12-2 9440300990
Grid Code DECS-250
High and Low Voltage
The High Voltage region in Figure 12-1 is defined by two settings: Max Voltage for Disconnect and Max
Voltage for Continuous Operation. When grid voltage is within the range defined by these two settings,
the Voltage Disconnect timer is active.
The Low Voltage region in Figure 12-1 is defined by two settings: Min Voltage for Disconnect and Min
Voltage for Continuous Operation. When grid voltage is within the range defined by these two settings,
the Voltage Disconnect timer is active.
Out of Range
When grid voltage or frequency are outside of the regions shown in Figure 12-1, the Grid Disconnect
timer is active.
Disconnection Timers
When the Frequency Disconnect Timer, Voltage Disconnect Timer, or the Grid Disconnect Timer expires,
the generating unit is permitted to disconnect from the grid.
Rather than performing the disconnection, the DECS-250 issues a logic
indication which can be used to energize a physical output. See the
BESTlogic™Plus chapter for details on the GCC Disconnected status input.
The duration of the Frequency Disconnect timer is defined by the Frequency Disconnect Time Delay
setting, the Voltage Disconnect timer is defined by the Voltage Disconnect Time Delay setting, and the
Grid Disconnect timer is defined by the Grid Disconnect Time Delay setting. The Grid Disconnect timer
may be set to 0 for immediate disconnection.
Grid Recovery Mode
Once the generating unit has disconnected from the grid due to expiration of the Grid Disconnect timer,
the DECS enters Grid Recovery Mode. In this mode, grid voltage and frequency are monitored and must
remain within certain limits for a period of time to ensure stability. The grid recovery frequency limits are
defined by the Max Frequency for Reconnect and Min Frequency for Reconnect settings. The grid
recovery voltage limits are defined by the Max Voltage for Reconnect and Min Voltage for Reconnect
settings. The grid recovery stability time is defined by the Grid Reconnect Stability Timer setting.
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