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
Discuss all the five software interrupt instructions. The INTEL family microprocessor consist of software interrupts INT, INT0, INT3 and BOUND and IRET. Out of all these five

Q. The electric field intensity due to a point charge in free space is given to be Determine the location and the value of the point charge.

By a simple time multiplexing of natural samples over a single line, a large radar site transmits 85 analog signals, each with 200-Hz bandwidth. If the sampling is done at twice th

1.   Work out the  voltage for the following arrangement of 1.5V cells : (to achieve a pass grade, solve problems with cells in series, parallel and series-parallel) 2.

This example is concerned with steady-state sinusoidal analysis by using mesh equations and MATLAB. Let us consider the circuit shown in Figure and find the input impedance at the

The system diagram for the proposed unit is shown below. The system operates on the principle of Time to Rate Conversion. Signals from the heart beat sensor are amplified

The goal of this project is to model a system and to design a controller for the system so that the closed-loop system performs satisfactorily.

Explain Contact resistance. Contact resistance: It is measured as the voltage drop from tail to tail of the mated contacts along with specified current flowing through the cont

1. A modi?ed NRZ code known as enhanced-NRZ (E-NRZ) operates on 7-bit words; invert- ing bits 2,3,6 and 7; and adding one parity bit to each word. The parity bit is chosen to make

Explain the Sequential Circuits? The Logic circuits whose outputs, at any instant of time, depends not merely the present input but as well the past output called sequential ci