Electronic current transducer (ECT) for high-voltage dc lines. Final report

Abstract

The development of a bipolar electronic current transducer (ECT) for measuring the current in a high-voltage dc (HVDC) power line at line potential is reported. The design and construction of a free-standing ECT for use on a 400-kV line having a nominal line current of 2000 A (1 pu) is described. Line current is measured by a 0.0001-..cap omega.. shunt whose voltage output is sampled by a 14-bit digital data link. The high-voltage interface between line and ground is traversed by optical fibers which carry digital light signals as far as 300 m to a control room where the digital signal is converted back to an analog representation of the shunt voltage. Two redundant electronic and optical data links are used in the prototype. Power to operate digital and optical electronics and temperature-controlling heaters at the line is supplied by a resistively and capacitively graded 10-stage cascade of ferrite-core transformers located inside the hollow, SF/sub 6/-filled, porcelain support insulator. The cascade is driven by an SCR (silicon-controlled-rectifier) inverter which supplies about 100 W of power at 30 kHz. Specification goals called for operation over the temperature range -40 to +50/sup 0/C to an output accuracy of +-0.6% at 0.1 pumore » and +-0.3% between 0.3 pu and 1.0 pu. A frequency response greater than 370 Hz and a step response time of less than 2 ms was desired. Initial tests indicate that these goals have been met in the prototype structure. The unit is now installed and being evaluated at the Sylmar converter station of the HVDC Pacific Intertie in California.« less