# Transformers

## Variable Frequency Transformer

Variable Frequency Transformer | Application: So far we have considered transformers which operate at fixed frequency (50 Hz). Their purpose is to transform electric power from one voltage level to another; their performance measures being high efficiency and low voltage regulation. Small transformers (usually iron-cored) are used for coupling purposes in electronic circuits for communication, …

## Autotransformer

Autotransformer | Definition | Use of Auto transformer: So far two-winding transformers have been discussed wherein the windings are electrically isolated. When the primary and secondary windings are electrically connected so that a part of the winding is common to the two as shown in Fig. 3.35 (core is not shown here), the transformer is …

## Switching Transients in Transformer

Switching Transients in Transformer | Transformer Inrush Current: Switching Transients in Transformer – In the earlier discussion earlier steady-state operation was assumed so that v1 and Φ are both sinusoidal, Φ lagging v1 by 90° as shown once again in Fig. 3.33(a). The Φ – i0 relationship is shown in Fig. 3.33(b). The normal exciting current …

## Excitation Phenomenon in Transformer

Excitation Phenomenon in Transformer: It was stated already that the no-load current in a transformer is nonsinusoidal. The basic cause for this Excitation Phenomenon in Transformer, which lies in Transformer Hysteresis and Saturation non­linearities of the core material, will now be investigated; this can only be accomplished graphically. Assume that the voltage v1 applied to …

## Voltage Regulation Formula of Transformer

Voltage Regulation Formula of Transformer: Voltage Regulation Formula – Constant voltage is the requirement of most domestic, commercial and industrial loads. It is, therefore, necessary that the output voltage of a transformer must stay within narrow limits as the load and its power factor vary. This requirement is more stringent in distribution transformers as these …

## Transformer Efficiency Formula

Transformer Efficiency Formula: Power and distribution transformers are designed to operate under conditions of constant rms voltage and frequency and so the efficiency and voltage regulation are of prime importance. Transformer Efficiency Formula is the rated capacity of a transformer is defined as the product of rated voltage and full load current on the output …

## Per Unit System

Per Unit System: While carrying out the analysis of electrical machines (or electrical machine systems), it is usual to express voltage, current, VA and impedance in Per Unit System (or percentage) of the base or reference values of these quantities. The per unit (pu) value of any quantity is defined as the ratio of: While …

## Sumpner Test of Transformer

Sumpner Test of Transformer: While OC and SC tests on a transformer yield its equivalent circuit parameters, these cannot be used for the ‘heat run’ test wherein the purpose is to determine the steady temperature rise if the transformer was fully loaded continuously; this is so because under each of these tests the power loss …

## Transformer Testing Methods

Transformer Testing Methods: Two chief difficulties which do not warrant the Transformer Testing Methods by direct load test are: Large amount of energy has to be wasted in such a test, It is a stupendous (impossible for large transformers) task to arrange a load large enough for direct loading. Thus performance characteristics of a transformer …

## Different types of losses in transformer

Different types of losses in transformer: The transformer has no moving parts so that its efficiency is much higher than that of rotating machines. Different types of losses in transformer are enumerated below: Core Loss in a Transformer: These are hysteresis and eddy-current losses resulting from alternations of magnetic flux in the core. Their nature …

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