Switching general-purpose inverter frequency conversion and power frequency line with relay - News - Global IC Trade Starts Here.

Photocoupler

2. Working Principle

The SA is a switch used to select the operating mode. When the SA is set to "Power Frequency Operation," pressing the start button SF1 activates the intermediate relay KA1, which latches itself on. This causes KM3 to engage, allowing the motor M to enter the "Power Frequency Operation" state. Pressing ST1 stops the motor M.

When the SA is switched to "Frequency Conversion Operation," pressing SF1 again activates KA1, which then triggers KM2. This connects the motor M to the output of the inverter (UF). At the same time, KM1 also engages. Then, pressing SF2 activates the intermediate relay KA2, which connects the FWD and CM terminals of the inverter, allowing the motor to start and operate in "Frequency Conversion Mode." Once KA2 is activated, the stop button ST1 becomes disabled to prevent direct power cutoff from the inverter, ensuring safe operation.

During inverter operation, if the UF trips due to a fault, the circuit between "30B~30A" opens, causing KM2 and KM1 to de-energize. This disconnects the inverter and the power supply from the motor M. At the same time, "30B~30C" closes, triggering an audible and visual alarm via the buzzer HA and indicator HL. Simultaneously, the time delay relay's KT coil is energized. After a set delay, the contact closes, activating KM3 and allowing the motor M to automatically switch back to "Power Frequency Operation." At this point, the operator should manually set the SA to the "Power Frequency Operation" position, which will deactivate the alarm.

If the stop button ST2 is pressed while the inverter is running, the intermediate relay KA2 is de-energized, disconnecting the FWD from the CM terminal of the inverter. This causes the motor M to gradually decelerate and shut down safely.

3. Application

This system enables seamless switching between frequency conversion and power frequency modes, offering flexibility and reliability in industrial applications where continuous motor operation is essential.