We have two GE frame 5 MS 5001P gas turbines which were commissioned in 1982. These turbines are equipped with one accessory gear driven hydraulic supply pump. This pump is of make DELAVAN Model PV 3200 R rated for 18 GPM at 1200 Psig. Our Gas Turbines do not have accumulators in hydraulic supply system.

We intend to install auxiliary hydraulic oil pump (AHOP). GE has provided the proposal for auxiliary hydraulic supply pump but GE has recommended to shut down the unit to avoid possible damage in case AHOP cuts in due to low pressure. The proposed AHOP is rated for 9 GPM and accumulators are not included in proposal.

In view of above please advise following

1) What advantages we can gain by installing AHOP considering the fact that GE recommends to shut down gas turbine in case AHOP cuts in in normal operation

2)What possible damage can occur if gas turbine keeps running in case AHOP cuts in

 

FSX,

I presume the reason for installing the Aux Hyd Pump would be to prevent the need for cranking the turbines when stroking/calibrating fuel valve- and IGV LVDTs?

Do the MS5001P units have "bang-bang" (two-position; open or closed) IGVs or variable (modulated) IGVs?

Do the MS5001P units use L.O. Pump discharge pressure or Hyd. Pump discharge pressure for the Control (Trip) Oil system?

Most GE heavy duty gas turbine hydraulic systems are basically "static" systems that only have high flows when a hydraulically-operated actuators are being commanded to move. Once the device is in the correct position there is essentially no more hydraulic flow to that actuator. (Units which use hydraulic pressure for Control (Trip) Oil do have slightly higher hydraulic oil flow-rates under all conditions than units which use L.O. Pump pressure for Control (Trip) Oil system.)

A hydraulic accumulator on a GE-design heavy duty gas turbine serves to prevent dips in hydraulic pressure when high flows suddenly occur (such as when the IGVs are commanded to move suddenly). GE-design Frame 5 heavy duty gas turbine hydraulic actuators are relatively small and don't require high flow-rates because the stroke is "short". Compared to most of the other turbines in the product line they don't generally require accumulators, but were provided on some units. I believe the change in design philosophy with regard to using hydraulic accumulators on Frame 5 units corresponded with the change from two-position ("bang-bang") IGVs to modulated (variable) IGVs.

It's possible the original pump is slightly over-sized (GPM) and GE are just proposing a suitable pump for off-line stroking/LVDT calibration. Did your site/Company ask GE to provide a quote for the addition of Aux. Hyd. Pumps; if so, for what purpose?

Or is GE just proposing to add Aux. Hyd. Pumps? If so, for what purpose?

As for the question of 'what possible damage can occur if gas turbine keeps running in case AHOP cuts in', that would depend on how the Aux. Hyd. Pump is "manifolded" to the Main Hyd. Pump. Which really depends on what's the main reason for wanting to add an AC motor-driven hydraulic pump? For offline stroking/calibration, or for running reliability in case the Main Hyd. Pump is lost?But, in my personal philosophy, the purpose of an Aux. Hyd. Pump is to be able to allow continued operation in the event of loss of pressure/flow from the main Acc. Gear-driven Hyd. Pump.

And, in my personal opinion, there is too much emphasis placed on "calibrating" hydraulically-operated devices. ENTIRELY TOO MUCH.

People think they are calibrating the valve or the IGVs, or the servo-valve on the hydraulic actuator of the valve or the IGVs. When, in fact, they are only calibrating the LVDT position feedback--and they don't even know to check to see if the LVDT position feedback needs adjustment or fine-tuning (it almost NEVER does!!) before just "calibrating" the valve or IGVs (which they're not really doing!!). Because OEM engineers are seen "calibrating" valves or IGVs every time there is a suspected problem site technicians do the same thing.

The real truth is that LVDTs rarely go "out of calibration." LVDTs, the same LVDTs used on many GE-design heavy duty gas turbines, are also used on commercial and military aircraft, and we don't see pilots or technicians "calibrating" flaps and ailerons in flight whenever the plane encounters turbulence.

