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Thursday, April 23, 2009

Variable Frequency Transformers

With Variable Frequency Transformer power transfer can be done smoothly without noise.


America cannot produce all the power it drinks. It has to get help from its neighbouring countries like Mexico to satisfy her. So power transfer between two grids must take place.

Circuits employing semi conductor devices were used for this purpose. But there is a problem. The power flowing in grid is in the form of AC-alternating current. This AC cannot be controlled using semiconductors. For that purpose we convert the AC to DC-Direct Current. Using the circuits we can alter any parameters of the power such as amplitude, frequency, phase etc. After that, DC is converted back to AC, ie we synthesize AC. But this AC is not as good as natural AC. The problem is harmonic distortions. As we change DC to AC a spike appears at each pulse, which is a noise and is undesired, but hard to eliminate.

With the help of new technology, VFT-Variable Frequency Transformers can do this. Variable Frequency Transformers can convert this power to and from grids without converting the power into DC thus eliminating the harmonic distortions. Another advantage with VFT is that we can have infinite phase shifts between the two powers where as in conventional devices we could have only few predefined phase shifts.

Even though VFTs employs latest technology, someone looking at the Variable Frequency Transformer will recognize it as a hydro generator. In fact AEP-American Electric Power, who has currently installed a VFT between Mexico-US grid, buys it from the same manufacturers who makes standard hydro generators.clip_image002


Although Variable Frequency Transformers looks like a hydro generator, it seems like VFT has hydrophobia. There is not a drop of water involved here, although it is a hydro generator. The rotor of the Variable Frequency Transformer, is a big three phase electro-magnet which is connected to one grid and the stator, another three phase winding, a stationary winding which is connected to the other grid. When power starts to flow, the phase difference between stator and rotor cause the motor to rotate. The rotor shaft is connected to another motor, called a control motor. We apply torque on the shaft and can rotate the motor in any direction and the direction of the motor determines the direction of power flow. The Variable Frequency Transformer is like a phase shifter having infinitesimally small steps.

 By Amit Samantaray


harish said...

goood collection.......

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