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Manual 35018V1
505XT Digital Control System for Steam Turbines
Woodward
59
With this function, when a ‘START’ command is given:
The Automatic Start Sequence ramps the speed set point to a low idle set point
Holds at this setting for the set duration
Ramps the speed set point to the Idle-2 setting
Holds at this setting for a the set duration
Ramps the speed set point to Idle-3 setting
Holds at this setting for the set duration
Then finally ramps the speed set point to the programmed rated turbine speed setting
All ramp rates and hold times are programmable for both hot start and cold start conditions. The control
differentiates between hot and cold starts by using a “Hours-Since-Trip” timer or a contact input. When
using the “Hours-Since-Trip” timer, the timer starts when a shutdown has been executed and turbine
speed has decreased below the low idle speed setting.
Figure 3-9. Automatic Start Sequence
With this sequence, a set of hot-start ramp rates and hold times is programmed for use when a ‘START’
command is given and the turbine has been shut down for less than the programmed ‘HOT START’ time
setting. A set of cold-start ramp rates and hold times is also programmed for use when a ‘START’
command is given and the turbine has been shut down for longer than the programmed ‘COLD START’
time setting.
If a turbine ‘START’ command is given when the length of time the system has been shutdown is
between the ‘HOT START’ and ‘COLD START’ time settings, the control can be configured to interpolate
between the hot and cold programmed start values to determine starting rates and hold times.
Table 3-1. Automatic Start Sequence Settings:
COLD START (> xx HRS)
=
22
HRS
HOT START (< xx HRS)
=
2
HRS
LOW IDLE SETPT
=
1000
RPM
LOW IDLE DELAY (COLD)
=
30
MINIMUM
LOW IDLE DELAY (HOT)
=
10
MINIMUM
USE IDLE 2
=
*TRUE
RATE TO IDLE 2 (COLD)
=
5
RPM/S
RATE TO IDLE 2 (HOT)
=
15
RPM/S