We have Mark V control System for frame 6 GE gas turbine. The problem is that suddenly the Auxilary hydraulic oil Pump started by itself during freq. change (fluctuation) of the power network by less than 0.5 HZ. the pressure switch is checked and found OK.

Does any one has advice for what happen
Thanks

 

It's next to impossible to say why the pump started when it shouldn't have--especially with the information supplied and without access to the CSP (Control Sequence Program) or to know how long the frequency excursion lasted or how the unit was being operated at the time or whether or not the Hyd. Accumulator is properly charged or any other number of possible factors which might have contributed to the event.

What's the real problem here? The Aux. Hyd. Pump starting when it shouldn't have--which doesn't cause any problems with unit operation--OR, it took some time to determine how to shut down the Aux. Hyd. Pump?

How did the Aux. Hyd. Pump get stopped?

markvguy

 

If you get a sudden system fluctuation it will move either the Gas or Liquid Fuel control systems rapidly. This will cause a fluctuation in the Hydraulic supply pressure which can cause the Aux. Hydraulic pump to be tripped on. It happens very quickly and recovers very quickly, even if your pressure switch is correctly set, it can be difficult to see the pressure drop because of the speed of drop and recovery. If you have precharged accumulators either in your Gas Fuel system or your IGV control system, make sure that they correctly charged with Nitrogen to the correct pressure.

 

The Main Hydraulic Pump's pressure setting may be too close to the low hydraulic pressure switch setting, or, the relief valves may not be set correctly. This author has run across dozens of units where technicians have adjusted pump discharge pressure with the relief valves--which is not correct. If the relief valve is being used to control hydraulic system pressure, the Hyd. Pump is flowing too much oil, which can cause any system disturbance to have adverse affects on unit operation, or to start the Aux. Hyd. Pump when only the Main Hyd. Pump should be running.

Several of these sites had experienced "nuisance" actuation of the Aux. Motor Overload Process Alarm, which was traced to actuation of the Aux. Hyd. Pump motor overload. A couple sites had also had problems with the couplings between the hyd. pump and the A.C. motor or the Acc. Gear. After adjusting the relief valves properly the nuisance overload alarms stopped occurring and the coupling failures also stopped occurring.

To adjust the relief valves, one has to increase the pump output pressure above it's normal pressure to test/adjust the relief valve setting. Then, the pump pressure must be re-adjusted to normal AFTER the relief valve setting is verified/adjusted. Again, if the relief valve is being used to set the system pressure, then the pump flow is excessive and even if the accumulator is properly adjusted it can't usually compensate for sudden hydraulic flow demands, whether they be due to frequency/speed fluctuations or emergency conditions.

markvguy