paralleled generator load go uncontrolled 4

[pinojman]

first post and hopefully, experts can guide me to find the answers.
problem started few weeks ago, routine test paralleling diesel engine with main turbine generator almost create shutdown to our plant. this test is weekly program, never find this problem before.

diesel engine 2x1.5 MW/ 6.6 kV ; main generator 7 MW/6.6 kV. normal load 5.5 MW.
synchronizing process running good, until the time when diesel engine orderred manual to take load from main generator. when load reach approx. 380 kW, suddenly load diesel generator each, increase almost max power it can handle (1.5 MW), it happened, even without manual ordered from speed faster in diesel.

already check for contact faster condition, all orders faster to woodward governor,and even restroke diesel actuator, all seems to be normal.
troubleshoot test repeated for almost 5 times, the problem still exist.
is there any spot, that we missed to checked? or problem begin from the main generator?

already replace the diesel generator with same parameter, problem still there.

thanks before.

 

[waross]

This is very important:
Did the Kilo-Watts increase or did the Current increase. The only way for the generator to pick up load that way is for the engine to get more fuel.
This may be a governor actuator problem, a problem internal to the engine with the fuel racks, or the engine may be somehow ingesting lube oil.
If you are seeing the current increase, this may be an over excitation problem. If the excitation goes high, the set will produce more reactive current but not actually develop any more Kilo Watts. In this instance there may be a problem with the AVR or the operating mode of the AVR may have been changed.
Many plant operators with a mechanical background assume that the ammeters are telling them how much load they have. Works most of the time, but in an instance like this the difference is very important to trouble shooting.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Another possible issue: Is either of the sets in isochronous mode? If the governor is set to isochronous mode when the set is paralleled any frequency error will result in the set hogging the load.
Sorry for the multiple posts. It's been a very long day.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Another possible issue: Is either of the sets in isochronous mode? If the governor is set to isochronous mode when the set is paralleled any frequency error will result in the set hogging the load. Check this first.
Sorry for the multiple posts. It's been a very long day.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[iceworm]

Assuming that when you said "KW" you meant power, as opposed to KVA: As waross said, the only way for the DGs to pick up to max power is for the throttles to go wide open (or also as waross alluded - a broken engine).

I'm really making a lot of guesses. Be easier if I could nail down some of your operating methods. Just so I am clear:

You have done this many times before and it always worked fine. There has been no changes to the procedure.

You have two each, 1500kw DGs, operating in parallel, receiving the same load commands. When under routine test, the two generators are paralleled onto a bus with a single 7MW TG.

Is this true so far? If not forget the rest.

If so, looking at the problem is the throttles on both generators are being commanded to go wide open:
A normal setup is for the DGs to be programmed for constant KW (possibly also load share) when paralleled with the TG, and Droop (also load share) when the two DGs are paralleled together, but not paralleled with the TG. The few like this I have seen, the DGs are paralleled on to the bus one at a time.

The TG can either be isoc or Droop - doesn't matter if paralleled or not.

Just looking at the two DGs, there are several required operating modes. One I worked had three controllers feeding the control signal to the DG governor.

Where I am going is: Can you get a meter on the signal going to the DG governors? Is it as it shold be?

Is this true so far? I'll stop here until you straighten me out.

ice



Harmless flakes working together can unleash an avalanche of destruction

 

[waross]

Two sets will not parallel well if both are in iso control mode. If one governor is set even one half cycle faster, that governor will hog the load. Someone who may have a lot of experience with single sets but not much with parallel operation may have thought that the DG set should be in iso mode. In iso mode, the set will pick up load until it has either reached the limit of the fuel delivery rate or it has unloaded the paralleled set enough that the frequency rises enough to eliminate the error.
If both sets are in iso mode the set with the slower setting assume an over frequency issue and will be shedding load.
If this is true KW loading the most likely cause is iso mode. The other possible causes are to be checked out after checking the governor mode. It is possibly the easiest to check as well as the most likely cause of KW loading.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[catserveng]

Maybe a little more information from the OP would get better possible answers. Bill is right on with his comments IF all three units have speed control governors only. If this is a newer system with all units having isoch governors and load share controls it opens up a bunch of other possible contributors. If the system is less than 10 years old is a good possibility that the diesel engine driven generators have electronic governors in their on board ECM's.

So, start with some details about the turbine, like what kind of speed control governor does it have and does it use some form of load controller like a Woodward 505, DSLC, CGCM, or 2301A load share governor?

What kind (make/model) of diesel engines? What kind of governor? You said Woodward in original post, what is the model or part number? Is there a load control system, same questions pretty much as for the turbine (except probably not a 505).

