UNDERSTANDING UPS OPERATIONEATON Powerware® 9390 UPS (100–160 kVA) Installation and Operation Manual 164201604 Rev D www.powerware.com7-2The emergency bypass consists of a continuous-duty static switch and backfeedprotection contactor K5. The backfeed protection contactor is located in series withthe static switch. For manual transfers to bypass, the static switch is also used. Thestatic switch is armed and ready during both types of transfers.The UPS module may be configured for standalone, single module, Reverse Transfer(RT) operation or multiple module, parallel redundant and/or parallel capacity operation(see paragraphs 7.1 and 7.2).7.1 Single Module Reverse Transfer (RT)A single module operates independently to support an applied load from the inverter,providing conditioned and uninterruptible AC power to the critical load from the outputof the module. During an outage, the inverter continues to operate, supporting powerto the load from the battery supply. If the unit requires service, applied loads aretransferred to the internal bypass, continuous-duty static switch either automaticallyor manually. With the exception of a battery cabinet, no other cabinets or equipmentare required for the single module to successfully support its applied loads.7.1.1 Single Module RT ModesThe Powerware 9390 UPS supports a critical load in three different modes ofoperation. The UPS can automatically use all three modes, as required. The standardoperation modes are: Normal mode – The critical load is supplied by the inverter, which derives its powerfrom rectified utility AC power. In this mode, the battery charger also providescharging current for the battery, if needed. Battery mode – The battery provides DC power, which maintains inverter operation.The battery supports the critical load. Bypass mode – The critical load is directly supported by utility power.The UPS continually monitors itself and the incoming utility power, and automaticallyswitches between these modes as required, without operator intervention. Thesophisticated detection and switching logic inside the UPS ensures that operatingmode changes are automatic and transparent to the critical load, while internalmonitoring systems indicate the current mode of operation. The UPS switchesoperating modes in response to these system events: A command is an intervention that is externally initiated by an operator or by somesite action. A command causes the UPS to switch operating modes; it usually doesnot require any further action. A notice is a minor system event that may or may not require attention. An alarm is a system event that requires immediate operator intervention.System events, alarm horns, and indicator lights are described in Chapter 11,“Responding to System Events.”The following paragraphs describe the differences in the three UPS operating modes,using block diagrams to show the power flow during each mode of operation.
