Product Description:

The PST6250.321-L thyristor power unit is manufactured by Bosch Rexroth Indramat within the PST Thyristor Power Units series. Designed to switch and regulate high-current industrial heating transformers, the unit supplies controlled three-phase power to resistive loads, thereby forming an integral element of closed-loop automation where precise thermal profiles are required. It combines solid-state switching with fieldbus communications so that temperature controllers or PLCs can modulate energy delivery in furnaces, dryers, or ceramic kilns without mechanical contactors.

At the output, the device can conduct a continuous load of 200 A, and its firing electronics are rated for a 50% duty cycle, matching batch processes that alternate between heating and standby. The assembly is air cooled, yet reliable operation is limited to ambient temperatures up to 55 °C; above that value, the thyristor junctions cannot dissipate heat quickly enough. Supplemental airflow must not exceed 45 °C to stay within the cooling-air limit, and under those conditions cabinet heat loss is held to 70 W. The integrated control function gates each phase together with a 2.2 kΩ de-excitation resistor and MOV overvoltage protection. A PS5 IBS I/O board links the unit to an INTERBUS-S serial bus, while the dedicated INTERBUS timer segment synchronizes zero-cross detection. With a 250 kVA transformer rating, the power stage feeds medium-size isolation transformers used in heat-treatment equipment.

For installation, the unit can be mounted in switchgear rooms up to 2000 m above sea level without derating. Line and load cables enter a terminal block that accepts conductors up to 95 mm², enabling short runs to busbars. Control electronics draw 24 V DC logic power from the machine supply, isolating firing circuits from mains disturbances. Despite the high current capability, the power assembly weighs only 12.5 kg, which helps simplify cabinet handling.