Unit 5 series motor (universal)motors
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Transcript of Unit 5 series motor (universal)motors
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.
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 commutatormotor.
ECE 441 9
The Commutator Bar and Brushes are a switch that reverses the current in the armature coil as it rotates
ECE 441 10
Force on conductor B is upwards, rotation is counter-clockwise (CCW)
Flux “Bunching”
+Positive Half-Cycle+
ECE 441 11
Force on Conductor B is upwards, rotation is counter-clockwise (CCW)
Flux “Bunching”
Negative Half-Cycle
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
The compensating winding may beshort circuited on itself, inwhich case the motor is said to beinductively compensated
Phasor Diagram of a.c. Series MotorThe schematic diagram and phasor diagram for the conductivelycoupled single-phase ac series motor are shown in fig. below.
Schematic diagram of conductively coupled ac series motor
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 control2.Field flux control3.Armature voltage control
Method 1 is used for small motors, for large size motors method 3 is common.