s requirements and expectations. We place an equal importance on technical capability, manufacturing to deadlines, and providing documentation and drawings in a concise and timely manner.
An extensive range of resistor elements allows selection of the most efficient and cost effective solution for any required duty. Fortress can manufacture NERs with rated times from a few seconds to continuous, any required initial current, and for system voltages up to 66kV.
The change in resistance with temperature during operation is small and predictable. This means that protection levels can be predetermined accurately. A Fortress NER will not induce unpredictable phase changes or resonances into the fault current, as may occur with an earthing reactor.
NERs may only be called upon to operate a few times in their service life, which may be 25 years or more. Reliability is essential; elements from Fortress have been proven over many years in conditions of severe vibration and extreme climate worldwide.
Features of all Fortress Earthing Resistors include:
- Full compliance with ANSI-IEEE 32, Terminology and Test Procedure for Neutral Grounding Devices
- Stainless steel resistors as standard
- Enclosures ratings from IP00 to IP56
- Type-tested standard designs (certificates available)
- Supply of resistor banks only for incorporation into customers’ own enclosures
- Cyclone Wind Loading rated enclosures
- Compliance with AS/NZ 2081.5:2002 Mining Standard for Earth-fault current limiters
- Provision of NER Monitoring at time of manufacture
- Provision of CTs, heaters, special cabling, and other accessories
- Interlocked off-load by-pass isolators
- Single or multiple vacuum contactors or circuit breakers