Powerware 9390 UPS 100160 kVA - Manual (Page 59)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9390 UPS (20–80 kVA) Installation and Operation Manual S 164201603 Rev 2 www.powerware.com 7-7
If at any time during the battery discharge the input power becomes available again,
contactors K1 and K5 close and the rectifier begins to supply DC current to the
converter and inverter. At this point, the unit returns to Normal mode. Depending on
the total load and the duration of the battery discharge, battery current limit alarms
may be seen for a short time due to the current required to recharge the battery.
The system's total operating time on battery depends on many factors. Some factors
that affect battery support times are battery type and capacity, number of parallel
strings, environmental temperatures, age of the battery, and fluctuations in load
demand during the discharge. The greater the load, the less support time the battery
has. Decreasing the load generally increases the battery support time.
7.2 Multiple Module Parallel System
Parallel operation extends the normal operation of Powerware 9390 UPS units 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. See
Drawing 164201603-4, sheets 3 of 5, 4 of 5, and 5 of 5 in Appendix A, for a detailed
relationship of the parallel system.
The output of the system is normally supplied by several uninterruptible power
modules (UPMs). 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 UPM static
switches.
Communication is required between the UPMs for system metering and mode
control. System level communication and control are accomplished using a
Powerware Hot Sync
® CAN Bridge Card. A single building alarm in each UPM,
connected to the other UPMs in parallel, and tied to the bypass contactor auxiliary
contacts in each UPM are used for a secondary communication path. This
arrangement ensures bypass control even if the CAN bus is lost.
Up to four units can be paralleled for redundancy or capacity without any additional
cabinets.
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.