UNDERSTANDING UPS OPERATIONEATON Powerware® 9390 UPS (100–160 kVA) Installation and Operation Manual 164201604 Rev D www.powerware.com7-4The neutral from the system input is connected to the neutral regulator in the DCcapacitors. The output neutral of the system is connected with the required neutralsupplied at the utility bypass input and should never be bonded to ground at themodule's output.The inverter produces a three-phase AC output to a customer's load without the useof a transformer. The inverter derives regulated DC from the rectifier and uses IGBTdevices and pulse-width modulation (PWM) to produce a regulated and filtered ACoutput. The AC output of the inverter is delivered to the system output through theoutput contactor K3.If the utility AC power is interrupted or is out of specification, the UPS automaticallyswitches to Battery mode to support the critical load without interruption. When utilitypower returns, the UPS returns to Normal mode.If the UPS becomes overloaded or unavailable, the UPS switches to Bypass mode.The UPS automatically returns to Normal mode when the overload condition iscleared and system operation is restored within specified limits.If the UPS suffers an internal failure, it switches automatically to Bypass mode andremains in that mode until the failure is corrected and the UPS is back in service.7.1.3 Bypass Mode – RTThe UPS automatically switches to Bypass mode if it detects an overload, load fault,or internal failure. The bypass source supplies the commercial AC power to the loaddirectly. Figure 7‐3 shows the path of electrical power through the UPS system whenoperating in Bypass 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 – RT
