92 Eaton 93PM UPS (400V/480V Four-Wire – 100 kW Frame) Installation and Operation Manual 164000566—Rev 0455..22..55 BBaatttteerryy MMooddeeThe UPS automatically transfers to Battery mode if a utility power outage occurs, or if the utility power does notconform to specified parameters. In Battery mode, the battery provides emergency DC power that the inverterconverts to AC power.Figure 42 shows the path of electrical power through the UPS system when operating in Battery mode.During a utility power failure, the rectifier no longer has an AC utility source from which to supply the DC outputvoltage required to support the inverter. The rectifier switchgear opens and the battery instantaneouslysupplies energy to the battery converter. The converter boosts the voltage so that the inverter can support thecustomer's load without interruption. If bypass is common with the rectifier input, the bypass switchgear alsoopens. The opening of the rectifier and bypass switchgear prevent system voltages from bleeding backwardsthrough the static switch and rectifier snubber components to the utility source.If the input power fails to return or is not within the acceptance windows required for normal operation, thebattery continues discharging until a DC voltage level is reached where the inverter output can no longersupport the connected loads. When this event occurs, the UPS issues another set of audible and visual alarmsindicating SHUTDOWN IMMINENT. Unless the rectifier has a valid AC input soon, the output can be supportedfor only two minutes before the output of the system shuts down. If the bypass source is available, the UPStransfers to bypass instead of shutting down.If at any time during the battery discharge the input power becomes available again, the rectifier and thebypass switchgear close and the rectifier begins to supply DC current to the converter and inverter. At thispoint, the unit returns to Normal mode. Depending on the total load and the duration of the battery discharge,battery current limit alarms may be seen for a short time due to the current required to recharge the battery.Figure 42. Path of Current Through the UPS in Battery ModeBypass InputRectifier Input OutputBypass SwitchgearRectifierSwitchgearInverterSwitchgearBatterySwitchgearClosedOpenMain Power FlowTrickle CurrentEnergizedDe-EnergizedSwitchgearRectifier InverterStaticSwitchBattery ConverterBatteryUnderstanding UPS Operation
