Manual 35018V1 505XT Digital Control System for Steam Turbines
Woodward 55
4. Raise the 505’s VALVE LIMITER at a controlled rate.
When turbine speed increases to the minimum controlling speed, the 505’s Speed PID will take
control of turbine speed by controlling turbine inlet valve position.
5. Raise the 505’s VALVE LIMITER to 100%.
Speed remains controlled at the minimum controlling point until action is taken by the operator or the
‘AUTO START SEQUENCE’, if programmed, begins controlling.
The valve limiter will open at the ‘Valve Limiter Rate’ and may be moved using the 505 keypad, external
contacts or Modbus communications. The ‘Limiter Max Limit’, ‘Valve Limiter Rate’ and ‘Rate To Min’
settings are tunable in the Service mode.
Figure 3-6. Semiautomatic Start mode Example
Automatic Start Mode
The following start-up procedure is employed when the Automatic start mode is configured:
1. Issue a RESET command (to reset all alarms and shutdowns). The LP demand and LP Limiter
behavior is determined by the turbine type.
a. Extraction Only: The LP Limiter will ramp to 100%
b. Admission Only or Extraction/Admission: The LP Limiter will ramp to 100%. The LP valve
position will vary to maintain zero admission flow, defined by the steam map.
i. For Full-Decoupled configurations with any admission control, the LP Valve Limiter
will remain at the LP Minimum demand.
2. Open the Trip & Throttle valve (verify that the turbine does not accelerate)
3. Issue a START command
At this point the 505 will ramp open the governor valve to its “HP Max at Start” setting at the ‘Valve
Limiter Rate’ setting.
The speed set point will ramp from zero to the minimum controlling speed setting at the ‘Rate to MIN’
rate.
When turbine speed increases and matches the ramping speed set point, the 505’s Speed PID will
take control of turbine speed by controlling turbine inlet valve position.
Speed remains controlled at the minimum controlling point until action is taken by the operator or the
‘Auto Start Sequence’, if programmed, begins controlling.
Once the Speed PID begins controlling turbine speed, the HP Limiter will automatically ramp to the
‘Vlv Lmtr Max Limt’.
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