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14 comments
Associate

Join Date: Dec 2005
Posts: 27

Diesel Generator Problem

11/06/2007 8:53 PM

Hi, one of our 56kw Gens started "chasing".....the frequency guage would go down as low as 35 Hz and then up to 75Hz. It keeps doing this all the time from the time it starts.

What could cause this and how to fix it ?

I was thinking that it could be the governor, what do you think.

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Commentator

Join Date: Nov 2007
Location: Work Hawaii, Home Connecticut
Posts: 67
Good Answers: 4
#1

Re: Diesel Gen Problem

11/07/2007 1:02 AM

It does sound like a governor problem, though not exclusively. Check the governor has the proper level of oil, that the oil pressure or feed is adequate, check all linkages for tightness and/or slop. Can be stability adjustment.

You have not given enough information, is the governor a simple mechanical governor, hydraulic, electronic, have it's own oil reservour, get oil supply from engine oil gallery? Lots of variables.

Also can be caused by air in the fuel supply, an air leak in fuel supply, plugged filter, sticky linkages, plugged oil filter, dirt in governor oil.

Give me more specific information, engine make, governor make and model, I'll try to answer question with more info.

Regards CEKM

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Associate

Join Date: Dec 2005
Posts: 27
#2
In reply to #1

Re: Diesel Gen Problem

11/07/2007 5:00 AM

The Governor is Electronic, with a Controller Card and Magnetic Pickup.

Sometime before I had this problem and I adjusted I think the Gain Setting, and it stabalized the Engine but not 100%

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Guru

Join Date: Aug 2007
Location: Ohio USA
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Good Answers: 58
#3

Re: Diesel Gen Problem

11/07/2007 8:43 AM

It sounds like the governor is too sensitive. Reducing the gain should help. If you have a response time setting, increasing the delay will also help. You'll have to be careful not to slow down so much the engine stalls on a load increase.

I had the same problem on a Cat 3516. When we did startup testing, the acceptance requirements included the ability to take a step change in load from 0 to 100% (2000 KW). In order to prevent stalling, the governor had to be set for a very quick response (high gain, short time). After commissioning, the unit started fine during the first power outage, but it started swinging as soon as the first significant load was put on it. The governor entered a self-sustaining oscillation, where the fast response to load change caused overshoot of the frequency setpoint, then the governor would cut back on fuel too quickly and undershoot, then back overshoot again, and so on.

The root cause was that we had originally set the governor for theoretical worst case (100% step change) loading instead of actual worst case (30% step change). I backed off the gain, bias and response time setpoints, and tested several times with real-world conditions to fine tune. It has worked well now for 2 years.

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Commentator

Join Date: Nov 2007
Location: Work Hawaii, Home Connecticut
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Good Answers: 4
#4

Re: Diesel Generator Problem

11/07/2007 1:34 PM

Hi Sounds like pwrtothepeople has a good handle on the cause. I have had a similar problem with electronic governors, once traced it to a metal particle lodging on the speed sensing magnetic pickup. The speed sensing magnetic pickup is located somewhere where it counts the teeth usually on the flywheel starter ring gear. occasionally a sliver or fragment breaks off the starter pinion gear or the flywheel ring gear, and is attracted to and sticks to the magnet on the speed sensing pickup. This Will result in a weak or distorted signal from the mag pickup.

Cure is to remove, examine and clean the pickup. Be very careful to mark exactly the position of the pickup before removing, and return to exactly that position. Checking the clearance between the pickup and a gear tooth to verify it is within spec is advisable. Output from pickup when cranking should be about seven volts,

While pickup is removed use compressed air to blow out any particles or debris that may have accumulated in the bell housing. Removal of the starter to gain better access may be necessary.

Regards CEKM

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Anonymous Poster
#5

Re: Diesel Generator Problem

11/07/2007 10:59 PM

If this happen continously after starting DG set then most probably your govenor setting need to adjust.

Same time you also check AVR fuction from Electrical dept.

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Engineering Fields - Piping Design Engineering - New Member Technical Fields - Architecture - New Member

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Location: Bangalore India
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#6
In reply to #5

Re: Diesel Generator Problem

11/08/2007 12:56 AM

You contact Woodwords the Governer manafacturers for support.

crm

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Guru

Join Date: Jun 2007
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#7
In reply to #6

Re: Diesel Generator Problem

11/09/2007 1:00 AM

The engine is hunting between 35 hz and 75 hz.It could be governor problem.or may be fuel supply also erratic.

