Understanding UPS Operation7-6 EATON Powerware® 9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev E powerware.com7.2.3 Bypass Mode – RTThe UPS automatically switches to Bypass mode if it detects an overload, load fault, orinternal failure. The bypass source supplies the commercial AC power to the load directly.Figure 7-3 shows the path of electrical power through the UPS system when operating inBypass mode.C A U T I O NThe critical load is not protected while the UPS is in Bypass mode.StaticSwitchK5Rectifier InverterK1 K3BatteryConverterBatteryBatteryBreakerMain Power FlowTrickle CurrentEnergizedDe-EnergizedClosedOpenBreakers ContactorsFigure 7-3. Path of Current Through the UPS in Bypass Mode – RTIn Bypass mode, the output of the system is provided with three-phase AC power directlyfrom the system input. While in this mode, the output of the system is not protected fromvoltage or frequency fluctuations or power outages from the source. Some power linefiltering and spike protection is provided to the load but no active power conditioning orbattery support is available to the output of the system in the Bypass mode of operation.The internal bypass is comprised of a solid-state, silicon-controlled rectifier (SCR) staticswitch (SSW) and a backfeed protection contactor K5. The static switch is rated as acontinuous-duty device that is used anytime the inverter is unable to support the appliedload. The static switch is wired in series with the backfeed protection contactor, andtogether they are wired in parallel with the rectifier and inverter. The static switch, beingan electronically-controlled device, can be turned on immediately to pick up the load fromthe inverter while the inverter output contactor K3 opens to isolates the inverter. Thebackfeed protection contactor is normally always closed, ready to support the static switchunless the bypass input source becomes unavailable.