So, what's the main reason for wanting to add Aux. Hyd. Pumps?

 

CSA,

Thanks for your detailed reply.

Our units have "bang bang" two position IGV's.
LO pump Discharge Pressure is used for trip oil system.

Our company asked GE to propose Auxiliary Hydraulic Supply pump. we believed that this pump will support main pump in event of loss of pressure from main pump.

In their proposal GE has said that they recommend to shut down gas turbine in case auxiliary hydraulic supply pump cuts in to prevent possible damage. This is surprising for us.

Initially GE did not agree to provide auto cuting of AHOP. upon our request they agreed to provide auto cut in but they recommend that there will be alarm in case Aux Hyd pump starts with gas turbine operating and operator should shut down the gas turbine

We agree with the point that "Hydraulically Operated Devices in MS5001P rarely require calibration. we have never done this since 1982.

Now we are not sure what advantages we can have by installing AHOP. In fact should we install it?

What damage can occur if we keep gas turbine operating after AHOP cut in?

 

CSA

Sorry in my previous reply I forgot to clarify one point
We primarily intended to install AHOP to support main pump in case of loss of pressure.We believed that off line calibration of fuel valves will also be an added advantage

The P&I Diagram provided by GE indicates that this pump will have its own Hydraulic manifold assembly containing a relief valve VR-22, Air Bleed Valve VAB-2 and check valve CV-2

Its suction will be from lube oil header downstream of 26QA. This is same line from which main pump takes suction

Discharge of AHOP will add into existing system downstream of cv-1

However GE has mentioned note on drawing that "AHOP ti be used only for off line IGV's and Fuel valve calibration without spinning turbine"

As mentioned in my previous reply our units have "Bang-Bang" two position IGV's

Lube Oil pump discharge pressure is used for trip oil system

 

FSX,

Did you specifically ask GE to provide Aux. Hyd. Pumps that could support continued operation in the event of loss of pressure/flow from the Main Hyd. Pump? (If so, GE has not really responded to your request for quotation....)

From the information provided the only reason I could think they would make the recommendation to shut down the unit if the Aux. Hyd. Pump were to start would be the flow-rate of the pump being provided does not meet expected flow-rate requirements for some operating conditions (large, fast load swing, for example).

I think for GE-design heavy duty gas turbines with Speedtronic turbine control systems and Aux. Hyd. Pumps that when low Main Hyd. Pump pressure is detected there is an alarm, but I don't recall if there is an alarm when the Aux. Hyd. Pump starts.

If your units have bang-bang IGVs, I wouldn't think a large load swing would require a LOT of hydraulic flow since the IGVs wouldn't be moving. You haven't said what fuel(s) the unit burn, but in any case the actuators for gas fuel valves aren't that large (compared to other GE-design heavy duty gas turbines) and neither is the liquid fuel flow control actuator (we don't know if the units have liquid fuel if they have a variable high pressure liquid fuel pump or a liquid fuel bypass valve).

I wonder if the reason the Aux. Hyd. Pump was sized for half the flow-rate of the existing Main Hyd. Pump is because there isn't an available MCC bucket for a larger motor starter, or there is some problem with available space for a larger hyd. pump or the AC motor to drive it. There's something like that going on here that isn't known that's causing them to make this recommendation.

It also seems odd that they say there needs to be an alarm indicating the Aux. Hyd. Pump is running and if it's annunciated the operator should shut the unit down. So, they're not saying the unit will automatically be shut down? If they're worried about "damage" why aren't they initiating either an auto shutdown or a trip if the Aux. Hyd. Pump starts during loaded operation?

You say these units are 1982-vintage and you haven't calibrated LVDTs since then. So, they seemingly don't run very often, and they likely have Mark II controls and so GE is a little apprehensive about making modifications to the control system? Or, is this quote in addition to a control system upgrade you are contemplating? Or has the Mark II already been retrofitted with some other control system?