To broadly trouble shoot the problem, you may run the set without any speed bias signal from controller to governor control,if the set works without any hunting then the problem is governor-controller.

Otherwise the problem in fuel supply--choked fuel supply,airlock in fuel line,less fuel pressure etc.

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Guru
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#8

Re: Diesel Generator Problem

11/09/2007 8:17 AM

Was there a particular reason for you indicating the problem in Hertz rather than saying the engine was hunting...........e.g. 1450rpm - 1850rpm?

Just curious.

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Guru

Join Date: Jun 2007
Location: chennai,India
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#9
In reply to #8

Re: Diesel Generator Problem

11/09/2007 9:14 AM

The member has indicated the frequency in his note therefore I have followed the thread,further we may not know the rated speed of engine, it could be 375,750 ,1000 or 1500.Therefore I have indicated the hunting in hz.

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Guru
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#10
In reply to #9

Re: Diesel Generator Problem

11/10/2007 7:31 AM

To my way of thinking, we are looking at the problem here, a gen set that is faulty.

First take a look at the "big picture," is the fault with the alternator or the prime mover. I would certainly hope that one would know the rated speed of the diesel. One may also ask, among other things, whether or not the voltage was stable

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Anonymous Poster
#12
In reply to #10

Re: Diesel Generator Problem

11/15/2007 10:12 PM

Since the crankshaft is conneted to the alt. the speed of the engine in RPM is directly proportional to the generated HZ.

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Associate

Join Date: Dec 2005
Posts: 27
#11

Re: Diesel Generator Problem

11/11/2007 9:45 AM

I investigated the Magnetic Pickup and there were tiny hairlike metal pieces around the tip. I removed them and then fired back up, the Gen was back to normal.

Before, the frequency was fluctuating and increasing, but the output voltage remained constant.

Thanks CEKM for that useful advice !!!

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Commentator

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#13
In reply to #11

Re: Diesel Generator Problem

11/22/2007 8:11 PM

Thanks for the reply, glad I could help. I believe in the KISS approach (Keep It Simple Stupid), explore all the simple solutions before moving on to the complicated solutions.

I once sailed as second assistant engineer on a tankship, the emergency generator wouldn't start, a requirement for sailing. The tugs were alongside, the pilot aboard. The Chief, and the second decided the governor module was at fault and needed to be changed, a six hour procedure to replace and adjust. They made it plain that my assistance was not wanted. I persisted in the simple approach and determined that the magnetic pickup wires were loose due to an improper crimp of a ring connector.

We sailed on time!

Another time I was sailing as Chief on a ship, I had a young woman fresh out of the academy as an assistant, I gave her a job I thought she could easily solve to bolster her confidence, and get a sense of accomplishment. The problem was that water was getting by the fuel purifier. She spent days trying all sorts of cures, changing dam rings, checking motor speed etc. I finally had to intervene because we were running short of purified fuel. I took out the baffle seperating the heavy phase from the light phase and held it up to the light. It looked like a starry night, lots of pinholes rusted through.

I"m not perfect, and sometimes forget my previous experiences, and regret it.

Remember the KISS approach

Regards CEKM

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#14
In reply to #13

Re: Diesel Generator Problem

11/22/2007 10:46 PM

Dear CKEM

You are right smiler problems i have faced when i was second engineer on board ships we tend look at complicated solution's and waste time where as solutions are very simple which can be implemented with out extra outside help or-cost.one example i can never forget was lube oil contamination with metal warning lamp used to be indicated on engine instrument panel we spent lot of money to find source of metal particles in the engine oil after all exercises with out any results Finlay we found on chemical analysis we found oil cooler coil had developed pin holes and see water was mixing with lube oil sodium chloride was detected ,engine warning system was sensing sodium chloride as a metal and indicated metallic contamination .after changing engine oil cooler the warning lamp stopped flashing.another incidence was engine was not picking speed and was tripping showing low lobule in crank case on investigation oil level in the crank case was normal when checked with dipstick ultimately we found engine radiator water level senor was not fitted but the feature was enabled on the engine instrument panel ,once we disabled the feature the problem disappeared we fitted the sensor after entering the port. lesson is use your common sense in solving the problem.

regards

crm

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Anonymous Poster (2); CEKM (3); crm (2); MOBI (2); pwr2thepeople (1); ramvinod (2); watdefak (2)

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