A New AC Current Testing Method for Non-Destructive Insulation Tests

A new nondestructive diagnosis method is developed mainly for stator coil insulation of high voltage rotating machines as a result of analysis and experience on the behavior of a current of a sample under ac voltage application. A newly-defined parameter Y, measured in this method, equals tan, plus y, where y closely relates to void volume ratio in a sample. A new apparatus to measure Y automatically is also developed which shows experimentally several advantages in a practical test. Y-V patterns and y-V patterns by this method are verified to correlate well to insulation condition and residual breakdown voltage of a sample.