April 2008 Electrical Apparatus

April 2008 Electrical Apparatus

This is a summary of the Electrical Apparatus April 2008 featured technical article,  by Richard L. Nailen, P.E.  

Although many features of a-c motors have long been highly standardized, servicing practices were largely left up to the motor user until the 1968 issuance of the National Fire Protection Association Standard 70B, “Recommended Practice for Electrical Equipment Maintenance.” Similar guidelines are now available in the InterNational Electrical Testing Association’s ANSI/NETA MTS document, “Standard for Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems.”

Attention has more recently been focused on motor repair as users became concerned about how rewinding may affect efficiency. The first response to that was IEEE Standard 1068, “Recommended Practice for the Repair and Rewinding of Motors for the Petroleum and Chemical Industry” (published in 1989). The repair industry then issued (in 1998) the more general ANSI/EASA AR 100, “Recommended Practice for the Repair of Rotating Electrical Apparatus.”

A gap existed in the combined coverage of those documents: lack of specific guidance on specific tests to reveal specific defects either existing or developing. Furthermore, existing recommendations generally lacked a systematic method of diagnosing the basic cause of a failure occurring despite sound maintenance practices. Such “root cause failure analysis,” emphasizing not just “what happened” but “why it happened,” has become important in enhancing machine reliability.

To fill that gap, in 2007 the IEEE issued Standard 1415, “Guide for Induction Machinery Maintenance Testing and Failure Analysis.” Stressing the “when” and “why” of testing rather than the “how,” it includes a complete diagnostic flow chart leading to a “repair or replace” determination. Some novel concepts are introduced, such as the use of various unbalances between winding phases to indicate specific problems. Unfortunately, tests developed for other types of apparatus are invoked without full explanation of how they apply to motors. Still, the overall approach is useful, making IEEE 1415 a useful addition to the earlier standards.

To order a back issue with the full article, “IEEE Guide Enters Motor Diagnostic Field,” call 312-321-9440 or visit our online webstore.

Share Button