1. Fractional Horse Power (FHP) Motor
Ms. A. A. Lande E & TC Dept

2. Course outcome Use FHP motors for diversified applications.
Ms. A. A. Lande E & TC Dept

3. SINGLE PHASE INDUCTION MOTOR
Ms. A. A. Lande E & TC Dept

4. Single Phase Induction Motor
It is more convenient to use single phase ac motors instead of d.c. motors. Practically single phase a.c. motors are used in most of the applications.
Construction:
A single phase induction motor has two main parts namely stator (the one which is stationary) and rotor (the one which is rotating).
The stator winding is connected across a single phase a.c. supply. The ac supply produces a rotating magnetic field in the airgap between the stator and rotor.
Ms. A. A. Lande E & TC Dept

5. The field rotates at a speed called synchronous speed and it is denoted by Ns.
The induction motor actually rotates at a speed which is slightly less than the synchronous speed.
As shown in fig.(1), the rotor consists of copper or aluminium bars which are permanently short circuited at both the ends using the conducting rings called end rings.
Ms. A. A. Lande E & TC Dept

6. Fig.(1): construction of a squirrel cage rotor
Ms. A. A. Lande E & TC Dept

7. Principle of operation:
A single phase ac supply is connected to the stator winding. This forces an alternating current through the stator winding. This current produces an alternating flux in the air gap between stator and rotor.
The alternating flux passes over the rotor conductors and induces an emf into it due to transformer action.
Due to this induced voltage, a current starts flowing through the rotor conductors. This current will then produces its own flux called as rotor flux
The main flux produced by the stator winding interacts with the rotor flux to produce the torque.
Ms. A. A. Lande E & TC Dept

8. Types of single phase induction motor:
The rotor flux gets produced due to the principle of induction hence it is called as induction motor.
But single phase induction motor are not self starting, like DC motors.
Types of single phase induction motor:
Some of the methods used to make an induction motor self starting. Based on these techniques, the single phase induction motor are classified as follows:
Split phase induction motor
Capacitor start induction motor
Capacitor start, capacitor run induction motor
Shaded pole induction motor.
Ms. A. A. Lande E & TC Dept

9. Resistive Split Phase Induction Motor
The construction of split phase induction motor is as shown in fig.(1).
This motor consists of two winding namely the main winding and the auxillary (starting) winding which are displaced from each other by an angle 900.
The main winding is highly inductive while starting winding is resistive.
Ms. A. A. Lande E & TC Dept

10. Ms. A. A. Lande E & TC Dept

11. Principle of operation:
The current flowing through the main winding (Im) lags behind the V by 900 since the main winding is highly inductive.
The current flowing through the starting winding (Ist) is almost in phase with the supply voltage V as this winding is resistive.
The fluxes produced due to these currents will be placed 900 with respect each other. And the resultant of these fluxes will be a rotating magnetic field. Due to the RMF a non-zero starting torque acting in one direction will be produced.
The centrifugal switch connected in series with the starting winding gets automatically open circuited when the motor speed reaches about 70% to 80% of the synchronous speed.
After that the motor rotate only on the main winding. Thus under the running condition the auxillary winding remains out of the circuit.
Ms. A. A. Lande E & TC Dept

12. Reversal of rotation of motor:
The direction of rotation of split phase motor can be reversed by reversing the terminals of either main winding or starting winding. The direction of rotation changes due to the reversal in direction of rotating magnetic field.
Applications:
The starting torque of this motor is poor. So it is used in following applications:
Fans and blowers
Washing machines
Centrifugal pumps
Ms. A. A. Lande E & TC Dept

13. Capacitor Split Phase Motor
These motors are commonly called as capacitor motors.
This type of motor is similar in construction to resistance split phase type, single phase induction motor, except that the resistance in series with the auxiliary winding is replaced by a capacitor.
Following are the main types of the capacitor motor:
Capacitor start induction run motor
Capacitor start capacitor run motor
Permanent capacitor motors

