The following report explores the research and design of a 3-phase,25KVa, core-type, distribution transformer connected in a star-star configuration, for the purpose of stepping-down high voltages from electricity producers to make it useable for consumers. In order to go about the design process, ...
School of Electrical, Electronic and Computer
Engineering
Electrical Design 3 (ENEL3EAH1)
Transformer Design
i. Declaration
Plagiarism
Plagiarism is the presentation of work that has been copied in whole or in part from another
person’s work, or from any other source such as published books, periodicals, internet,
newspapers, films etc, without due acknowledgement in the text. Plagiarism is considered a
contravention of Rule 9(e)(i)(ff) of the UKZN Student Disciplinary Rules Handbook (2004).
Collusion
Collusion is the presentation of material that is the result in whole or in part of unauthorised
collaboration with another person or persons.
Consequences of Plagiarism and Collusion
In a case where a student has been involved in plagiarism or collusion, the matter will be
referred to the University Proctor for prosecution or will be dealt with through an Admission
of Guilt procedure.
We, the undersigned do understand the definitions and consequences provided above. We
confirm that all content of this report is the work of the authors listed, except where otherwise
referenced or cited. If this statement is found to be untrue, we accept that disciplinary action
will be taken.
1
,
,ii. Abstract
The following report explores the research and design of a 3-phase,25KVa, core-type,
distribution transformer connected in a star-star configuration, for the purpose of stepping-
down high voltages from electricity producers to make it useable for consumers. In order to
go about the design process, extensive research on transformers, configuration types, as well
as material choices was conducted, according to the design specifications provided. Once a
thorough understanding of transformers was gained, the vital calculation iterations to obtain
the dimensions of the transformer were performed until the given result met minimum
requirements, keeping in mind certain clearances were met. Once the calculation iteration
process was complete, the resistance values were calculated in order to obtain power losses
which ultimately aided in determining the efficiency of the transformer. An equivalent per
phase circuit and phasor diagram was also drawn from the resulting resistance values
determined and lastly the voltage regulation was calculated. The result was a theoretically
functional transformer with an acceptable efficiency of 95.28 % , a V . R of 0.71 % and
dimensions above minimum clearance.
Contents
i. Declaration.........................................................................................................................................i
Plagiarism...........................................................................................................................................i
Collusion............................................................................................................................................i
Consequences of Plagiarism and Collusion........................................................................................i
ii. Abstract............................................................................................................................................iii
iii. List of figures.................................................................................................................................vii
iv. List of tables..................................................................................................................................viii
v. Table of abbreviations....................................................................................................................viii
vi. List of Symbols................................................................................................................................ix
1. Introduction.....................................................................................................................................12
1.1 Design Specifications of transformer.........................................................................................13
2. Theoretical Background...................................................................................................................14
2.1 Introduction to transformers.......................................................................................................14
2.2 Working Principle of a Transformer..........................................................................................14
2.3 Transformer application.............................................................................................................19
2.3.1 Step-up transformers...........................................................................................................19
2.3.2 Step-down transformers......................................................................................................19
2.4 Transformer construction...........................................................................................................20
2.4.1 Transformer Core................................................................................................................20
2.4.1.1 Transformer core-types....................................................................................................21
, 2.4.1.2 Core design......................................................................................................................23
2.4.1.3 Core cross section............................................................................................................24
2.4.2 Window dimension.............................................................................................................27
2.4.3 Design of yoke....................................................................................................................29
2.4.4 Design of transformer windings..........................................................................................30
2.4.5 Bushings.............................................................................................................................37
2.4.6 Transformer insulation........................................................................................................38
2.5 Transformer losses....................................................................................................................39
2.5.1 Iron losses...........................................................................................................................40
2.5.2 Copper losses......................................................................................................................41
2.5.3 Stray losses.........................................................................................................................42
2.5.4 Dielectric losses..................................................................................................................42
2.6 Star – star connection (Y-Y)......................................................................................................42
2.7 Transformer Equivalent Circuit.................................................................................................43
2.8 Voltage Regulation....................................................................................................................45
3. Design Calculation..........................................................................................................................46
3.1 Transformer Design Calculation................................................................................................46
3.1.1 Core design.........................................................................................................................46
3.1.2 Core Window dimension design.........................................................................................47
3.1.3 Yoke Design.......................................................................................................................48
3.1.4 Overall dimensions.............................................................................................................49
3.2 Design of Winding.....................................................................................................................49
3.2.1 Low Voltage winding calculations......................................................................................50
3.2.2 High Voltage Windings.......................................................................................................51
3.3 Resistance value calculations.....................................................................................................52
3.4 Equivalent transformer circuit....................................................................................................54
3.5 Efficiency and voltage regulation calculations...........................................................................55
3.6 Phasor diagram..........................................................................................................................57
4. Results.............................................................................................................................................58
4.1 Core dimensions........................................................................................................................58
4.2 Winding dimensions..................................................................................................................59
4.3 Other calculations......................................................................................................................59
4.3.1 Resistance values................................................................................................................59
4.3.2 Equivalent transformer circuit values..................................................................................59
4.3.3 Transformer efficiency and voltage regulation....................................................................60
4.3.4 Phasor diagram....................................................................................................................60
5. Discussion........................................................................................................................................61
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