Woodward 85018V1 Turbine Control Parameters

The Extr/Adm control can also receive a programmable (optional) droop

feedback signal to increase the stability of the extraction control loop.

The Extr/Adm setpoint is adjustable with raise or lower commands through the

keypad on the front of the control, the remote contact inputs, or the

communication links. Also, the setpoint can be directly set by entering the new

setpoint from the keypad or through either Modbus communications link. In

addition, a remote extr/adm setpoint analog input can be programmed to

remotely position the Extr/Adm setpoint.

Remote Extraction/Admission Setpoint

One of the 4–20 mA inputs can be configured to remotely adjust the Extr/Adm

setpoint. The remote setpoint input directly affects the 505E’s Extr/Adm setpoint.

The maximum rate at which the remote input signal can change the setpoint is

programmable and can be changed in the Run mode. When the remote setpoint

is enabled, the Extr/Adm setpoint will move at a much slower rate until the two

settings are matched, at which point the setpoint will be allowed to move at the

maximum rate. The remote setpoint function can be enabled and disabled as

required from the front-panel keypad, the remote contact inputs or either Modbus

communication link.

Ratio/Limiter

The Ratio/Limiter receives input signals from the speed (or aux) and extr/adm

control PIDs. The ‘ratio’ logic uses these signals and, based on the turbine

performance parameters, produces two output signals, one to control the HP

actuator and one to control the LP actuator. The ‘limiter’ logic keeps the actuator

outputs within the boundaries of the turbine steam map.

The ratio logic controls the interaction of both HP and LP valves to maintain

desired turbine speed/load and extraction/admission pressure/flow levels. By

controlling valve interaction, the ratio logic minimizes the effects of one controlled

process on the other controlled process.

When speed/load or extraction/admission demands cause the turbine to reach an

operating limit, the limiter logic limits the HP or LP valves to maintain speed/load

or extraction/ admission demands depending on the priority selected