NEMA Publishes AC High-Voltage Circuit Breakers Standard

The National Electrical Manufacturers Association (NEMA) has published SG 4-2009 Alternating Current High-Voltage Circuit Breakers. The standard, which NEMA published under license from IEEE, was revised by the High-Voltage Power Circuit Breaker Voting Classification of the Switchgear Section of NEMA.

The previous revision of SG 4 was published in 2000 and reaffirmed in 2005. The material in the 2000 revision of SG 4 dealt with two areas, the first relating to construction and test issues for high-voltage circuit breakers, and the second with recommendations for handling and maintenance of high-voltage circuit breakers. The material in the second area was removed from the 2009 edition of SG 4, and published separately as SG 11-2008. This was done to keep the information available to those interested in high-voltage circuit breakers while the IEEE Switchgear Committee working groups consider this material for possible incorporation into revised editions of IEEE Std. C37.04 and IEEE Std. C37.09.

SG 4 applies to all types of high-voltage circuit breakers, with the exclusion of those used in metal-enclosed or metal-clad switchgear, and automatic circuit reclosers. High-voltage circuit breakers are most frequently installed in outdoor switchyards, used in utility transmission and distribution substations, and in large industrial power substations. Among the areas covered by the revised SG 4, not covered in existing IEEE standards, are:

• Requirements for circuit breaker operating mechanisms
• Bushing terminal connector requirements
• Ground terminal requirements
• Current transformer thermal and short-time capabilities, and accuracy classes
• Multi-ratio current transformer tap connections
• Current transformer lead identifications and polarity conventions
• Radio Influence Voltage (RIV) tests and limits
• Noise levels for outdoor circuit breakers located in switchyards
• Repetitive duty requirements for special purpose arc-furnace switching circuit breakers

The material in SG 4-2009 has been offered to IEEE for inclusion in revisions of C37.04 and C37.09. This material is presently not addressed in these IEEE documents, but is considered as important information for those who use or specify high-voltage circuit breakers. For example, this information includes the arrangements and terminal identifications of current transformers associated with such circuit breakers, and this information is not included in other standards at this time. Therefore, NEMA continues to publish this information as a service to those interested in high-voltage circuit breakers.

Ted Olsen, chair of the SG 4 technical committee that prepared this document, discussed this revision of SG 4 and stated that the willingness of NEMA to continue to publish this information demonstrates the close relationship between the members of the NEMA SG 4 technical committee and the IEEE Switchgear Committee that has existed for a number of decades. It is anticipated that the IEEE working groups will consider this material for addition to C37.04 and C37.09 in their revision projects that are ready to begin in the next few months.