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# Principles of Special Motors

Different Types of Special Motors In Engineering

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### Principles of Special Motors

1. 1.  Principles of :  AC Series motors  Universal motor  Stepper motor  Shaded pole motor
2. 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 series dc motor. It is a varying-speed machine.  It has low speeds for large loads and high speeds for light loads.
3. 3.  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.
4. 4. MOTORS 5 Universal Motor
5. 5.  Series-connected ◦ Rotor and Stator are connected in series  Operates on either ac or dc MOTORS 6
6. 6. ECE 441 7
7. 7. ECE 441 8 Armature (Rotor) Field Winding Field (Stator)
8. 8. ECE 441 9 The Commutator Bar and Brushes are a switch that reverses the current in the armature coil as it rotates
9. 9. ECE 441 10 Force on conductor B is upwards, rotation is counter-clockwise (CCW) Flux “Bunching” +Positive Half-Cycle+
10. 10. ECE 441 11 Force on Conductor B is upwards, rotation is counter-clockwise (CCW) Flux “Bunching” -Negative Half- Cycle-
11. 11.  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
12. 12.  A special type of synchronous motor which is designed to rotate a specific number of degrees for every electric pulse received by its control unit.  It is a motor that can rotate in both directions, move in precise angular increments, sustain a holding torque at zero speed, and be controlled with digital circuits.  It moves in accurate angular increments known as steps, in response to the application of digital pulses to the electric drive circuit.  Step motors are either bipolar, requiring two power sources or uni polar requiring only one power source.
13. 13. 2 2 1 N S 1 S N Stators Rotor Cross Section of a Stepper Motor
14. 14. 2 2 1 1 S N S N NN S S 1 a b Winding number 1 2 a b Winding number 2 One step6 pole rotor
15. 15. The top electromagnet (1) is turned on, attracting the nearest teeth of a gear- shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from electromagnet 2 The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the nearest teeth slightly to the right. This results in a rotation of 3.6° in this example. Practical Stepper motor operation
16. 16. The bottom electromagnet (3) is energized; another 3.6° rotation occurs. The left electromagnet (4) is enabled, rotating again by 3.6°. When the top electromagnet (1) is again enabled, the teeth in the sprocket will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation in this example.