A variable transformer, reactor having a core combining at least two complete core elements wiht a common yoke; primary winding divided into two independently fed sets of phase coils wound in opposite direction, arranged on symmetrical legs of core elements and separated by the common yoke; secondary...http://www.google.com/patents/US4837497?utm_source=gb-gplus-sharePatent US4837497 - Variable transformer, reactor and method of their control
