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MAYURBHANJ SCHOOL OF ENGINEERING

LAXMIPOSI,BARIPADA

757107

DEPARTMENT OF ELECTRICAL ENGINEERING

5^TH SEM

SUBJECT: (EC-II)

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..COMMUTATOR MOTOR..

PREPARED BY

DR.MRUTYUNJAY DAS

AY: 2021 – 22

�������AC Series Commutator Motors

Characteristics:

1. It can be used with either dc or ac supply.
2. It provides high starting torque.
3. It can operate at high speeds.
4. It is used in kitchen equipment, drills, mixers, and vacuum cleaners.
5. The stator and rotor are made of laminated steel to reduce core losses.
6. The types of ac series motors are: universal motors - repulsion motors.

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Universal motors

DC Excitation

Developed torque :

If magnetic linearity is assumed, then::

E.M.F. :

AC Excitation

Let :

The back emf is :

The rms value of the back emf is :

Torque :

Note that: the instantaneous torque varies at twice the supply frequency, and this fluctuating torque makes the motor operation noisy.

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The average torque developed can be expressed as:

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If magnetic linearity is assumed, then:

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The electromagnetic (or mechanical) power developed is:

P_mech = E_a . I_a

The voltage equation for ac excitation is:

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DC versus AC Excitation:

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For the same current:

It can be concluded from the above equation that for the same terminal voltage and armature current (i.e., same torque) the speed will be lower for ac excitation.

Disadvantages of ac operation of the universal motor:

a) The motor produces pulsating torque.

b) It has poor power factor due to the reactance voltage drop.

c) It has lower speed due to the reactance voltage drop.

How to reduce the effect of armature reaction?

1. Adding compensating winding in series with the armature ( conductively compensated).
2. Adding short circuited compensating winding (inductively compensated).

Compensated universal motor

Inductive compensation of the universal motor

DC operation:

E_a| _dc = 120 - 0.6 x 20 = 108 v

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AC excitation:

THANK YOU