| 摘要 |
PURPOSE:To monitor variation in the insulation performance of each cable at any time and to measure even the absolute value of tandelta of each cable by detecting the difference between sheath currents of two adjacent cables by a current comparator. CONSTITUTION:The current comparator 5 is connected from sheaths to grounding lines 3 and 4 at the connection point J between conductors 1 of cables C1 and C2 which are supplied with a high voltage (e). Coils N1 and N2 of the comparators 5 are wound having the opposite polarities at such a turn number ratio that a voltage based upon the difference between sheath currents is not developed at an output coil Nd in the beginning of installation. New cabled right after being laid are therefore equal in tandelta and the output voltage G of the coil Nd is zero. If one cable varies in insulation performance during use, the output voltage Eg is outputted from the coil Nd. In general, tandelta increases according to the deterioration of the insulator and never decreases, so the development of the output voltage Eg is caused by an increases in tandelta of one of the cables C1 and C2 and this output is used as an alarm signal to operate the monitoring device of, for example substration.
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