FK Series Composite Switch | Low Voltage Capacitor Switching Device for APFC Cabinets

The FK Series Composite Switch is a low-voltage switching device for the capacitor branches of a power factor correction cabinet. It is rated AC-6b — the utilisation category defined specifically for capacitor switching — which is what separates it from a general-purpose contactor asked to do the same job. The FK-△-400V-45A version is the delta-connected type used for three-phase common compensation, rated 400 V and 45 A, and it connects and disconnects each capacitor branch on command from the compensation controller.

A composite switch combines two switching elements in one device: a semiconductor stage that makes and breaks the circuit at the voltage zero crossing, and a mechanical contact that carries the continuous current. The semiconductor absorbs the transient, so the capacitor is never exposed to the inrush current and contact arcing a plain contactor would produce, while the contact closes to carry the load current with negligible loss and no continuous heat generation. The practical results are no inrush current, no welded contacts, a long electrical life, and no additional harmonic distortion introduced into the network.

Indication and communication are built in. Four LEDs show power and per-phase A, B and C status, and two RS485 ports allow the switch to be linked to and addressed by the controller. Control connections are made at terminals K1 to K3, with the main circuit terminated at the top and bottom poles. The device carries Ith = 80 A for conventional thermal current and Ui = 690 V for rated insulation voltage, with Ue = 400 V and Ie = 45 A as its operational ratings. To confirm the right model, tell us your system voltage, the capacitor branch rating, and whether the compensation is common or per-phase.