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Once the host controller establishes primary and secondary CGCM-DLR unit
roles, they remain in their respective modes indefinitely. You can force a transfer
by disabling excitation on the primary unit. The disabling of excitation causes the
secondary unit to sense a loss of tracking information, switch to Primary mode,
and take over-excitation control.
After a transfer, if the original failed primary CGCM-DLR unit is repaired and
returned to service, it detects tracking information from the primary unit and
remain in Secondary mode. In this state, it ican take over if the primary unit fails.
In a typical redundant CGCM-DLR unit application, the host Logix controller
determines the generator offline or online status by monitoring the status of the
generator breaker. When operating offline, the CGCM-DLR 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, which is with the generator breaker closed and the
generator operating in parallel with other generators or the power grid, the
CGCM-DLR 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-DLR unit as
appropriate. When operating online, the generator voltage is relatively fixed;
therefore the host controller can monitor another 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-DLR 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 EtherNet/IP communication
Redundancy Tracking
The CGCM-DLR unit provides a tracking function between the secondary and
primary CGCM-DLR units in a redundant system, to reduce the potential for
instability that can occur when control is transferred between the two units. Two
settings you configure are provided. The redundant tracking rate defines the rate
at which the primary CGCM-DLR unit matches the output of the secondary
CGCM-DLR unit with its own output and is scaled in seconds per full-scale
excursion of the excitation output.
Rockwell Automation Publication 1407-UM002B-EN-P - February 2019
CGCM-DLR Unit Operation
Chapter 3
73
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