As for what kind of damage could occur if the Aux. Hyd. Pump were to start if the unit was running, I simply cannot imagine what could possibly happen, other than an inability to maintain speed/load because of low hydraulic pressure/flow. But, if the Aux. Hyd. Pump can maintain pressure/flow for off-line calibration I don't see what the difference is between off-line hydraulic operation and on-line hydraulic operation.

Again, the hydraulic system is basically a static system; the only time there is flow is when a hydraulically-operated device is commanded to move. When the device is at the required position the hydraulic flow stops.

Is hydraulic pressure used for something else on the turbines at your site other than fuel control/stop valves and IGVs? Are these units compressor drive units that use hydraulic pressure for seal oil on the compressor? Model P units are usually single-shaft, generator-drive units. Is hydraulic pressure/flow being used for jacking oil (which shouldn't be the case when the turbine is running producing power)?

Either there's something we don't know about the configuration of the hydraulic system on the turbines at your site (it sounds typical, but ...) or there's some size/space availability limitation that is limiting the pump to a lower flow-rate. Most of the hydraulic pumps I've seen on GE-design heavy duty gas turbines with accessory gear-driven AND AC motor-driven hydraulic pumps are exactly the same pump just one is driven by the Acc. Gear and the other driven by an AC motor. GE has used a couple of different vendors, Delaval and Hartman (sp?) for pressure-compensated, axial piston hydraulic pumps over the years. Perhaps the currently available pumps can't produce the same pressure/flow as the older existing pumps in the same space/size?

Anyway, your main concern seems to be what kind damage could be caused if the unit were to be run at load with only the Aux. Hyd. Pump. I just can't think of any damage that could be done. I could see where the turbine would not be able to maintain load if the hydraulic pressure/flow wasn't sufficient, and eventually it would trip on either reverse power (if driving a generator) or loss of flame. Trips are desirable, but Frame 5s can probably tolerate them MUCH more than any F-class turbine can tolerate trips.

If the Aux. Hyd. Pump is capable of supplying sufficient pressure for off-line LVDT calibration activities, then it would certainly seem it can be used to run the turbine, too.

I just thought of one possible scenario for your turbines! I have heard of some older units with bang-bang IGVs having problems with collapsed combustion liners when tripped from load. I've never seen the phenomenon myself, and don't quite understand the mechanism (perhaps someone else reading this thread might; otised, perhaps?) so I can't offer any more information than this. And, it is a pretty substantial risk....

Perhaps you could ask GE if this is the "damage" they are referring to? (If you haven't already asked them....) The thing to note here is that the same risk exists if the Main Hyd. Pump fails during normal operation (and there's no automatic start of an Aux. Hyd. Pump).

So, this is very interesting. Please write back when--and if--you get details/information. And, let us know how you decide to proceed, and what your reasoning was for your decision.

You know, also, that there are other suppliers for modifications like this.... Non-OEM, of course.

 

CSA,

Thanks for detailed reply. I will surely write back to you after final recommendation from GE.

 

CSA

We operate on gas fuel only. Our units are in continuous service since 1992.Our units are generator drive units. Hyd oil is used only for fuel control/stop valves and IGVs

We requested GE to provide proposal for Hydraulic Supply Pump that can act as back up of main pump and after comprehensive correspondence from GE following is their reply

"The auxiliary hydraulic oil pump quoted with proposal REV.02 is the standard GE design, to be used for off-line calibration (with GT unit not running), that is not intended as backup to the main hydraulic oil pump.

We have GT FR7 application that uses the auxiliary hydraulic pump as back-up of the main. Such application are provided with additional oil accumulator on pump discharge line.

We are evaluating the possibility to customize the FR7 hydraulic oil pump design to your FR5/1 unit, in order to match your requirements, specifically about the request about “…no change in turbine load and any operating parameters”.

Our internal process needs further verification and final approval by our eng. dpt before submitting the proposal. We are trying to expedite at the maximum our answer."

