For example, for a motor with a power of 30 kW, if the service factor is 1.15, then its actual output maximum power is 30 × 1.15 = 34.5 kW.
The common working standards of the motor include S1 continuous duty, S2 short duration, and S3 to S7 cycle time. The unusual S8 variable speed continuous duty cycle system and the S9 load and speed non-periodic change working system. When the operation mode is not consistent with any of the standard modes S1 to S9, if the motor is required to run continuously under variable load, the combination of S1 continuous duty + service factor can be used to constrain and characterize the motor performance. Although the "work system + service factor" combination is indeed a working standard, it cannot be said that the service factor is a working standard.
The service factor is a comprehensive indicator that is numerically equal to the maximum overload rate. According to the operating characteristics of the three-phase asynchronous motor, the service factor is generally stipulated to be 1.15-1.25, because the use of a low service factor does not actually have substantial application efficiency; the service factor is high, and the economical operation of the motor is not ideal.
Taking a screw air compressor as an example, the size of the motor load changes periodically, and it changes with the user's demand for air volume. When the maximum working pressure set by the user is reached, the air compressor starts to unload, when the pipe network When the working pressure drops to the minimum working pressure set by the user, the compressor is automatically loaded.
The power selection of the electric motor is to make the electric motor work under the expected load generally with the highest efficiency and large power factor. However, the shaft power of the motor must be able to operate at full load at the same time, that is, to adapt to the actual conditions of the customer's long-term overload operation. In general, the choice of motor power at full-load operation is expected to multiply the economical operating shaft power by 1.1 times.
Directly using 1.1 times the expected economic operating shaft power to select the motor power without what we call "service factor", the consequence is that the efficiency and power factor of the motor are relatively low, resulting in a waste of energy and costs. Therefore, the "service factor" is actually an important parameter to ensure the efficient and economical operation of air compressors.