Manual 35018V1 505XT Digital Control System for Steam Turbines
Woodward 102
The MAX HP FLOW value is the flow where the HP=100 line crosses the HP-axis (about 54 000 lb/h; 24
494 kg/h).
Point A is where the P=0 extr/adm and LP=100 lines intersect (MAX POWER @ 0 EXTR/ADM = about 11
625 kW; MAX HP FLOW @ 0 EXTR/ADM = about
62 000 lb/h; 28 123 kg/h).
MAX ADMISSION = about 20 000 lb/h (9072 kg/h).
Point B is where the LP=0 and P=100 lines intersect (MIN POWER @ MAX EXTRACTION = about 1504
kW; MIN HP FLOW @ MAX EXTRACTION = about 28 000 lb/h; 12 701 kg/h).
Point C is where the LP=0 and zero extraction & admission flow lines intersect (MIN POWER @ ZERO
EXTRACTION/ADMISSION = about –205 kW; MIN HP FLOW @ ZERO EXTRACTION/ADMISSION =
about 8000 lb/h; 3629 kg/h).
An additional parameter, MIN HP LIFT (%), would also be set to 4000/54000 = 7.4%.
Operational Modes for Extraction/Admission turbines –
The 505XT will support several different modes of operation for Extraction/Admission turbine
configurations. In simple terms the 505 has 2 control valves so therefore it can control 2 parameters as
long as neither a parameter or a valve has reached a limit. Prior to configuring the 505XT control it is
important to understand which parameters are planned to be controlled by the 505 for the specific
plant/process steam turbine application. The typical configuration is to control Speed and Extraction
pressure (called Base mode below), however Inlet and/or Exhaust Pressure can also be achieved if the
unit has the process variable and the control mode is configured for use.
The table below shows the operational modes available in the configuration of the 505XT. To use a
mode, the listed control must be enabled for use as a Controller and the appropriate PV for that loop is
healthy.
Table 3-7. Alternate Modes for Ext/Adm turbines
MODE Control 1 Control 2 Ratio
Limiter
Used
Comment
Startup
Mode
Speed Only NO
Mode 0 Speed Extraction YES Base mode
Mode 1 Speed Inlet YES Alternate mode
Mode 2 Extraction Inlet YES Alternate mode
Mode 3 Speed Exhaust YES Alternate mode
Mode 4 Extraction Exhaust YES Alternate mode
Mode 5 Inlet Exhaust YES Alternate mode, but Decoupled
Mode 6 Inlet Exhaust YES Alternate mode
Fully
Decoupled
Speed Extraction NO Speed=HP Extraction=LP
During the startup of the turbine – the unit is in Speed control mode (Speed Only) and has full authority
over the HP inlet valve (Speed PID = Valve Demand). On a mechanical drive applications, once the
startup is complete the unit is considered ‘Online’. For a generator application once the generator breaker
is closed and the unit is, producing power the unit is considered ‘Online’.
Once the unit has reached ‘Online’ status, Extraction control can be enabled and the control will transfer
into Ratio Limiter control and enter into Speed/Extraction control mode. From this base mode the unit can
be transferred into any of the Alternate modes listed in the table above (if configured to do so). The
505XT supports multiple alternate modes – but any transition into an alternate mode must be initiated
from the base mode (Speed/Extraction).
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