| 摘要 |
PROBLEM TO BE SOLVED: To accurately measure only a signal due to deterioration by applying DC voltage superposed with an AC voltage between a conductor and a shielding layer of a CV cable, and measuring change of current flowing to the cable. SOLUTION: A switch 4 is opened, AC voltage is applied between a conductor 1A and a shield layer 1B of the CV cable 1 from an AC power source 2, and current I0 flowing to the cable 1 is measured. Then, the switch 4 is closed, DC voltage from a DC power source 3 superposed with the AC voltage is applied, and current I flowing to the cable 1 is measured. And, deterioration of the cable 1 is judged from a value of changeΔI=I1 -I0 of both the currents. A capacitor 5 is inserted as a bypass for inhibiting flow of the current flowing to the cable 1 to the source 3. Thus, only a signal due to water treeing degradation can be accurately measured irrespective of magnitude of a contact resistance of the metal shield layer with an external semi-conducting layer.
|
