Equivalent circuit of Induction Motor

This presentation describes the per-phase equivalent circuit of induction motor - Power flow diagram - Ratio of air gap power, rotor copper loss and mechanical power developed.

1. EQUIVALENT CIRCUIT OF THREE PHASE INDUCTION MOTOR
PER PHASE EQUIVALENT CIRCUIT OF STATORPER PHASE EQUIVALENT CIRCUIT OF ROTOR
To study & predict the performance of Induction Motor
ITS SIMILAR TO TRANSFORMER
That’s why IM called as ROTATING TRANSFORMER!
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2. PER PHASE EQUIVALENT CIRCUIT OF ROTOR
Slip rpm S* Ns= Ns-N
Rotor circuit
frequency
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parameters such as
reactance and EMF will be
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We Cant Combine Stator & rotor equivalent circuit directly!
Problem 1 : Stator & rotor circuit are operating @ different frequency
Problem 2 : Air-gap is between the stator and rotor
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3. To overcome the problem 1
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4. To overcome the problem 2
(Speaker
resistance
referred to the
primary side)
Air gap
Air gap
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5. PER PHASE TOTAL EQUIVALENT CIRCUIT OF IM REFERRED TO STATOR SIDE
Air gap
(a = S to R
turns ratio)
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6. The air-gap power associated
with the equivalent circuit is
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copper
loss
Pcu2
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Mechanical
Power
Pmech
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(1-S)
PowerFlowDiagramofIM
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Pcu2
Pmech
P electric
Pcore+ Pcu1

7. Ratio of Air-gap power , Rotor copper loss & Mechanical power developed
Pag: Pcu2: Pmech= 1 : S : (1-S)
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Important Note
By operating at low slip rotor copper loss can be minimized
& mechanical power can be increased or in other words
Efficiency of IM will increase

8. IMPORTANT POINTS TO REMEMBER IN TORQUE-SLIP CHARACTERISTICS
•TorqueisdirectlyproportionalinlowslipregionofIM
•TorqueisinverselyproportionalinhighslipregionofIM
•Lowslipregioniscalledstableregion
•MaximumtorqueobtainediscalledpullouttorqueinIM
•Theslip@whichthepullouttorqueoccursiscalledcriticalslip
•Criticalslip=R2/X2
•Byincreasingtheresistanceinrotoritispossibletoincreasethestartingtorque(Thisispossible
onlyinslipringIM!!).MaximumtorqueisirrespectivetoRotorresistance!

9. IMPORTANT POINTS TO REMEMBER IN EQUIVALENT CIRCUIT OF AN INDUCTION MOTOR
•EquivalentcircuitofIMisusedtostudyandpredicttheperformanceofIM
•Fromsolvingtheequivalentcircuitweunderstandthat,fromthetotalair-gappower,afractionof
“slippower”Sisdissipatedintheresistanceoftherotorcircuit(rotorcopperloss)
•Afractionof(1-S)isconvertedintomechanicalpower
•Soweunderstandthelowertheslip–higherthemechanicalpowerandlessertherotorcopper
lossorhigherefficiency.
•AllEquivalentcircuitparameters(E,I,R,X)canbefoundfromNoloadtestandBlockedrotortest
(Documentgiveninthedescription!)

10. INDUCTION MOTOR DRIVES