Torque is an important performance index of motor products, which directly reflects the ability of the motor to drive the load. In motor products, the starting torque, rated torque and maximum torque reflect the ability of the motor in different states. Different torques correspond to There is also a big difference in the magnitude of the current, and the relationship between the magnitude of the current and the torque is also different under the no-load and load states of the motor.
The torque generated by the motor at the moment when voltage is applied to the motor at a standstill is called starting torque. The size of the starting torque is proportional to the square of the voltage, increases with the increase of the rotor resistance, and is related to the leakage reactance of the motor. Usually, under the state of full voltage, the instantaneous starting torque of AC asynchronous motor is more than 1.25 times of the rated torque, and the corresponding current is called starting current, which is usually about 5 to 7 times of the rated current.
The motor under the rated operating state corresponds to the rated torque and rated current of the motor, which are the key parameters under the normal working conditions of the motor; when the motor is overloaded during operation, it involves the maximum torque of the motor, which reflects the resistance of the motor The capacity of overloading will also correspond to a larger current under the condition of maximum torque.
For the finished motor, the relationship between the electromagnetic torque of the asynchronous motor and the magnetic flux and rotor current is shown in formula (1):
Electromagnetic torque = constant × magnetic flux × active component of each phase current of the rotor… (1)
It can be seen from formula (1) that the electromagnetic torque is directly proportional to the product of the air gap flux and the active component of the rotor current. The rotor current and stator current basically follow a relatively fixed turn ratio relationship, that is, when the magnetic flux does not reach saturation, the electromagnetic torque and current are positively correlated. The maximum torque is the peak value of the motor torque.
The maximum electromagnetic torque is of great significance to the motor. When the motor is running, if the load suddenly increases for a short time and then returns to normal load, as long as the total braking torque is not greater than the maximum electromagnetic torque, the motor can still run stably; otherwise, the motor will stall. It can be seen that the greater the maximum electromagnetic torque, the stronger the short-term overload capacity of the motor, so the overload capacity of the motor is expressed by the ratio of the maximum electromagnetic torque to the rated torque.
Post time: Feb-17-2023