Title Electrical Machine Types Instruction manuals 822.8 KB 15
##### Document Text Contents
Page 1

TRANSFORMERS (I)TRANSFORMERS (I)

EPO540
ELECTRICAL MACHINES

prepared by Kanendra

Page 2

1. INTRODUCTION

 Static machine

 Not an energy conversion device - necessary & essential in many energy

conversion

 Consist of two or more windings coupled by a mutual magnetic field

 Ferromagnetic cores usually used to provide tight magnetic coupling and high

flux densities – – IRON CORE

 IRON CORE used in high-power applications

 AIR-CORE used in low power electronic circuits

prepared by Kanendra

Schematic representation of a two winding transformerSchematic representation of a two winding transformer

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4. DETERMINATION OF EQUIVALENT
CIRCUIT PARAMETERS

 In order to predict the behavior of the transformer, circuit parameters (R 1, X1,
R 2

’’, Xl 2’,’, R c, Xm) has to be known

 These parameters can be calculated from the dimensions and properties of the

materials used – – design data of transformer

 Difficulty in obtaining data and some required parameters

 A simple and direct method is used to obtain these parameters – – performing

two different tests: “No“No Load (Open Circuit) Test”Test” & “Short“Short Circuit Test”Test”

prepared by Kanendra

Page 8

 Open circuit HV side and apply low voltage on LV side

 Low voltage power supply is readily available

prepared by Kanendra

 =


 =>  =




 =



 = 
2 − 

2

 =




Wiring diagramWiring diagram

Equivalent circuitEquivalent circuit

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8. EFFICIENCY

 Copper loss (Pcu) function of load current - determined through winding

currents and resistances

Pcu = I1
2 R 1 + I2

2 R 2

= I1
2 Req1 = I2

2 Req2

 Therefore, given any load condition (with power factor)

Pout = V2 I2 cos ϴϴ2

η =
VV22

II22
cos cos 22

VV22

II22

cos cos 22

+ PPCC

+ II22
22 Req Req22

prepared by Kanendra

Page 15

9. AUTOTRANSFORMER

prepared by Kanendra

 Common winding mounted on a core, secondary is taken from tap on the

winding

1. Reduced weight and size

2. Lower losses

3. Lower exciting current

4. Lower cost – – less copper used

5. Variable output voltage

1. Direct connection between primary and

secondary windings / no isolation

AutotransformerAutotransformer



2

=


2

= 


2

=
1