9440300990 Rev J
57
DECS-250
Limiters
Limiters
DECS-250 limiters ensure that the controlled machine does not exceed its capabilities. Overexcitation,
underexcitation, stator current, and reactive power are limited by the DECS-250. It also limits the voltage
during underfrequency conditions.
Overexcitation Limiter
BESTCOMSPlus Navigation Path:
Settings Explorer, Operating Settings, Limiters, OEL
HMI Navigation Path:
Settings, Operating Settings, Limiters, OEL
Operating in the overexcited region of a generator’s capability curve can cause excessive field current
and field winding heating. The overexcitation limiter (OEL) monitors the level of field current supplied by
the DECS-250 and limits it to prevent field overheating.
The OEL can be enabled
A
in all regulation modes. OEL behavior in manual mode can be configured to
limit excitation or issue an alarm. This behavior is configured in BESTlogic™
Plus
.
Two styles of overexcitation limiting are available in the DECS-250: summing point or takeover
B
. OEL
settings are illustrated in Figure 44, Figure 45, and Figure 47.
Summing Point OEL
Summing point overexcitation limiting compensates for field overcurrent conditions while the machine is
offline or online. Offline and online OEL behavior is dictated by two separate groups of settings. Primary
and secondary setting groups (selectable in configurable logic) provide additional control for two distinct
machine operating conditions.
Offline Operation
For offline operation, there are two levels of summing-point overexcitation limiting: low and high. Figure
42 illustrates the relationship of the high-level and low-level OEL thresholds.
Figure 42. Summing Point, Offline, Overexcitation Limiting
The offline, low-level OEL threshold is determined by the low-level setting
C
. When the excitation level is
below the low-level setting, no action is taken by the DECS-250. The generator is permitted to operate
indefinitely with this level of excitation.
The offline, high-level OEL threshold is determined by a high level
D
and high time
E
setting. When the
excitation level exceeds the high level setting, the DECS-250 acts to limit the excitation to the value of the
high-level setting. If this level of excitation persists for the duration of the high time setting, the DECS-250
acts to limit the excitation to the value of the low-level setting.
Online Operation
For online operation, there are three levels of summing-point overexcitation limiting: low, medium, and
high. Figure 43 illustrates the relationship of the low-, medium-, and high-level OEL thresholds.
F
IE
L
D
C
U
R
R
E
N
T
TIME IN SECONDS
High
Current
Time
CONTINUOUS
P0063-09
0-10sec
Low
Current
Level
High
Current
Level
Содержание DECS-250
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Страница 32: ...16 9440300990 Rev J Voltage and Current Sensing DECS 250 ...
Страница 40: ...24 9440300990 Rev J Synchronizer DECS 250 ...
Страница 52: ...36 9440300990 Rev J Auxiliary Control DECS 250 ...
Страница 56: ...40 9440300990 Rev J Contact Inputs and Outputs DECS 250 ...
Страница 84: ...68 9440300990 Rev J Limiters DECS 250 ...
Страница 108: ...92 9440300990 Rev J Power System Stabilizer DECS 250 Figure 85 PSS Function Blocks and Software Switches ...
Страница 114: ...98 9440300990 Rev J Power System Stabilizer DECS 250 Figure 96 PSS Parameter Settings ...
Страница 124: ...108 9440300990 Rev J Stability Tuning DECS 250 ...
Страница 126: ...110 9440300990 Rev J Mounting DECS 250 Figure 103 Overall and Projection Mounting Dimensions ...
Страница 127: ...9440300990 Rev J 111 DECS 250 Mounting Figure 104 DECS 250 Escutcheon Plate Dimensions ...
Страница 128: ...112 9440300990 Rev J Mounting DECS 250 Figure 105 Panel Cutting and Drilling Dimensions for DECS 250 Panel Mounting ...
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Страница 210: ...194 9440300990 Rev J CAN Communication DECS 250 ...
Страница 304: ...288 9440300990 Rev J Maintenance DECS 250 ...
Страница 316: ...300 9440300990 Rev J Specifications DECS 250 ...
Страница 334: ...318 9440300990 Rev J Analog Expansion Module DECS 250 ...
Страница 341: ...9440300990 Rev J 325 DECS 250 Contact Expansion Module Figure 188 CEM 2020 Input Contact and Output Contact Terminals ...
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