Electrical Machines LSEGG216A 9080V

Transformer Operation Week 4

Transformer Operation V+ CIVIL VoltageCurrent Magnetic Flux

Transformer Operation Applied Voltage Induced Voltage Induced Voltage in Secondary Resultant Current V1V1 V’ 1 V’ 2 IMIM

Induced Voltage Φ max =Maximum instantaneous flux F = Frequency N = Number of turns B max = Maximum permissible flux density in Wb A = CSA of core in m 2

Transformer Operation V1V1 IMIM IeIe IoIo I e = Iron loss current I o = No load current

V1V1 V’ 1 V’ 2 IoIo I’ 2 I’ 1 I1I1

Transformer Operation V1V1 V’ 1 V’ 2 IoIo I’ 2 I’ 1 I1I1

Transformation Ratio Magnetic flux is common coils Therefore the voltage can be varied by changing the number of turns

V1=V1=N1N1 N2N2 V2=V2= = k = Transformation Ratio

Transformation Ratio V 1 x I 1 N1N1 N2N2 =V 2 x I 2 = I1I1 I2I2

Transformation Ratio V 1 x I 1 VA V 2 x I 2 kVA Power InPower Out

Transformation Ratio V 1 x I 1 V 2 x I  200V100V 400  K = 2

Voltage Regulation E I Voltage Drop Due to R Voltage Drop Due to X L V Resistance Inductance Coils have both

Voltage Regulation E I V Lagging PF of 45  V less than E

E I V Leading PF of 45  V More than than E

100 x V No Load – V Full Load V Full Load R% = If PF = Unity 100 x I x (R x cos  + X L x sin  ) V Full Load R% =

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

Open Circuit Test Used to determine Iron Losses Supply = Rated Voltage

Wattmeter reading V1V1 IMIM IoIo IeIe Supply Voltage Ammeter reading

Short Circuit Test Used to determine Copper Losses Supply Adjusted = Rated Secondary Current