phase-shifting transformer[′fāz ¦shif·tiŋ tranz‚fȯr·mər]
(fazoreguliator), an electromechanical device, usually in the form of an asynchronous electric machine with a blocked phase-wound rotor. Such a machine operates as an electrical transformer and makes it possible to alter the phase shift between the voltage at the supply terminals and the voltage at the load terminals.
The stator winding, which functions as the primary winding of the transformer, is connected to a three-phase power distribution system; the rotor winding, the secondary winding, is connected to the load through slip rings. The currents in the stator winding create a rotating magnetic field, which induces emf’s in the stator and rotor windings. The phase shift between these emf s is determined by the relative position of the stator and rotor, that is, by the angle of the mutual shift of the electrical axes of the phase windings. Turning the rotor in relation to the stator by means of some mechanical device, such as a worm mechanism, results in a smooth change in the phase shift between the emf’s (and, consequently, between the primary and secondary voltages) within the range from 0° to 360°.
There are cases when it is necessary to change the voltage phase in relatively low-powered, single-phase AC circuits. In the devices used for this purpose, the rotating magnetic field is produced by two windings. If an electric capacitor is connected to the device, the magnetic flux in one of the windings can be shifted in phase relative to the flux in the other winding by one quarter of a period.
In automation, telemechanics, conversion technology, and measuring technology, the changes in phase shift between voltages or currents are produced by phase-shifting transformers that are essentially four-pole networks. Such networks, consisting of resistors, induction coils, and electric capacitors, are called phase-shift circuits or phase shifters.
REFERENCEElektrotekhnicheskiispravochnik, 5thed., vol. 1. Moscow, 1974.
G. M. VOTCHITSEV