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# Transformer

## Three Phase Transformer Construction

A transformer consists of two or more electrical windings that are linked together by a magnetic ﬁeld. Except for special-purpose transformers, the coupling is enhanced with a ferromagnetic core. Transformers are often drawn as shown in Figure 1, with the primary coil on one leg and the secondary coil on …

Autotransformer Definition The autotransformer has a single winding on an iron core. One of the coil terminals is common to both input and output, and the other output terminal is movable so that it can make contact with any turn on the winding. Step-Up/ Step-Down Autotransformer An autotransformer can be …

## Three Phase Transformer Connections Phasor Diagrams

Three Phase Transformer Connections A three-phase transformer is built for a specific connection and voltage transformation and the unit will have a nameplate with the internal connections shown. When a single unit or bank of three is used, there are four types of connections. The four basic connections are: Y-Y, Y-∆, ∆-Y, and ∆-∆. …

## Transformer Nameplate Details Explained

Transformer nameplates contain several standard items of information and other optional information. Transformer nameplate must specify the following parameters: Volt-Ampere (VA) or kilovolt-amperes (kVA) rating The voltage rating of both the primary and secondary circuits The impedance rating of the transformer (normally restricted to 25 kVA or larger) The required …

## Transformer Polarity Test

Transformer windings are marked to identify terminals with the same polarity. Polarity marks may either be dots or + marks. Alternatively, polarity marks may be shown by assigning the same subscripts to corresponding primary and secondary labels, H and X, respectively. Thus, when the primary terminals are named H1 and …

## Transformer Losses and Efficiency Calculation

Transformer Efficiency Definition The efficiency of the transformer is defined as the ratio of the power output Poutput and power input Pinput, both expressed in watts. Thus, $\begin{matrix} \eta =\frac{{{P}_{out}}}{{{P}_{in}}} & {} & \left( 1 \right) \\\end{matrix}$ Or since the input is the output plus losses, \[\begin{matrix}   \begin{align}  & \eta …

## Determination of Transformer Equivalent Circuit Parameters

In order for a model to be useful, there must be a way to determine the values of the model parameters. Two simple tests are used to determine the values for the parameters of the transformer equivalent circuit of Fig. 1 (a) and (b). The two tests are the short-circuit …

## Voltage Regulation of Transformer at Unity, Lagging, and Leading Power Factor

Voltage Regulation of Transformer The voltage regulation of a transformer can be described as the change in the secondary voltage as the current varies from full load to no load while keeping the primary voltage constant. Generally, a transformer is utilized to supply loads that operate at basically constant voltage. …