There would be no induced voltage in the rotor and no rotor current. If rotor of an induction motor was rotating at synchronous speed, the rotor bars would be stationary relative to the stator magnetic field. The synchronous speed can never be reached with an induction motor. MG 1-2016, Motors and Generators, 2016).Īt no load, the rotor of an induction motor would rotate at near synchronous speed.
Torque in pounds at a foot radius (lb ft) is equal to the horsepower times 5252 divided by the full speed in rounds per minute ( NEMA Standards Publication No. It is the torque necessary to produce the motor rated horse power at full speed. The full load torque is the steady-state torque developed during operation. The breakdown torque is the maximum torque that the motor is capable of developing. The pull up torque is the minimum torque developed by the motor as it accelerates from standstill to the speed at which breakdown torque occurs. This torque is sometimes also referred to as the starting torque. The locked rotor torque is the torque developed by the motor at standstill. Typical induction motor torque-speed curve. The total rotational losses of a motor are often considered to be constant with changing speed, since the component losses change in opposite directions with a change in speed.įig.
Therefore, these three categories of losses are sometimes lumped together and called rotational losses. On the other hand, the higher the speed of the motor (up to n s), the lower its core losses. The higher the speed of an induction motor, the higher the friction, windage, and stray losses. The synchronous speed is shown as an angular synchronous speed ω s and the rotor speed is shown as an angular rotor speed ω m.
The remaining power is the output of the motor P out. Finally, friction and windage losses and stray losses P misc are subtracted. After the power is transferred to the rotor, some of it is lost as I 2 R losses, that is, the rotor copper loss P RCL, and the rest is converted from electrical to mechanical form P conv. This power is called the air gap power P AG of the machine. The power remaining at this point is transferred to the rotor of the machine across the air gap between the stator and rotor. Some amount of power is lost as hysteresis and eddy currents in the stator P core. The first losses encountered in the machine are I 2 R losses in the stator windings, that is, the stator copper loss P SCL. The input power to an induction motor P in is the three-phase electric power.