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Transformers: Principles and Ratios for ETCH 213 - Prof. Bret C. Allen, Study notes of Electrical and Electronics Engineering

This document, provided by faculty b. Allen for etch 213, introduces the concept of transformers, explaining their structure, mutual inductance, transformer action, loading, coefficients of coupling, transformer ratios, voltage ratios, power and current ratios, impedance ratio, maximum power transfer theorem, impedance matching, winding and phase, dot convention, transformer types, ratings, testing, and losses.

Typology: Study notes

Pre 2010

Uploaded on 08/16/2009

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Online Resource for ETCH 213
Faculty: B. Allen
Introduction to Transformers
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Online Resource for ETCH 213 Faculty: B. Allen

Introduction to Transformers

Online Resource for ETCH 213 Faculty: B. Allen

Transformers

Transformer – A device consisting of two or morecoils that are used to couple electrical energy fromone circuit to another while maintaining electricalisolation between the two.Primary Winding – First winding of a transformer thatis connected to the source.Secondary Winding – Output winding of atransformer that is connected to the load.

Online Resource for ETCH 213 Faculty: B. Allen

Transformer action

Online Resource for ETCH 213 Faculty: B. Allen

Transformer loading

Unloaded

Loaded

Online Resource for ETCH 213 Faculty: B. Allen

Transformer ratios

Turns Ratio – Ratio of the number of turns in thesecondary winding to the number of turns in theprimary winding of a transformer.

S P

N N

Ratio

Turn

Online Resource for ETCH 213 Faculty: B. Allen

Voltage ratio

S P S P N N V V =

Online Resource for ETCH 213 Faculty: B. Allen

Step-down transformer

Step-Down Transformer – A transformer in which the ac voltage inducedin the secondary is less (due to fewer secondary windings) than the acvoltage applied to the primary.

Online Resource for ETCH 213 Faculty: B. Allen

Power and current ratios

P S S P p S s P P P V V I I N N = = =

Online Resource for ETCH 213 Faculty: B. Allen

Maximum power transfer

theorem

The maximum power will be absorbed by theload from a source, when the impedance of theload is equal to the impedance of the source.

Online Resource for ETCH 213 Faculty: B. Allen

Impedance matching

Online Resource for ETCH 213 Faculty: B. Allen

Dot convention

A standard used with transformer symbols to indicatewhether the secondary voltage will be in phase or outof phase with the primary voltage.

Dot

Dot

Online Resource for ETCH 213 Faculty: B. Allen

Transformer types

Fixed turns ratio transformersVariable turns ratio transformersCenter tapped transformersMultiple winding transformersSingle winding Transformers(autotransformers)

Online Resource for ETCH 213 Faculty: B. Allen

Testing transformers

Open primary or open secondary

No voltage across the load

Partial or complete short in primary winding

Excessive secondary current and a blown fuse

Partial or complete short in secondary winding

Excessive secondary currentExcessive primary current and a blown fuse

Online Resource for ETCH 213 Faculty: B. Allen

Transformer losses

Copper loss – Also called I 2 R loss, it is the power lost in transformers, generators,connecting wires, and other parts of a circuitbecause of current flow (I) through theresistance (R) of the conductors.