Several torque modes of electric motor

The output torque of the motor in normal operation varies with the load, but in general, the output torque of the motor refers to the rated output torque M at rated power and rated speed, M=9550N/n. That is, the motor power is certain, the speed is certain, and the torque is certain. Under rated conditions, the motor output torque is certain, but the starting torque is a multiple of the rated torque. For general three-phase asynchronous motors, such as Y and Y2 series motors, the relevant data can be found in the motor sample, which represents the starting ability of the motor under load. For example, the starting multiple of special high slip motors is much higher, and for winding motors: such as YR series, it is even higher, and you can check the relevant samples.

Rated torque: The electromagnetic torque generated on the motor shaft under rated voltage and rated load is called the rated torque of the motor.

Starting torque: When voltage is applied to an asynchronous motor in a stopped state, the torque generated by the asynchronous motor is called starting torque. Starting torque characterizes the starting ability of the motor, which is related to the starting method (such as star-delta starting, variable frequency speed control starting, etc.). Direct starting squirrel cage type is generally 0.8 to 2.2 times the rated torque. Usually the starting torque is more than 125% of the rated torque. The corresponding current is called starting current, which is usually about 6 times the rated current.

For DC motors, the starting torque is very large, so the starting current is also very large, so they cannot be started directly. Of course, this is for large DC motors, and small DC motors including permanent magnets are exceptions. For AC motors, the torque is not very large, so the current is not very large, and they can be started directly. Of course, AC motors have a small starting torque, so they cannot be started with load.

Maximum torque: The point where the motor torque enters the unstable zone from the stable zone. In other words, if the load torque is greater than the maximum torque of the motor, the motor's output torque will decrease and enter a stalled state.

Stall torque: After entering the stall state, the speed is zero, and the torque that the motor can output is the stall torque.

Static torque: The torque when the stator locks the rotor when the motor is powered but not rotating.

Usually, maximum torque > stall torque > rated torque. The ratio of maximum torque to rated torque is called the overload factor of the motor.

The maximum torque multiple and the stall torque multiple are indeed two important performance indicators to measure the performance of the motor, but the bigger the better is not necessarily true. The larger the maximum torque multiple, the more capable the motor is of overloading, but at the same time, it is also a very important assessment of the size and materials of the motor.

It is good to have a larger stall torque multiple, especially for large motors, which generally have a larger moment of inertia. If the stall torque multiple is larger, the motor will start faster and rotate more freely. However, the stall torque multiple cannot be as large as possible.

The larger the two torque multiples, the greater the starting current of the motor will generally be, and the greater the impact on the power grid will be. Therefore, the Dalan Motor manufacturer reminds everyone that when choosing a motor, you should choose the appropriate value according to the actual working conditions and keep a certain margin. In general, the stall torque multiple is 1.8-2.2. The maximum torque multiple is 2.0-2.8 (depending on the size of the motor).

Due to the existence of static torque of the motor, be sure to turn off the power of the motor before performing special operations on the motor, otherwise the gears of the motor gearbox are easily damaged when forced to operate. In addition: In order to reduce the speed of the motor output shaft, many gears are combined into a gearbox. Each gearbox has a limit torque, called the damage torque. If the torque generated by excessive external force acts on the gearbox, it will cause the gear to be damaged.