*SPECIAL MOTOR( SINGLE PHASE INDUCTION MOTOR )Universiti Kuala Lumpur Malaysia France InstituteFEB 24083 Electrical MachinesMOHD YUSOFF MOHD YUNUS

* More single phase ac induction

motors use than total of all the other types. Least expensive Lowest maintenance

More commonly used, where portable or mobile equipment is required. Floor polishing equipment, cement mixer, pressure washers,

portable conveyor, etc. Widely used due to economics, practicality and electrical safety.

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*Basic Principles

The stator field in the single phase motor does not rotate.Voltage is induced in the rotor will result of magnetic induction.Thus, magnetic field is produced around the rotor.This field will always be in opposition to the stator field.The interaction between the rotor and stator fields will not produce rotation.

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STARTING SINGLE PHASE INDUCTION MOTOR

These starting technique differ in cost and in the amount of starting torque produced.

The three major starting technique are :

1.Split phase winding 2.Capacitor type winding 3. Shaded stator poles

* consists of a main stator winding ( M ) and auxiliary winding ( A ). Aux. winding is designed to be switched out of the circuit at some speed by

centrifugal switch. Aux. winding have a higher resistance / reactance ratio than the main winding. Current in Aux. winding leads the current in the main winding.

Split phase winding

*Capacitor-Start Motors ( CSIR )

With the capacitor in the circuit, starting current now leads the line voltage

rather than lagging as does the main winding. Start winding containing slightly more turns in its coils than the main

winding. New resultis a time phase shift closer to 90 degrees than with the split

phase motor. A stronger rotating field is therefore created and starting torque is higher than with the split phase design.

* A centrifugal switch and mechanism ( or relay ) must be used to protect

the start winding and capacitor from overheating.

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*Permanently Split Capacitor Motors ( PSC )

Windings are arranged like split phase and capacitor start designs. Capacitor capable of running continuously replaces the intermittent

duty capacitor of the capacitor start motor and the centrifugal switch of both the split phase and capacitor-start motors. Current lags the line voltage. Start winding and capacitor remain in the circuit at all times. Produces an approximation of two phase operation at the rated load point. This result better efficiency, better power factor.

* Different starting and running characteristic can be achieved by

varying the rotor resistance. In addition, by adding extra main winding in series with the original main

windings, PSC motors can be designed to operate at different speeds. For full load torque, less breakdown torque and therefore a smaller motor

is required with the other previously discussed designs.

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*Capacitor Start-Capacitor Run Motors ( CSCR )

Have a run capacitor and an auxiliary winding permanently connected

in parallel with the main winding. in addition, a starting capacitor and a centrifugal switch are also in parallel

with the run capacitor. The switch disconnects as the motor accelerates. CSCR utilizes the same winding as the permanently split capacitor when

running a full load speed and the same winding as a capacitor-start motor during startup.

* The advantage of CSCR is derived from start winding and run capacitor

remain in the circuit at all times. ( similar to PSC ). and produce an approximation of two phase operation at the rated load

point, plus with an additional capacitor in series with the start winding circuit ( similar to Capacitor-start motor ), The starting current leads the line voltage, rather than lagging as does

the main winding. This will result increasing starting torque. CSCR feature a low running current due to an improved power factor

caused by the run capacitor. This results better efficiency, better power factor, increasing starting

torque. CSCR is a combination of the Capacitor-start and PSC. The best of the single phase motor.

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*Analysis of Equivalent circuit

*Where :

Rs = stator windingRr= rotor winding Xm= magnetizing reactanceXL= leakage reactanceIm= magnetizing currentIs= actual stator currentIs= effective stator current ( Is Im )s= SlipEaf= forward emfEab= backward emf

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Calculation of forward , backward impedance and total impedance

Calculation input current ( stator current ) and power factor

*Calculation input power and air gap powerCalculation of Mechanical power, output power and efficiency

*Calculation of generated torque and output ( shaft ) torque

*Example :

A single phase induction motor has the following data :

1 Hp, two pole, 240 V, 50 Hz.Stator winding, Rs = 1.6 Rotor winding ( referred to stator ), Rr = 6.02 Magnetizing reactance, Xm = 63.2 Leakage reactance, XL = 8.68

Calculate the shaft torque and efficiency when the motor is operatingat a speed of 2800 r/min with rotational losses, Pw = 70 W

*Solution

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*Exercise:

A single phase induction motor has the following data :

1 Hp, two pole, 110 V, 50 Hz.Stator winding, Rs = 1.52 Stator inductance, Xs = 2.1 Rotor winding ( referred to stator ), Rr = 3.13 Magnetizing reactance, Xm = 58.2 Leakage reactance, XL = 1.56

When the motor is operating at a slip of 0.05 with rotational losses, Pw = 35 W. Determine :-

Zf, Zb and Is.Pag,( f ), Pag, ( b ) and Pag.Pm, Po and Efficiency.