Repairing The Failed Ups Unit In Parallel Operation System - Liebert UPS System User Manual

Chapter 8 Parallel System
2. Normal mode to bypass mode
Press the "inverter shutdown" button on the UPS panels one by one, all the UPS
can transfer to bypass mode.
In the above operation, if the total capacity of all the inverters is smaller than the
load capacity, all the UPS unit will transfer from normal mode to bypass mode.
3. Bypass mode to normal mode
Q1 has already been switched on, press the "inverter start" button on the UPS
panels one by one until the total capacity of all inverters is bigger or equal to load
capacity, all the UPS units will transfer from bypass mode to normal mode.
4. Battery mode to normal mode
If the utility is normal and the Q1 of all the UPS units are switched on, the UPS will
transfer from battery mode to normal mode automatically.
5. Normal mode to maintenance bypass mode
Follow the Steps 1～4 in section 8.5.2 to switch the UPS from normal mode to
maintenance bypass mode.

8.5.4 Repairing the failed UPS unit in parallel operation system

1. Shut down and isolate the failed UPS in parallel operation system
When some UPS unit fails in the system, isolate it and let other UPS units continue
to operate, the procedures are given below:
1) press "inverter shutdown" button to shut down the inverter of the UPS. Note:
Before switching off this UPS, verify whether the remaining UPS units can power
the load;
2) switch off this failed UPS unit's Q5, Q2 and Q1;
3) switch off this failed UPS unit's battery switch QF1;
4) maintenance work can be done after waiting for 8 minutes( that is, after the DC
bus capacitor discharges to zero voltage).
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