水泵变频控制系统工作原理及切换流程 - 详细解析 - 常规

The sequence of operations for the pump system is as follows:\

KM1 is energized to engage the electromagnetic coil, and pump 1 starts running in variable frequency mode.\
When the working frequency of pump 1 reaches the upper limit of 48Hz, KM2 is energized to engage the electromagnetic coil. Pump 1 switches to operate in mains frequency mode. Then, KM3 is energized to engage the electromagnetic coil, connecting the variable frequency drive (VFD) to pump 2 for soft starting. Pump 1 continues to operate in mains frequency mode while pump 2 operates in variable frequency mode.\
When the working frequency of pump 2 decreases to the lower limit of 15Hz, KM2 is de-energized, and pump 1 stops running. At this point, pump 2 continues to operate in variable frequency mode as a standalone pump.\
When the working frequency of pump 2 reaches the upper limit of 48Hz, KM4 is energized to engage the electromagnetic coil. Pump 2 switches to operate in mains frequency mode. Then, KM5 is energized to engage the electromagnetic coil, connecting the VFD to pump 3 for soft starting. Pump 2 continues to operate in mains frequency mode while pump 3 operates in variable frequency mode.\
When the working frequency of pump 3 decreases to the lower limit of 15Hz, KM4 is de-energized, and pump 2 stops running. At this point, pump 3 continues to operate in variable frequency mode as a standalone pump.\
When the working frequency of pump 3 reaches the upper limit of 48Hz, KM6 is energized to engage the electromagnetic coil. Pump 3 switches to operate in mains frequency mode. Then, KM1 is energized to engage the electromagnetic coil, connecting the VFD to pump 1 for soft starting. Pump 3 continues to operate in mains frequency mode while pump 1 operates in variable frequency mode.\
When the working frequency of pump 1 decreases to the lower limit of 15Hz, KM6 is de-energized, and pump 3 stops running. At this point, pump 1 continues to operate in variable frequency mode as a standalone pump. This cycle continues.\
During the operation in mains frequency mode, the motor overload is protected by a thermal relay, and there is an alarm indication.\
Each pump's VFD and mains frequency contactor must have electrical interlocks and mechanical interlocks externally.\
The switching process involves the following steps: First, the MRS (Manual Reset Switch) is closed, stopping the output of the VFD with a delay of 0.2s. Then, the VFD contactor is opened with a delay of 0.5s, and the mains frequency contactor is closed. After that, there is a delay to close the next VFD contactor and disconnect the MRS contact, allowing the switching between VFD and mains frequency. \
The switching between VFD and mains frequency is controlled by the temperature of the cooling water or the upper and lower limit switching frequencies of the VFD.