GE Frame 7EA Loss of Flame/TripOil


Thread Starter




We have two GE Frame 7B turbine (converted to EA when we purchased them) running on natural gas. We run in peaking mode, so winter runs are typically minimal. We did emissions tuning in spring of 2012 on both units and ran heavily in summer of 2012 with no issues. This problem started occurring around April 2013 on only one of the units.

Problem Description:

After light off (900rpm), the unit will spool up to just below 1000RPM when the high pres. trip oil pressure starts dropping (as seen on the gauges at the gas control house and on the turbine accessory compartment). It goes from about 1300PSI down to 400PSI. The hydraulic oil pressure gauge in the sump indicates that it remains at 1500PSI throughout the startup and trip.

Approximately 15 seconds after the pressure starts dropping, the SRV valve closes. 4 seconds later, the GCV closes and we get a loss of flame trip at the same time. No other trips or alarms are present. We have RPM, SRV position, GCV position, and trip timestamps from probably 12+ different occurrences of this trip and they are all basically the same.

The trip oil pressure does NOT drop instantly. It takes about 10-15 seconds to reach 400PSI, which is approximately when the SRV closes. We don't have a trip oil pressure transmitter, so this is approximate.

Finally, this problem does not occur consistently. Sometimes the unit starts right away, sometimes it starts after one trip, and sometimes it takes multiple starts.

Other Info:

SRV and GVC calibrations both check out OK. We have stroked both valves

We have an L63QA (Lube Oil Pressure Low) alarm come in approximately 2 minutes before the loss of flame alarm. From our drawings, it appears to be unrelated.

We have confirmed that our dump and trip solenoids are not causing this issue.

What would cause this type of pressure loss, and what can we do to trace it down?

Are you sure the low lube oil pressure is unrelated ? The Model B's I remember have a Low Bearing Pressure Trip Valve which creates trip oil (OHT) from the hydraulic supply (OH). If lube oil header pressure goes low (as suggested by the 63QA alarms), this trip valve trips OHT. The trip valve is shown on the Control Oil schematic.
Thanks for the reply!

Regarding the lube oil - I do see where the OH is turned into OHT before going to the overspeed bolt, SRV, GCV, etc. This is a hydraulically operated valve (VHII-1 ??hard to read), which is operated by lube oil pressure (25PSI on the drawing) coming through an electrically operated dump valve (20HD-1).

From day 1, this unit has had issues with lube oil pressure due to an unusually sized bearing (apparently from the B to EA conversion). To "compensate", GE lowered the 63QT setpoint to 6.5PSI during commissioning and installed a larger impeller on the lube oil pump.

The 63QA alarm has been coming in for the last couple years and we have never had a problem like this before. Our normal operating pressure (as read on the lube oil gauge on the turbine accessory compartment) is normally around 15 to 20 PSI.

During the last startup we did, the lube oil pressure fluctuated between 17 and 19 PSI. There was no correlation to the loss of trip oil pressure.

Do these readings sound reasonable, or should we continue to look at the lube system? What pressure would you expect the hydraulically operated valve VHII-1 to dump the OHT at?

In the one very old Model B instruction book I have, the control oil schematic doesn't even show any device "name". (If yours has a device name, perhaps you can find it listed in the device summary ?) Otherwise, unless someone on this forum knows the answer, a last resort might be to dig out a part number and have GE look at the drawing (they have most very old drawings available on-line.) Maybe those GE Controls Connect people that speak up from time to time on this forum can do it. (Would be an interesting test to see how useful they are.)
It does seems odd how slow OHT drops in your video. I looked at some ancient transient data I have from a test with pressure transducers on an similar vintage unit. When 20HD is de-energized, OHT drops to zero within 1 second. Unless your OHT pressure gauge has a snubber valve that is slowing it down, it seems like something else is going on.

Can you relate to anything else that's happening just below 1000 rpm when this occurs ? When it was modified to a 7EA, were there any mods to the trip oil system (replacing Limitorque IGV actuator with hydraulics, for example) ? You say you did emissions tuning, so if the unit is now DLN1, was the speed ratio valve replaced with a low pressure trip oil version modified somehow to work with your high pressure trip system ? It's simple to say, but hard to troubleshoot: could be trash floating around in the OHT supply orifice, or perhaps a leak in the OHT system that is somehow intermittent.
Here's an overview of our high pressure hydraulic system (as shown on prints):

1. Aux Hydraulic Supply Pump and Main Hydraulic Supply Pump each feed into check valves. We have a pressure gauge after the check valves. This gauge remains at 1500PSI before, during, and after the trip.

2. After check valves, oil is fed into the filter. After the filter, this is the OH header and feeds three other systems. We have a low pressure alarm 63HQ supposed to be set for 1350PSI. We are going to verify calibration of this switch later today and that it brings an alarm in. This will confirm whether the problem is with OH or not. From there, the oil feeds A) starting clutch B) IGV servo C) "Control Oil".

