Generator Not Able to Take Load

Dear,

I just looked your problem.

I think U followes 'A' check First Then

Check The Your Synchronizing Panels Load manager Setting,

Check your Automatic Power factor Control Pannel working Auto mode When you give the D.G. Backup that time it should Be Off Condition

Thank you sir, Sorry its a single running DG set. There are no complicated genset controller or the Synchro panel. It is still using the traditional analog meters for the lub oil level etc.

Check engine governor

Engine Maker insist Governor is ok. They decided to change the injection timing to boost the efficiency of the Engine. Still waiting if this method could help the genset to achieve 110% loading.

This is just a guess based on farm machinery that will act in a similar way at times.

When an engine hunts or wont stay stable its very common to have fuel quality issues. White smoke at load typically can indicate water of some non combustible contaminate is in the fuel. Or possibly a partially blown head or manifold gasket is letting coolant leak in when heavily loaded. The engine itself may have a bad temp sensor and may not actually be up to proper temperature.

If its turbo charged white smoke at load can also indicate a bad shaft seal in the turbo charger itself. Engine oil is being leaked into the exhaust but does not have sufficient oxygen or heat to burn and can result in light colored smoke at times also. Or if its getting drawn into the intake there are some types of oils that don't burn when passed through the engine and they too can cause odd exhaust coloring. The turbo charger may not be working properly resulting in to low of compression for the diesel fuel to properly burn too.

I would start with a fuel quality analysis first. Most diesel engine power problems are fuel related and still the fuel itself is the last thing looked at by most. Not all diesel fuel is created equal or shipped in clean tanks or properly handled from beginning to end going from the refinery to the end use point.

Just some things to think about.

Dear tcmtech, Appreaciate your kind reply. I've received a call last evening from the technicians that adjusting the injection time does not improve the performance of the DGset. I agreed with you that there might be some issues pertaining with the engine. However, the Engine Maker is still confident that the issue is not lie with them but the poor efficiency of the Alternator. Now they might de-couple the existing Siemens licenced alternator with either Stamford, Marathorn or Mecce alte alternator just to prove that the engine is fine and the entire problem lies with alternator. I am totally disagreed with their decision to change another alternator make and still looking for ways to help to solve this issue. FYI last year, this Siemens licenced alternator with a poor AVR is the cause of similar issue but now we have change to a better AVR supplier so i should say the problem does not lies with the alternator.

Thanks for the response. I am by no means an expert on large diesel generators by any means but still I just went by what I have personally observed in common diesel engines.

Like I said before fuel quality has a lot to do with the peak power of a diesel engine. I have driven many diesel farm tractors before pulling plows and other heavy drag implements and I can honestly say that the fuel quality can make the same plow pull one gear higher or one gear lower than typical in identical field load conditions. That is a bad batch of fuel can knock a diesel engines output down by over 20% of what it will put out with a good grade of fuel.

Its the energy in the fuel itself that limits the peak output power. No engine or fuel system modifications are going to get the same power out of bad fuel as it does out of good fuel. And there are a lot of fuel suppliers selling cheap quality and bad low grade fuel under false labels of being good high quality fuel.

If the engine is good and the fuel system adjustments have not changed the output, possibly just switching to a different fuel source or supplier may be all thats needed to get your generator back up to its rated power output. Around here certain fuel suppliers a well known for selling low grade fuels labeled as good high grade fuels. Its obvious when you get some. Equipment and vehicles get far worse fuel economy and use more yet they are noticeably down on power and just don't seem to run as smooth.

It all could come down to a bad tank of fuel and nothing more. It happens to farming and construction equipment fairly often so I see no reason why it couldn't have also happened to you and your big gen set.

Dear tecmtech, i noted your points and will check with them the fuel that they used. FYI those people in the third world country do not applied better fuel just to save cost. Sometimes the fuel is reused time and time again, because fuel (diesel) is consider expensive at their end.

we r using the 625 kva (.5MW) d.g too....s ooo man just see one thing urgently that the load is resistive and so the power pactor is 1 heyyyyyyyyy not joking man......

so the dg will work as 500kva dg or 500kw dg...so u will be loading just 80%of the rated current.....now u have overloaded it....hey stop this bull shit.......... ok see the power factor ok???????????????????????????//

your dg is 625kva at .8 power factor which is usal

Dear Sir, Pls advice why you are just loading up to 80%? Why are you limiting to 80% load? For our usual testing, it is 100% to 110% load. The power factor is around 0.8 PF lag.

