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Manual 35018V1
505XT Digital Control System for Steam Turbines
Woodward
58
If a 505 contact input is programmed to select between Idle or Rated speeds, Idle Speed is selected
when the contact is open and rated speed is selected when it is closed. The Idle/Rated contact can be
either open or closed when a trip condition is cleared. If the contact is open, it must be closed to initiate a
Ramp-to-Rated speed. If the contact is closed, it must be opened and re-closed to initiate a Ramp- to-
Rated speed.
When the turbine is used for mechanical drive applications, rated speed may be set at the minimum
governor speed setting. When the turbine is used to drive a generator, the ‘rated speed’ setting may be
set at or between the minimum governor and synchronous speed settings.
All pertinent Idle/Rated parameters are available through the Modbus links, refer to Chapter 6 for a
complete listing.
Figure 3-8. Idle/Rated Start
Automatic Start Sequence
This function is not the same as the ‘AUTOMATIC START
MODE’. The Automatic Start Sequence can be used with any
one of the three start modes.
The 505 can be configured to utilize an Automatic Start Sequence to start the turbine. This sequencing
logic allows the 505 to perform a complete controlled system start-up from zero speed to rated speed.
With this function, the turbine’s starting ramp rates and idle speed hold times depending on either the
length of time the unit was shut down or upon optional temperature input signals. This sequence logic
may be used with any of the three start modes (manual, semiautomatic, automatic), and is initiated by a
‘RUN’ command.