Powerware 650825 kVA Multiple UPS Distributed Bypass System, Multiple UPS Parallel System Modes

UNDERSTANDING UPS OPERATION

6.4Multiple UPS Distributed Bypass System

Distributed bypass parallel operation extends the normal operation of Powerware 9395 UPSs by offering increased capacity and/or redundant capability. The parallel system continues to maintain power to the critical loads during commercial electrical power brownout, blackout, overvoltage, undervoltage, and out-of-tolerance frequency conditions.

The output of the system is normally supplied by several Uninterruptible Power Modules (UPMs) contained in each UPS. Multiple UPMs are connected with their outputs in parallel (tied together) to provide a load level greater than the rating of one UPM and/or for redundancy. The paralleled UPMs supply the output load with protected power as long as the load does not exceed the combined rating of the paralleled UPMs.

The power system is redundant as long as one of the UPMs can be disconnected from the output bus and the remaining UPMs can continue to supply power to the load without exceeding their ratings.

When the load is being supplied by the UPMs, the system output bus is continuously monitored for an overvoltage or undervoltage condition. If an out of limits condition is detected, the paralleled UPMs transfer the load to bypass using the UPS static switches.

Communication is required between the UPSs for system metering and mode control. System level communication and control are accomplished using a Controller Area Network (CAN). A single building alarm in each UPS, connected to the other UPSs in parallel and tied to the bypass contactor auxiliary contacts in each UPS, are used for a secondary communication path. This arrangement ensures bypass control even if the CAN bus is lost.

The system is paralleled for redundancy (1+1) in a system where two UPMs are paralleled together and the load is less than the supporting capability of one of the UPMs. The system is paralleled for capacity (2+0) if both UPMs in a system are required to support the load.

A parallel capacity system can also be redundant (2+1), as long as there is always one or more UPMs online than required to support the load.

6.4.1Multiple UPS Parallel System Modes

Similar to the single UPS system, the Powerware 9395 UPS parallel system supports a critical load in three different modes of operation. The standard operation

modes are:

SIn Normal mode, the paralleled UPMs supply the critical load with clean, filtered power. Each UPM battery charger also provides charging current for the battery if needed.

SIn Battery mode, the battery provides DC power, which maintains UPM operation. The UPM batteries support the critical load.

SIn Bypass mode, the critical load is directly supported by utility power through the continuous−duty static bypass switch in each UPS.

EATON Powerware® 9395 UPS (650–825 kVA) Installation and Operation Manual S 164201725 Rev 2 www.powerware.com 6−21