Eaton 93PM UPS (400V/480V Four-Wire – 100 kW Frame) Installation and Operation Manual 164000566—Rev 04 9155..22..44 BByyppaassss MMooddeeCAUTIONThe critical load is not protected from voltage or frequency fluctuations or power outages while the UPS is inBypass mode.The UPS automatically switches to Bypass mode if it detects an overload, load fault, or internal failure (ifconfigured for capacity). If configured for redundancy (N+1) the UPS would remain on line in Normal mode ifone UPM failed. The UPS can also be transferred from Normal mode to Bypass mode manually. The bypasssource supplies the commercial AC power to the load directly. Figure 41 shows the path of electrical powerthrough the UPS system when operating in Bypass mode.In Bypass mode, the output of the system is provided with three-phase AC power directly from the systeminput. While in this mode, the output of the system is not protected from voltage or frequency fluctuations orpower outages from the source. Some power line filtering and spike protection is provided to the load but noactive power conditioning or battery support is available to the output of the system in the Bypass mode ofoperation.The internal bypass is comprised of a solid-state, silicon-controlled rectifier (SCR) continuous static switch, andbypass switchgear. The static switch is used instantaneously anytime the inverter is unable to support theapplied load. The continuous static switch is wired in series with the bypass switchgear, and together they arewired in parallel with the rectifier and inverter.The static switch, being an electronically-controlled device, can be turned on immediately to pick up the loadfrom the inverter while the inverter switchgear opens to isolate the inverter. The bypass switchgear is normallyclosed, ready to support the static switch unless the bypass input source becomes unavailable.If the UPS transfers to Bypass mode from Normal mode due to any reason other than operator intervention,the UPS automatically attempts to transfer back to Normal mode (up to three times within a ten minute period).The fourth transfer locks the critical load to the bypass source and requires operator intervention to transfer.Figure 41. Path of Current Through the UPS in Bypass ModeBypass InputRectifier Input OutputBypass SwitchgearRectifierSwitchgearInverterSwitchgearBatterySwitchgearClosedOpenMain Power FlowTrickle CurrentEnergizedDe-EnergizedSwitchgearRectifier InverterStaticSwitchBattery ConverterBatteryUnderstanding UPS Operation
