Electrical Machines

LSEGG216A9080V

Transformer Transformer OperationOperation

Week 4 Week 4

Transformer Transformer OperationOperation

V+ CIVILCIVIL

Voltage Current

Magnetic Flux

Transformer Transformer OperationOperation

Applied Voltage

Induced Voltage

Induced Voltage in Secondary

Resultant Current

V1

V’1V’2

IM

Induced VoltageInduced Voltage

• Φmax =Maximum instantaneous flux• F = Frequency• N = Number of turns• Bmax = Maximum permissible flux density in Wb• A = CSA of core in m2

fN44.4V max AfNB44.4V max

Transformer Transformer OperationOperation

V1

IM

Ie

Io

Ie= Iron loss currentIo = No load current

Transformer Transformer OperationOperation

V1

V’1V’2

Io

I’2

I’1

I1

Transformer Transformer OperationOperation

V1

V’1V’2

Io

I’2 I’1

I1

Transformation Transformation RatioRatio

Magnetic flux is common coils

fN44.4V max

Therefore the voltage can be varied by changing the number of turns

Transformation Transformation RatioRatio

V1= N1

N2V2== k = Transformation Ratio

Transformation Transformation RatioRatio

V1x I1

N1

N2

= V2 x I2

=I1

I2

Transformation Transformation RatioRatio

V1x I1

VA

V2 x I2

kVAPower In Power Out

Transformation Transformation RatioRatio

V1x I1V2 x I2

200

200V 100V

400

K = 2

Voltage Voltage RegulationRegulation

EI

Voltage Drop Due to R

Voltage Drop Due to XL

V

• Resistance• Inductance

Coils have both

Voltage Voltage RegulationRegulation

EI V

Lagging PF of 45

V less than E

Voltage Voltage RegulationRegulation

EI

V

Leading PF of 45

V More than than E

Voltage Voltage RegulationRegulation

100 x VNo Load – V Full Load

VFull Load

R% =

If PF = Unity

100 x I x (R x cos + XL x sin)

VFull Load

R% =

Transformer Basic Transformer Basic TestsTests• Open Circuit Test• Short Circuit Test• Oil Tests• Electrical Insulation• Polarity• Continuity

Open Circuit TestOpen Circuit TestUsed to determine Iron Losses

Supply = Rated Voltage

Open Circuit TestOpen Circuit Test

Wattmeter reading

V1

IMIo

Ie

Supply Voltage

Ammeter reading

Short Circuit TestShort Circuit TestUsed to determine Copper Losses

Supply Adjusted = Rated Secondary Current