When the output frequency of the VFD is 0, the motor can not start because the motor does not have enough starting torque. Only when the output frequency of VFD reaches a certain value, the motor starts to accelerate, and the output frequency of VFD is the starting frequency FS. The starting current and the starting torque are larger than the time. The setting of starting frequency is to ensure that the motor has enough starting torque to prevent the motor from starting or causing over-current trip during starting. Generally, the startup frequency should be set according to the characteristics of the load driven by VFD.

On the one hand, it is necessary to avoid the low-frequency under-excitation area to ensure that the motor has enough starting torque; on the other hand, it should not set the starting frequency too high, otherwise, it may cause a big current shock when the motor starts, even over-current tripping. The startup frequency depends on the specific load.

How Do I determine the startup frequency?

In general, most motors accelerate from 0 Hz, but in some special cases, it is necessary to accelerate directly from a certain frequency. At this point, the VFD in the start-up instant output frequency is the start-up frequency. Typically, you need to set the startup frequency when,

1.A system in which multiple pumps supply water at the same time

For the use of more than one pump at the same time water supply system, because the water supply pipe usually has a certain water pressure, if the 0HZ start, pump is difficult to start. In this case, you need to start directly from a frequency in order to successfully start the rotation.

2. load

If the VFD is load-driven and has high static friction, it is difficult to start at 0 Hz. In this case, it is necessary to set the starting frequency to ensure that a certain start-up impact force is generated at the start-up moment to make the system start smoothly.

3. Tapered motor

During the start-up process, there will be friction between the stator and the rotor, so it is necessary to set the start frequency to ensure that sufficient magnetic flux is built up quickly at the start-up moment, so that a certain air gap is maintained between the stator and the rotor, enable the motor to start smoothly.

VFD starting frequency setting method

(1) constant torque load. In general, the synchronous speed of the motor should not exceed the rated slip rate when starting. Namely: where P is the pole number of motor: δn-rated Slip, δn = n1-ne; n1-synchronous speed;

(2) square torque load. Because square wave torque load at low speed positive torque is small, so can appropriately increase the starting frequency.

In practical application, the starting frequency should be set to solve the problems of motor starting difficulty and over-current gate. For the motor with large starting torque, the suitable starting frequency parameters should be set first, and then a reasonable torque lifting curve should be set according to the actual load. If the starting VFD current is too high, or even overcurrent trip, can be extended by accelerating time to solve. But generally speaking, as long as there is no excessive flow of the situation, speed up as short as possible to improve efficiency.

Source: internet (for study only, intrusion and deletion)