Fan frequency control system design: The main circuit three-phase power frequency is connected through the circuit breaker, the contactor KM1 is used to connect the power supply to the input terminals R, S, T of the frequency converter, and the contactor KM2 is used to connect the output terminals U, V, W of the frequency converter to Motor, KM3 is used to connect the commercial power supply directly to the motor. The contactors KM2 and KM3 are absolutely not allowed to be switched on at the same time, otherwise the consequences of damage to the inverter will be caused. Therefore, there must be a reliable interlock between KM2 and KM3. The thermal relay KR is used for overload protection during power frequency operation. The control circuit is provided with "frequency conversion operation" and "power frequency operation" switching, and the control circuit is selected by a three-position switch SA. When SA is connected to the "power frequency operation" mode, the start button SB2 is pressed, the intermediate relay KA1 operates and self-locks, and the contactor KM3 is operated, and the motor enters the power frequency operation state. When the stop button SB1 is pressed, the intermediate relay KA1 and the contactor KM3 are powered off, and the motor stops running. When SA is connected to the "inverter running" mode, the start button SB2 is pressed, the intermediate relay KA1 operates and self-locks, and the contactor KM2 is operated to connect the motor to the output end of the inverter. After the KM2 action, the KM1 is also actuated, the power frequency power supply is connected to the input end of the frequency converter, and the motor is allowed to start. At the same time, the normally closed contact of KM2 connected to the coil control circuit of the contactor KM3 is disconnected, ensuring that KM3 cannot be turned on. When the button SB4 is pressed, the intermediate relay KA2 operates, and the motor starts to accelerate, and enters the "frequency conversion operation" state. After the KA2 is actuated, the stop button SB1 is disabled to prevent the motor from being stopped directly by cutting off the power supply to the inverter. In the frequency conversion operation, if the inverter trips due to a fault, the "30B-30C" protection contact of the inverter is disconnected, the contactors KM1 and KM2 coils are all powered off, and the main contact is cut off between the inverter and the power supply. And the connection between the frequency converter and the power supply. At the same time, the time relay has electricity, and the contact delay is closed for a period of time, so that the KM3 acts and the motor enters the power frequency operation state. When the operator finds an alarm, immediately turn the selector switch SA to the "power frequency operation" position, the alarm stops, and the time relay is de-energized. ZDR6.10D Series Pressure Valves Zdr6.10D Series Pressure Valves,Stacked Pressure Reducing Valves,Stacked Pressure Reducing Valve,Stacked Pressure Control Valve Shanghai Jinhai Hydraulic Co.,Ltd , https://www.shanghaijinhai.com