Low-Resistance Neutral Grounding (NGR, Industrial)

A neutral earthing method for industrial medium-voltage networks in which the star point of a transformer or generator is earthed via a neutral grounding resistor (NGR) with a relatively low resistance value, such that a single earth fault produces a substantial, readily measurable earth fault current — typically between several hundred amperes and a few kiloamperes, in contrast to the strongly limited current (often <10 A) under high-resistance neutral earthing. This relatively high current enables selective, fast tripping of the faulted feeder by earth-fault relays without having to de-energise the entire network, which is particularly important in industrial networks with multiple parallel feeders and a need for operational continuity. The trade-off is that, unlike high-resistance earthing, the NGR does not allow the installation to continue operating for some time on a network with reduced insulation during the fault, and sizing the resistor requires balancing sufficient fault current for detection against limiting damage to equipment and the earthing system.