Generally, most motors start to speed up from 0Hz, but in some special cases, it is necessary to start directly from a certain frequency. At this time, the frequency output of the VFD at the moment of activation is the activation frequency. In general, you need to set the activation frequency in the following situations.
1. A system in which multiple pumps supply water together
Regarding the system of using multiple pumps to supply water together, because there is generally a certain water pressure in the water supply pipe, it is difficult for the pump to start if it is started at 0Hz. In this case, it is necessary to start directly from a certain frequency in order to spin smoothly.
2. Load
If the VFD is driven by a load, the friction is high when it is static, and it is difficult to start from 0Hz. When this situation is presented, it is necessary to set the starting frequency to ensure that the certain starting impact force occurs at the moment of activation, so that the system can be started smoothly.
3. Tapered motor
In the process of starting, friction will occur between the stator and the rotor, so it is also necessary to set the starting frequency to ensure that sufficient magnetic flux is quickly established at the moment of starting, so that the stator and the rotor adhere to a certain air gap, so that the motor can start smoothly.
VFD starting frequency setting method
(1) Constant torque load. Generally, the synchronous speed of the motor should not exceed the additional slip rate when starting. Namely:
where P is the number of poles of the motor; △n - extra slip, △n = n1-ne; N1 - synchronization speed; ne - extra speed; (1) Square torque load. Because the square wave torque load has a small resistance torque at low speed, the starting frequency can be increased appropriately.
In practical application, the starting frequency should be reasonably set to deal with the problem of motor starting difficulty and overcurrent tripping. For motors with large starting torque, it is necessary to first consider setting the appropriate starting frequency parameters, and then set a reasonable torque improvement curve according to the actual load conditions. If the VFD current is too high at starting, or even overcurrent tripping, it can be handled by extending the acceleration time. However, generally speaking, as long as there is no excessive traffic, the acceleration time should be as short as possible to improve efficiency.
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