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NEMA publishes SG 4 for AC circuit breakers


August 23, 2009
By Anthony Capkun

The National Electrical Manufacturers Association (NEMA) has published SG 4-2009, “Alternating Current High-Voltage Circuit Breakers”. Published under license from IEEE, the standard 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
C37.04 and IEEE 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 has been offered to IEEE for inclusion in
revisions of C37.04 and C37.09 (presently not addressed in those
documents).

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