Wednesday, April 25, 2018

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SPEEDTRONIC Mark VI Control Software Philosophy

  • Gas turbine control for example if the exhaust temperature exceeds the allowed limit, the fuel supplied to the turbine will be reduced

  • The operating conditions are changing based on the sensor detected values

  • The control is realized by the use of different control loops

Control software philosophy

  • Major control loops: startup, speed, temperature

  • Secondary control loops: acceleration, manual, shutdown

  • Fuel Stroke Reference (FSR) is the output command signal to the fuel flow

  • Minimum selector receives the output of the control loops

  • The lowest FSR value will be always active and controlling the fuel flow

  • Correct speed detection is very important

Startup control loop

Speed relays detect the current speed of the shaft:

  • L14HR –Zero speed(below0.3% of max.speed) -turbine shaft started to rotate

  • L14HM –Minimum firing speed (above15%) -turbine reached minimum firing speed

  • L14HA –Acceleratingspeed (above 50%) -acceleration phase, turbine startup is in progress

  • L14HS –Min. operation speed (above 96%) -the turbine hasreached the operational speed

The startup control loop operates using different preset levels of FSR stored as Mark VI constants:






  • During the startup process the different FSR values are applied by the startup control loop to the fuel flow, based on the current speed of the shaft.

  • The shaft speed is detected by 3 magnetic pickup sensors (77NH-1,2,3)

  • The current speed -TNH (actual speed) is calculated from the sensors’ signals

  • The reference speed –TNR is the desired speed

  • Proportional regulator calculates FSR based on the TNH and the TNR(reference speed)

  • TNR typically changes between 96-102% of speed

  • Under manual control the operator may change the TNRwithin the range above

Acceleration control loop

  • The acceleration control loop monitors the increasing rate of the turbine speed

  • If during the startup process a predefined acceleration limit is reached, the acceleration control loop takes over the FSR control from the startup control loop to limit the acceleration and protect the instrument

Temperature control loop

  • Maintains allowed operating temperatures by limiting fuel flow to the turbine

  • Uses 24 exhaust thermocouples as input temperature values

  • A regulator is used to calculate the FSR based on the current values and predefined values.

  • If the calculated FSR is lower than the current FSR, the temperature control loop will take over the FSR control according the minimum selector

Proceed to SPEEDTRONIC Mark VI Protection Systems

Go back to SPEEDTRONIC Mark VI Software Description

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