Overview

The low-voltage intelligent composite switch is a sophisticated, energy-saving capacitor switching device meticulously developed to address the inherent drawbacks of thyristors and AC contactors in low-voltage reactive power compensation applications. It is ideally suited for controlling the switching of low-voltage reactive power compensation capacitors. Its basic operating principle involves paralleling a thyristor module with an AC contactor (magnetic latching relay). Through internal chip-based analysis and precise control, the switch automatically identifies the optimal moment for energizing (or de-energizing) the capacitor. This ensures that, during switching operations, the composite switch benefits from the zero-crossing switching advantages of the thyristor, while maintaining the energy-efficient, low-power characteristics of the AC contactor during normal operation.

Technical Specifications

Operating voltage: 380V/220V ±20%
Rated frequency: 50 Hz ± 5%
Control capacity: Three-phase common compensation △-type ≤ 30 kVar
Single-phase split-compensation Y-type ≤10 kVAR × 3
Insulation rating: Under normal atmospheric conditions ≥10 MΩ
Control voltage: DC 12V
Input impedance: ≥3 kΩ

Technical Features

1. Zero-Voltage Switching: The fundamental working principle of the composite switch is to connect a thyristor module in parallel with an AC contactor (magnetic latching relay), enabling zero-voltage turn-on and zero-current turn-off. This design allows the composite switch to benefit from the zero-crossing switching advantages of thyristors during both connection and disconnection, while maintaining the low-power consumption characteristic of the contactor during normal operation. The implementation method is as follows: When turning on, the thyristor is triggered at the exact moment the voltage crosses zero; once stable, the AC contactor (magnetic latching relay) is engaged to complete the circuit. Afterward, the thyristor is deliberately delayed to turn off at the next zero-crossing point. Conversely, when turning off, the magnetic latching relay is first disconnected, followed by a controlled delay before the thyristor turns off at the next zero crossing, ensuring current-free disconnection.
2. A dedicated chip is used to control the switching operations and intelligently monitor the operational status of thyristors, relays, and the input power supply, thereby providing comprehensive protection features. When the working power supply is cut off, the switch refuses to close; however, if the working power supply is restored after a power interruption, the system automatically disengages from operation.
3. No Harmonic Injection: Since the thyristor is triggered at zero crossing during turn-on, and the AC contactor (magnetic latching relay) engages to conduct only after a delay, no harmonics are generated.

4. Low Power Consumption: By incorporating an AC contactor (magnetic latching relay), the control device consumes power only during the switching operation—specifically, at the moment of energizing or de-energizing—and remains completely dormant otherwise. Additionally, thanks to the low contact resistance of the AC contactor (magnetic latching relay), heat generation is minimal. This eliminates the need for external heat sinks or fans, further reducing both costs and power consumption, thereby achieving the goal of energy conservation and efficiency improvement.
5. Input control signals are optically isolated from the composite switch: This provides strong anti-interference capability and ensures safe, reliable operation.

Model Naming

SFK- T2 Series Synchronous SwitchesModule
SFK - T2 / 30 / S / 450 / A
丨 丨 丨 丨 丨 丨
① ② ③ ④ ⑤ ⑥
①: Product Code: SFK
②: Product Category: T2 Series
③: Rated Capacity: 5–50 kvar
④: Compensation Method: (F: Partial Compensation, S: Shared Compensation)
⑤: Rated Voltage: 250V, 450V
⑥ : A: 12V B: 12V + Miniature Circuit Breaker
C: Network Port D: Network Port + Miniature Circuit Breaker

Indicator Light Function Description

1. Power Indicator Light: After each power-on, the indicator light flashes to perform an internal reset and fault detection. During this process, the system is in a protective state and does not execute any switching operations. Once everything returns to normal, the flashing stops, and the light remains steadily on, signaling that operations can proceed. However, if an internal fault occurs, the power indicator light will continue flashing continuously.
2. Running Lights ABC: When the light is on, it indicates that the item has received the start-up signal and has already completed the start-up action.

Important Notes

1. Never reverse the connections for AC input and output.
2. Ensure the correct polarity for the level signal input: Connect terminal V to the controller’s common terminal M, and terminal K to the controller’s output terminal.
3. To prevent the magnetic latching relay from inadvertently conducting due to strong vibrations during transportation—resulting in the input and output contacts remaining closed—the composite switch automatically resets to its normal initial state once power is applied.

Installation diagrams and wiring diagrams:

External dimensions: 95 x 155 x 95 mm
Note: The F and S smart composite switches have the same installation dimensions.

Note:
The wiring terminals on both sides of the switch are labeled N and M. Users only need to connect the N and M terminals of the first switch to the controller, while the remaining N and M terminals can be interconnected via the N and M wiring ports on either side.

Note: The wiring terminals on both sides of the switch are labeled N and M. Users only need to connect the N and M terminals of the first switch to the controller, while the remaining N and M terminals can be interconnected via the N and M wiring ports on either side.