GE Industrial Solutions Galaxy Vector Controller GCM3 - Manual (Page 39)

Galaxy Vector Controller GCM2, GCM3
Issue 4 January 2008 Operation 3 - 5
The two lowest thresholds are preset at the factory but can be
adjusted through the Vector control panel or remotely. The third
threshold (ISHVSD) is generated by the controller by adding
1.50V to the very high voltage threshold. This value is then
transmitted to the rectifier and stored. Each rectifier compares its
own output voltage to this threshold value and initiates internal
shutdown if the value is exceeded. “Very High Voltage” and
“High Float Voltage” are set in the Vector in the Configuration
mode. See Section 4, Installation, Configuration and Operation.
The Vector is equipped to detect a high voltage condition on the
system bus. Such a high voltage condition may typically be
caused by lightning-induced transients on the commercial ac or
a rectifier failure may cause an individual rectifier to go high. To
prevent a high voltage condition from damaging the connected
load, the Vector also sends a signal for the rectifiers to shut down
if the plant voltage goes above a second threshold.
When the system voltage increases above the threshold for
“High Float Voltage,” it issues the High Float Voltage minor
alarm. If the voltage continues to rise and reaches the threshold
for “Very High Voltage,” that alarm is issued as a major alarm
and a shutdown signal is issued simultaneously to the plant
rectifiers. Any rectifier which is producing at least 10% of its
rated capacity and is 10% over the average of all rectifier outputs
in the plant, responds to this shutdown signal by shutting down
with a RFA or ALM condition active and reports back to the
Vector. A restart attempt initiated by the controller occurs 4
seconds after the controller receives the RFA signal from the
rectifier. The rectifier then attempts to restart three times. During
the restart sequence, the rectifier, recognizing that its output
current exceeds the average rectifier current, shuts down and
tries again up to three times.
For plants with the battery thermal lower temperature
compensation disabled, the High Float Voltage threshold is
usually set approximately 0.75V above float for a 48V plant and
0.5V above float for a 24V plant. High Voltage shutdown
threshold is then usually set approximately 2.5V above float for
a 48V plant and 1.0V above float for a 24V plant. In plants with
battery thermal lower temperature compensation enabled, the
High Float Voltage threshold is usually set approximately 0.8V
above the maximum voltage due to low temperature in a 48V
plant and 0.5V in a 24V plant.