Normal Operating Condition; Phase Error Control; Figure 7 Synchronization Components For Dual Bus System - Vertiv Liebert MBSM User Manual

Figure 7 Synchronization Components for Dual Bus System
Power Bus A
Bus A
Remote
CNTRL
Bus B
Remote
CNTRL
Power Bus B
2.7.1

Normal Operating Condition

During normal operation it is assumed that commercial power is present both on Bus A and Bus B
and UPS systems A an B running. Each UPS system performs, in real time, the analysis of the
commercial power present on the relative bus (amplitude and frequency) and gives a feedback
signal to the Liebert MBSM confirming the availability of the bus within the specific electrical
limits.
If one UPS system is shut down, the power bus control is not available: Under this condition, the
power bus related to the UPS system that is shut down is always considered inside limits
(feedback signal to the Liebert MBSM locked to OK condition).
The Liebert MBSM will select one of the two buses to generate the frequency reference. The
reference bus selection is random if both of them are inside preset limits. A manual selector on
the Liebert MBSM permits a priority on one specific bus. This manual selector has three positions:
• Automatic (no priority)
• Priority on Bus A.
• Priority on Bus B.
Should the selected bus fail, the Liebert MBSM will automatically select the other bus
independently from the preferred source selection.
If neither bus is available (not present at all or declared out of limits by the UPS systems), the
Liebert MBSM will source the frequency reference by an internal quartz oscillator tuned on the
system nominal frequency.
2.8

Phase Error Control

During normal operation, each UPS system will synchronize its inverter output to the input power
bus; the Liebert MBSM will constantly monitor the phase error between the two buses making an
indirect measure of the phase difference between the two secure buses.
Should the phase error overtake a preset limit (customizable from 5° to 15°), the Liebert MBSM
will switch to the active mode of operation.
™ ®
Vertiv | Liebert MBSM
System A CNTRL
MSBM
Auto
A B
System B CNTRL
™
User Manual |
UPS
System A
Frequency Reference
UPS
System B
Secure
Bus A
Secure
Bus B
13