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Our gas turbine 9E starts up on distillate fuel and "change over to low calorific gas" is available at 37.5 MW GT load. We are initiating changeover on 50MW. Now the problem is that Gas turbine successfully changeover to gas but immediately gas pressure P2 low alarm appears and Automatic Changeover to startup fuel is initiated. We have noted that it is happening due to Cavity backflow protection which says that if P2 pressure is not 5psig more than CPD within 20 seconds of L3GRV becomes 1, auxgas is locked out. We have noted that P2 has reached this threshold in 273 seconds instead 20s stipulated time. During last successful changeover it took 19.52s. I have noted that frcrout is increasing very slowly from initial value of -40%(SD_ref) (when L3GRV became 1) to -8%(when pressure reached its threshold).Valve opening was from -0.07% to 0.2%. My vendor says it should reach to 0% within 1 sec or less. He is analysing this anomaly. Anybody has some idea. We have done the stroking of SRV and it is closely following the position reference.
Shahab
shahab.qader [at] gmail.com
Shahab
shahab.qader [at] gmail.com