Neutral Earthing Resistors for fault protection
A Neutral Earthing Resistor restricts the flow of current during an earth fault on an AC distribution system. It is connected between the neural point of a transformer or generator and earth. Although a Neutral Earthing Resistor will probably be active for just a few seconds during its operational life, it must offer dependable protection at all time in case of fault. Application can be found in power distribution, mining and industrial installations, indoors and outdoors. Iresco Neutral Earthing Resistors are designed to cope with the most climatic conditions and saliferous atmospheres. These resistors offer distinct advantages of durability and reliability. They meet IEE Standard 32-1972.
Capacity : A Neutral Earthing Resistor has a resistance value specified to limit the fault current within a system to a pre-determined value which is sufficiently low to prevent damage yet high enough to operate fault-clearing relays.
Each system is designed according to current and timeratings, which are specified to be compatible with the protection switch gear. The range available includes; current to 3000 amps; time to 60 secondsl and system voltage to 66kV. The resistance value is precise and determined at the manufacturing stage, remaining constant throughout life.
Materials : Iresco Neutral Earthing Resistors are made from tough steel grids of a high quality iron-chrome-aluminium or AISI 304 SS allow. They are non-corroding and offer good electricity stability.
Insulation : Mica and ceramic insulators throughout.
Ventilation and Cooling : Neutral Earthing Resistors and contained in fully protected and ventilated steel enclosures.
Construction : Neutral Earthing Resistors consist of wire or plate grid elements mounted ceramic insulators with a filamic tube between their base and the plated high tensile steel support rod. Adjacent elements are bolted together to provide connections unaffected by heating and cooling cycles.
Groups of elements are mounted together between end plates to form a bank. Banks are then connected in series or parallel to provide the current and ohmic value required. Adjacent banks are insulted from each other and the metal framework.
All interconnections of banks are in solid copper strip. Connection to the HT side is made via an entrance bushing and to the earthside via a brass terminal stud, suitably rated. Standard enclosures provide a minimum of IP23 protection.
If required, insulated cable boxes are available for incoming and outgoing cables on the side or top of the unit, with removable covers and gland plates. These Neutral Earthing Resistors are virtually maintenance free.