I recently had a similar problem with two older Cummins units paralleling to a Solar turbine, the Solar had a 2301A load share governor, as did both of the Cummins units, and also had SPM-A synchronizers, in this particular instance it was one of the SPM's not seeing the RUN command go away and kept putting a positive bias on the speed reference. Point is depending on system complexity, there may be a number of possible contributors. Sometimes it is as simple as a control input not picking up or dropping out to change a control mode, other times it could be something much harder to troubleshoot. Since this seems to have been a working system with a new problem, need to see if something has changed, like did this happen after a component replacement or a service of some kind?

Mike L.

 

[pinojman]

thank you for all the responds and guides,
i forgot to inform that the system in island mode, with TG controlled with woodward 505 and in isoch mode, whereas DG's controlled with Woodward ProAct II, both in droop mode when in paralleled.
first DG synchronized with TG, and load increased manually, and stable to 200 kW. when the second DG syncronized to the system, odly took the load from the first DG. and after that, normally operator will loading both DG to for each 400 kW manually with mommentary switch speed faster, taking the load from TG. but, after load approx 380 kW each, both DG took load from TG without controlled from operator, both surge to almost their peak capacity.
load taken are in kW, not ampere, voltage relatively stable.
and, yes it's a routine weekly test, never found this trouble before. we already ensure for signal speed faster command to the ProAct II controller, even we already open the circuit to this terminal, in the case when the load keep increase.

attachment below, show load trend captured when trouble arise.

http://files.engineering.com/getfil...5-41b5-9c8e-4bb6fe18e443&file=load_curve.xlsx

 

[pinojman]

iceworm,the DG's unit paralleled to TG in step by step, first DG synch'd, took 200 kW, after that second DG synch'd took another load with their own speed faster, and governor it self. and yes, i can get the meter signal from governor DG, for example, when this problem arise, opening DG's fuel actuator was orderred to increased by the ProAct II, BUT there were no order from the operator, or from another control speed faster command, because we already open this, through breaker we inserted, while the load keep increasing.
Diesel engine are Deutz with AvK generator, and we didn't make any repairement or replacement along this normal test, with next trouble test happened.
additional information, TG frequency is very high about 50.5 Hz for normal 50 Hz. when we asked operator to decrease to normal, they reluct and stay in this condition because worried to disturb their normal operation, pressure pump etc.
is it any relation with this high frequency system? we have already leave to check the DG, because all test and troubleshoot found to be normal. so we move checking to the TG system.
thank you for all your kind responds and guides.
attachment are speed faster controler to the woodward ProActII

http://files.engineering.com/getfil...c-b2dcf490c12d&file=control_speed_faster.xlsx

 

[waross]

Has there been a change in operators recently?? It may be that the switch is ramping up the setpoint faster than the output responds. I have seen this issue. Try operating the speed switch with a series of short applications and wait between each application for a speed response.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[iceworm]

TG controlled with woodward 505 and in isoch mode, whereas DG's controlled with Woodward ProAct II, both in droop mode when in paralleled.

Okay, that's pretty standard. When paralleled, the two DG are in droop and the TG is in isoch.

It is always bad when no one has made any changes to the DGs, programming, wiring, procedures, and yet the operation changes. I really hate those.

On more thing I'm not clear on is the speed control. I will restate and see if I understand:
There are two RAISE-LOWER" switches - one for each DG. The first DG is brought on line. It's R-L switch is used to load it up to 200KW. The Second DG is brought on-line. It takes part of the load from the first. Both R-L switches are then used to load up the two DGs. At 380KW load, both generators load up with out any further Operator input to near max load.

If this is true, then as Bill and Mike L said, now is when you verify the DGs are in fact in droop and not in isoch. You are verifying someone did not sneak in during the night and change the programming.

It is not likely that both DGs broke the same way at the same time.

As for the TG having a problem that is affecting the DGs, my understanding is there is no control between the TG and the DGs. Other than the bus, the two are completely separate.

Is this true?

If so, look at the TG frequency. If the TG frequency drops, this will cause the two DG (in Droop) to load up. If the frequency drops from 50.5 Hz to 50 Hz, that is like a 1% change to the DGs. They would try to load righ up. However, I would expect you would see that of the frequency meter immediately.

Look for anything that the two DGs have in common. And if the TG controls are separate from the DG controls, about the only thing the TG can do to affect the DGs is to change frequency.

I'm curious, where do the two DGs get their bus frequency signal. Any chance both come from the same place and that could be malfunctioning.

I'm not going to be much help. It's hard to troubleshoot looking at a keyboard and amonitor. But there are others on here that have better X-ray vision than I do. Hopefully they can help.

But I am interested. Let us know what you find.

ice.

Harmless flakes working together can unleash an avalanche of destruction

 

[catserveng]

Something still missing here I think, a ProAct II is an electric actuator system, not a governor, so something has to drive a control signal into it, like a 2301 or 700 series speed control, unless you have a ProAct II Digital Speed Control System. Is that the case?