3. "Control Oil" then feeds into VHII-1 and VHII-2 which are hydraulically operated from 20HD-1 and 20HD-2 dump valves, respectively. VHII-1 and 2 both have orifices.

3A. VHII-2 feeds "OHT-2" to the trip valve for the IGV after going through an orificed check valve. Our IGV drawing (which is several years older than the rest of our control oil drawings) calls the trip oil "OLT" instead of "OHT", so it must have been retrofitted for a high pressure system.

3B. VHII-1 feeds the overspeed bolt, the GCV, and an orificed check valve that feeds SRV. The pressure gauge after VHII-1 is in the video.

4. As mentioned, VHII-1 is actuated from 20HD-1 with Lube Oil pressure. After we check 63HQ's calibration, we are going to try to slowly bleed the pressure down on the lube system (unit off, of course) to see if we are near the tripping point of VHII-1.

5. From the check valve to the SRV, there is another gauge, L20FG trip solenoid, and three 63HG OHT low switches. The gauge at this point exhibits the same behavior as the one in the video.

Other info:
-The 63HG switches are set low enough that we trip on flameout before we trip on loss of OHT. The flameout trip is what causes the gauge to drop from 400PSI to 0PSI right away in the video.

-When we run the hydraulic system and force L20FG or L20HD off, we get instantaneous drops in pressure, similar to what you describe. Our overspeed bolt trip lever and manual trip do the same. So, no snubbers on the gauges.

-We thought maybe the SRV or GFV had some kind of leak. So we stroked each valve very slowly through their positions during startup but it had no effect on OHT-1 pressure.

I guess the next step is to confirm that 63HQ is functioning correctly, and to see how our actual lube pressure is to VHII-1's trip point. If both of those prove negative, we will know the leak is in OHT-1, but not sure what to do from there.

Thanks again,

I am still trying to get my head around your trip oil system, I wish I had a oil schematic, I am more familiar with the low pressure systems. I am going to look at some of the drawings I have to try and better understand your system.

The two things that come to mind for me are these:

1) Since this system is flow limited from the orifices, could you have a leak in a fitting that is intermittent?

2) Is it possible that the overspeed bolt mechanism is leaking by sometimes causing a loss of pressure that is not always there?

As said I am going to look at drawings I have and see if I can come up with any better ideas. Please keep us informed!
It is a bit difficult without seeing the prints. Unfortunately, all our drawings have proprietary stamps on them...

More info...

1. We were looking at the wrong gauge for lube oil header pressure. The gauge we were looking at was the emergency (electric) lube oil pump. We took a video of the entire gauge panel during the trip this morning. On our second start, the unit came up to speed successfully. We tried two more times in the afternoon, both were successful. We can post videos of the entire gauge panel for trip & successful start if that would be useful.

2. The actual lube oil header pressure fluctuates around 10 PSI. We haven't been able to find our VHII-1 valve yet. Since we can't drain the lube oil header pressure, we are going to try to attach a pressure pump to see where it starts to drop out at.

3. We have an inspection plate next to our overspeed bolt. We were able to reach in and push the mechanism that the shaft rides on. It resulted in an instant drop of OHT. Therefore, we are quite certain the bolt is not the problem.

4. We looked at our historical data. Around when our problem began, we had 6 consecutive failed starts. After that, we had 4 successful runs. That was followed by 7 more failed starts, and then the three successful startups today.

5. Since SRV, L20FG are downstream of an orifice, we are certain these are not related.

6. We have an inspection window in the dump area of the SRV and GCV. Both valves appear to drop a lot of oil in midposition. We assume this is normal (?).

So, we're down to lube oil, VHII-1, or GCV.
Just a quick update... we found that our VHII-1 valve (actuated from 25PSI lube oil) is right on the edge. It appears that our lube oil pressure is marginal and drops slightly during startup, pinching off the supply to OHT (but not actually dumping the fluid). We are now investigating the lube oil system.

My Background is:
I work where there are five GE Frame 7EA Gas Turbines with multiple conversions, one to DLN, upgrades on compressors, combustion components, and also a control system upgrade.

Just a few suggestions:

It sounds to me like you may be getting low pressure on your hydraulic trip system from too low a pressure on your lube oil bearing system. The lube oil system goes to 20HD-1 which in turn shuttles VH11-1, the "Low Bearing Pressure Trip valve". This valve may start to drop out giving you the low hydraulic trip pressure. You should also check the orifices in valve VH11-1. Our units have an orifice of .078' diameter that feed the hydraulic trip system. also check to make sure the orifices on the liquid fuel system and gas fuel systems are in place or not too big, which would drag down the hydraulic trip pressure. The orifices on our fuel oil and gas systems are .020" diameter each.

Hopefully, this may help you in finding the problem.