NOISE REMOVING METHOD IN INSULATION DIAGNOSIS BASED UPON PARTIAL DISCHARGING PHASE CHARACTERISTICS

PURPOSE:To extract precisely only pulse current and to improve insulation diagnozing accuracy by comparing partial discharging phase characteristics (phi-n distribution) found from an apparatus to be diagnozed with a reference phi-n distribution pattern for applying the deciding condition of noise. CONSTITUTION:Current flowing into the earth line 2a of an apparatus to be diagnozed 2 is intermittently detected by a detector 2b and a phi-n distribution pattern (phi-n distribution) is found by a phi-n distribution detector 3. On the other hand, noise removing decision phi-n distribution is found by using an apparatus having the same insulating grade and the same voltage grade as that of the apparatus 2 and the found distribution is stored in a storage device 6. The stored contents are read out every detection and compared with the phi-n distribution of the diagnozed apparatus 2, a phi-n distribution output having no pulse condition is removed and only a partial discharging pulse is outputted by a phi-q distribution operator 3 to remove the influence of noise. Thus, the noise can be reduced and diagnozing accuracy in the insulating state can be improved.