A static inverter is primarily designed for use with emergency lighting systems and other safety-related applications, as well as in remote settings such as offshore.
It performs a similar role to a standard uninterruptible power supply, but provides backup for a much longer time, usually either 1 or 3 hours.
Inverters provide either a continuous or standby source of AC power from a DC supply, typically a sealed lead-acid battery or photovoltaic cell used as part of a solar panel array.
In effect, a static inverter performs in a similar way to a UPS system running in Standby operating mode with the bypass supplying the load and no filtering of the mains supply. When a mains failure occurs, the static inverter switches to running off batteries.
Static inverters must comply with the EN 50171 safety standard for Central Power Supply Systems. One of the criteria this involves is the capability to clear a final circuit fault and continue running without breaking its own circuit protection device.
The majority of standard UPS systems are not designed to meet EN 50171 specifications and therefore should not be used to back up emergency lighting and similar applications. However, there are specially-designed UPS for emergency applications to meet these requirements.