Demonstrative Video
Contents
Introduction to Single-Phase Motors, Construction and Qualitative Examination of \(1-\phi\) Induction Motors
Principle of Operation - Double Revolving Field Theory
Torque Produced in \(1-\phi\) Induction Motors
Types of \(1-\phi\) Induction Motors
Equivalent Circuit of \(1-\phi\) Induction Motors
Single-Phase Motors
Operate from a single-phase supply
Most commonly used electric motors in domestic and industrial applications
Small size motors of fractional kW ratings
Domestic applications - Fans, hair dryers, washing machines, vacuum cleaners, mixers, refrigerators, food-processors etc.
Industries - compressors, pumps, small power tools, office machinery, blowers, small farming equipments etc.
Motor manufacturing industry developed different types of motors designs to meet the user needs.
Classification of Single-Phase Motors
Classified based on their construction and methods of starting
Broadly classified into 3 main types:
Induction motors
Synchronous motors
Commutator motors
Single-Phase Induction Motors
Similar to three-phase IM, except
stator is provided with single-phase winding
auxiliary or starting winding for starting purpose
Distributed stator winding and a squirrel-cage rotor
Single phase supply \(\Rightarrow\) stator winding \(\Rightarrow\) alternating flux \(\Rightarrow\) alternates along one space axis only
Not synchronously rotating flux as developed by two or three phase stator winding supply
Alternating flux cannot rotate a stationary squirrel-cage rotor that is only possible with rotating flux
Single-phase IM are not self-starting
If initially the rotor is rotated by hand or using a small motor, in either direction, torque will produce and accelerate to its final speed
Possible only when the applied torque is not too high
Construction and Qualitative Examination
Laminated iron core with two windings arranged perpendicularly
Two windings : main and auxiliary
Stator winding is distributed in slots for a sinusoidal mmf space distribution.
Single-phase winding generates equal forward and backward rotating mmf waves.
Due to symmetry, the motor exhibits no starting torque at standstill, producing equal torque in both directions.
An auxiliary winding resolves this, creating a net torque in the intended direction for motor initiation and sustained operation.
“single-phase” motors are truly two-phase machines
squirrel cage rotor, which has a laminated iron core with slots
Squirrel cage rotor:
Aluminium bars are molded on the slots and short-circuited at both ends with a ring.