What will happen when we give more voltage but same power into an AC motor ?Can we calculate the RPM and TORQUE that the 1Kw AC motor will produce when we give it ( input ) :1. 200 VAC 5.0 Ampere2. 400 VAC 2.5 AmpereWhich input will make the faster RPM ?Which input will make the stronger TORQUE ?
Won't happen. If you double the voltage into a motor, you will double (at least) the current. And the speed will go up, as will the torque. Unless this is about two different motors, but you don't state that, you specifically only mention one motor.
Also, the mechanical design of the motor is probably not designed for such speed. Vibration and put on may reduce the life of the motor with out adequate load to gradual it down. The motor may begin to screech from such vibration and oscillation.
The most commonly used AC motors are induction or synchronous motors. Their speed is determined by the frequency of the supply and not by the voltage. If 200 VAC is the motor's rated voltage, then doubling the voltage to 400 would theoretically mean that the current needed to supply the load torque is reduced to half. So (in an elementary consideration) nothing would happen to speed but current would be halved and power would be the same. it is anyway the load which basically determines the power required - i.e. you don't give the power in, it is the load which draws it from the source via the motor. In practice however the above would not work. The doubled voltage would need to double the flux in the motor to generate a back-emf. It could not do this because the magnetic circuit would run severely into saturation. You would get some reduction in the current needed to supply the load but a large increase in magnetising current. Windings and core would overheat quite fast and fairly soon you'd burn out the motor due to insulation failure. The insulation design would be based on 200V and a certain temperature limit (say 130 C). At double voltage and under overheating it would not hold out long. If it held long enough, then the core (at high saturation) would eventually burn out.
