| 摘要 |
PROBLEM TO BE SOLVED: To enable two simultaneous measuring by measuring tanδof a cable from the relation of cable application voltage and ground wire current, mounting a current transformer and measuring partial discharge generated in the cable from its output. SOLUTION: Alternating voltage V is impressed on the conductor 17 of a cable 11, passes capacitance between the conductor 17 and a sheath 12 between edge-cut parts 16, and current of a difference in phase caused by insulation characteristic between the voltage V and the cable 11 is flowed in a ground wire 13. A tanδmeasuring instrument 14 is inserted in the ground wire 13, and tanδis calculated from the current flowing in the ground wire 13 and reference current flowing between the conductor 17 and an ideal capacitor C. When the voltage V is increased to measure tanδat each voltage and local insulation breakage occurs in the sheath 12 together therewith, current by partial discharge flows in the ground wire 13. A current transformer 18 is mounted on the ground wire 13, and pulse current is taken out in a partial discharge measuring apparatus 15 via a lead 19 without changing the phase of measuring current. Discharge start voltage and tanδare simultaneously found by the observation.
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