500 kVa Perkins Natural Gas Generator Unstable Frequency

Based on the fact that it used to pull twice the amperage & now it can only pull 50% with unstable rpm (frequency), I would say that there may be 2 possibilities:

(1) as you suspect, the fuel pressure (at the carbuerator) is not keeping up with the load. If it goes really lean (lack of fuel), you will have low power followed by unstable combustion and eventually significant misfire as you approach the lean air/fuel ratio combustion limit (about 27:1). Look for problems with the natural gas regulator final pressure feed at the mixer (venturi) - which should run very close to atmospheric pressure. Note: I assumed here that you don't have natural gas injection as that is too advanced for a small machine.

(2) as the load (amrerage) and manifold pressure go up, the spark energy required to jump the gap increases. Check your spark plug(s) for proper gap and condition. Also check the coil and plug wire for arcing in a dark room - you can sometimes find the location for the breakdown. In a pinch you can gap the plug down from say 1.0 mm (0.0394 ") to reduce the spark energy needs to perhaps 0.75 mm (0.030") to avoid misfire or arcing if the system is marginal on the secondary or primary side. But that is just a band aid - not a real solution. It may tell you if the spark is the issue.

Good luck.

Hi awelch,

Many thanks for your prompt reply, i will be forwarding your advised to the mechanic and the technician to have it check and consider on their trouble shooting. I will post the results after these exercise.

In addition yesterday, they replaced the whole turbo and manifold up to the gas pressure regulator side beside tha engine, when we try to load same thing, still hunting at 50% load.

Kind regards

Problem is restricted fuel supply. which comes to expression under heavier loads. Another possibility is air leak between injection pump and injectors.

Hi wangito,

air leak is make sense, however it doesn't have injection pump.

many thanks for your input we will ask the mechanic to consider your point.

Sounds to me like a governor problem, if the governor is a mechanical type. If you have not done the maintenance on the governor in awhile, I suggest you get out the tech manual and do that first. If the governor is electronic, check the speed sensor and all wiring.

Hi nukesub629,

Thanks for, it was an electronic governor. The head mechanic will be arriving on Friday and we will consider your input and will post whatever the problem found to rectify the fault so everyone will be updated.

However, more idea on probable caused and solution are most welcome.

Many thanks

It is not properly controlled. This type of hunting occurs due to automatic control of fuel supply when engine's rpm drops (48 Hz) then controller adjusts speed by increasing the fuel delivery too much, which drives it up to higher speed (54 Hz).

To solve the problem some additional information is needed:

Is the generator a free standing or it operates in parallel to more generators?

Perhaps the generator is supplying a grid?

It is also esencial to know if this is electronic controller or hydraulic? or pneumatic?

Perhaps digital? perhaps analogue?

Anyhow whatever it is just do not be afraid to fool around with adjustments and start by lowering its sensitivity a little bit. Do not forget to mark knob position first so you could come bak here you are now and do it when hunting occurred.

It could also be a loosen screw connecting lever that actuates fuel push. Perhaps wearing of the rode etc. A very difficuld to spot

Also you might try to lower or add load when hunting has occurred.

Stan

Dear Sirs/Madam: I have operated a few Diesel Generators, in my 23 yrs as Power Plant Technician Trouble Shooter, prior to Retirement. Sounds Like You Have A Frequency/ Governor Adjustment Requirement. Does A Natural Gas Pump have a "DROOP SCREW"? IN Some Manuals It Could Be referred to as "THE SENSATIVITY ADJUSTMENT" which controls how far the Frequency is allowed to go Below or Above 60 Hz (for any reason). It Appears you are adjusting your Pump under a NO LOAD CONDITION. When We could not get permission to ADJUST ENGINE SPEED LOADED< WE HAD A DUMMY LOAD, WE COULD SWITCH IT OVER TOO> We used to try to set up the Speed Control to Produce 60 Hz Plus or Minus 1/2 Hz. or (59.5hz to 60.5hz). There are a few possibilities where Your 48hz to 54hz Set to suitable tolerence Above & Below 50hz( for 50hz System). It is still as previously stated " The Sensativity Adjustment".

Hi All,

Thanks for all of your response on this and I would like to update everyone on what we found, the # 7 cylinder piston,ring, and the sleeve was partially damaged that is why probably everytime the load raised to 350 amps the frequency and the voltage becomes unstable and hunting. the parts was on order and soon it will fit and run I will update everyone. the possible caused of the damaged was could be the small sand which not due to the gas supplied with no in line filter and this will be part of the correction measure.

Kind regards

Roman

Dear house,

please can any body give me solution to my generator problem 500kva perkins,is doing hard starting ,will check the fuel line no problem their but the engine is hard to start but when the engine is run for at lest 1 hour if you start ,the engine will start .

thanks house i will expect your replied . Tony or you can mail me the solution,tonybamy@yahoo.com

Hi Guest,

It would help if you can give more information like what is your fuel? Natural gas or Diesel etc. a lot of member can give you porsitve response.

Battery problem..Check your charging system.