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ITGlossary · UPS technology
Static Switch
A thyristor-based switch with no moving parts that transfers the load between inverter and mains within a fraction of a cycle.
Technical level:Advanced
A static switch has no moving contacts: it uses power semiconductors, usually thyristors, to change the current path. The transfer therefore completes within a fraction of a 50 Hz cycle, much faster than an electromechanical relay, and without arcing or contact wear.
In a UPS it is the component that implements the static bypass, moving the load from the inverter to the mains and back. It is also used in standalone static transfer switches (STS) that select between two independent sources for critical loads.
For a disturbance-free transfer, both sources must be synchronised in phase and frequency. If the UPS reports that it is not synchronised with the mains, the transfer to bypass may be delayed or blocked.
Related terms
- InverterThe component inside a UPS that converts DC power from batteries back to usable AC power.
- Transfer SwitchA manual or automatic switch that connects the load to one of two sources, such as the grid and a generator, never both at once.
- Offline (Standby) UPSA UPS that leaves the load on the mains and switches to battery only when the mains fails, with a short transfer time; the simplest and cheapest topology.
- TransformerAn electrical component that changes voltage levels or isolates circuits.
- Static BypassAn electronic path inside the UPS that instantly and automatically transfers the load to the mains on overload or internal fault.
- Online (Double Conversion) UPSA UPS that continuously converts incoming AC to DC and back to AC, so the load is always fed by the inverter with clean, stable power.