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    Heat Aging Characteristics of Insulating Varnishes

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    Insulating varnish serves two important functions in the insulation system of electrical equipment: 1. Bonding together of wires and insulating components. 2. Protection against the entrance of moisture, dirt, or other contaminants. As the insulation system is exposed to operating or high ambient temperature, physical changes occur in the insulation for which changes in the insulating varnish are in part responsible. When the varnish no longer bonds together the insulation structure, or loses flexibility so that cracks and discontinuities develop, the system is subject to failure, mechanically or electrically. Many methods have been used to study the thermal degradation of insulating varnish. Some of these methods are indirect, such as loss in weight or changes in infrared spectra. Such methods give important insight into the mechanism of the aging process but seldom can be translated into functional significance. It is proposed, herein, to describe two methods for determining flexibility of aged insulating varnish: 1. The mandrel flexibility test. 2. A film rupture test making use of a deflected beam.

    Author Information:

    Morgan, H. I.
    General Electric Co., Schenectady, N. Y.

    Mathes, K. N.
    General Electric Co., Schenectady, N. Y.

    Committee/Subcommittee: D09.17

    DOI: 10.1520/STP46787S