Torque is the basic load form of the transmission shaft of various working machinery, which is closely related to the working capacity, energy consumption, efficiency, operating life, and safety performance of the power machinery. As a typical power machine, torque is a very important performance parameter of the electric motor.
Different operating conditions have different requirements for the torque performance of the motor, such as wound rotor motor, high slip motor, ordinary cage motor, frequency conversion speed control motor, etc.
The torque setting of the motor is all around the load, and different load characteristics have different requirements for the torque characteristics of the motor. The torque of the motor mainly includes the maximum torque, the minimum torque and the starting torque, the starting torque and the minimum torque are considered to deal with the changing load resistance torque during the motor starting process, involving the starting time and starting current, which is reflected in the way of accelerating torque. The maximum torque is more often the embodiment of the overload capacity during the operation of the motor.
Starting torque is one of the important technical indicators to measure the starting performance of the motor. The greater the starting torque, the faster the motor accelerates, the shorter the starting process, and the more it can start with heavy loads. These all indicate good starting performance. On the contrary, if the starting torque is small, the starting is difficult, and the starting time is long, so that the motor winding is easy to overheat, or even cannot start, let alone start with heavy load.
Maximum torque is an important technical indicator to measure the short-term overload capacity of the motor. The greater the maximum torque, the greater the ability of the motor to withstand mechanical load impact. If the motor is overloaded for a short time in the operation with load, when the maximum torque of the motor is less than the overload resistance torque, the motor will stop and the stall burnout will occur, which is what we often call overload failure.
Minimum torque is the minimum torque during motor starting. The minimum value of steady-state asynchronous torque generated between zero speed and corresponding maximum speed of the motor at rated frequency and rated voltage. When it is less than the load resistance torque in the corresponding state, the motor speed will stagnate in the non-rated speed state and cannot be started.
Based on the above analysis, we can conclude that the maximum torque is more of the performance of the overload resistance during the operation of the motor, while the starting torque and minimum torque are the torque under two specific conditions of the motor starting process.
Different series of motors, due to the different working conditions, there will be some different choices for the design of torque, the most common are ordinary cage motors, high torque motors corresponding to special loads, and wound rotor motors.
Ordinary cage motor is normal torque characteristics (N design), generally continuous working system, there is no frequent starting problem, but the requirements are high efficiency, low slip rate. At present, YE2, YE3, YE4, and other high-efficiency motors are representatives of ordinary cage motors.
When the winding rotor motor is started, the starting resistance can be connected in series through the collector ring system, so that the starting current can be better controlled, and the starting torque is always close to the maximum torque, which is also one of the reasons for its good application.
For some special working loads, the motor is required to have a large torque. In the previous topic, we talked about forward and reverse motors, constant resistance loads where the load resistance moment is basically constant than the rated torque, impact loads with large moment of inertia, winding loads that require soft torque characteristics, etc.
For motor products, torque is only one aspect of its performance parameters, in order to optimize torque characteristics, it may be necessary to sacrifice other parameter performance, especially the matching with the dragged equipment is very important, systematic analysis and optimization of comprehensive operation effect, more conducive to the optimization and realization of motor body parameters, system energy saving has also become a topic of common research between many motor manufacturers and equipment supporting manufacturers.
Post time: Feb-16-2023