| 摘要 |
<p>PURPOSE:To achieve the evaluation of deterioration in the cable section alone free from effect of the head section by determining the quantity of charge being absorbed of a cable insulation layer from the difference in measured values of charge absorbed in a cable head to detect a water tree. CONSTITUTION:A cable 1 provided with an insulation layer 1b, a shield layer 1c and a sheath 1d on a conductor 1a is buried in the ground and a head 3 connected to the end thereof as earthed separately from the layer 1c. After a charging with a DC power source 4, a discharge is caused from the head 3. An instantaneous discharge current in the initial discharge is bypassed S2 and then, after the setting of the time for a timer 6, the discharge current in after effect is measured 5 as charge absorbed to detect the pressure of a water tree therefrom. In the case, after the earthing of the layer 1c, a power is applied for a specified time and then, the conductor 1a is short-circuited and discharged to measure the quantity Q1 of charge absorbed of the head section and the quantity Q2 of charge absorbed of the layer 1b. After the connection of the layer 1c to the conductor 1a, a power is applied for a specified time and following the earthing of the layer 1c, the conductor 1a is short-circuited and discharged to measure the quantity Q1, Q2 is determined from (Q1+Q2)-Q1 to detect the water tree.</p> |
