Generator Frequency Dips

If all is working as it ought to be, really, like phase balance of load, then I would suggest checking to make sure that the ground and neutral are good.

Basically the speed (frequency of alternator)of the machine will come down as you load the machine.When the speed comes down the controller(governor) will try to increase the speed to the required level,provided the drop in speed is within the range.

In your case there are two probables, 1) Speed drop is beyond range,2) controller not correcting the speed drop.

Speed drop beyond range will occur when the load is very high

Therefore ,you have to check the Load on the machine or the controller for malfunction.

If the generator is stalling then there should be very heavy load on the generator.try and load the generator in stages say 25 %,50 %75% and 100% and watch the performance.

Let us have feed back,if there is any thing.

Hello Sapper

I've run into the diesel fungus problem years earlier, in several installations.

New Zealand Railways got a load of fungus contaminated diesel, back in the early 1970's, and it took them a few weeks before they realised what the trouble was.

Generally these days there is a fungal inhibitor included in diesel fuel, also jet fuel, which used to get the same bug.

Petrol back in the early 1970's, when there were carless days in New Zealand, and because you could not fill up "extra containers" with fuel at the Service Station, caused me to fill three 13 gallon drums with petrol, via siphoning from the car tank, so that an urgent trip could be made, in emergency.

The fuel already had the bug, and when a year later I went to use the petrol, there were spider-web-like threads all through the fuel, and over half was wasted, trying to strain out the fungus.

If the fuel is contaminated, all traces of that fuel need to be removed, the tank and pipelines cleaned with detergent, then washed thoroughly with undiluted bleach.

Fuel filter elements need to be burned.

Kind Regards....

Sparkstation,

I Know what you mean...It took two days of running a mix of Detergent, Disinfectant and Kero through the Tank & Fuel system.

The only Upside was that it was a Containerised Generator on Hire and the hire company wore the cost...They didn't charge us for the Hire either, but it still blew the project time lines that it was supporting out.

Regards,
Sapper.

Sparky

There is a device which was invented right there in NZ which I have seen to overcome the problem of 'bug' in diesel fuel, even heavily contaminated stuff. I've just forgotten the name, but it's an array of rare earth magnets in an alloy housing through which passes the fuel. The guys say that it 'implodes' the 'bug' at a cellular level.

I argued, originally, but it works. I was amazed that the 8V92 just roared on better than ever.

For what it's worth.

Cheers,

Stu.

A really good post.

Sometimes its the basics that bite us in the Butt, yours was a good "Head up" !!

Sorry Sapper,

I put my 2cents worth in before reading yours.

I think you're on the money. GA

Cheers

Stu

Fuel/filter would be the first place I would look, also, especially for a standby generator where the fuel has been sitting for an extended period in an isolated tank. You should have ammeters on the system- it would be pretty obvious if the problem were electrical load.

I understand today's fuel is only stable for a short period in storage. A diesel engine may idle fine, even with some problems in the chain, but when a load is applied, it may falter or stall for a shortage of any of the 3 items needed for a fire to burn: fuel, air, and an ignition source. The greater the load, the more you need. The fuel gauge may indicate that there is sufficient fuel, when there isn't. When the engine runs out of fuel, it may take some time to get it primed. I've had diesels stall for a number of reasons, but during my limited experience with generators, the power source only stalled when the load was too great or it was applied all at once, rather than in steps. Remember to start the hungriest loads first in order of their starting power requirements.

good luck.

Contaminated fuel would be the first thing I would be looking for.

The next step is to run at no load idle, then progress through to full throttle no load gradually. This will eliminate the possibility of it being caused by the load interface with the governor. If you can see your exhaust fumes while this is happening monitor the colour. I had a case with a 500 kW gen set that at idle was a dream but as the revs increased even without load it would start to miss behave.

It turned out to be a faulty injector that only played up as more was expected of it. The dripping caused the exhaust fumes to indicate a rich mixture (Blue Black Smoke).

The fuel or fuel system is the most likely culprit, but it may be worth checking your air inlet for a bird nest or other obstructions. Again you could get a situation where at idle there is enough air to perform but not when the load increases and the need for air increases.

I have this theory that diesel gen sets are all female and that if you keep that in mind when you are dealing with them it helps you to get along much better.

Please keep us informed as you eliminate the possibilities.

