Interphase Transformer Designing 1

I must design and make an IPT for a 3 phase 12 pulse Rectifier(with two transformer Delta-star & Delta-Delta).
Which specifications must this IPT have?
How is general methode for designing an IPT?

 

[electricuwe]

The interphase transformer (sometimes the device is refered as interphase reactor, but thats wrong) can be designed as an autotransformer operating at six times line frequency (in your particular case).But some special issues have to be considered

- controlled or uncontrolled rectifier ?
- saturation: an airgap might be necessary to avoid saturation,
saturation might be caused by: current imbalance, fast regulation of the controller

Interphase transformers for high current rectifiers with low output voltage can be economical designed by using busbars and UI-laminations.

 

Thanks electricuwe

But how we can find how many turns an IPT must be have?
and is it probable that "current imbalance" be so high that
cause an saturation in core?
I think it contains two coil that are wound so that their flows oppose each other..is it right?

 

[electricuwe]

For calculation of the voltage across the interphase transformer see:

Bird, B.M.;King, K.G.; Pedder, D.A.G.: "An Introduction to Power Electronics", Wiley, 1993

This book shows the calculation of the voltage across the interphase transformer in six-pulse midpoint connection.

The current imbalance can be caused by one or more of the following reasons:
firing angle imbalance
transformer reactance imbalance
existing harmonic voltages caused by rectifiers of lower pulse number

Some rectifier controlls are able to balance currents by adjusting the firing angle of the two bridges independendly, but even in this case there still might be a small imbalance due to errors.

Regarding your last question you're right, but thats not in contradiction to my statement as long as magnetizing current is neglected. Beside this, this is the reason why the term interphase transformer is correct and interphase reactor is wrong.

 

It is supposed that wants to design a rectifier, controlled or not, with double bridge.
The advantages of this solution is that has a minor rate of harmonics in the current of net and a low ripple.
There are some interesting questions of design that might give place to points of discussion.
1) According to the power it is possible to use a transformer with two secondary or two independent transformers.
2) Is better a solution star/star and star/delta that others. A better balance of charges is obtained in secondary. Better efficiency, rate of harmonics and Vac ripple.
3) If one wants to reduce ripple is not sufficient of putting a condenser. One would warm and modify the distribution of charges in the secondary ones. It is necessary to put a filter L-C.
4) The design is totally similar to that of a normal bridge. A margin of safety power must be given by if the distribution of charges is not good. The secondary tensions in star and delta are identicals.
Excuse my English.
Best whises.

 

[jbartos]

Suggestion to kam-elec (Visitor) Jul 22, 2002 marked ///\\I must design and make an IPT for a 3 phase 12 pulse Rectifier(with two transformer Delta-star & Delta-Delta).
Which specifications must this IPT have?
///Essentially, this will depend on your downstream converter. Usually, phase shifters are designed for diode rectifiers. The controlled rectifier often form so-called Active Front End (AFE). Sometimes, it is possible to use off the shelf transformers. It depends what W, or kW or MW size of conversion you are dealing with.\\How is general method for designing an IPT?
///Usually, they are sized higher than the load, e.g. 1.4 times, to account for harmonics. There is a good more theoretical publication available from IEEE Press:
Paice D. A. "Power Electronic Converter Harmonics - Multiple Methods for Clean Power," IEEE Press, NY, 1996.
However, the more practical reference will be needed if detail calculations are required. See

http://www.amazon.com

http://www.barnesandnoble.com

Transformer and Inductor Design Handbook
by Colonel Wm. T. McLyman, Colonel William T. McLyman

Handbook of Transformer Design and Applications
by William M. Flanagan (Hardcover)

Handbook of Transformer Applications
by William M. Flanagan\\