The conditions and process of normal motor starting

Starting is a topic that cannot be avoided in any motor application. Starting torque and starting current, which constitute the combination of starting parameters of a motor, characterize the starting performance of a motor. In order to ensure the safety of the motor body, the power grid and the equipment being dragged during the starting process, it is always desirable to have a large starting torque and a small starting current.

However, it is a very interesting topic to know how much torque is more suitable and what conditions can be met to ensure smooth starting of the motor.

The motor starting process is the process of changing the state of the motor, the speed of the motor from 0 speed to accelerate, and finally reach the rated speed of the motor. We can understand it this way: in order to make all the processes of speed inertia change tend to accelerate, or the motor starting process to maintain acceleration, we must ensure that the driving torque is greater than the resistance torque, that is, the electromagnetic torque at any speed that does not reach the rated speed of the motor, must be greater than the corresponding load torque, when the electromagnetic torque and resistance torque has a difference, we call it acceleration torque. If there is no acceleration torque, the motor can only maintain the original speed state or even stall, and cannot realize the motor starting. Therefore, the basic condition that the motor can be started smoothly is that there is acceleration torque in any speed state of the starting process; if the acceleration torque is large, the motor starting time is relatively short, and if the acceleration torque is small, the motor starting time will be lengthened to varying degrees.

Whether the motor electromagnetic torque or load torque, there is a certain relationship with the motor speed, electromagnetic torque and motor input voltage is closely related, therefore, for different load characteristics, should be targeted to select the starting torque and starting mode; in addition to the starting characteristics, must also take into account the changing characteristics of the load during the operation of the motor, which involves the motor starting torque, maximum torque, starting current between the This involves a trade-off between starting torque, maximum torque and starting current.

For the starting process of the motor, whether the minimum torque is satisfied depends on whether the starting process of the motor will form a dead point, and only when the dead point is successfully passed can the starting process be completed. The maximum torque is to ensure that the motor can resist short time overload and shock resistance during operation. The selection and trade-off of these parameters may involve the contradiction of "fish and bear's paw", and the designer of the motor needs to make a targeted tendency to ensure according to the actual operating characteristics.