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