Manual 35018V1 505XT Digital Control System for Steam Turbines
Woodward 91
Figure 3-19. Transitions between Speed only and Ratio Limiter Control – Auto Mode
The LP valve limiter may be stopped at any time during the automatic enabling routine by momentarily
issuing a LP limiter raise or lower command (or by entering a valid setpoint). Stopping the automatic
enabling routine halts the LP valve limiter. The Extr/Adm PID’s output will continue to be enabled. This
allows an operator to manually adjust the LP valve limiter as desired. By reissuing an enable command,
the enable routine will continue lowering the LP valve limiter. If a contact is programmed for this function,
it will have to be opened and re-closed to re-issue an enable command.
Upon receiving a disable command, the 505XT will instantly step the LP valve limiter to the LP valve’s
present position, then raise the LP limiter to its maximum (open) position at the “LP valve limiter rate”
setting. At some point, depending on system conditions the Extr/Adm PID will lose control of its process.
Manual Enable / Disable -
Enabling is done by the operator manually lowering the LP limiter value from 100% to 0%. The LP
demand output will follow this value until it reaches the LP demand output value of the ratio limiter block.
The control will enable Ext/Adm control when this value is reached. The operator should continue to ramp
the LP to 0% unless it is desired to limit the amount of extraction flow.
Disabling is done by the operator manually raising the LP limiter value from 0% to 100%. The LP demand
output will not follow this value until it exceeds the LP demand output value of the ratio limiter block. At
this point it will raise the LP demand as the operator continues to raise the limiter. The control will not
disable Ext/Adm until the limiter reaches 100%.
To Next Page
Loading...
Need help?
General
