AC Motors are of various types and have different opera […]
AC Motors are of various types and have different operating principal.
Primarily we can categories AC motors as:
3 Phase Induction motor
Single phase AC motor
Two Phase servo motor
There are also other types of AC motors and those cases can also be discussed but from Industry point of view above mentioned motors are mainly used.
3 phase induction motor are mostly used in industry as they are self starting in nature and required low maintenance as compared to DC motor. DC motor suffers from frequent maintenance of Brushes and slip rings and sparking problem in commutator section .
So lets discuss what would happen if DC supply is given to 3 phase induction motor.
In 3 phase induction motor starting current varies from 6 to 8 times of full load current and it starts decreasing as motor speed increases. At the time of starting Motor takes high current due to absence of Back emf . As motor develops back emf, current reduces. 3 Phase Induction motor are self starting in nature as 3 phases are 120 degree apart both electrically & mechanically (winding are physically placed 120 degree apart). This results into Rotating magnetic field.
Now if DC is given to 3 Phase induction motor then very high current will flow. Magnitude of this current will be higher than starting current which develops when 3 phase supply is given to induction motor as in case of DC there will be Zero inductive reactance offered to current. and it will be only limited by resistance of winding. DC supply don`t produce rotating magnetic field hence such very high current will flow which will leads to burning of winding.
Now lets talk about single phase induction motor.
Single phase induction motor is not self starting in nature . Single phase induction are of various types. common types include shaded pole and split phase motor.
In shaded pole motor, small single-turn copper "shading coils" create the moving magnetic field. In split phase motor we have different starting method like resistance starting, capacitance start , capacitor start and capacitor run motor. Split phase motor have two windings main winding and startup winding. Our ultimate goal is to provide phase difference between the current which is flowing through two windings. By providing phase difference between two windings current we can produce rotating magnetic field same is done by above mentioned starting methods.
So if we apply single phase induction through dc then it will not start and high current will flow as inductive reactance X= 2*pi*f*l will be zero as frequency of DC is zero.
Now lets talk Servo motors:
Construction and operating principle of Ac and DC servo motors are different so AC servo motor will not work on DC.
Now Lets talk about universal motor:
Universal motor can work on both AC and DC. They are like DC series motor with slight modification and often referred to as an AC series motors.