| 摘要 |
PROBLEM TO BE SOLVED: To surely prevent complete grounding fault by estimating the time of grounding of an AC motor with accuracy without stopping the motor. SOLUTION: When an AC motor 12 is grounded, current in an earth wire 14 is supplied to a filter circuit 18 and DC components which indicate semi- grounding fault are extracted from the current. Then, the DC components are amplified by a current transformer and then are further amplified by a DC amplifier 22 and then are converted into a voltage signal. Then, a change in voltage based on the DC components is recorded in a recorder 24 to make it recognize the semi-grounding fault. The recorder 24 functioning as a recognizing section gives warning, for example, by emitting an alarm and quickly detects the semi-grounding fault before the complete grounding fault to detect abnormality in the AC motor. |
