What happens if we give mechanical input to induction motor?
Answers
Explanation:
AC supply will flow supply-frequency (f) currents in rotor winding. This will establish a rotating magnetic field(RMF) at synchronous speed (Ns) around the rotor. This RMF will induce emf in the stator winding and slip-frequency(s.f) currents flow in stator windings.
Thus, stator will also have its own field around it which is moving at slip-speed (s.Ns). The interaction of rotor and stator fields will induce a torque which tries to rotate the stator. Since the stator cannot move, the rotor will start moving in opposite direction to RMF with speed (Nr). So net speed of rotor field becomes (Ns+(−Nr)) which must match with stator field speed (s.Ns) for motoring action to occur.
Ns+(−Nr)=s.Ns
Ns−s.Ns=Nr
Nr=Ns(1−s)
which is a familiar equation for induction motors. When operated in this fashion, machine is called a rotor-fed induction motor in contrast to the conventional stator-fed induction motor. Another name for this machine is inverted induction motor.
You're probably wondering why rotor must rotate in opposite direction. This is because the rotor movement will be such that effect(induced emf/current in stator) opposes its cause(relative speed with rotor field). That is to say, the relative speed must be reduced just like in a stator-fed induction motor.
Explanation:
the induction motor will rotete