After few days GE replied as follows

"Please note that after internal review with our engineering, in order to proceed with verification, we need following technical information:

1- Confirmation that coupling is the rupture element (in case of mechanical pump failure)

2- Picture of the main hydraulic pump and its coupling to the accessory gear box

After feasibility is confirmed, if you are interested to proceed with auxiliary hydraulic pump as back up of the main, an additional oil accumulator can be necessary to handle transient conditions, and budgetary estimation is around...."

Please note that hydraulic supply pump on our gas turbines is coupled to accessory gear through coupling manufactured by LoveJoy/Sierbath. Its a gear coupling which consists of two metallic hubs with external teeth and a Nylon sleeve with internal teeth

I have seen a TIL from GE indicating that quill shaft used to drive atomizing air compressor is a shear coupling designed to break in case Atomizing Air Compressor Seizes.

Does the hydraulic supply pump soupling also serves as rupture element in case of main hydraulic suply pump seizure ?

As hydraulic supply pump and main LO pump are installed on same shaft (shaft No 4) with Hyd Supply pump on outer side and LO pump on inner side what acts as rupture element in case main LO pump damage/seizure occurs.

If its quill shaft in LO pump then I think nylon sleeve in Hydraulic Supply pump coupling must be a rupture element. Main LO pump requires 35 HP and Aux LO pump requires 9 HP.

Is it safe to put aux hyd pump of half capacity on auto cut in and use it to operate gas turbine without accumulators?

 

CSA

Below is final reply from GE

"the coupling in nylon can save the GT from possible critical conditions in case of Hydraulic Supply pump seizure.
However in case auxiliary pump cuts in due to low hydraulic oil pressure GE cannot assure, in any case, that GT can continue to work without any safety risk. Also in actual installation GE suggests that in case of low pressure (on high pressure oil system) the GT should be shut-down.

The time in which it must be done cannot be quantify due to the several ways and modes of brakes for main pump or eventual other parts.

Also this time GE recommends to shut-down the GT in case of this failure rise-up.

However in this case the pump will be useful to shut-down the GT providing the correct oil pressure to perform the operation."

 

FSX,

It's pretty clear the individual responding to your requests for additional information is not a native English-speaker. Worse, it's also clear this person does not have any real-world experience with hydraulic systems.

One could understand how it would be advisable to have a hydraulic accumulator to help with the loss of hydraulic pressure/flow during a failure of the Main Hyd. Pump. The Aux. Hyd. Pump will be started on low hydraulic pressure, which will only occur after hydraulic pressure/flow from the Main Hyd. Pump has started decreasing. The rate of decrease of pressure/flow could be slow or it could be fast.

And, there will be some time lag between the run signal given to the Aux. Hyd. Pump and the time when its output pressure/flow is sufficient to start increasing the hydraulic system pressure back to rated.

So, in this case a properly-size hydraulic accumulator would definitely be a help in keeping the turbine running without much disturbance.

If there were no hydraulic accumulator AND the rate of decrease of hydraulic system pressure were such that the Aux. Hyd. Pump could not restore hydraulic pressure quickly enough to keep the fuel stop valves from closing then one could understand how the turbine could be tripped. How damage could result from such a condition is still a stretch of the imagination, because if there were no Aux. Hyd. Pump and the Main Hyd. Pump fails the turbine is going to trip anyway, right?

For positioning valves and IGVs there is virtually no hydraulic flow when the turbine is operating at a stable load. Hydraulic pressure is required to keep the fuel stop valve open (SRV or Liq. Fuel Stop Valve), but there is no flow required--just pressure.

So, the issue is maintaining hydraulic pressure long enough during the loss of the Main. Hyd. Pump and the starting of the Aux. Hyd. Pump to keep the fuel stop valve open to prevent tripping. A hydraulic accumulator would definitely help, especially if the Aux. Hyd. Pump was sized for only half the rated flow of the Main. Hyd. Pump. (Which is still not clear to me why it couldn't be sized closer to the Main Hyd. Pump rating....)

Also, this whole business about couplings is just very, very odd....

There must be something about the hydraulic manifold (the two check valves and two air-bleed check valves necessary to prevent back flow and eliminate air from the hydraulic system) and/or the available space for hydraulic filters or the available space for the AC motor for the Aux. Hyd. Pump or something like this for the units at your site that is dictating this low pump size.

