Method and apparatus for selective cancellation of subsynchronous

Abstract

Apparatus and process for the selective cancellation of harmonic frequencies of current produced in a multiphase dynamic stabilizer. A plurality of multiphase dynamic stabilizers providing electrical stabilization are interconnected to a multiphase AC electrical network via a coupling transformer. The leakage reactances and turns ratios of the windings of the transformer are such that the phases of selected harmonic frequencies of current produced in each of the stabilizer means are rotated with respect to those of the other stabilizer means with the selected harmonic frequencies being substantially cancelled in each of the stabilizer means. The harmonics are not the cause of subsynchronous resonance. The cancelled harmonic frequencies are dependent upon the number of dynamic stabilizers used. Where a dual stabilizer system is utilized, the coupling transformer is forked wye transformer having the primary windings connected in delta with the principal secondary windings connected in wye and each principal secondary winding having two auxiliary secondary windings connected thereto. By forming the auxiliary secondary windings such that the ratio of the number of turns therein with respect to the principal secondary winding is about the ##EQU1## and the leakage reactance of the principal secondary winding being equal to about twice the common leakage reactance of the auxiliary secondary windings, the phases of the harmonic currents produced in each stabilizer rotates by approximately 30 electrical degrees with respect to one another leading to the substantial cancellation of harmonic currents of each stabilizer characterized by the series 5, 7, 17, 19 . . . n, p where n=5+z; p=7+z; and z=multiples of 12. Addition of shunt capacitors across each of the primary windings creates a static VAR generator having the same harmonic current cancellation attribute.