Variable frequency transformer
- Variable frequency transformer
A variable frequency transformer is used to transmit electricity between two asynchronous alternating current domains. The VFT is a relatively recent development (first deployed in 2004). Most grid interties use high-voltage direct current converters.
For instance, the Langlois Substation in Québec has installed a 100 MW variable frequency transformer to connect the asynchronous grids in Québec and the northeastern United States.
AEP Texas installed a VFT substation in Laredo, Texas in early 2007. It connects the power systems of ERCOT (in the United States) to CFE (in Mexico). See [http://www.ettexas.com/projects/vft.asp The Laredo VFT Project]
Smaller VFTs are used in large land-based wind turbines, 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 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.
* [http://www.gepower.com/about/press/en/2004_press/052504j.htm GE press release for the Langlois installation]
* [http://www.spectrum.ieee.org/nov07/5714 Power Transmission Without the Power Electronics]
Look at other dictionaries:
Variable-frequency drive — A variable frequency drive (VFD) is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor.cite book | first=Sylvester J. |… … Wikipedia
Rotary variable differential transformer — A rotary variable differential transformer (RVDT) is a type of electrical transformer used for measuring angular displacement.More precisely, a Rotary Variable Differential Transformer (RVDT) is an electromechanical transducer that provides a… … Wikipedia
Linear variable differential transformer — The linear variable differential transformer (LVDT) is a type of electrical transformer used for measuring linear displacement. The transformer has three solenoidal coils placed end to end around a tube. The centre coil is the primary, and the… … Wikipedia
Transformer — This article is about the electrical device. For the toy line franchise, see Transformers. For other uses, see Transformer (disambiguation). Pole mounted distribution transformer with center tapped secondary winding. This type of transformer is… … Wikipedia
Frequency changer — A frequency changer or frequency converter is an electronic device that converts alternating current (AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to… … Wikipedia
Transformer types — Circuit symbols Transformer with two windings and iron core. Step down or step up transformer. The symbol shows which winding has more turns, but not usually the … Wikipedia
Variable capacitor — Rotary variable capacitor A variable capacitor (also known as a variable air condenser ) is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically. Variable capacitors are often used in L/C… … Wikipedia
High frequency — (HF) radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted Medium frequency… … Wikipedia
Electric motor — For other kinds of motors, see motor (disambiguation). For a railroad electric engine, see electric locomotive. Various electric motors. A 9 volt PP3 transistor battery is in the center foreground for size comparison. An electric motor converts… … Wikipedia
Inverter (electrical) — An inverter is an electrical device that converts direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits. Solid… … Wikipedia