The document discusses AC series motors and universal motors. It provides the following key points: 1) A universal motor can operate on either AC or DC power sources. It has series-connected rotor and stator windings. 2) An AC series motor is electrically similar to a DC series motor but uses special construction materials to reduce losses from eddy currents. 3) Speed control of an AC series motor is similar to a DC series motor and can be achieved through armature resistance/reactance control, field flux control, or armature voltage control. Armature voltage control is commonly used for large motors.

1. Topic covered :
 AC Series motors
 Universal motor
 Phasor Diagram of a.c. Series Motor
 Speed control

2.  A series ac motor is the same electrically as a dc
series motor but construction differs slightly.
 Special metals, laminations, and windings are
used which reduce losses caused by eddy
currents, hysteresis, and high reactance.
 Dc power can be used to drive an ac series
motor efficiently, but the opposite is not true.
 The characteristics of a series ac motor are
similar to those of a dc series motor. It is a
varying-speed machine.
 It has low speeds for large loads and high
speeds for light loads.

4.  Motor that can be used with a single-
phase ac source as well as a dc source of
supply voltages are called universal
motor.
 The stator and rotor windings of the
motor are connected in series through
the rotor commutator.
 The universal motor is also known as an
AC series motor or an AC commutator
motor.

5. MOTORS 5
Universal Motor

6.  Series-connected
◦ Rotor and Stator are
connected in series
 Operates on either
ac or dc
MOTORS 6

7. ECE 441 7

8. ECE 441 8
Armature
(Rotor)
Field Winding
Field
(Stator)

9. ECE 441 9
The Commutator Bar and Brushes are a switch
that reverses the current in the armature coil as
it rotates

10. ECE 441 10
Force on conductor B is
upwards, rotation is
counter-clockwise (CCW)
Flux
“Bunching”
+Positive
Half-Cycle+

11. ECE 441 11
Force on Conductor B is
upwards, rotation is
counter-clockwise (CCW)
Flux
“Bunching”
Negative Half-Cycle

12.  How do you reverse the direction of rotation?
◦ Reverse the direction of the current in either the field or in
the armature, but not both!
 How do you control the speed of the motor?
◦ Reduce the voltage applied to the motor
 Use an autotransformer or SCR/Triac
 This reduces the armature current, reducing the torque,
reducing the speed
 Applications
◦ Portable power tools
◦ Small appliances
ECE 441 12

13. The compensating winding may be
short circuited on itself, in
which case the motor is said to be
inductively compensated

14. Series motor with inductively
compensated winding

15. Phasor Diagram of a.c. Series Motor
The schematic diagram and phasor diagram for the conductively
coupled single-phase ac series motor are shown in fig. below.
Schematic diagram of conductively
coupled ac series motor

18. Speed control of ac series motor
The method adopted for the speed control of
d.c series motor is also applicable to a.c series
motor .
1.Armature resistance or reactance control
2.Field flux control
3.Armature voltage control
Method 1 is used for small motors, for large
size motors method 3 is common.