Allen-Bradley 1407-CGCM, User Manual, Page: 67 / 252

Rockwell Automation Publication 1407-UM001H-EN-P - November 2014
CGCM Unit Operation #HAPTER
If a loss of communication between redundant CGCM units occurs, the primary
CGCM unit remains primary and the secondary CGCM 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 (for example disable excitation to one CGCM unit) when this condition
occurs.
2EDUNDANCY2ELAY/UTPUT
The redundancy relay output is energized (sinks current) when the CGCM unit
is in Primary mode. If the CGCM 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 unit to
the generator field.
When the excitation outputs from two CGCM 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.
2EDUNDANCY/PERATION
CGCM 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 unit configurations match.
CGCM units 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 unit starts out in a
Secondary mode. When the host controller enables excitation on the first
CGCM unit, it checks for tracking information on the redundancy
communication channel. If no tracking information is received, the CGCM unit
switches to Primary mode. When the host controller subsequently enables
excitation on the secondary CGCM unit, it begins receiving tracking
information and remains in Secondary mode. The primary CGCM unit
indicates its status by setting the
Spare1 tag in the software interface to the host
controller.
If the primary CGCM 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-excitation control. It remains primary until the host controller disables its
excitation.