Rockwell Automation 1407-CGCM Combination Generator Control Module - Manual (Page 68)

68 Rockwell Automation Publication 1407-UM001G-EN-P - April 2013
Chapter 3 CGCM Unit Operation
Once the primary and secondary CGCM unit roles have been established by the
host controller, they remain in their respective modes indefinitely. You can force a
transfer by disabling excitation on the primary unit. This causes the secondary
unit to sense a loss of tracking information, switch to Primary mode, and take
over-excitation control.
Following a transfer, if the original failed primary CGCM unit is repaired and
returned to service, it detects tracking information from the primary unit and
remain in Secondary mode. In this state it is capable of taking over if the primary
unit fails.
In a typical redundant CGCM unit application, the host Logix controller
determines the generator's offline or online status by monitoring the status of the
generator breaker. When operating offline, the CGCM unit normally regulates
generator voltage in AVR mode. The host controller monitors generator voltage
and other conditions. If those conditions indicate a failure of the primary unit the
host controller initiates a transfer by disabling excitation to the primary unit. The
secondary unit senses the loss of tracking information from the primary unit,
designate itself the primary, energize its redundancy relay output and take
over-excitation control.
When operating online, that is with the generator breaker closed and the
generator operating in parallel with other generators or the power grid, the
CGCM unit normally operates in VAR or PF mode to regulate reactive power
flow. The host controller monitors generator conditions as in the offline
condition and initiates a transfer to the secondary CGCM unit as appropriate.
When operating online, the generator voltage is relatively fixed; therefore the
host controller can monitor a different set of conditions, such as over-excitation
or under-excitation.
Host controller operation is dependent on user-provided logic programming.
These events cause a CGCM unit to stop communicating to the backup:
• A fault of the digital signal processor
• A loss of redundant communication
• A watchdog time-out
• A loss of ControlNet communication
Redundancy Tracking
The CGCM unit provides a tracking function between the secondary and
primary CGCM units in a redundant system, to reduce the potential for
instability that can occur when transferring control between the two units. Two
settings you configure are provided. The redundant tracking rate defines the rate
at which the primary CGCM unit matches the output of the secondary CGCM
unit with its own output and is scaled in seconds per full-scale excursion of the
excitation output.