Neutral Earthing (NER) resistors are convection-cooled, high-voltage. They are used to protect against irreversible equipment damage to the transformer, cables and other equipment, due to a short-circuit between the phase and neutral. NER resistors are used in industrial power grid systems and can withstand the nominal system current for a specified time, usually 10 to 30 seconds.
For low ohm value NER’s, steel grid blocks are used. For high ohm values, ceramic wirewound resistor tubes are used. The grid blocks or wirewound tubes are built in a cabinet. Mica-insulated steel rods support the grids or tubes. Standard enclosures are made of galvanized steel. Stainless steel and custom enclosures are available on request.
The choice of steel and alloy varies with application. Even though requirements vary, minor customization enables standard Danotherm NER resistors to be used for most applications.
NER resistors are offered for 6 / 12 / 17.5 / 24 / 36 / 52 / 72.5 kV grid system voltages. Resistors with different dimensions can be selected depending upon the maximum temperature withstand requirements.
Upon request, the following types of tests can be conducted:
- Temperature rise test
- Impulse voltage test
- AC dielectric test
- Ingress protection test
- Seismic test
Danotherm NER resistors are compact, reliable, and robust and can be used indoors and outdoors. The standard protection ratings range from IP00 to IP23, and IP54-rated NER resistors are available on request. Connection options include cable and bushings. A current transformer is available as an option.