I believe what the GE person is referring to is the Frame 7E/EA Main/Aux. Hyd. Pump scheme, complete with hydraulic accumulator--that is also used on Frame 6Bs, Frame 9Es, Frame 7Bs, Frame 7Fs, and most GE-design heavy duty gas turbines. I've worked on a LOT of Frame 5s that had both an Accessory Gear-driven Main Hyd. Pump and an AC motor-driven Aux. Hyd. Pump and a Hydraulic Accumulator. I've also worked on several FRame 5s that only had an Access. Gear-driven Main Hyd. Pump.

As for your question in your other thread about Process Alarms when the Aux. Hyd. Pump is running, yes. There is a Process Alarm to indicate when the Aux. Hyd. Pump is running when the unit is above approximately 95% speed. It also prevents automatic synchronization if the Aux. Hyd. Pump is running when the unit is being started and the turbine speed is above 95%. But, if the generator breaker is already closed and the Aux. Hyd. Pump starts, there is only the Process Alarm, 'Aux. Hyd. Pump Running,' which does not otherwise affect unit operation.

Please let us know how this exercise (in futility) goes.

I would also like to know if you've experienced Main. Hyd. Pump failures, and if so, what was the mode of failure? Or, is this being done to increase running reliability for capacity payment purposes?

Thanks!

Last, I hope MIKEVI can provide Hyd. Pump sizing information from the Frame 7EA units at one of the sites he works at. If not, if he could just compare the pump part numbers to see if they are the same (which would indicate the size is the same, or not) that would be a great help.

 

CSA,

Thanks for detailed reply. Its very informative. you are right the person responding to us is not native English speaker.

Any way your replies on this thread were very useful.

 

I know that at least in distant history GE has provided many frame 5 gas turbines with accessory gear driven main hydraulic pumps and electric motor driven backup auxiliary hydraulic oil pumps. There were many of these provided to industrial customers, both mechanical drive and generator drive machines. While most of the single shaft units were M or R machines, all the 2-shaft units had this arrangement, including the 5002B machines which are essentially a 2-shaft version of the 5001P.

I cannot tell you what all the differences in the hydraulic systems are between the industrial gas turbines and the utility gas turbines, so it is quite possible that different main pumps were used on the industrial units along with the other differences that have been mentioned in this thread. But I can tell you that they could run for extended periods on the auxiliary pump as long as there wasn't a break in the piping or main pump casing. There was also an alarm any time the auxiliary pump was running (except during startup when it was used until reaching 14HS).

So, it can be done. The cost of a proper retrofit may be high, however.

 

FSX, and CSA.

I will work to get some part numbers for the pumps that I am familiar with. The pumps I am familiar with are manufactured by Hartmann hydraulics. I have seen these installed and in use on frame 5's using a hydraulic pump driven from the accessory gear and one from an AC motor. The frame 5's I am familiar with have the two pumps, but are not using an accumulator.

I'll do what I can to help with information, standby.

 

Dear FSX,

this is the information I can provide. The manufacturer of the hydraulic pumps I am familiar with is Hartmann hydraulics. It is possible that your pumps are manufactured by a different company since GE uses various manufacturers.

For the Frame 5 unit I maintain the part numbers of the accessory driven pump are:
GE#255A4806P001
HARTMANN MODEL # PV320R-32002-40

For the Fr7 unit the accessory driven pump is:
GE #351A9554P001
HARTMANN CONTROLS INC. MODEL#PV320R

In my GE drawings the hydraulic pump on the accessory gear and the one driven by the electric motor show the same part number.

The model number of the pumps for the FR5 and FR7 show to be the same model, possibly with different internals and or compensators for different pressure adjustments.

Depending on your english skills you may be able to talk to the folks at Hartmann, they have been very helpful in the past when I have spoken to them.

FSX, I hope this information is helpful.

 

MIKEVI,

Thanks very much; we all know how time-consuming it can be to look up information in the GE Parts List drawing books.!.!.!

