Manual 35018V1
505XT Digital Control System for Steam Turbines
Woodward
68
In some extreme cases, where the utility grid frequency is unstable, and changes significantly (day/night),
it is possible to change the unit’s:
Frequency set point (50 Hz/60 Hz ±2.5 Hz) via front panel
Frequency dead-band (±3 Hz). Used to reduce/prevent constant valve corrections due to a
constantly changing grid frequency.
To configure the 505 for generator load control when paralleled to a infinite bus, check the ‘Use KW
Droop’ option on the Operating Parameters page of the configuration menu. The 505 must also be
configured to accept a KW Load signal either from an analog input from a Watt transducer sensing
generator load, or from a Woodward Power Management product/device via a digital communication link
(Woodward Links). To configure the 505 for turbine valve position control when paralleled to an infinite
bus, uncheck the ‘Use KW Droop’ option. The generator load or turbine inlet valve position droop
percentage cannot be set greater that 10%, and is typically set to 5%.
If the 505 is programmed to control unit load using turbine inlet valve position droop (LSS bus position),
the 505 calculates load based on the valve position at the time the generator breaker was closed. This
valve position is considered to be zero load. In a typical application where turbine inlet and exhaust
pressures are at rated levels when the generator breaker is closed, this type of calculation allows unit
load to be accurately sensed, and controlled.
In an application where turbine inlet or exhaust pressures are NOT at
rated levels when the generator breaker is closed, the considered zero
load level will be incorrect when system pressures do reach rated
levels.
If turbine inlet or exhaust pressures are not at rated when the breaker closes, it is recommended that the
user do the following:
Use the available tunable in Service mode to correct the valve position at zero load once the system is
operating at rated steam pressure. To do this, adjust the Zero Load Value, (under the Service mode’s
‘BREAKER LOGIC’ header) and set this value to the correct valve position demand at Sync no load
condition
Speed Set Point
The Speed PID’s set point may be adjusted from the 505 keypad, external contacts, Modbus/OPC
commands, or through a 4–20 mA analog input. A specific set point setting can also be directly entered
through the 505 keypad or Modbus communications. The Cascade PID also directly controls this set point
when it is used.
The Speed PID’s set point may be adjusted from the 505 keypad, external contacts, or through Modbus.
It can be directly entered to a specific value from the 505 keypad or through Modbus commands. It can
be remotely set by the Remote Speed Set Point analog input or it can be manipulated by the Cascade
controller to control the Cascade input parameter.
The speed set point range must be defined in the Configuration mode. Program settings ‘Min Governor
Speed Set Point’ and ‘Max Governor Speed Set Point’ define the normal operating speed range of the
turbine. The speed set point cannot be raised above ‘Max Governor Speed Set Point’ setting unless an
Overspeed Test is being performed. Once the speed set point is taken above the ‘Min Governor Speed
Set Point’ setting, it cannot be varied below this setting again unless the Idle/Rated ramp-to-Idle
command is selected or a Controlled Stop is selected.