Thermal Endurance of Polyester Enameled Wires Using Twisted Wire Specimens. Statistical Analysis of Test Results

Thermal endurance tests to AIEE Standard 57 [1] have been performed in six laboratories each using self-prepared varnished specimens made from a common sample of polyester enameled wire and polyester varnish. The results have been analysed to test the hypothesis of the departure from linearity of the relationship between the logarithm of life and the inverse of the absolute temperature, with the object of subsequent limited extrapolation. Two features of this paper are the inclusion of a distribution-free test for further confirmation of the significance of the departure from linearity, and the presentation of the extrapolated results in the additional form of estimated temperatures for a number of specified mean lives. The variation between the results of different laboratories and methods involving a reduction in testing time are considered. Comparison is made with previous work [2] undertaken in six laboratories on PVA enameled wire specimens, prepared and impregnated with an oil-modified phenolic varnish by a single laboratory, and with published AIEE results.