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Single phase AC motors performs great variety of useful services at home ,office,farm,factory and in business establishments.single phase AC motors are generally manufactured at fractional HP below 1 HP for economical reasons Single phase motors are also manufactured in the range of 1.5,2,3 HP as a special requirement. CONSTRUCTION OF SINGLE PHASE INDUCTION MOTOR 1)Stator: It is the stationery part of the motor . it has three main parts (i) outer frame (ii) stator core (iii) stator winding (i)Outer frame: It is the outer body of the motor. its function is to support stator core and to protect inner parts of the machine.Usually it is made of cast iron.to place the motor on the foundation,feet are provided in the outer frame as shown in figure. (ii)Stator core: The stator core is to carry the alternating magnetic field which produces hysteresis and eddy current losses.To minimise these losses high grade silicon steel stampings are used to build core. the stampings are assembled under hydraulic pressure and are keyed to the outer frame.The stampings are insulated from each other by a thin varnish layer. the thickness of the stamping are usually varies from 0.3 to 0.5 mm. slots are punched on the inner periphery of the stampings to accommodate stator winding. (iii)Stator winding: the stator core carries a single phase winding which is usually supplied from a single phase AC supply system. The terminal of the winding are connected in the terminal box of the machine.the stator of the motor is wound for definite number of the poles, as per the need of speed. 2)Rotor: It is the rotating part of the motor.A squirrel cage rotor is used in single phase induction motors. It consists of laminated cylindrical core of some high quality magnetic material. Semi closed circular slots are punched at the outer periphery.Aluminium bar conductors are placed in these slots and short circuited at each end by aluminium rings, called short circuiting rings as shown in figure.thus the rotor is permanently short circuited. The rotor slots are usually not parallel to the shaft but are skewed. skewing of the rotor is following advantages. (i) It reduces humming thus ensure quiet running of the motor. (ii) It results in a smoother torque curves for different positions of the motor. (iii) It reduces the magnetic locking of the stator and rotor. (iv) It increase the rotor resistance due to the increase length of the rotor bar conductor. TYPES OF SINGLE PHASE MOTORS Single phase motors are mostly divided into two categories. 1.Single Phase Induction motors 2.Single phase Commutator type motors Further this type of motors are classified into several types as follows SINGLE PHASE INDUCTION MOTORS (i) Split phase motors (ii) Capacitor start induction motors (iii) Capacitor start capacitor run motors (iv) Shaded pole motors SINGLE PHASE COMMUTATOR TYPE MOTOR (i) Repulsion motors 1) Repulsion start induction run motor 2) Repulsion induction motor (ii) AC series motor (Universal motors) SYNCHRONOUS MOTORS (i) Reluctance motor (ii) Hysteresis motor DOUBLE FIELD THEORY OF SINGLE PHASE MOTORS Consider two magnetic field represented by OA and OB of equal magnitude revolving in opposite directions as shown above fig. The resultant of two magnetic fields of equal magnitude rotating in opposite direction is alternating. therefore an alternating current can be consider as having two components which are all of equal in magnitude and in opposite directions. From the above it is clear that when a single phase AC current is supplied to stator..the field produced is in alternating nature which can be divided into two components which are of equal in magnitude and one revolving in clockwise and other in counter clockwise directions. If we put normal squirrel cage rotor is kept in such field equal forces in opposite directions..and this makes rotor only vibrate and there will be no rotation. But if we will give small jerk in any direction in this condition ,it will go on revolving and develop torque in that particular one direction ..Single phase motors have only one winding and it is self stating motor. to make it self starting any one of the following method is adopted. (i) by splitting in phase (called split phase motor) (ii) by shading the poles(Called Shaded pole motor) PRINCIPLE OF SPLIT PHASE INDUCTION MOTOR The basic principle of operation of a split phase induction motor is similar to that of a poly-phase induction motor.the main difference is that the single phase motor does not produce a rotating magnetic field but produces only a pulsating field. Hence to produce the rotating magnetic field for self starting.phase splitting to be done to make the motor to work as at two phase motor for starting. WORKING OF SPLIT PHASE MOTOR In split phase motor has two windings named as main winding and starting winding are provided.at the time of the starting , both the main and starting windings should be connected across the supply to produce the rotating magnetic field. The rotor is of a squirrel cage type and the revolving magnetic field sweeps part the stationery rotor, inducing emf in the rotor . As the rotor bars are short circuited, a current flows through them producing a magnetic field. This magnetic field opposes the revolving magnetic field and will combine with the main field to produce a revolving field.by this action, the rotor starts revolving in the same direction of the rotating magnetic field as in the case of a squirrel cage induction motor. Hence, once the rotor starts rotating, the starting winding can be disconnected from the supply by some mechanical means as the rotor and stator fields from a revolving magnetic field. there are several types of split phase motors are available. (i) Resistance start induction run motor (ii) Capacitor start induction run motor (iii) Capacitor start capacitor run motor (iv) Shaded pole motor