Unit 5 series motor (universal)motors

series motor (universal)motors

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

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 .  AC SERIES MOTOR

3. SPEED –TORQUE CHARACTERISTICS OF AC AND DC SERIES MOTORS

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. Ac series motor (UNIVERSAL MOTOR)

5. MOTORS 5 Universal Motor

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

7. ECE 441 7 Equivalent Circuit

8. ECE 441 8 A Closer Look 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 Check the Direction of Rotation Force on conductor B is upwards, rotation is counter-clockwise (CCW) Flux “Bunching” +Positive Half-Cycle+

11. ECE 441 11 Opposite Half-Cycle 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 Other Considerations

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

16. 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.