INSULATION DIAGNOSTIC DEVICE

PROBLEM TO BE SOLVED: To provide a small-sized, lightweight and functional insulation diagnostic device at a low cost. SOLUTION: At least two cycles of data obtained by a partial discharge sensor and a noise sensor are taken (Step 11). (N) data are obtained (Step 12) per second (Step 13) to obtain data synchronizing with commercial frequency. (N) data are averaged (Step 14) or a piece of representative data is taken out to eliminate synchronous noise. A difference between a partial discharge signal and a noise signal is computed (Step 17) to eliminate asynchronous noise. A periodic peak point and a 1/4 cycle point are calculated from the computed difference (Step 18). The data of the periodic peak point and the 1/4 cycle point are compared to determine whether there is any partial discharge or not (Step 19).