Explain working of three-phase transformers, Electrical Engineering

Q. Explain working of three-phase transformers?

Transformation in three-phase systems can be accomplished in either of two ways: (1) connecting three identical single-phase transformers to form a three-phase bank (each one will carry one-third of the total three-phase load under balanced conditions); or (2) a three-phase transformer manufactured for a given rating. A three-phase transformer, compared to a bank of three single-phase transformers, for a given rating will weigh less, cost less, require less floor space, and have somewhat higher efficiency.

The windings of either core-type or shell-type three-phase transformers may be connected in either wye or delta. Four possible combinations of connections for the three-phase, two- winding transformers are Y- Δ, Δ -Y, Δ -Δ , and Y-Y. These are shown in Figure with the transformers assumed to be ideal. The windings on the left are the primaries, those on the right are the secondaries, and a primary winding of the transformer is linked magnetically with the secondary winding drawn parallel to it. With the per-phase primary-to-secondary turns ratio (N1/N2 = a), the resultant voltages and currents for balanced applied line-to-line voltages V and line currents I are marked in the figure.

2459_Explain working of three-phase transformers.png

As in the case of three-phase circuits under balanced conditions, only one phase needs to be considered for circuit computations, because the conditions in the other two phases are the same except for the phase displacements associated with a three-phase system. It is usually convenient to carry out the analysis on a per-phase-of-Y (i.e., line-to-neutral) basis, and in such a case the transformer series impedance can then be added in series with the transmission-line series impedance. In dealing with Y- Δ and Δ -Y connections, all quantities can be referred to the Y-connected side. For Δ- Δ connections, it is convenient to replace the -connected series impedances of the transformers with equivalent Y-connected impedances by using the relation.

2044_Explain working of three-phase transformers1.png

It can be shown that to transfer the ohmic value of impedance from the voltage level on one side of a three-phase transformer to the voltage level on the other side, the multiplying factor is the square of the ratio of line-to-line voltages, regardless of whether the transformer connection is Y-Y, Δ -Y, or Δ -Δ . In some cases, where Y-Y transformation is utilized in particular, it is quite common to incorporate a third winding, known as tertiary winding, connected in delta. Such multiwinding transformers with three or more windings are not considered in this text.

Posted Date: 6/27/2013 12:20:36 AM | Location : United States







Related Discussions:- Explain working of three-phase transformers, Assignment Help, Ask Question on Explain working of three-phase transformers, Get Answer, Expert's Help, Explain working of three-phase transformers Discussions

Write discussion on Explain working of three-phase transformers
Your posts are moderated
Related Questions
Using Nyquist theorem, determine the sampling rate for an analog signal with frequencies from 3000Hz to 86000Hz and for a signal with ahorizontal line in th

Q. Why FET is called a voltage-controlled device? Why its input resistance is high? In the case of a FET the output current ID is a function of the voltage VGS applied to the i

Q.‘Pentium processor has a superscalar architecture'. Describe the meaning of statement. Ans:Pentium microprocessor is organized with three execution units. One executes float

Q. Explain the classification of amplifiers on the biasing conditions? Based on the amount of transistor bias and amplitude of the input signal, amplifiers can be classified as

Q. Antinoise Systems — Noise Cancellation? Traditionally sound-absorbing materials have been used quite effectively to reduce noise levels in aircraft, amphitheaters, and other

Dielectric Heating Dielectric  losses  occur in  insulating materials. These are same  as hysteresis losses  in magnetic materials. When  an alternating  electric  field  is a

Fourier transform  (filtering) (i) Perform low pass filtering in the frequency domain. Write and m-file lowfft.m which does this operation. lowfft.m function lowfft im

Mode 2 In this  mode transistor  gets turned off by  the negative output  of PWM  current  flows  through  inductance L diode D then  divide into two  parts one flows through

Explain the working of an npn transistor. Working of npn transistor: In an npn transistor is demonstrated in the figure. The emitter base junction is forward biased whereas

Develop and execute a PSpice program to solve for the current I 2 in Figure.