Usually the gen-sets are rated in KVA and kW. The KVA rating is based on the maximum current that can be delivered by the generator ( for which the wiring is sized), while the kW rating referes to the driving engine (Diesel or other).

That means, for example that a generator rated 100 kVA/80 kW ( assume 3 phases, voltage phase-to-phase 400V) will have its wiring sized for the output current of 144A.

The driving engine has an output power (mechanical power at the shaft) of (assume) 85 kW ( to cover 80 kW output active power at generator + 5 kW losses).

If you try to load up the generator with a purely resistive load of 100 kW, the driving engine simply cannot deliver that power ( 100 + 5) at the set values ( torque & speed (that sets the output frequency)).

The same generator driven by a more powerful engine can deliver 100 kW (the corresponding current is the same 144A) , the 85 kW drive engine limits the output power of the gen-set at 80 kW.

You can load up the gen-set for instance at 90 kVA/70 kW (corresponding power factor of 0.777) 100 kVA/70 kW (power factor of 0.7) , 80 kVA/80 kW (power factor 1) but not at 90 kVA/90 kW (also power factor 1) because you exceed the 80 kW engine output.

Sometimes there is a limit of a minimum output power factor either because of the excitation wiring sizing lower power factor requires higher excitation current versus higher power factor load at the same apparent power output (kVA)) or because of the electronic voltage regulator.

Extreme low power factors (either inductive/lagging or capacitive/leading) may place the generator in an unstable zone, especially because the unlinearities in the elements used.

Dear Tomad, Thanks for your advise on the Power factor limit the output power. I agreed on most of the details you have touched on. For our usual testing the 100% load is a must, while the 110% test is usually done for roughly 10 mins. Alternator side has no issue to handle 110% load for 1 hour in six without suffering any change due to over heating. For the Engine side, usually they will adjust the injection timing and pump to maximize the output power. For my current situation is the load bank is a resistive one, so power factor is roughly 1, so the genset could be able to hit to a higher power at PF 0.8 lag. For my case it was supposed that the Power of genset could reach 500KVA/500KW at 100% at pf 1 load but it fails to do so. At 95% the engine starts hunting and white smoke appears, though it seems like its an Engine issue but all fingers are pointed at the alternator which they said is the main cause. The AVR used is having +/- 1% (4% engine governing)

if you want to load 100% or more dont take resistive load take inductive load too so that p.f is .8

ok this is what done while the d.g is checked

Why would that help?

Dear Tarangsoloman, i have noted your points. But usually we test with resisitive load bank for lower KVAs gensets while 1000KVA and above we will borrow inductive load bank. Resistive load bank is readily available.

Dear PWA,

base from your DG Load Test history would suggest to have recalibrate the Feul Pump and the Injector, i suspect the engine can,t take load to 90% or above.

i aggre with you about power factor 0.8lag. In normal condition DG load test, the load should able to carry load up to 110% or to 115% Subject to Engine and Alternator Spec (refer to your Engine Manual or maker).

good luck

Dear Sir, Thanks for your advise. At this moment, the engine maker told me that they do not want to touch the Engine parts as they are confident that their Engine is working fine. They have recalibrate the injected timing to another 5% which could push the Engine to further 6-7% power. But it does not help in the overall power for the DGset. I understand that the same model of engine with the same KVA perform differently. I am not sure using the different brand alternator of the same KVA will actually perform better with the current alternator that i have. FYI, the alternator that is used now is Full-pitched winding. Siemens licenced alternator still stick with the traditional winding while other manufacturers have applied 2/3 pitched. Anyways, its not much of the relevance here, just share with all of you here.

A completely silly question: does the optimum rotation rate of the motor match the specification for the alternator.

Dear Sir, if you can kindly advise me what you mean by optimum rotation rate? The Engine is rated at 625KVA continuous and Alternator is rated at 625KVA continuous.

What he means it Motor is X KVA @ Y RPM does theis Y RPM match with Alternator Synchronous speed?

