Manual 35018V1
505XT Digital Control System for Steam Turbines
Woodward
135
Cascade Control Menu
USE CASCADE CONTROL?
dflt= NO (Yes/No)
Select YES to configure the cascade control function. Select NO if the cascade function is not used.
PROCESS SIGNAL
dflt= Cascade Input
Select which input the control should use. The input selected here should be configured as an
analog input, which is used as the process value for this controller.
INVERTED?
dflt= NO (Yes/No)
Select YES if the cascade control will be reverse acting. If NO is selected, the control will be forward
acting. Typically this will be set to NO, the only time the input would be inverted is if the valve needs
to open when the input exceeds the set point. An example where the invert would be YES is for
turbine inlet pressure control.
MIN CASCADE SETPOINT (UNITS)
dflt= 0.0 (-20000, 20000)
Set the minimum cascade set point. This value is the minimum set point value that the cascade set
point can be decreased/lowered to (lower limit of cascade set point).
MAX CASCADE SETPOINT (UNITS)
dflt= 100 (-20000, 20000)
Set the maximum cascade set point. This value is the maximum set point value that the cascade set
point can be increased/raised to (upper limit of cascade set point).
(Must be greater than the ‘Min Cascade Setpt’ Setting)
CASCADE SETPOINT RATE (UNITS
/s
)
dflt= 5.0 (0.01, 1000)
Set the cascade set point rate. This value is the rate (in units per second) at which cascade set point
moves when adjusted.
USE SETPOINT TRACKING?
dflt= NO (Yes/No)
Select YES or NO. If YES, the cascade set point tracks the cascade input to provide bumpless
transfer to cascade control when it is enabled. If NO, the cascade set point remains at the last
position except on power-up or exiting the Configuration mode.
SETPOINT INITIAL VALUE (UNITS)
dflt= 100.0 (-20000, 20000)
Set the set point initialization value. When not using the Set Point Tracking function, this is the value
that the cascade set point initializes to upon power-up or exiting the program mode.
(Must be less than or equal to the ‘Max Cascade Setpt’ Setting)
SPEED SETPOINT LOWER LIMIT (rpm)
dflt= 3605 (0.0, 20000)
Set the minimum speed set point that the cascade controller can lower the speed set point to. To
protect the unit, this value should be at or above rated speed if the unit is a generator.
(Must be greater than or equal to the ‘Minimum Governor Speed Setpt’ Setting)
SPEED SETPOINT UPPER LIMIT (rpm)
dflt= 3780 (0.0, 20000)
Set the maximum speed set point that cascade controller can raise the speed set point to.
(Must be less than or equal to the ‘Maximum Governor Speed Setpt’ Setting)
MAX SPEED SETPOINT RATE (rpm
/s
)
dflt= 20 (0.1, 100)
Set the maximum rate at which the cascade control can vary the speed set point.
CASCADE DROOP (%)
dflt= 0.0 (0.0, 100)
Enter the droop percentage. If needed, typically set between 4–6%.
PID PROPORTIONAL GAIN (%)
dflt= 5.0 (0.0, 100)
Enter the cascade PID proportional gain value. This value is used to set cascade control response.
This value can be changed in the Run Mode while the turbine is operating. If unknown, a
recommended starting value is 5%.
PID INTEGRAL GAIN (%)
dflt= 0.3 (0.001, 50.0)
Enter the cascade PID integral gain value. This value is used to set cascade control response. This
value can be changed in the Run Mode while the turbine is operating. If unknown, a recommended
starting value is 0.3%.
PID DERIVATIVE RATIO (%)
dflt= 100 (0.01, 100)
Enter the cascade PID derivative ratio. This value is used to set cascade control response. This
value can be changed in the Service Mode while the turbine is operating. If unknown, a
recommended starting value is 100%. When this value is between 0.01 and 1.0 the derivative term is
considered to be ‘input dominant’ and the derivative is equal to (Deriv Ratio)/(Integral Gain). When
this value is between 1.0 and 100 the derivative term is considered to be ‘feedback dominant’ and
the derivative is equal to 1.0/[(Deriv Ratio)*(Integral Gain)].
USE REMOTE CASCADE SETPOINT?
dflt= NO (Yes/No)
Set to YES to allow the Cascade set point to be adjusted from an analog input.
(Must program a ‘remote cascade set point’ analog input