PST Thyristor Power Units

PST Thyristor Power Units are two-phase power control units used in AC resistance welding systems to regulate industrial welding transformers. The PST platform combines the power unit, control functions, and an integrated weld timer CPU in one cabinet-mounted device. Modular expansion slots allow the unit to be configured with a type-specific I/O interface, an optional fieldbus module for programming, and an optional retrofit quality module for added monitoring and process-control capability. These units are designed with an IP20 device rating and are intended for installation inside switchgear cabinets that provide at least IP54 protection. Depending on the version, cooling is handled through forced air or water cooling, with required cabinet clearances to support heat removal. The series is built for 50/60 Hz supply systems in the 400–600 V range and is available in sizes matched to transformer capacity, including air-cooled models for approximately 76 kVA transformer ratings and higher-capacity versions up to approximately 250 kVA. Reliability features include temperature monitoring through a thermostatic switch, which prevents additional welding cycles if the unit overheats. Proper sizing is based on duty cycle and load diagrams so the welding system can avoid overload conditions and thermal shutdown.