Basler Electric DECS-250N - Manual (Page 73)

9440500990 Rev D 57
DECS-250N Limiters
Limiters
DECS-250N limiters ensure that the controlled machine does not exceed its capabilities. Overexcitation,
underexcitation, stator current, and reactive power are limited by the DECS-250N. 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-250N 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-250N: summing point or takeover. B OEL
settings are illustrated in Figure 45, Figure 46, 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-250N. 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-250N 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-
250N 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