Dear SB, thanks for the explaination. Yes it matches. Engine is 625KVA/500KW 1500RPM, Continuous ratings. 4 cycle, Water cooled, V type , Turbo-charge and intercooled. Alternator is 625KVA 1500RPM, 50HZ Continuous Rating, Full pitched windings. 400V

PWAK,

Where did you get the Engine as "625KVA/500KW 1500RPM" ?

For a Diesel/other drive machine there is no "KVA" rating.

Dear Tomad, The Engine is 500KW at 0.8 pf and 723 BHP Prime), or 550KW and 781 BHP at 0.8 pf at Standby. The Genset is rated at 625KVA

Internal combustion engines are NOT rated in KVA, which is a specifically electrical measuring unit. The same is valid for power factor (pf). The rating of an engine ( Diesel, etc) is given either in kW or HP (horse-power). Since there is an equivalence between HP and kW ( 1 HP = 736 W for SI and 1 HP = 746 W for Imperial System), both should be valid.

The genset as a whole may be rated in kVA/kW as shown in an other post, but it is set by the engine-generator assembly.

The difference between a continuous and a standby source rating comes from the fact that in the first case the genset is expected to run "continuously", while in the second case it will run only if the main source of power is out ( a shorter period of time) and therefore can be loaded up more than the first one (in the case shown 500/550 kW).

Dear Tomad, your explaination is very clear. for my current issue, the load bank has changed to a new resistive load bank, speed controller changed, governor and injected timing adjusted. Alternator has replaced to Leroy somer for further test. So far, at 95% voltage and frequency is unstable and cause Engine to 'hunt' but there is no white smoke coming out from the Engine.

hi pwak. have you rectified your frequency hunting issue? I also have the same problem with a small 215 kW Caterpillar engine driving a leroy somer alternator. Caterpillar tried to tell me it was the injectors and so on their promise that if it wasnt, they would refit the old injectors. Turns out it wasnt. Leroy Somer suggested that the cause may be the AVR. I tried a spare and turns out it wasnt. Currently i am awaiting Caterpillars instructions. Im very interested to know if you have solved your fluctuating/hunting frequency.

Hi Guess, Thanks for your reply. Currently i have 2 units of alternators for the end users to test. I have change to Balser AVC 63-7F AVR for the second genset unit (Doosan with Siemens Alternator) and problem is solved. No voltage flucuations or hunting. But the genset not able to load to 110% yet as there is some fuel problem,technicans will adjust the actuator to see if they can fix the fuel problem. However, for the first genset (MAN Engine with Siemens alternator), there is some slow response on the voltage that is whenever a new load is added, the voltage rises and take a few secs to stabilised. This situation only happen in 80% load and above. But along the way when there is some hunting on the engine, we adjusted the speed controller's gain and stability and the freq/hunting issue disappears. But end users cannot accept this 1st unit of genset due to the slow response. I believe the slow response is due to the voltage feed from the aux winding of the alternator and the 3 phase sensing from the alternator to the AVR, since there is no adjustment for this Basler AVR for the response adjustment. Load Bank is PF:1 MAN Engine : 597KW DOOSAN Engine: 500KW Alternator : 625KVA/500KW PF 0.8 lagging Voltage : 380Volts Full load current at 100% is 759A

Dear all, After much troubleshooting, i realized that the hunting issue with the engine could be due to the limitation of the alternator. During the troubleshooting, we raise the voltage from 380V to 415 V and the genset is able to delivered 110% load. For 415V , PF 1 At 100% full load : IFL = 500,000/(1.732*415) = 696 A. At 110%, IFL= 696*1.1 =760A. But for the 380V at full load, IFL = 500,000/(1.732*380) = 760 A Therefore the alternator has already reach its full capacity at 380V thus resulting the MAN and Doosan Engine to overspeed or hunting. I suppose that adjustment of the AVR is for the voltage and stability and little a realized that it has such an impact of the loading factor. Another case is when we used a bigger KVA alternator of 670KVA and couple Doosan Engine of 500KW, no issues at 380V at 110% because alternator can take 110% load 536000/(1.732*380)=814 A. => Alternator 500000/(1.732*380)= 760A => Engine at 100% But at 110%, 760*1.1= 836A . (no problem) there is no hunting at 110% for bigger alternator. Therefore should an alternator be rewind differently between 415V and 380V? Hope some experts here can kindly advise me. Thanks.