So, as suspected, the Main- and Aux. Hyd. Pumps are the same on each of the Frame 5P and Frame 7EA units. Yes; it's likely the pressure compensators are slightly different between the pumps on each of the two units since there are different flow-rates. (I suspect the Frame 7EAs at your site, MIKEVI, have a hydraulic ratchet cooldown system which uses Aux. Hyd. Pump pressure so the pump is probably sized slightly larger than would otherwise be necessary if the unit did not have a ratchet cooldown system (Frame 7EAs with H2-cooled generators).

MIKEVI, I presume you don't run the Frame 5s very much, and probably don't have much experience with the effects of a loss of Main Hyd. Pump pressure resulting in a start of the Aux. Hyd. Pump to know if the turbine(s) experienced any load swings or, worse, trips.?.?.?

In my personal opinion, FSX, I would say if GE will only provide an Aux. Hyd. Pump with a smaller rating then it would be best to also install a hydraulic accumulator for the most running reliability. If they would provide an Aux. Hyd. Pump with the same rating as the existing pump it would probably be satisfactory for most situations when there would be a loss of Main. Hyd. Pump pressure when the turbine(s) is(are) running. They are positive displacement pumps, and the smaller 3-phase AC motors (probably 5 HP or less) will come up to speed pretty quickly and since the suction of the Hyd. Pumps is pressurized by the L.O. Pump discharge (or is it Bearing Header pressure.?.?.?--but it is pressurized, nonetheless) the Aux. Hyd. Pump should come on fairly quickly and help to maintain turbine operation with possibly a small load swing.

Actually, I think it would be best to install a hydraulic accumulator for the most running reliability in either case, but I'm sure that's not inexpensive.

There will be an alarm when the Aux. Hyd. Pump runs above 14HS; and if it's running when you reach FSNL a running Aux. Hyd. Pump will prevent syncyhronisation (easily "bypassed"). But, if the turbine is running and synchronized when the Aux. Hyd. Pump starts and runs, there will only be an alarm; typical GE sequencing does not initiate an automatic shutdown when the Aux. Hyd. Pump starts.

Hope this helps!

And, thanks, again, to MIKEVI for providing the information about pumps and P/Ns!!!

 

MIKEVI and CSA,

Thanks a lot for all this information. I am extremely thankful for cooperation from both of you. For last four years GE is supplying main hydraulic supply pump of make HARTMANN with following details<pre>
Dwg No : 255A4806P1
P/N : RPO 10017
Manufacturer : HARTMANN
Model V-3200 R-32002-40</pre>
Originally main hydraulic supply pump at our units was of make DELAVAN.

Thanks again for all the time and effort you guys have spent assisting me

 

CSA,

We have a MS5001P/R in our chemical plant with the AC motor driven auxiliary hydraulic oil pump. Unfortunately, the nylon sleeve wore out in service on the main HOP (accessory gearbox driven), so our aux came on without a blip and we run months until a chance to change the coupling sleeve. But, I want to know what life do you get out of the nylon sleeve? What have you seen on other similar installations? Our unit was installed in 1979 and there were no issues with the sleeve until 2004 and again in 2009 and now in 2014.

Rdavis

 

For sure these nylon couplings do wear out. It is a little strange that you are getting less life after the first time replacement. Are you sure that you are replacing the new coupling correctly and the alignment is OK? Five years seems a bit short, I would have expected a bit more like 10 years.

 

First, I "can not confirm nor deny" that the sleeve was not changed out in the early years. I just couldn't find any paperwork to that effect. I think some of these small items get changed and not recorded. Our main hydraulic pump has a piloted fit like a "C" flange motor, so there is not much alignment done. For what its worth, the coupling supplier is telling me that even four years is a "long life".

> For sure these nylon couplings do wear out. It is a little
> strange that you are getting less life after the first time
> replacement. Are you sure that you are replacing the new
> coupling correctly and the alignment is OK? Five years seems
> a bit short, I would have expected a bit more like 10 years.