Manual 35018V1
505XT Digital Control System for Steam Turbines
Woodward
114
When programmed as a Trip relay, the respective relay will function like the dedicated Shutdown relay
(normally energized and de-energizes on a shutdown) to indicate the position of the dedicated Shutdown
relay.
Controlled Shutdown
The Controlled Shutdown function is used to stop the turbine in a controlled manner, as opposed to an
Emergency Trip. When a STOP command (controlled shutdown) is issued, the following sequence is
performed:
1. Cascade, Auxiliary, Inlet, and Exhaust PID controllers (if used) are disabled. If unit is Ext/Adm unit it
will return to coupled mode prior to disabling Inlet or Exhaust (Speed and Extraction control)
2. If unit is Ext/Adm turbine the control will transition from ratio limiter control to speed control only
mode. It will then disable Ext/Adm control
3. The Speed Set Point is ramped to min load set point at normal rate (only for generator application).
4. When at min load (only for generator application), the controller will wait until the generator breaker
opens (only if “Reverse Power Protection?” = True). If a relay output is configured as “generator open
pulse (2s)”, then this relay will temporarily energize for 2 seconds.
5. The Speed Set Point is ramped to its low idle level.
6. Once the speed set point has reached its low idle point, the HP valve limiter is then ramped to zero
percent at a controlled rate. At this point if the “Controlled Stop & Trip” setting is configured to “no” the
control will then wait for a Start command to restart the turbine. However, if the “Controlled Stop &
Trip” setting is configured to “yes” the control will then execute a turbine shutdown.
With the control in the run mode and the turbine turning, when the 505’s “STOP” key is pressed, the
control will display a message prompting the operator to verify the command (“Initialize Normal Stop?”).
At this point, if the “OK” command is issued, the control will perform the controlled shutdown sequence
explained above. Issuing the “Cancel” command will cause no change in the 505’s operation and the
Normal Stop confirmation pop-up box will disappear. This verification feature prevents an unwanted
shutdown if the STOP key is accidentally pushed.
A controlled shutdown can be initiated or aborted from the 505 front panel, a programmed contact input,
or either Modbus communication link. Verification is not required if a controlled shutdown command is
initiated by a programmed contact input or Modbus communication link.
The controlled shutdown sequence can be aborted at any time. During a controlled shutdown sequence,
by pressing the STOP key, the 505 will display a “Abort Normal Stop?” message. Selecting “OK” from this
screen will cause the shutdown sequence to be aborted. At this point the shutdown sequence can be re-
initiated when desired, or the unit can be brought back to a fully operational state.
If an external contact is programmed to issue a controlled shutdown command, closing the contact will
initiate the controlled shutdown sequence. The shutdown sequence will go through the same steps
described above, with the exception that verification of the shutdown sequence is not needed. Opening
the programmed contact will stop the sequence. The contact can be either open or closed when a trip
condition is cleared. If the contact is open it must be closed to issue the command. If the contact is closed
it must be opened and re-closed to issue the command. The Modbus initiated Control Shutdown
Sequence requires two commands, one to start the sequence and the other to stop it.
The speed sensor failure trip, generator breaker open trip, and tie breaker open trip commands are
overridden when a controlled shutdown is initiated.
This command can be disabled through the Service Mode, if desired
(see Key Options). When disabled, the Controlled Stop feature is
disabled from front panel, Modbus, and contact commands.