Eaton Power Xpert 9395C Installation And Operation Manual

96 Eaton Power Xpert 9395C UPS Installation and Operation Manual 164000821—Rev 0666..44 MMuullttiippllee UUPPSS DDiissttrriibbuutteedd BByyppaassss SSyysstteemmDistributed bypass parallel operation extends the normal operation of 9395C UPSs by offering increasedcapacity and/or redundant capability. The parallel system continues to maintain power to the critical loadsduring commercial electrical power brownout, blackout, overvoltage, undervoltage, and out-of-tolerancefrequency conditions.Communication is required between the UPSs for system metering and mode control. System levelcommunication and control are accomplished using a Controller Area Network (CAN). A single building alarm ineach UPS, connected to the other UPSs in parallel and tied to the bypass contactor auxiliary contacts in eachUPS, are used for a secondary communication path. This arrangement ensures bypass control even if the CANbus is lost.66..44..11 MMuullttiippllee UUPPSS PPaarraalllleell SSyysstteemm MMooddeessSimilar to the single UPS system, the 9395C UPS parallel system supports a critical load in five different modesof operation. The standard operation modes are:• In Normal mode, the paralleled UPMs supply the critical load with clean, filtered power. Each UPM batterycharger also provides charging current for the battery if needed.• In Energy Saver mode, commercial AC power is supplied directly to the critical load through the continuousstatic switch and transfers automatically to Online mode if an abnormal condition is detected. The EnergySaver mode requires a UPS with a continuous static switch. Energy Saver mode in a parallel systemoperates the same as it does in a single UPS system (see paragrap6.2.3 Energy Saver System (ESS) Mode).• In Bypass mode, the critical load is directly supported by utility power through the bypass circuit in eachUPS.• In Battery mode, the battery provides DC power, which maintains UPM operation. The UPM batteriessupport the critical load.The UPSs continually monitor themselves and the incoming utility power and automatically switch betweenthese modes as required, without operator intervention, except when manually switching to Bypass mode. Thesophisticated detection and switching logic inside the UPSs ensures that operating mode changes areautomatic and transparent to the critical load, while internal monitoring systems indicate the current mode ofoperation. The UPSs switch operating modes in response to these system events:• A command is an intervention that is externally initiated by an operator or by some site action. A commandcauses the UPSs to switch operating modes; it usually does not 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 intervention.The following paragraphs describe the differences in the parallel system operating modes, using blockdiagrams to show the power flow during each mode of operation.66..44..22 OOnnlliinnee MMooddee DDiissttrriibbuutteedd BByyppaassssIn Online mode, utility AC power is supplied to the UPSs. Each UPS then conditions the incoming AC powerand provides clean, regulated AC power to tie cabinet or distribution panel for parallel systems up to fourmodules. The applied load is shared equally among the available UPMs in the system.Figure 59 shows the path of electrical power through the parallel system when operating in Online mode.If the utility AC power is interrupted or is out of specification, the UPSs automatically switch to Battery mode tosupport the critical load without interruption. When utility power returns, the UPSs return to Normal mode.Understanding UPS Operation