JP2635701B

PURPOSE:To detect the partial discharge of the winding of electric machinery by certainly detecting only the magnetic field component of an electromagnetic wave discharged with partial discharge without taking complicated constitution. CONSTITUTION:The first and second loop circuits 4, 5 positioned at a detection distance of 10cm or less from the winding of electric machinery and respectively outputting the first and second voltage signals whose phases become reverse to each other are arranged and a differential circuit 10 for detecting the difference voltage of the first and second voltage signals is provided. When an electromagnetic wave interlinks the circuits 4, 5, the first and second voltage signals are respectively outputted from the circuits 4, 5. At this time, since the signal components outputted from the circuits 4, 5 become the same phase, the signal components accompanied by partial discharge are set off mutually, when the difference voltage of the first and second voltage signals is detected by the differential circuit, to be made ineffective. Therefore, by measuring the intensity of the difference voltage due to the circuit, the magnetic field of the electromagnetic wave interlinking the circuits 4, 5 can be detected.