PURPOSE: To accurately detect the net charge current of each phase cable by detecting the currents flowing to the earth wires of the respective cables constituting a multiphase cable line and operating the difference between the detected currents of two earth wires.
CONSTITUTION: When the charge current of an A-phase cable 1a is calculated, the current detected by a current detector T1 is outputted as it is. When the charge current of a B-phase cable 1b is calculated, the detection output by the detector T1 is subtracted from the detection output by a current detector T2 to calculate a net charge current. Since the charge currents of the cables 1a, 1b together flow in the ground through an earth line 8bc, the difference between both of them is taken. In the same way, the charge current of a C- phase cable 1c is calculated on the basis of the difference between the detection output of a current detector T3 and that of the detector T2. For example, the voltage applied to the cable 1b is detected by a voltage detector 40 and, on the basis of this voltage and the net charge current of each cable, tan δ is operated by a tan δ measuring part 30.
YAMAOKA MASARU
TAKAHASHI KAZUHIKO
FUJIWARA YASUTAKA
EBINUMA YASUMITSU
SHOWA ELECTRIC WIRE & CABLE CO