Static Transfer Switch definition
Static Transfer Switch. (“STS”) is defined as an electrical distribution component that accepts multiple input power sources and automatically and instantaneously switches the flow of electricity among those sources to the equipment drawing electricity from the output.
Static Transfer Switch. The static transfer switch shall use silicon controlled rectifiers and other static devices required to automatically transfer loads from the "Normal" source to the "Alternate" source. The static transfer switch shall conform to the following requirements: Capacity, Equal to the continuous full load continuous capacity of the inverter Capacity, peak 1000 percent of continuous rating for 5 cycles Voltage 120/208 volts, three-phase Frequency 60 hertz Transfer time, 1/4 cycle maximum. Transition shall be including sensing "make before break." Voltage failure shall be sensed on the output of the static switch. Failure shall cause the static switch to transfer. The static switch shall also transfer on over-current prior to the inverter reaching a current limit mode. Voltage transfer Automatic transfer to alternate source to "Alternate" when output voltage of inverter deviates source plus or minus 10 percent from nominal. Overcurrent Continuously adjustable from inverter transfer to continuous rating to inverter current "Alternate" source limit rating Retransfer to Return to normal shall be automatic for "Normal" source all externally caused transfers such as overload or clearing of a branch circuit fuse but shall be manual for all internally caused transfers such as inverter, filter, or normal patch failure. Overload 125 percent for 2 minutes Line voltage 170 volt peak above normal line voltage transient tolerance Ambient 50 Degrees Celsius maximum, 35 Degrees Celsius normal temperature Cooling Natural convection or forced air cooling Duty rating Continuous The static switch shall be provided with protective fuses in both "Normal" and "Alternate" power sources. The static transfer switch shall be furnished mounted in enclosures described later in these specifications.