14. Capacitor Start Induction Run Motor
The construction of this motor is as shown in fig.(1a).
As shown in fig, the starting winding connected in series with the capacitor draws a leading current while the main winding continues to draw the lagging current.
Due to this the fluxes produce a rotating magnetic field which result in the rotation of the motor.
The current (Im) through the main winding will lag behind the source voltage as the main winding is inductive. But the current (Ist) through the starting winding leads the supply voltage by some angle due to the presence of capacitor. Hence the angle between the fluxes produced by Im and Ist will be large as shown in fig.(1b).
Ms. A. A. Lande E & TC Dept

15. Due to this large angle, the starting torque produced by the capacitor start motor produces a larger starting torque as compared to that produced by the split phase induction motor.
As soon as the speed reaches 75% to 80% of the maximum speed, the centrifugal switch is automatically open circuited and the starting winding alongwith the capacitor goes out of the circuit.
The induction motor will then be running only on the flux produced by the main winding.
Ms. A. A. Lande E & TC Dept

16. Fig.(1): Capacitor Start Motor
Ms. A. A. Lande E & TC Dept

17. Capacitor Start Capacitor Run Motor
The Capacitor Start Capacitor Run Motor has a cage rotor, and its stator has two windings known as Main and Auxiliary Windings. The two windings are displaced 90 degrees in space.
There are two capacitors in this method one is used at the time of the starting and is known as starting capacitor. The other one is used for continuous running of the motor and is known as RUN capacitor. So this motor is named as Capacitor Start Capacitor Run Motor. This motor is also known as Two Value Capacitor Motor.
Connection diagram of the Two valve Capacitor Motor is shown below.
Ms. A. A. Lande E & TC Dept

18. Fig.(2): Capacitor Start Capacitor Run Motor
Ms. A. A. Lande E & TC Dept

19. There are two capacitors in this motor represented by CS and CR
There are two capacitors in this motor represented by CS and CR. At the starting, the two capacitors are connected in parallel.
As the motor reaches the 75 to 80% of synchronous speed, the starting capacitor Cs is disconnected from the circuit by a centrifugal switch Sc. The capacitor CR is connected permanently in the circuit and thus it is known as RUN Capacitor. 

20. Permanent Capacitor Motor
Fig. shows the construction of Permanent capacitor motor. It shows that there is no centrifugal switch, hence the capacitor will not go out of the circuit at all.
The main advantage of these motors is the high starting torque that they can produce. The starting torque can be as high as 300 to 400% of the full load torque.

21. Fig.(2): Capacitor Start Capacitor Run Motor
Ms. A. A. Lande E & TC Dept

22. Reversal of rotation of motor:
Reversal of direction of rotation can be obtained in all types of capacitor split phase motors by changing the terminal connections of one of the windings.

23. Fans and air conditioners Refrigerators
Applications:
Due to high starting torque, the capacitor start or capacitor start capacitor run motors are used in the following applications:
Grinders
Compressors
Conveyers
Fans and air conditioners
Refrigerators
Ms. A. A. Lande E & TC Dept

24. Shaded Pole Induction Motor
Fig.(1), shows the construction of a shaded pole induction motor.
Every stator pole is divided into two parts by keeping a small slit in the pole face and the smaller portion is covered with a thick short circuited copper wire called shading band.
When stator winding carries current, the main pole produces a flux øm.
This flux links with the shading band and this band acts as a shorted secondary winding, stator winding being its primary. Circulating currents induced in the band produced another flux øs.
Ms. A. A. Lande E & TC Dept

25. At instant t1 current is increasing. The induced emf tries to oppose it. Thus flux øs opposes it and resultant flux is in unshaded part.
At instant t2 current is almost constant. Induced emf and flux øs are negligible. Resultant flux is almost at the center of the pole. Thus it has shifted its position.
At instant t3 current is decreasing. The induced current and flux øs try to oppose this decrease. Resultant flux lies in shaded part.
This action continues and the resultant field rotates from unshaded part to shaded part. Hence rotor also rotates in the same direction.
Such motor develops low starting torque and it has a low power factor..
Ms. A. A. Lande E & TC Dept

26. Reversal of rotation of motor:
The direction of rotation cannot be reversed unless position of shaded ring is changed from one part of pole to another part.
Applications:
Table fans
Blowers
Washing machines
refrigerators
Ms. A. A. Lande E & TC Dept

