Eaton 93PM UPS (400V/480V Four-Wire – 100 kW Frame) Installation and Operation Manual 164000566—Rev 04 8955..22..22 EEnneerrggyy SSaavveerr SSyysstteemm MMooddeeWhen the UPS is operating in ESS mode, commercial AC power is supplied directly to the critical load throughthe internal bypass with the power module in a standby state. Surge protection and some filtering is alsoprovided, ensuring that clean power is delivered to the load equipment. If a commercial power brownout,blackout, overvoltage, undervoltage, out-of-tolerance frequency condition occurs, or any other disturbance isdetected in the incoming power, the system forward transfers to normal mode (double-conversion ondemand). In case of a complete utility outage or if input power is outside the tolerances of the system, the UPStransfers to battery mode and continues to supply conditioned, clean power to the critical load. When the inputline returns to normal operating range, the UPS returns to ESS operation. For charging batteries, the UPS willnot enter ESS mode until charger is 25% or less of maximum charger current.When operating in ESS, the UPS superior detection and control algorithms continuously monitor incomingpower quality and allow the fast engagement of power converters. Typical transition time to double conversionis less than two milliseconds, which is practically seamless. If the UPS detects a fault condition while operatingin ESS, it is also able to detect and determine whether the fault is caused by the load or if it is upstream fromthe UPS. A fault at the bypass source results in an immediate switch over to the inverter; a fault in the loadkeeps the UPS in Energy Saver System (ESS) mode.When power conditions are within acceptable limits, the UPS operates as a high-efficiency, energy-savingsystem — providing surge protection for IT equipment and ensuring clean power is delivered to the facility.Energy saver system increases system efficiency to 99% at 100% linear load and nominal Vin.Figure 39 shows the path of electrical power through the UPS system when the UPS is operating in Normalmode.ESS mode is a normal operating mode, and not an alarm condition. While the UPS is in this mode, theNORMAL light on the front display will illuminate.Figure 39. Path of Current Through the UPS in Energy Saver System ModeStaticSwitchBypass InputRectifier Input OutputBypass SwitchgearRectifierSwitchgearInverterSwitchgearBatterySwitchgearClosedOpenMain Power FlowTrickle CurrentEnergizedDe-EnergizedSwitchgearRectifier InverterStaticSwitchBattery ConverterBatteryUnderstanding UPS Operation
