9492600990 9-1
DECS-150 Limiters
9 • Limiters
DECS-150 limiters ensure that the controlled machine does not exceed its capabilities. Overexcitation,
underexcitation, stator current, and reactive power are limited by the DECS-150. It also limits the machine
voltage during underfrequency conditions.
Overexcitation Limiter
BESTCOMSPlus Navigation Path: Settings Explorer, Operating Settings, Limiters, OEL
Operating in the overexcited region of a machine’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-150 and limits it to prevent field overheating.
The OEL can be enabled 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-150: Summing Point or Takeover. OEL
configuration settings are illustrated in Figure 9-1.
OEL Voltage Dependency
The OEL voltage dependency function is applicable to only Summing Point style. It is used to enable the
OEL High-Level setting when a fault is present. The OEL High-Level setting is enabled when the dv/dt
level is less than the setting. Otherwise, only the Medium-Level and Low-Level settings are enabled.
OEL Shutdown
When this setting is enabled and the OEL limiter is active, the DECS-150 will shut down after the
Shutdown Delay time expires.
Figure 9-1. OEL Configure Screen
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.
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