| 摘要 |
PURPOSE:To trace and monitor the degree of insulation deterioration of a live cable by measuring a voltage across a resistor inserted between the screening edge of a cable to be measured and the ground while eliminating commercial frequency components according to a low-frequency single-phase AC voltage. CONSTITUTION:For measuring an index expressing the change in the degree of deterioration of a cable 14 to be measured by a measurement cable B, a noise voltage drop before operating a low-frequency single-phase power supply 13 for feed is read by an AC voltmeter 17. Then, when a switcher 5 is closed and the output of the power supply 13 is fed to a high-voltage bus 1, a remaining low-frequency voltage which is attenuated by the coil-winding impedance of an equipment 2 for grounding remains in the bus 1. With the voltage as a measurement source voltage, a voltage drop by a low resistor 16 due to current through the insulation layer of the cable 14 is read with the voltmeter 17. When the value is, for example, five times or more larger than the previously read noise voltage drop, the value is used as an index expressing the change in the degree of insulation deterioration of the cable 14 by determining that a reliable measurement was made. |
