Factors relating to system selection of magnet wire and varnish to avoid compatibility failure of rotating equipment

Premature failure of rotating equipment may be caused by improper selection of varnish and wire. Proper selection has become more difficult because of the multitude of new wire and varnish polymer systems which have recently evolved. Some of these systems do not exhibit straight line thermal degradation curves. Further, too much emphasis has been given to system selection based upon thermal life data for varnished twisted pairs. Although the basic method of test is good, the results can be misleading if consideration is not given to other important factors. These factors, screening tests, and typical wire-varnish systems, are presented in this paper to help the electrical design engineer select the best combination of wire and varnish.