Electric valve motor control circuit

Photocoupler

The electric valve control circuit is composed of three key parts: the main line, the control line, and the energy braking line. The main line includes the power switch QF, the main contacts of the three-phase AC contactors KM1 and KM2, the components of the thermal relay FR, and the three-phase AC motor. The control circuit involves control buttons SB1 to SB5, lines BH of AC contactors KM1 to KM3 and their auxiliary contacts, power transformers Tl and T2, signal indicators HL1 to HLA, flash switches S1 and S2, state selection switches SA1 and SA2, and position switches SQ1 and SQ2. The energy consumption circuit includes a bridge rectifier UC, a current-limiting potentiometer RP, a storage capacitor C, and the main contact of the AC contactor KM3. The electric valve motor control circuit is illustrated in Figure 4-35.

In the hot standby state, the main line can be either controlled or uncontrolled depending on the switch positions of SA1 and SA2. When SA1 (SA2) is on the left, the coil of KM1 (KM2) is deactivated. When the system is operational, if SA1 (SA2) is on the right, the coil of KM1 (KM2) is activated. When SA1 (SA2) is on the left, the signal indicators light up, allowing operators or maintenance personnel to verify if the control circuit is powered. When SA1 (SA2) is on the right, the signal indicators remain off until the valve motor starts, at which point the indicators HL1, H12 (HL3, HIA) begin to flash. By closing the power switch QF, setting the selector switch SA1 to the right, and pressing SB1 (or SB2), the current flows through Vll-SB1 (or SB2)-KM2 contact (2-3)-KM1 coil-SO2-SA1-FR contact (7-9)-KM3 contact (9-10)-SB5-W11. This energizes the KM1 coil, causing the valve motor to open the valve. Once the contact (5-6) of KM1 closes, the flash switch S1 activates, flashing the red light HL1 and the green light HL2.

When the valve reaches its open limit position, SQ2 disconnects, de-energizing the KM1 coil, resetting its main contact, disconnecting the power supply to the valve motor, and halting its operation. Setting selector switch SA2 to the right and pressing SB3 (or SB4) triggers the current flow via Vll-SB3 (or SB4)-KM1 contact (13-14)-KM2 coil-SQ1-SA2-FR contact (7-9)-KM3 contact (9-10)-SB5-W11. This energizes the KM2 coil, rotating the chain to close the valve. After KM2's contact (12-15) closes, the flash switch S2 operates, flashing the red light HL3 and the green light HLA. When the valve reaches its closed limit position, SQ1 disconnects, de-energizing the KM2 coil, resetting its main contact, disconnecting the motor's power supply, and stopping the valve.

If an obstacle occurs during the valve-opening process and the stop button SB5 is pressed, the breaking contact disconnects, de-energizing the KM1 or KM2 coil and stopping the motor. Simultaneously, the moving contact (19-W11) of SB5 closes, energizing the KM3 coil. Its contact (9-10) disconnects to prevent KM1 or KM2 from malfunctioning, while its main contact closes, activating the bridge rectifier’s output and the stored energy in the capacitor to generate a braking torque that stops the motor instantly. This ensures the valve stops precisely at the desired position. In Figure 4-35, the potentiometer RP serves as a current-limiting device, adjusting the braking current. Typically, the braking current is set to 4.5A. For the electrolytic capacitor, choose one based on the valve's power. If the valve motor power is below 2kW, use a capacitor of 100-200μF. If the power is between 2 and 5.5kW, select a 400μF capacitor. The capacitor's voltage rating should exceed 600V.