Application of superconducting coils to reactive power control in electric power systems

Abstract

A novel type of static thyristor-controlled reactive power compensator, called SAVAR, consisting of a multipulse Graetz bridge controlled in a variable free wheeling mode and connected to a superconducting coil is described. Each thyristor of the Graetz bridge is fired twice during a cycle in a cyclic order that results in a constant average coil current which flows through the line during part of a cycle and free wheels through the bridge during the rest of the cycle. By varying the fraction of a cycle during which the coil current is free wheeling, the line current can be varied continuously between a minimum and maximum limit according to the required reactive current demand. The control algorithm for the variable free wheeling mode of the bridge and the methods to produce a low loss superconducting coil subjected to high voltage harmonics are described. Experimental results of a prototype unit with an existing non-optimized superconducting coil are given, providing the proof-of-principle of the SAVAR system. Preliminary cost and performance data for a 40 MVAR SAVAR reference design are compared with those obtained from a conventional static reactive power compensator.