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# Transformer

## Three Phase Transformer Connections

In this section, we’ll review the operating characteristics of basic delta-delta, wye-wye, delta-wye and wye-delta connections of the transformer. The construction of a three-phase transformer can be represented as shown in Figure 1. The shell type core has three sets of primary and secondary windings. How these windings are connected …

## Ideal Transformer | Theory | Equations | Example Problems

In all transformers, single phase or three phase, the primary winding gets energy from the mains and the secondary winding is connected to the load(s). If the secondary circuit is turned off by a switch, there is no load on the secondary winding. Ideal Transformer Theory Nevertheless, the primary winding is …

## Single-Phase Transformer | Construction | Theory

In the same way that single-phase AC and three-phase AC are different, although both are alternating current electricity, single-phase and three-phase transformers cannot be interchanged. Nevertheless, most of what can be said for single-phase transformers is later on extended to three-phase transformers because they work based on the same principle. …

## Power Transformer Differential Protection

A power transformer’s main task is to transform an electrical power from one voltage level to the other voltage level. A power transformer is the most important part of the electrical system as well as well the most expensive part. The function of all other electrical equipment (e.g. circuit breakers, …

## Exciting Current in Transformer | Inrush Current in Transformer

A practical transformer is not ideal and will require current into the primary winding to establish the flux in the core. The current that establishes the flux is called the exciting current. The exciting current magnitude is usually about 1%-5% of the rated current of the primary. By Faraday’s law, …

## Buck-Boost Transformer Working Principle

A buck-boost transformer is a type of transformer which is primarily used to adjust the voltage level applied to various electric equipment. Buck-boost transformers are utilized in in several applications such as uninterruptible power supplies (UPS) units for computers. When an existing AC electrical circuit suffers from excessive voltage drop …

## 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 …