Application of a hybrid grounding scheme to a paper mill 13.8 kV generator

Many paper mills and other industries use turbine generators to supply critical process steam and electrical generation needs within the plant. The loss of a generating unit for an extended period would result in very costly replacement power and repair costs for any paper mill. As machine insulation systems age over decades, aging mechanisms progress to increase the risk of a possible ground fault internal to the generator. An IEEE/IAS Working Group Report submitted in 2002 discusses grounding and ground fault protection for medium voltage generator stators, highlighting their merits and drawbacks. The report is intended as a guide for engineers installing new or upgrading existing generator systems to minimize industrial bus connected generator damage from stator ground faults. This paper discusses a 13.8 kV generator upgrade at a paper mill employing the hybrid grounding scheme and ground fault protection evaluated favorably by the IEEE/IAS Working Group. Project tasks are described in detail. Issues and difficulties encountered during the course of the generator grounding upgrade which were not mentioned in the Working Group Report are presented for reference.