Hysteresis MotorHysteresis Motor

ConstructionConstruction

Continuously revolving magnetic field is requiredContinuously revolving magnetic field is required

StatorStator Split phase hysteresis motorSplit phase hysteresis motor Shaded pole hysteresis motorShaded pole hysteresis motor

RotorRotor No windingNo winding Smooth cylinder of hard magnetic materials with very Smooth cylinder of hard magnetic materials with very

large hysteresis loop (chrome ,cobalt steel)large hysteresis loop (chrome ,cobalt steel)

--high resistivity to reduce eddy current losshigh resistivity to reduce eddy current loss

Construction..Construction..

OperationOperation

B lags inducing magnetizing force H.B lags inducing magnetizing force H.δδ – hysteresis angle – hysteresis angle

Depends on the nature of material and hysteresis loop Depends on the nature of material and hysteresis loop - not on rotor - not on rotor

speedspeed constant from standstill to Ns.constant from standstill to Ns.

Th Th αα stator mmf * rotor mmf * sin stator mmf * rotor mmf * sin δδ

Rotor to accelerate Th>TRotor to accelerate Th>TLL

At Slip s,At Slip s, Ph = sPhPh = sPh00 ;Ph=Hyst. loss;Ph=Hyst. loss

Th= (Ph/s)*(1/Th= (Ph/s)*(1/ωωss) =Ph) =Ph00/ / ωωss

Th- independent of slip and speedTh- independent of slip and speed

AdvantagesAdvantages

Constant torqueConstant torque it can synchronize any load inertia coupled to

its shaft which it can accelerate

Smooth rotorSmooth rotor quite operationquite operation No magnetic and mechanical vibrationNo magnetic and mechanical vibration

LimitationsLimitations

the output is about one-quarter that of an induction motor of the same dimension

Low EfficiencyLow Efficiency

Low Power factorLow Power factor

low torque and available in very small low torque and available in very small sizes sizes

ApplicationsApplications

Constant speed applications Constant speed applications Electric clock (gear train used)Electric clock (gear train used)

Air conditionerAir conditioner

Sound recording and sound producing Sound recording and sound producing instrumentsinstruments Tape recordersTape recorders Record playersRecord players