Proper application & maintenance of molded case breakers to assure safe and reliable operation

This paper will discuss the importance of reliable and repeatable performance of molded case circuit breakers in today's power distribution systems. The paper will review existing standards for maintenance of molded case breakers including procedures outlined in NEMA AB4 and IEEE1458. Common misconceptions and system application issues regarding these devices will be discussed. Several examples of on-line infrared scans of circuit breakers over the course of a five year period will be presented and reviewed. Experiences at an integrated paper mill located in Longview, Washington USA explains documented cases where infrared thermography has been used as a predictive maintenance tool in determining potential problems with breakers while in service. Follow-up analysis by the circuit breaker manufacturer has generally validated mill maintenance decisions to remove a breaker from service and replace it, based on infrared scan results. Periodic infrared scanning used as a tool in identifying potential problems with sealed molded case circuit breakers will be discussed. This and other breaker off-line testing methods used at this site will be reviewed. Finally, overall reliability improvement and impact on the results of the existing mill-wide safety compliance programs will be summarized.