INSULATION DEGRADATION DIAGNOSING METHOD FOR POWER CABLE

摘要

PROBLEM TO BE SOLVED: To diagnose surely the insulation degradation of a cable by measuring residual voltage for a plurality of applied DC voltage for diagnosing on the basis of non-linear property for the applied DC voltage property of the residual voltage. SOLUTION: A DC power source Ws is a connected to a power cable 1 of a sample through switches SW1 -SW3 . The shielding layer of a cable 1 is grounded to close the switch SW1 and open the switch SW1 after DC voltage of -3kV for example is applied to a cable conductor for 10 minutes. Next, the switch SW2 is closed to ground the cable conductor through a resistor R of 1MΩfor 10 seconds. Next, the switch SW2 is opened to release the cable conductor from the ground and the switch SW3 is closed to measure for 10 minutes the residual voltage recovered to the cable conductor by a high impedance measuring means 2. A similar measurement is performed with DC voltage of -6kV0 -9kV to plot the residual voltage for the applied DC voltage on a graph and judge non-linearity from a regression type parameter of regression straight line/curved line for diagnosing the degree of degradation of the cable 1.