Variable-frequency transformer: Difference between revisions

Revision as of 15:46, 10 November 2008

Revision as of 17:02, 14 April 2009

Line 7:

Smaller VFTs are used in large land-based [[wind turbine]]s, so that the turbine rotation speed can vary while connected to a distribution grid.

== Construction and operation ==

A variable frequency transformer is a [[doubly-fed electric machine]] resembling a vertical shaft [[hydroelectric]] generator with a three-phase wound rotor, connected by slip rings to one external power circuit. A direct-current torque motor is mounted on the same shaft. Changing the direction of torque applied to the shaft changes the direction of power flow; with no applied torque, the shaft rotates due to the difference in frequency between the networks connected to the rotor and stator.

The variable frequency transformer behaves as a continuously adjustable [[Quadrature booster|phase-shifting transformer]]. It allows control of the power flow between two networks. Unlike power electronics solutions such as back-to-back [[HVDC]], the variable frequency transformer does not demand harmonic filters and reactive power compensation. Limitations of the concept are the [[current-carrying capacity]] of the slip rings for the rotor winding.

Variable frequency transformers have been installed at Langlois, Quebec and at an interconnection point between Laredo, Texas and the Mexican power system.

== External links ==