If you do have a speed control system, have you checked to see if terminal 16 is wired on the speed control(droop/isoch input, at least in the manual I have), usually Droop mode is active on a Woodward control when the input is open, is it possible there is a droop/isoch switch or control contact? Have you checked the controller to see what mode it is in?

What actuator do you actually have installed? a ProAct II has abut 5 ft/lbs of force, seems a bit light for a 1.5MW diesel depending on it's fuel system, usually on that size engine you would see a ProAct III actuator.

Have you watched the speed controller with the handheld? I'm assuming that is the version you have based on what has been provided so far. It should be possible to look at both the position command and the feedback position with the handheld, this can help you determine if you have a mechanical problem as Bill suggested above. If the command and feedback stay apart for more than a couple of update scans, it could be you have an actuator with a problem, or a sticking fuel rack.

Hopefully this gets you started in the right direction.

Mike L.

 

[pinojman]

waros, we already test offline for the mommentary switch faster for any stuck or sticky contact, the result are good, then when we test online running DG, raise load DG to 200 kW still normal, waiting it for about 3 minutes, load stable. after that increase again to 250 kW,260 kW, and 280 kW, load became increase without ordered. during that momment, we had open all circuit to terminal faster, but still increasing load, finnaly open DG VCB to stop the loading.
iceworm,you are definitely correct, both DG's have their own L-R switch, and again you are correct that this problem create us frustated, because happen in the both DGs. droop order come from PLC signal (used when during start up plant, without steam for TG, we use DGs to starting big induction motor, and load controlling the DGs),already verify with monitor contact lamp output PLC for Droop signal, and it is keep open, no change.
so after several test conducted and monitored all posible parameter in the DG, we change our curiosity to the TG. unfortunatelly, operator won't to decrease the TG's frequency, while maintenance crew try to monitor whether this item affecting the problem, next test is still to be suspend.
previous test we never check and monitor frequency trend, so we dont have any data whether the system frequency fluctuating.
and Mike, our speed controller consist with ProAct II Controller, with ProAct II Actuator and handheld that we can monitor actuator parameter,speed,feedback,include status signal droop,faster,slower. during several test we keep changing to monitor this parameter and we found that speed keep constant in approx 1516 rpm, it was match with the ratio freq (50.5/50)multiply the 1500 rpm rated speed.
our team not checked the droop signal through the contact 16 directly, but as a stated that we monitored it in PLC contact output that through the 24 VDC contactor, will open/close contact to the droop terminal, and it was still in open contact.
one of our great suspect was the feedback signal to to controller,and we already verify that this is not the problem, because during restroke the actuator using handheld we can get the consistent feedback value proportional with opening actuator.
is there any possibility problem arise from the mechanical side/engine? but what make us again frustating is, why this happen in the both engine in coincide time... wuhaaaaaaa

 

[waross]

I understand that the PLC controls the operating mode and switches between iso and droop. As a possible test consider disconnecting the mode control signal from the PLC and hard wiring the governor/controller in droop.
I did have an issue with a spring return actuator/fuel control valve. The valve/actuator combination developed more stiction than the return spring could overcome. When the load decreased the fuel valve would not close and the unit would trip out on over speed. The set was islanded. Had it been in parallel it would have started to hog the load.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[pinojman]

Thanks Bill for the advice, We will check the actuator spring return for any abnormality.

 

[pinojman]

Give the latest condition after several maintenance activities, here are the results:
1. we focused our troubleshoot to the steam generator side, because we already sure that both the diesel generator are fine, no trouble there.
2. during shut down period last december, Mechanic personel found that in steam generator turbine, lube oil system become somehow sticky and there was burnt oil marks in gear box area.
3. opening the control governor system, secondary oil through the pilot governor were also being sticky, do to the bad lube oil. we believe this condition lead to malfuction of governor moving during loading and unloading.
4. after cleaning and blowing the control oil line, and overhauling the governor we started to replace all the lube oil with different brand of lube oil based on lube oil manufacturer recommendation.
5. restroke the governor through the speed controller turbine during offline condition showing good result.
6. started the turbine, synchronized diesel generator, at first condition small hunting happen, after several times of trial, stable condition finnally occured.
7. Loading and unloading become normal, synchron with the diesel with loading up to diesel capacity become normal again.

I just want to say thank you for all support and sharing from this forum.

 

[waross]

Thanks for the update. We all learned a little from your experience. Tell myself again to remember:
When trouble shooting don't assume anything. Here we had assumed that the problem was in the wrong machine. (Diesel Vs Turbine)


Bill
--------------------
"Why not the best?"
Jimmy Carter