27. Fig.(1): shaded pole induction motor
Ms. A. A. Lande E & TC Dept

28. Universal Motor
The motors which can be operated satisfactorily on ac as well dc supply is universal motor.
Types of universal motors:
Uncompensated type universal motor
Compensated universal motor
Windings:
There are three windings used namely armature, main field and compensating winding.
Out of which compensating winding is used only for the compensated universal motor.
All the windings are connected in series with each other since this is basically a series motor.
Ms. A. A. Lande E & TC Dept

29. 1. Uncompensated universal motor:
The operating principle is same as that of dc series motor.
Field winding produces flux. It is stationary winding. Armature is a rotary winding.
These motors produces high starting torque but their speed decreases with increase in load. Their speed regulation is not very good.
These motors having low capacity. Normally it is designed for two pole structure.
Ms. A. A. Lande E & TC Dept

30. Fig.(1): Uncompensated Universal Motor
Ms. A. A. Lande E & TC Dept

31. 2. Compensated universal motor:
In this motor, main winding and compensating winding are distributed over entire stator.
Fig.(2) shows the schematic diagram of compensated universal motor.
This type of motor is better for higher speeds.
These motors are more expensive due to complicated construction. Hence they are preferred for higher capacity loads.
Ms. A. A. Lande E & TC Dept

32. Fig.(2):compensated Universal Motor
Ms. A. A. Lande E & TC Dept

33. Small drilling machines Vaccum cleaners Sewing machine Hair driers
Reversal of rotation:
For universal motors, reversal can be achieved by reversing the connections to either the field or the armature winding.
Applications:
Washing machine
Mixers and grinders
Food processors
Small drilling machines
Vaccum cleaners
Sewing machine
Hair driers
Electric shavers
Ms. A. A. Lande E & TC Dept

34. Stepper Motor
A stepper motor is an electrical motor which converts electrical input in the form of series of pulses into discrete angular movements, commonly called as steps.
Types of stepper motors:
Variable reluctance motor
Permanent magnet motors
Hybrid motors

35. Variable-Reluctance Motor
This is most basic type of stepper motors.
The stator usually made of laminated silicon steel has six salient poles or teeth and is wound for three phases located 1200 apart.
The two coils wound around diametrically opposite poles and connected in series form a stator phase.
The three phases thus formed are energised from a dc source in a specified sequence through an electronic switching device.
Rotor is also normally made of silicon steel laminations and has four salient poles without any exciting winding.

36. Fig.(1): Construction Of Stepper Motor
Ms. A. A. Lande E & TC Dept

37. When poles A & A’ are excited by closing Switch Sw1 the rotor teeth nearest to these align to have minimum reluctance between the A-A’ stator poles. (poles A and A’ are opposite in nature).
Next if poles B & B’ are excited by opening Sw1 and closing Switch Sw2 then the rotor moves anticlockwise angularly by 30o to align with these poles.
Thus if we provide 12 such voltage pulses sequentially by proper opening and closing of switches we get one full rotation in 12 equal steps.
If the sequence of application of these pulses is A/A’ – C/C’ – B/B’ then we obtain clockwise rotation.
By changing the no of rotor teeth proportionally we can have smaller angular steps.
Ms. A. A. Lande E & TC Dept

38. Permanent-Magnet Stepper Motor
This type of stepper motor employs a permanent magnet in its rotor construction, it is called a permanent magnet stepper motor.
As shown in fig., the stator has four poles around which exciting coils are wound. The rotor is of cylindrical type and made of ferrite material which is permanently magnetized.
If the phases are excited in sequence A-B-C-D, due to electromagnetic torque developed by the interaction between the magnetic field set up by the exciting winding and the permanent magnet, the rotor will be driven in clockwise direction. In this case, the step angle will be 900.

40. Applications of stepper motor:
The stepper motors are very widely used in computer peripherals such as serial printers, floppy disc drives etc.
It is also used in numerical controls of machine tools and workpieces.
Other applications include process control systems, facsimiles, space crafts, watches, semi automatic wiring machines for printed circuit boards.