HV3.5.7 - 3.5.7 App Guide for Neutral Grounding in Elec Utility Systems WG

Steven Whisenant

Basic factors and general considerations in selecting the class and means of neutral grounding for a particular ac transmission or subtransmission system are covered. An apparatus to be used to achieve the desired grounding is suggested, and methods for specifying the grounding devices are given. Transformer tertiary systems, equipment-neutral grounding, and the effects of series compensation on grounding are discussed.

This part of the guide is concerned with the neutral grounding of single- and three-phase ac electric-utility primary distribution systems with nominal voltages in the range of 2.4 kV to 34.5 kV. For the purpose of this guide, the term "distribution" includes the substation providing power to distribution feeders, the distribution feeders, and the distribution transformers providing service at utilization voltages. The scope of this guide does not include the grounding of the low-voltage secondary systems supplied by distribution transformers or consumer-owned facilities that are covered by other documents such as the National Electrical Code(R) (NEC(R)) (NFPA 70, 2011 Edition)

Some basic considerations for the selection of neutral grounding parameters that will provide for the control of ground-fault current and overvoltage on all portions of three-phase electrical utility systems are presented. These considerations apply specifically to electric utility systems and do not recognize the neutral grounding requirements for dispersed storage and generation. They are intended to serve as an introduction to a series of standards on neutral grounding in electrical utility systems.

This guide is the introduction to the C62.92 series of five IEEE guides on neutral grounding in three-phase electrical utility systems. It provides system grounding definitions and considerations that are general to all types of electrical utility systems.

General considerations for grounding synchronous generator systems are summarized, focusing on the objectives of generator grounding. The factors to be considered in the selection of a grounding class and the application of grounding methods are discussed. Four generator grounding types are considered: unit-connected generation systems, common-bus generators without feeders, generators with feeders directly connected at generated voltage, and three-phase, 4-wire connected generators.

Basic factors and general considerations in selecting the class and means of neutral grounding for electrical generating plant auxiliary power systems are given in this guide. Apparatus to be used to achieve the desired grounding are suggested, and methods to specify the grounding devices are given. Sensitivity and selectivity of equipment ground-fault protection as affected by selection of the neutral grounding device are discussed, with examples.

The neutral grounding of single- and three-phase ac electric utility primary distribution systems with nominal voltages in the range of 2.4--34.5 kV is addressed. Classes of distribution systems grounding are defined. Basic considerations in distribution system grounding--concerning economics, control of temporary overvoltages, control of ground-fault currents, and ground relaying--are addressed. Also considered are use of grounding transformers, grounding of high-voltage neutral of wye/delta distribution transformers, and interconnection of primary and secondary neutrals of distribution transformers.

Basic factors and general considerations in selecting the class and means of neutral grounding for a particular ac transmission or subtransmission system are covered. An apparatus to be used to achieve the desired grounding is suggested, and methods for specifying the grounding devices are given. Transformer tertiary systems, equipment-neutral grounding, and the effects of series compensation on grounding are discussed.

Basic factors and general considerations in selecting the class and means of neutral grounding for electrical generating plant auxiliary power systems are given in this guide. Apparatus to be used to achieve the desired grounding are suggested, and methods to specify the grounding devices are given. Sensitivity and selectivity of equipment ground-fault protection as affected by selection of the neutral grounding device are discussed, with examples.

Basic factors and general considerations in selecting the class and means of neutral grounding for a particular ac transmission or sub transmission system are covered. An apparatus to be used to achieve the desired grounding is suggested, and methods for specifying the grounding devices are given. Transformer tertiary systems, equipment-neutral grounding, and the effects of series compensation on grounding are discussed.

The basic factors and general considerations in selecting the class and means of neutral grounding for synchronous generator systems connected to electrical utility systems are provided in this guide. It also provides the suggested methods and apparatus to be used to achieve the desired grounding. These guidelines apply to both large and small generators found in electrical utility systems. Definitions of grounding terms used in this the guide can be found in IEEE Std C62.92.1(TM)-2000.

The application of neutral grounding to three-phase electrical utility systems is described in this guide. It is Part 1 of the IEEE C62.92 series of guides for neutral grounding. This guide presents basic considerations of the selection of neutral grounding parameters that will provide for the control of overvoltage and ground-fault current on all parts of three-phase electrical utility systems rated greater than 1000 V.

Applications to three-phase electrical utility systems are described in this Part VI of the IEEE C62.92? series. Definitions and considerations related to system grounding where the dominant sources of system energization are current-regulated or power-regulated power conversion devices are provided.