Combined stress ageing of magnet wire enamels

The long-term reliability of magnet wire enamels has been ascertained conventionally using thermal endurance test procedures. Apart from the fact that this test method does not simulate the service conditions, it suffers from the disadvantage of being both subjective and time-consuming. With a view to developing quicker test methods which are objective and simulate more realistically the service conditions in the laboratory, experiments under combined thermal and electrical stresses were performed on magnet wire enamels. The authors describe the results of investigations on polyester and dual-coated polyesterimide wires under the simultaneous effect of thermal and electrical stresses. It is concluded that the combined stress test method for wire enamels not only simulates more realistic service conditions but can also detect changes in degradation mechanisms which are not so evident from the other available test methods