Ground-fault protection of an emergency or stand-by power system with multiple neutral-to-ground connections

Abstract

In the operation of an engine-generator set, when used for emergency power, it is required that the neutral conductor be connected to the nearest available effectively grounded electrode. Therefore, any three-phase, four-wire system with properly grounded engine generator sets will have multiple neutral-to-ground connections. One connection will be at the service entrance with the other connection at each engine-generator set. When an electrical system has multiple neutral-to-ground connections, there may be problems in obtaining proper sensing of ground fault currents as well as nuisance tripping with unbalanced loads. These problems persist with the system in either its normal or emergency supply modes of operation or both. This paper discusses some of these problems and the methods of solution. A new and special ground-fault sensing scheme which can overcome these problems for such a multiple neutral-to-ground system is also presented.