EARTH STATIC CAPACITY MEASURING METHOD AND APPARATUS FOR ONE WIRE EARTHED THREE-PHASE THREE-WIRE CABLE WAY

摘要

PURPOSE: To measure the earth static capacity by inserting a designated capacitor between one and the other non-earthed cable ways and the ground in such a manner as to be connected and disconnected in a three-phase three-wire cable way, one wire of which is earthed by an earthing line. ;CONSTITUTION: A series circuit comprising relay switches SW₁, SW₂ and a capacitor C₀ is inserted between non-earthed cable ways 1, 2 and the ground, an arithmetic control unit AR turns off the switches SW₁, SW₂, and the leakage current fed back to an earthing line EL is detected by ZCT and amplified by an amplifier A to be input to synchronism detectors M₁, M₂. A current component perpendicular to the voltage between cable ways 1-3, and a signal corresponding to a current component of the same phase as that of the voltage between the cable way is 2-3 are output as the outputs of detectors M₁, M₂ and A/D converted to be stored in a memory. Only the switch SW₁ is turned on, subsequently only the switch SW₂ is turned on, and signals corresponding to the current components are respectively A/D converted to be stored in a memory. The arithmetic control unit AR uses stored current components and constants to make computation in order to output the output corresponding to the earth static capacity of a cable way to OUT₁. Similarly, the values corresponding to the earth static capacity of non-earthed cable ways 1, 2 are output to output terminals OUT₂, OUT₃.;COPYRIGHT: (C)1993,JPO&Japio