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Rockwell Automation Publication 1407-UM002B-EN-P - February 2019
Chapter 3
CGCM-DLR Unit Operation
Under-excitation Limit
The Under-excitation limit (UEL) operates in all modes except FCR mode. UEL
senses the leading VAR input of the generator and limits any further decrease in
excitation to prevent loss of synchronization and the excessive end-iron heating
during parallel operation. UEL operates in the area below the Armature Core
End-iron Heating Limitation curve in the generator capability curve.
A customizable UEL limiting curve is defined by a piecewise linear curve that is
specified by five points you select. An example is shown in the
diagram.
When the generator is operating in the area of its characteristic curve below the
UEL curve, the UEL alarm tag
UEL_Active
= 1. In FCR mode, the UEL limit is
not active although the tag is set. This tag is in the Scheduled Read table.
Figure 34 - Typical UEL Limiting Curve
TIP
The UEL function is not designed to prevent the loss of excitation
function from operating.
Real Power Generate (W) x 1000
0.0
7.5k 15.0k 22.5k 30.0k 37.5k 45.0k
0.0
2.5k
5.0k
7.5k
10.0k
12.5k
15.0k
Reactive Power Absorb (var) x 1000