Shreem Electric's STM Series Thyristor Switching Modules are solid-state switches for dynamic power factor correction, used to switch capacitor steps in and out quickly and smoothly in applications with rapidly fluctuating loads. The modules use zero differential voltage switching, which avoids the inrush currents and transients that come with conventional contactors, and they are driven by a 12V/24V DC or TTL control signal that draws less than 5 mA. They are available in four ratings, 12.5, 25, 50 and 100 kVAr, with a 220 V AC auxiliary supply, 50/60 Hz operation and an over blocking voltage of 1800 V (2200 V optional). Each module has LED indications for switch ON and temperature, and built-in protection against over-temperature and dv/dt. The 12.5 kVAr module is naturally air cooled, while the 25, 50 and 100 kVAr modules use forced air cooling. All models are rated IP00 and operate from -10°C to 50°C at rated load (up to 60°C at 75% load), with humidity of 10 to 95% without moisture. The modules are compact, ranging from 205 x 195 mm up to 275 x 300 mm in length and width, and weigh from 4.3 kg to 10.5 kg depending on the rating.