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Rockwell Automation Publication 1407-UM002B-EN-P - February 2019
Chapter 3
CGCM-DLR Unit Operation
If a loss of communication between redundant CGCM-DLR units occurs, the
primary CGCM-DLR unit remains primary and the secondary CGCM-DLR
unit switches to primary also. Because in this state both units are supplying
current to the field, the host Logix programmable controller must be
programmed to take corrective action when this condition occurs. For example,
disable excitation to one CGCM-DLR unit.
Redundancy Relay Output
The redundancy relay output is energized (sinks current) when the
CGCM-DLR unit is in Primary mode. If the CGCM-DLR unit experiences a
failure or operates in Secondary mode, the redundancy output is de-energized.
The output is used to energize your relay that connects excitation output of the
primary CGCM-DLR unit to the generator field.
When the excitation outputs from two CGCM-DLR units are connected
through relays to the generator exciter field, you must place flyback diodes across
the generator field winding to provide a path for exciter current during a transfer.
To prevent errors in field current measurement, place three or four diodes in
series. If fewer diodes are used, the field current splits between the external diode
and the internal circuitry and prevent the current measurement circuit from
sensing the total field current.
Redundancy Operation
CGCM-DLR units in a redundant system must both be connected to the
generator and bus VTs and the generator and cross-current CTs, as applicable.
Connect the units excitation outputs through the relays you provide to the
generator exciter field. In addition, properly connect the redundancy
communication cable and verify that the CGCM-DLR unit configurations
match.
CGCM-DLR units that are used in a redundant configuration are normally
designated as primary and secondary, depending on the order in which the host
controller enables excitation. With excitation disabled, each CGCM-DLR unit
starts out in a Secondary mode. When the host controller enables excitation on
the first CGCM-DLR unit, it checks for tracking information on the
redundancy communication channel. If no tracking information is received, the
CGCM-DLR unit switches to Primary mode. When the host controller then
enables excitation on the secondary CGCM-DLR unit, it begins receiving
tracking information and remains in Secondary mode. The primary
CGCM-DLR unit indicates its status by setting the
Spare1
tag in the software
interface to the host controller.
If the primary CGCM-DLR unit fails or if its excitation is disabled, it stops
sending tracking data on the redundancy communication channel. When the
secondary senses a loss of tracking data, it automatically switches to Primary
mode and takes over the excitation control. It remains primary until the host
controller disables its excitation.