Generator for home power supply. Frequency drop

[aillas]

Hi all,
My house is power supplied by a diesel generator. The load is purelly single phase, so basically
never balanced as AC`s are starting and stopping at any time. It is not uncommun to measure 20
Amps on the neutral in this situation. The fact is the generator as difficulties to maintain the
frequency at 50Hz (the standard here). The frequency frequently drops below 45Hz damaging equipments
or switching on the UPS.
I have two hypothesis for that. I observed that the generator is not grounded so I guess it is more difficult for
the DVR to find its balance. As it is frequency/load related I also suspect the governor.
Here are my questions:
1. For the grounding of the neutral. Can I proceed and ground the neutral even with such currents (20A) in it.
2. I am correct to suspect the governor?
3. Any references or online reading on the above subjects so I could go further in my learning of the problem


Thanks and regards.

 

[itsmoked]

Unless you are seeing voltage drops or over voltages at 50Hz I would blame [red]most[/red] of it on your governor.

The governor is a "constant speed" governor and that is it's job, keeping things at 50Hz.

Are you sure you are not overloading the generator as then the gov has no say. The engine speed will drop and the voltage with it.

You aught to provide more info..
What make generator?
What size generator? kW?
Do you know the horsepower?
What kind of governor?
Any ideas how many hours are on the gen set?

Tell us about the house.. All electric? Just the water heater? Dryer?

Do you know your house's typical draw?

Does this problem always happen? Just happened once?

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[waross]

Hello aillas;
Re the neutral grounding. Your system should heve the neutral grounded at one point. This is usually done in the main breaker panel. An additional neutral ground at the transformer is not recommended.
However it is wise to ground the generator frame for safety. This should be done with a cable to the ground connection in the main panel. A ground rod at the generator may be added but the cable to the main panel is still required.
Frequency. Is the frequency drop momentary, when an air conditioner starts? This usually does not do any damage and it will bring on your UPS for a few seconds. This is a result of the generator being a little undersized.
There are several factors that may cause the frequency to go down and stay down.
The generator may be undersized.
The governor may have too high a droop setting. If the generator has been put together with and industrial diesel rather than bought as a complete unit the droop will probably be a problem. Gen-sets typically use much less droop than industrial diesels for other purposes.
The dead rack adjustment may be improperly set. This happens when someone tries to set the speed and gets the wrong sdjustment. Taken to extremes, I once encountered a 60 KW set that could not start a 5 KW refrigeration unit because of a bad dead rack setting.
No load speed should be 51.5 Hz or 52 Hz.
When you answer itsmoked's questions we will be able to provide more suggestions.
yours

If the frequency goes down and stays down there
If the frequency drop is steady

 

[aillas]

Ok, here is for the answers:
The genset is a powerpac with a Perkins engine with a certain amount of hours on the meter. The genset is probably more than 8 years old. The Gen is rated 60 KVA or 48 kW or 83 Amps. The house is all electric although the major consumers are the 8 AC`s of 10 to 15 amps each. I can read up to 45 amps on one phase with differences between phases of up to 15 amps.
The voltage is of course changing but less than the frequency which is droping most certainly when a compressor is starting. It sometimes comes back fast enough for the UPS to play its role but sometimes stays down long enough for the load to exhaust the battery. I am quite sure that it is not an overload situation has the situation can happen with 50% of the load.
Well the more I write the more I am thinking of the governor.


Thanks all for your valuable and appreciated answers

 

[waross]

aillas
Have you checked the fuel system? Filters, lines, is the pump getting weak? Any air leaks in the fuel system. Restricted fuel will often cause those symptoms. If an engine is starving for fuel, it will run but bog down when a heavy load comes online.
Has anyone done any work on the engine lately particularly the governor?
From your ratings I assume you're running three phase at 240 volts.
Is this a standby set or has it been the prime power for most of the 8 years?
respectfully

 

[itsmoked]

aillas; It does sound more like mechanical to me all the time. I doubt it is the engine since you are still running under half the rated load.

So the governor does still seem like the problem. I am not familiar with the governor style on that Perkins..

A few thoughts though would be; If you can be present during one of these low freq-low / speed episodes and if the governor is accessible I would attempt to "manually" help the governor. If you can raise the speed back up with a finger then this would confirm the problem is governor based.

Next. If this governor is oil powered, low oil pressure could easily be the actual problem. Oil that is too old, or the wrong type, or to low could be the culprit. Also a worn out oil pump or clogged filter or a defective filter(common), could cause low oil pressure that could detrimentally affect the governor's operation.

