Woodward 505XT User Manual

Manual 35018V1 505XT Digital Control System for Steam Turbines
Woodward 111
When a valid set point value is entered, the set point will ramp at the ‘Valve Limiter Rate’ to the newly
entered set point value. This ‘Entered’ rate is tunable through the Service mode.
During start-up, if the control is set to use Automatic start-up, and if the valve limiter as been manually set
for trouble shooting, it is possible to automatically ramp it back to 100%, by issuing a ‘Run’ command
again.
Refer to Volume 2 of this manual for further information on Service mode and on-line tunables. All
pertinent valve limiter parameters are available through the Modbus links. See Chapter 6 for a complete
listing of Modbus parameters.
LP Valve Limiter
The LP valve limiter, limits the actuator output signal (Ext/Adm valve position). Depending on the turbine
type, this limiter will feed either an LSS or an HSS. This limiter is used to manually bring a unit into
Ext/Adm control and can also be used as an aid in troubleshooting system dynamics.
In an Extraction turbine the output of the LP valve limiter is High-Signal-Selected with the output of the
Ratio Limiter controller. Lowering the limiter from maximum (100%) to minimum (0%) will manually enable
extraction control.
In an Admission turbine the output of the LP valve limiter is Low-Signal-Selected with the output of the
Ratio Limiter controller. In this type of turbine, the limiter is ramped from minimum (0%) to maximum
(100%) demand to enable admission control.
Manual Valve Demand
The manual valve demand feature functions just like the valve limiter except that, instead of providing an
input to the Low Signal Select to limit how high the valve demand can go, it disables all other controllers
(including speed) to ensure that manual demand has full control of the valve demand output. The intent of
this feature is to aid in the troubleshooting of plant stability or oscillation issues. It can be used to
temporarily hold the valve in its current position.
This feature can be selected using the Service Menu. In addition to holding the valve demand output,
manual demand allows the valve demand to be adjusted manually, preferably at a very slow and safe
rate. When selected, the valve ramp rate for this feature can be adjusted. This should be set to a value
that is safe and stable for speed, load, or any process and pressures associated with the turbine that will
be affected by moving this valve. Also, the timeout time can be adjusted. After this time the feature will
disable if no raise/lower manual demand commands are received. Every time a raise or lower manual
demand command is issued, the timer will restart.
Because of the risk associated with locking the valve in place there are many protections that disable this
function, which will return the unit to Speed PID control, in addition to the normal disable command
functionality and the timeout protection. All items that will disable this feature are as follows:
 Operator interface disable command
 Manual Demand not used (Service menu setting)
 Any Turbine Trip
 Startup not completed or Overspeed Test enabled
 Speed less than Minimum Governor
 Speed greater than Maximum Governor
 Both breakers not closed (generator applications only)
 Timeout due to inactivity

Woodward 505XT Specifications

General

Brand	Woodward
Model	505XT
Category	Control Unit
Language	English