The document discusses the universal motor, which can operate on both AC and DC power supplies. It describes the universal motor's construction, which includes laminated magnetic fields to reduce losses. The motor also uses a compensating winding to improve power factor and commutation. The document explains that the universal motor works by reversing its magnetic pole orientation with each reversal of the AC current. Speed control methods for universal motors include phase angle and chopper control.

1. A.C Machines (2140906)
Active Learning Assignment presentation
On
“UNIVERSAL MOTOR ”
prepared by : Guided by:
Shah Urvish Prof. Hitesh T Manani
Electrical Engineering Department
Batch – B3
1
(160123109016)

2. Synopsis
 Basics of universal motor
 Characteristics
 Control aspects
 Equivalent circuit
 A closer look
 Check the direction of rotation
 Analysis
 References

3. BACSIC OF UNIVERSAL MOTOR
 The universal motor is special type of motor which is designed to operate on either dc or ac supply at
approximately the same speed and output. It is basically a series wound motor and hence it has high starting
torque and variable speed characteristics.
 A dc series motor suffers form the following drawbacks when operated on ac supply
i. Its efficiency will poor due to hysteresis and eddy current losses.
ii. Power factor of the motor is low due to inductive reactance of the field and armature winding
iii. The sparking at the brushes will be excessive.
 Therefore, some modification are necessary for the satisfactory operation of the universal motor on ac
supply

4. i. To reduce the hysteresis and eddy current losses, the field structure is laminated.
ii. Power factor is improved by reducing the reactance of armature and field winding. the reactance of the
filed winding is reduced by using small umber of turns of thick wire
iii. To reduce the effect of armature reactance and thereby improve the commutation and to reduce the
armature reactance a compensating winding is used.
 The construction of universal motor is similar to dc series motor. However the whole magnetic field
structure is laminated to reduce the eddy current and hysteresis losses the armature is of wound type
with commutator and brushes and similar to small dc motor.

5.  The series field winding is connected in series with the armature. In order to improve commutation and
hence reduce sparking high resistance brushes are used.

6. CONSTRUCTION
 Manufactured in two types
1:- concentrated – pole , non – compensated
2:- distributed – field compensated
concentrated – pole , non – compensated
 In case of large rating universal motors, a compensating winding is used for reducing the reactance and to improve
commutation this winding may be connected in series with armature or may be short-circuit in itself. The
compensated winding is placed in the slot at 900
(elect.) with the main field axis.
 for high power ratings compensated type universal motors are used whereas for low power rating uncompensated
motor are used.

7. OPERARION

8.  With input dc power the stator coil as permanent magnet like a dc motor & continues to rotate in the same
direction
 The current though the rotor also reverses the current thought the electromagnets
 Every pole the motor changes from north to south or from south to north
 With input ac power it reverses the pole and thus the direction of rotation is obtained
 Experiences no torque during current reversal but the average torque is sufficient to run the motor as if it were
connected to a dc power supply
 The starting torque of universal motor is determined by the current that flows through the armature

9. SERIES FIELD WINDING

10. EQUVIVALENT CIRCUIT OF UNIVARSAL MOTOR

11. A CLOSER LOOK
Field Winding Field
(Stator)
Armature
(Rotor)

12. CANCLUSION
2
D p a
p a
D a
T B I
B I
T I
µ
µ
µ
The direction of rotation (and Torque) is
independent of the polarity of the AC
source!
TD = Developed Torque
Bp = flux density due to current in field
Ia = armature current

13. CHARACTERISTICS

14.  Torque is inversely proportional to speed & directly proportional to the current
 More current flows at high speed torque increases as magnetic flux density also increase
 Low speed tends to cause magnetic saturation deteriorates the characteristic of the motor
 In domestic application electrical motor the ability to control its speed
 There are two control method are used
 1 phase angle control
 2 chopper control

15. PHASE ANGAL CONTROL

16.  Phase angel control Is simple and cost-effective solution
 The speed of universal motor is controlled by using a triac
 The gate of the triac can be controlled directly by the out put ports of a microcontroller
 The whole circuitry Is usually connected
 CHOPPER CONTROL
 Pwm control
 The ac voltage from the mains is rectified and then switched at a high frequency by a power MOSFET or an IGBT
 Lower current ripple which reduces the harmonics
 Reduces the copper and iron losses…….

17. REFERENCES
 CHARLES I HUBER “ELECTRICAL MACHINES”
 B.L.THERAJA, A.K THERAJA “A TEXBOOK OF ELECTRICAL MACHINES”
 A TEXBOOK OF AC MACHINE “J.G.JAMNANI”