Even worn out internal springs can cause this kind of speed control loss.

Depending on your plans let me suggest another path if the governor is at fault.

We often have problems with 40-80kW generators on rail cars sagging with starts on large loads, primarily refrigeration. These cause all sorts of havoc with the extensive electrical systems filled with safeties and electronics. We started using soft starters on the compressors. This helped dramatically but still we had a few problems. This is extremely serious on a glass domed rail car filled with a hundred partying travelers moving at 70mph when some hiccup stops the 15 ton refrigeration system and then requires getting under the car to deal with. You cannot stop a train out in the middle of nowhere to work under it. (Not allowed)

When we had a flaky governor we decided to replace it with a modern Woodward Electrically controlled unit. They provide all the bits and pieces needed to adapt one of their controllers to any engine. We used the isochronous versions (someone else here can explain that). These governors are nothing short of amazing. The largest compressor starting on partially loaded systems do not cause more than a FRACTION OF A HERTZ dip when starting. You can only hear a minuscule subtle extremely short change in the exhaust note. There is ZERO blink of lights. All related problems ceased. We removed all soft starters as they no longer made any difference. Anyway they work. And Well!

http://www.woodward.com/pdf/ic/04106.pdf

They cost usually less than $1k.

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[waross]

Hi keith, What type of engines are used on the rail cars? I have installed over twenty Perkins gen-sets. A lot have been in service for ten years or more. I have not really had much governor trouble with the Perkins, or with John Deeres with similar governors. A problem that I have encountered both with mechanical governors and electronic governors is the dead rack adjustment. After a rebuild, this cannot be set properly without a load bank. A load bank is often not available so the adjustment is usually off the optimum setting. If it's too low, the engine can't produce rated power.
Re electronic, the electronic are better, but if a change made as much difference as you say (and I don't doubt you) then the existing governors were crap.
I had one installation where two cat generators were paralleled As I remember it was a 500 kw and a 450 kw. When the 400 horsepower hog started, we needed both generators paralleled even with a soft start. As you pointed out, when the oil is cold responce is slow. First thing in the morning when the oil was cold, we couldn't start the hog. The hydraulic governor couldn't keep up with the electronic governor, the electronic set would hog the load and trip the breaker. After 15 or 20 minutes of warm-up time, the mechanical governor could respond fast enough to match the response of the electronic governor and we could get the hog up and running.
I had another customer change the electronic governors on a pair of 60 kw sets from electronic to mechanical. Part of the load was a pair of icemakers that took the whole output of one set. We didn't see a noticable difference in motor starting after the change. (Well that was after the mechanic left and I reset the dead rack).
Why change back? He had lots of people locally who had experience with hydraulic and mechanical governors on old G.M diesels. He had to fly me in to work on the electronic governor. It wasn't so much the cost of the plane ticket as the time. At times they may have a couple of hundred dollars of product in the freezers and he didn't want to take a chance.
When I was younger I liked G.M. diesels, but now that I'm older, I don't like getting "Deaf and Dirty" any more.
Later
respectfully

 

[itsmoked]

waross;
We have Cummins, 4BTurbo, non turbo and 6BTurbo models.

We also have several Detroits; high performance 3-53s that put out about twice the standard ones and a couple of horizontal 3-71s pancakes.

Yanmar 4cyl

Cummins/Onan Genset

Stadco RailGen - Duetz powered.

Since the governors on the Detroits actually directly control the fuel racks they are more responsive than the Cummins that I described previously.

Yeah the rail companies have all ditched the Detroits because they couldn't meet the emissions. So even though most engineers hate GEs they cost less and are cleaner so the rail companies have gone to them in droves. GM now puts out nice 4 strokes but they are expensive and now I think GM dumped the whole division in their continuing orgy of miss-management.

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[tommom]

One other thing to bear in mind - small a/c units such as you are describing usually do not have a timer to delay compressor restarting after it shuts off. This can cause the a/c unit to try to start against the high-pressure in the coils, which it can not do. So, the compressor just sits there, drawing locked-rotor amps until it times out, and then it will try to start again.

Try disconnecting or shutting off a few of your air-conditioners (or all of them) at a time and see if the problem continues. If not, you can turn them on one at a time and see if the problem gets incrementally worse or if one a/c seems to be causing a problem.

50 to 45 hz is quite a drop in frequency for half load.