BAB

I agree with BAB injectors should be checked for peak performance re seat them if required. If the fuel rack is at max when on load it indicates the governing system is trying to compensate.and power is falling off to such an extent as you indicate then pumps injectors and fuel would seem to be the culprit.

Normally drop in frequency is indicative of excess load.Secondly the frequency variation limit is too close for a diesel engine set .Normally +- 5% and for such close frequency a MG is set is preffered.Were the set builders/suppliers were aware of this requirement?One what I can think is check the governing of the engine.Check the load (A thorough load study may be required)and if governing is ok then u may need a higher sized set may 630KVA.Pl. also check with the set supplier.In case u have already done that what do they say?

Check the fuel flow to the injector pump. There are a few things which could give you the problem you're experiencing, however as you are already part way through the test procedure, check to see if either or both the fuel filters are waxed up and not passing enough fuel to sustain the load. This often happens in stand-by machinery. Could also be bacterial contamination of the filters, or indeed the fuel lines, or the tank outlet, also reducing the fuel flow.

Bad mix of fuel, water contamination (internal rusting of the injector pump and governor can be a by-product of this too) will also bring the machine to it's knees. Can't give accurate diagnosis 'over the phone' as don't know the maker of the motor or the fuel system, but this is a place to start. Let's know the results.

My money is on the fuel system. The electrical stuff is very reliable, as is the mechanical section.

Cheers,

Stu

Have you checked for DC current from the load? Dc current produces dynamic breaking in rotating machinery. Use a clamp on meter that has a DC range to measure each phase. If you cannot find a DC clamp, use an AC clamp. You won't read anything but if it sticks, or you cannot open it while the load is on, you have many amps of DC current.

If you find DC current, check the different load branches. It is possible that an AC drive or a UPS has lost a diode and draw DC current.

Good luck

jjbadski,

What type of fuel does the generator use? Many on this thread are making the assumption that your system is diesel. In Southern California, because the Air Quality Management District (AQMD) does not allow diesel, other fuels such as compressed natural gas are often used.

Is the engine set up for the type of fuel it is being supplied?

Has this system ever operated?

Have any changes been made recently?

Read the org. post.

Prist is the brand name of the microbial inhibitor we put in Learjet tanks for avjet fuel.

Check the fuel filter and passage to governor. Reposnse of Governor is the prolem with increase in load. Also check Droop settings if ok for the givenm load. Also does it happen at a particular time whne load suddenly increases.

Check governor opeation and fuel pump and its circuit for choking of pies and filters.

Well you really caught me out there, what did you mean by:-

and its circuit for choking of pies and filters.

??????

"and its circuit for checking(?) of pies(??) and filters."

Most replies are addressing the engine side except a few.Is it possible to have such close level of frequency variation with a dg unless the set is over sized.Request forum to clarify this point

Yes I have commissioned ( 20 months back) 3 nos 2000 kVA ,caterpillar sets in chennai India, with woodward controller, we are getting frequency tolerance between 50.15 and 49.85 hz.It is possible to achieve.

Ues. It is possible with Kohler make DG sets.

I agree completely. We had big emergency Diesel generators in the RN in the 60's with similar tolerances. If it was possible then, it must be possible today.....

I love Ramvoid!

Absolutely...Essential Services site (eg Data Centres, Call Centres etc) all rely on these sorts of tolerances.

Sapper

Hello jJbadski,

A lot of posts have been made but no feedback.....

Few inputs....

a) The full load current.

b) Generator rated current

c) Total VSD application load

Check your grounding, and also bond neutral to ground.

Can you check the droop setting in the speed controller ? It might be set too high...

Hopefully you have checked the filter/fuel-fungus by now.

Any discussion can go ahead only if there is feedback...

Please keep us posted....

Dear sir

I do agree with you, most of the Guests do not report back , after their problems/issues are sorted out.

Their feed back will immensely help us for future reference.

TO ALL....

Thank you for all your valuable suggestions and insight. As it stands right now, the governor settings were adjusted during the recent testing and everthing seemed to work properly. However, a new issue arose and that being one of the VFD's controlling an air handling unit started to "fault out" during the testing.

This is currently being investigated and I will report back as soon as I get the results. The mfg of he VFD indicated it might be a simple solution of placing the required size line reactors at the VFD to stop the transients being caused by the testing/switchover procedures.

As always, any suggestion or insight is greatly appreciated.

Agian, I thank you all for you patience and help with this issue.

badski