Battery Voltage Imbalance Detection - ABB Pulsar Edge Product Manual

produced by the total number of rectifiers less one or the configured value for the desired redundancy.
If the measured load current exceeds the N (or adjusted) rectifier's capacity for over 1 min, the alarm
condition is activated. The alarm condition is latched on until the Clear Events command is activated
from the front panel.
This feature may be used by customers to determine if the load being served is greater than N
rectifiers worth, in an N+1 system. That is, the load requirements have changed such that the power
system is no longer operating as a redundant power system. An additional rectifier may be required to
ensure continuous redundant operation. More rectifiers may be required if more than N+1 redundancy
is configured and required.
If enabled, this feature will be disabled during battery discharge and recharge conditions. It will be
enabled when the battery charging current falls below 5A.

Battery Voltage Imbalance Detection

This feature requires the use of the ES771A Remote Voltage Monitoring Module. Note that this feature
is automatically enabled if the controller detects the presence of the ES771A module. This module is to
be placed in the electronics cabinet and utilizes the QS873A VT-Probes to measure the mid-string
voltage of the particular battery string being monitored. The VT-Probe is to be placed on the negative
battery terminal of the battery located in the middle of the battery string. The Pulsar Edge controller
has data on the system DC bus voltage. The half-string voltage measurement obtained from the ES771
monitoring the battery string is compared to the system DC bus voltage minus the value of the
half-string voltage measurement. If the comparison results in a difference of greater than 1.7V or the
value configured for this threshold for longer than 12 hours, the alarm is asserted. The alarm may be
retired by initiating the Clear Events command.
After this feature has been enabled, the system waits for 12 hours to ensure the battery strings are
stable. A battery string is considered to be stable if the charging current is less than 3A. If a stable
battery string yields a difference measurement greater than 1.7V or the value configured for this
threshold for over 12 continuous hours, a Battery Voltage Imbalance alarm is generated.
When the alarm is issued, the Float Set-Point (fsp) and the Battery On Discharge (BD) threshold values
are reduced by fsp/Number of Cells per string. Thus, for an fsp=54.5 the system DC bus voltage would
be reduced by 54.5/24 or approximately 2.27V. Once the alarm has been cleared by the Clear Events
(CLE) command, the plant reverts to its normal fsp; however, the BD threshold is maintained at the new
threshold for up to four minutes before reverting back to the old threshold. This is done to ensure the
batteries have had enough time to charge up to the nominal fsp and to prevent any spurious BD alarm
conditions.
This feature may be used by customers as part of their overall battery maintenance program in
determining the health of battery strings. A voltage imbalance of 1.7V or the value configured for this
threshold between half-string voltages may mean a shorted-cell exists somewhere in the string. A
service person can be sent out to the site and determine if the string is bad and should be replaced.
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