To extend the useful life of legacy metal-clad switchgear, many users have replaced air-magnetic circuit breakers with vacuum conversions or vacuum replacement circuit breakers. The existing switchgear (as described in ANSI/IEEE C37.20.2) often includes cubicle-mounted auxiliary switches that indicate the circuit breaker’s open or closed position. The operation of these switchgear mechanism-operated contacts (MOC) is driven via a mechanical linkage to the circuit breaker itself.

Jerry Hatfield, KCP&L, and Doug Edwards, Siemens PT&D, will discuss the following issues related to MOC operation at a session at the Finepoint Circuit Breaker Test and Maintenance Training Conference in the fall. These issues deserve particular attention to ensure that the new vacuum circuit breaker is a fully functional replacement of the original air‑magnetic circuit breaker:

1. Minimum energy required for reliable circuit breaker operation
2. MOC mechanical endurance capability under various worse case scenarios
3. Circuit breaker interchangeability

Hatfield

If the above issues are not addressed, the vacuum replacement breaker may fail to operate, the MOC may fail to operate, the control circuitry associated with the operation of the MOC switches may mis-operate, or the MOC linkages may become damaged due to excessive force.

These issues are particularly relevant when Westinghouse DH and DHP circuit breakers are being replaced by vacuum replacement circuit breakers due to the original Westinghouse MOC systems. Although the issues discussed are specific to the application of retrofit and replacement circuit breakers in the Westinghouse DH and DHP switchgear, the same evaluation criteria are appropriate for all circuit breakers and MOC systems.

Hatfield has a BSEE from the University of Missouri – Rolla and an MSEE from the University of Missouri – Columbia. He has worked in the electric utility industry for more than 30 years and has worked in a variety of settings including large end user, consulting design, and utility power generation design and maintenance. He is a registered professional engineer in four states.

Edwards

Edwards has been employed at Siemens PT&D since 1994 including three years in Berlin, Germany, and currently works as manager of MV Retrofit Products. He is licensed professional engineer and a senior member of IEEE. He is member of the IEEE Power Engineering Society’s Switchgear Committee, chair of the IEEE Subcommittee on Low Voltage Switchgear Devices, and is Working Group Chair and member of several standards’ Working Groups. He has over 20 years of design experience in the electric industry and has a BSEE from North Carolina State University.