Thermal aging studies of solenoid coil insulation systems

The Navy has been performing spot checks of solenoid coil insulation systems in accordance with a modification of a test(1) consisting of dielectric strength, insulation resistance, heat and moisture resistance. These tests have usually been performed at one temperature. The results were then compared with the results obtained with a typical Class A motorette system. However, these tests were limited in their usefulness since only one temperature point was obtained. In addition, the results were based on ground failures while it was evident that some coil systems would fail a turn-to-turn test from the flaking and cracking of the film insulation on the conductors.