| 摘要 |
PROBLEM TO BE SOLVED: To enable to judge the degree of water tree deterioration. SOLUTION: In this diagnosis method, a cable 1A for measurement and a first resistance element Rdx are connected in series through a first connection point 4, a cable 1B for standard and a second resistor element Rs are connected in series through a second connection point 5, insulator of the cable for measurement is regarded as a parallel circuit of a capacitance component Cx and a conductance component Gx, a voltage Vp containing a plurality of frequency components in a specified frequency range is applied to each of the cables, a voltage Vcx generated in the first resistance element by a current Icx flowing in the capacitance component of the insulator and a voltage Vcs generated in the second resistance element by a current Ics flowing in the cable for standard are canceled by adjusting the resistance value of the second resistance element, a current Ix flowing in the conductance component of the insulator is detected as a differential voltage V3 between the first connection point and the second connection point, and the degree of water tree deterioration in the cable is diagnosed on the basis of frequency characteristic of the current flowing in the conductance component.
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