Libratherm offers SCR / Thyristor Switch Card TSC-303 which is specially designed for APFC (Automatic Power Factor Correction) applications to switch ON and OFF, three-phase capacitor banks, based on the command from the APFC relay module. These SCR / Thyristor Switching Modules are developed to trigger solid state switch or silicon controlled rectifiers (SCRs) or thyristors. The gate/cathode triggering pulses are generated using zero cross over firing techniques, where gate/cathode triggering pulses are generated using zero cross over optically isolated integrated chips.

Each card can simultaneously trigger 2 sets of back to back SCR+SCR modules or 2 sets of back to back SCR+Diode modules to switch 3 phase capacitor banks. TSC-303 accepts the control signal in the form of relay contact or DC pulse from the APFC relay unit. When the command is ON, capacitors banks are connected to the power lines, and when the command is OFF capacitor banks are disconnected.

The Capacitor Bank Switching Card TSC-303 has the provision to accept 2 external thermostat contacts, which can be used to operate the cooling fan mounted on the heat sinks and to trip the circuit in case of overheating. On card LED indicates the on/off status of incoming DC power supply, ON/OFF status of capacitor banks, and status of heat sink temperature.

Normally, each of the power factor controllers gives 6 to 12 outputs to select that many capacitor banks of different KVAR depending on the total KVAR demand to maintain the unity power factor. Hence, for each output from APFC, it will be required to use an individual TSC-303 card. For example for 6 relay outputs, The APFC panel builders can use TSC-306 or TSC-303 cards as an independent firing card and can wire the SCR modules separately mounted on the heat sink in the panel. The physical isolation of electronic cards and SCR modules makes the overall system safer, reliable and it becomes easy to maintain and service.