Phase advancing, with particular reference to the scherbius shunt-wound advancer

An aggregate consisting of an induction motor and a Scherbius series advancer will operate with a good, and nearly constant, power factor from about half full load to its maximum overload. As the load decreases, however, the advancing e.m.f. also decreases, so that on light loads the power-factor improvement is slight. In the Scherbius shunt-wound advancer the exciting winding is shunted across the rotor of the induction motor. The advancer field, and therefore the advancing e.m.f., is proportional to the current in this winding. Within the working range of slip frequencies this current, and therefore the advancing e.m.f., is nearly constant. Further, the relationship between the e.m.f.´s is such that if the advancer and slip e.m.f.´s are at right angles for any particular value of slip, they will remain so for all slips. Consequently the motor operates with a constant power factor and with its normal slip at all loads.