We are facing an issue during the startup of one of our Gas Turbines Units. When the unit is on turning gear, Auxiliary lube oil pump (AC) is running and delivering normal pressure (around 6 Bars). However, during startup while unit is accelerating at 1500 RPM, the pump header pressure drops to around 4 bars and the bearing header pressure drops from 1.8 to 1.5 bars. Moreover, we observed that control oil pressure for IGV is also dropping from 3.8 to 1.9 bars.
All the above parameters reached to the minimum at around 1800 RPM, after that it starts to accelerate again gradually until it reach to the normal values near to FSNL speed. After loading the units, the parameters also are OK.


Remark : No recent activities were done on the units.

Please advise your thoughts and possibilities if someone faced similar experience before.

 

I haven't faced a similar problem yet

Maybe the seal oil has trouble to ajust during acceleration:
If it overflow you will find oil either in the generator casing or on the ground in excitation collector housing
The generator seal can be worn or misplaced and speed variation affect them a lot

Can you search how the oil flow through seal oil system behave during acceleration?

 

Can you check how the pressure in pump discharge and header is controller. There should be a PRV/PCV in the circuit that you may want to check the behavior.
If not most likely this maybe a pump issue assuming there is no leaks in the circuit

 

GE-design Frame 9E heavy duty gas turbines which use an Accessory Gear have the Main L.O. pump inside the Accessory Gear assembly. The Main L.O. Pump is a positive displacement pump and there is a relief valve (yes--relief valve) used to control the discharge pressure of the Main L.O. pump. The Auxiliary L.O. Pump is a centrifugal pump and does not use any kind of pressure regulating device. The discharges of the two L.O. pumps do join each other before entering the L.O. Bearing pressure regulator assembly to control bearing header pressure. There is usually a check valve in the Aux. L.O. Pump discharge to prevent back-pressuring the Aux. L.O. Pump by the Main L.O. Pump discharge and also to prevent Main L.O. pump discharge from flowing backwards through the Aux. L.O. Pump when the Aux. L.O. Pump is not running (which would reduce flow/pressure from the Main L.O. Pump to the other systems which use L.O. (Control/Trip Oil; Hydraulic Oil; Seal Oil (if required)).

ALL of this can be researched and verified using the L.O. P&ID. Using the L.O. P&ID one can see all of the various components of the system and make decisions about which components to check for proper operation/function. MANY troubleshooting systems are processes of elimination--working through various components/systems and possible scenarios to eliminate those which are found to be functioning properly until the source of the problem(s) are found and resolved. THIS is one of those problems where using the P&ID is required to make decisisons about which devices/components might be the cause of the problem. This particular problem is going to be more difficult to troubleshoot because some of the components are located in the L.O. tank/reservoir below the level of the oil. So, by using the P&ID and checking all of the components which are more easily accessible FIRST any decision about checking the other more inaccessible components/devices can be delayed until a more favorable time.

DO NOT overlook the Emer. L.O. Pump and it's components simply because it isn't running under normal conditions.

Logical troubleshooting is another term for 'process of elimination.' When working on an unfamiliar or complicated system one has to review and analyze the system (that's what the P&IDs are for!) and then make some educated guesses (yes--many times they are just guesses) based on configuration and accessibility one starts the process of working through various possibilities, eliminating devices and components based on sound testing until the cause(s) is(are) found and resolved.

Many older GE-design machines do not have pressure transmitters to monitor L.O. pressures (pump discharge; bearing header; Control/Trip Oil; Hydraulic system) and only use gauges on the Accessory Gauge Cabinet--and QUITE often these gauges are NOT tested/calibrated to ensure they are working correctly. Worse, the manual valves on the Acc. Gauge Cabinet are VERY OFTEN not properly set. Air in the lines (usually 1/8-inch tubing) is also a problem sometimes.

Please let us know what you find as you work through resolving this issue!

 

I will keep you guys updated once we resolve the issue.