Three Phase Thyristor Triggering Card – LZF-3

Libratherm offers a three-phase SCR firing card model LZF-3 for switching power to three-phase operated resistive or inductive loads. This card was developed to replace the electro-mechanical contactor with an electronic solid-state switch built using silicon-controlled rectifiers (SCRs).

When the electrical load is operated through contactors – the AC cycle is switched ON or OFF at any point of 0 to 180degree phase angle; this may lead to the generation of arcing on the contacts and may generate harmonics, which may cause electromagnetic disturbance in the power lines and may also cause the malfunctioning of other electronic instruments on the panel. The card featured here eliminates the generation of such harmonics because of the zero cross-over switching technique. No arcing or audible noise will be observed during the switching operations – since no mechanical switching contacts are involved in the solid-state device, the operation will be noiseless and silent.

LZF-3 accepts one standard linear signal of 4-20mA/0-5V/0-10V/Potentiometer or DC pulse/ potential free contact input from either temperature controller or PLC and generates three independent gate cathode triggering pulses (G1K1+G2K2) for 2 or 3 pairs of back-to-back connected SCRs. Hence, one can control a single 3-phase load in star or delta configuration (As shown in the DIAGRAM-2). The linear signal is pulse width modulated for burst fire to generate pulsating output with variable on/off duty cycle time of 2 to 30 seconds adjustable using an on- card potentiometer.