9440300990 7-9
DECS-250 Regulation
Internal Setpoint Tracking
In applications using a single DECS-250, internal tracking can be enabled so that the inactive regulation
modes track the active regulation mode.
The following examples demonstrate the advantages of internal tracking:
• If the excitation system is operating online with internal tracking enabled, a loss of sensing condition
could trigger a transfer to FCR mode. Autotracking minimizes the impact that a loss of sensing
condition has on the exciter’s ability to maintain the proper excitation level.
• While performing routine testing of the DECS-250 in backup mode, the internal tracking feature
allows a transfer to an inactive mode that will result in no disturbance to the system.
Two parameters control the behavior of internal tracking. A delay setting determines the time delay
between large system disturbance and the start of setpoint tracking. A traverse rate setting configures the
length of time for the inactive mode setpoints to traverse the full setting range of the active mode setpoint.
External Setpoint Tracking
For critical applications, a second DECS-250 can provide backup excitation control. The DECS-250 (style
xx2xxxx) allows for excitation redundancy by providing external tracking and transfer provisions between
DECS-250 controllers. The secondary DECS-250 can be configured to track the primary DECS-250
setpoint. Proper redundant excitation system design allows for removal of the failed system.
Periodic testing of the backup system must be performed to ensure
that it is operational and can be placed in service without warning.
Like internal tracking, external setpoint tracking uses enable/disable, delay, and traverse rate settings.
Figure 7-6. Autotracking Settings
Setpoint Configure
When the Auto Save setting is enabled, the DECS-250 automatically saves the active setpoint in
10-minute intervals. Otherwise, the setpoint which was last sent to the DECS-250 is retained. Figure 7-7
illustrates the Setpoint Configure screen.
Figure 7-7. Setpoint Configure Setting
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