Rockwell Automation 1407-CGCM Combination Generator Control Module - Manual (Page 52)

52 Rockwell Automation Publication 1407-UM001G-EN-P - April 2013
Chapter 3 CGCM Unit Operation
Over-excitation Limit
Over-excitation limiting (OEL) operates in all modes except FCR. The CGCM
unit senses and limits the field current to prevent field overheating. When the
limit is reached, the limiter function overrides AVR, VAR, or Power Factor
modes to limit field current to the preset level. OEL operates in the area above
the Field Winding Heating Limitation curve in the generator capability curve.
The generator operates in one of two different states, offline or online. The
generator is offline when it is operating in a constant-voltage mode. The CGCM
unit is considered online if any of these modes are enabled:
• Droop (reactive power) compensation
• Cross current compensation
• Line drop compensation
Two OEL current levels, high and low, are defined for offline operation as shown
in the graph below. The generator can operate continuously at or below the low
OEL current level and for a time at the high OEL current level that you
configure.
Figure 32 - Offline Over-excitation Limiting
Three OEL current levels, high, medium, and low are defined for online
operation as shown in the graph below. The high and medium current levels can
be maintained only for time periods you define. The generator can operate
continuously at or below the low OEL current level.
Figure 33 - Online Over-excitation Limiting
FIELD
C
URRENT
TIME IN SECONDS
High
Current
Time
CONTINUOUS
0…10 seconds
Low
Current
Level
0…15 A dc
High
Current
Level
0…30 A dc
FIELD CURRENT
TIME IN SECONDS
High
Current
Time
0…10 seconds
CONTINUOUS
Medium
Current
Time
0…120 seconds
Low
Current
Level
0.0…15 A dc
Medium
Current
Level
0.0… 20 A dc
High
Current
Level
0.0…30 A dc