Requirements for performance indicators of electric motors

1. Efficiency level is one of the most important technical and economic indicators of electric motors, which directly affects the effective material consumption and operating costs of electric motors. Higher operating efficiency can bring significant energy-saving effects to users, but the effective material consumption of electric motors will increase, resulting in higher costs and prices. Meanwhile, whether the higher efficiency can fully play its role is also related to the annual operating time and load rate of the motor during operation.

The operating load rate of low-voltage asynchronous motors is generally between 50% and 80%, mostly within the range of 60% to 70%. The variation of efficiency of asynchronous motors at different load rates is related to the distribution ratio of variable losses (stator and rotor winding copper losses) and constant losses (iron losses and mechanical losses) of the motor. In the total losses, variable losses increase while constant losses decrease, and the highest efficiency tends to approach the low load rate region. Therefore, when designing an electric motor, appropriately increasing the electromagnetic load will increase the variable loss, while the constant loss should be controlled as much as possible. This can enable the motor to have relatively flat efficiency characteristics over a wide range of load rates, which is beneficial for the motor to still have high efficiency at relatively low load rates.

2. Starting performance analysis of electric motors includes the entire process of connecting the motor to the power supply, from rotor blockage to reaching the rated speed. The electric motor should have sufficient locked rotor torque and minimum torque to drive the load machinery to start quickly and reach the rated speed for normal operation; At the same time, it should have sufficient maximum torque to ensure a certain overload capacity. And for the locked rotor current (or locked rotor apparent power), it should be limited to avoid excessive voltage drop caused by the power supply, which may affect the normal operation of other electrical equipment connected to the same power supply. In addition, excessive starting current will cause the motor winding to overheat and be subjected to excessive electromagnetic force impact.

The starting requirements stipulate that the motor is allowed to start continuously twice in a cold state (the motor should naturally stop between two starts), or start once in a hot state after rated operation, and specify the rotational inertia value of the load it drives.

3. The noise and vibration level analysis of electric motors is a comprehensive indicator reflecting the design, manufacturing process, assembly quality, and bearing quality of electric motors. It is also an important indicator for measuring environmental quality, and the requirements for motor noise and vibration will become increasingly strict.