For medium-voltage power generating schemes which have multiple diesel generating sets, it is necessary to ensure that one (and only one, to avoid the possibility of circulating currents) of the neutrals of one of the running generating sets is earthed at all times. Generator grounding can be most economically achieved by using a single earthing resistor of the appropriate rating (usually the full-load current of one phase) connected to each of the neutrals with a vacuum contactor which is controlled from the generating set panel.
Neutral Earthing Resistors (NERs) can be fitted with manual or motorised off-load isolators, either singly or in interlocked pairs if the purpose is to switch between resistance earthing and solid earthing.
Modular design with multi-contactor unit
Cressall pioneer modular multi-contactor neutral earthing resistors
The increasing demands for electricity and the prohibitive cost of transmission lines means more stand-alone and emergency generators are being installed in challenging locations. Previously effective grounding required expensive fully specified switchgear and a standalone resistor.
To solve such problems, Cressall introduced their modular range of neutral earthing resistors with standard cabinet designs to house 1, 2, 3, 6 and 9 contactors, for generators of 3.3 to 13.8kV system voltage.
This means costs and delivery times are considerably reduced while quality and reliability are improved.