MECHANICAL vs. ELECTRICAL OUTPUT

[nawao]

During the load test of a recently refurbished Genset the engine output data parameters does not match the measured electrical output.

The test was conducted sharing the available load of 3.3MW between three Gensets of identical characteristics in parallel.
Engine type: MaK 12M 282 AK
Output: 1990 kW
Speed: 1000 rpm

At full load the mechanical parameters (Fuel rack position and Charge air pressure after air cooler, according to the Engine Diagram) indicated that the engine under test (Gen 4) was delivering 101% of rated power (2017 kW)
kV A A A MW HZ KVA Cos fi
Gen 4 10.87 81 83 85 1.5 49.6 1586 0.95
Gen 6 10.87 56 58 55 0.9 49.6 1053 0.85
Gen 1 10.87 61 62 61 0.9 49.6 1153 0.78

How to solve this conflict when both parties seems to be right.

 

[nawao]

In my first posting one paragraph was omitted. Please read as follow:

During the load test of a recently refurbished Genset the engine output data parameters does not match the measured electrical output.

The test was conducted sharing the available load of 3.3MW between three Gensets of identical characteristics in parallel.
Engine type: MaK 12M 282 AK
Output: 1990 kW
Speed: 1000 rpm

At full load the mechanical parameters (Fuel rack position and Charge air pressure after air cooler, according to the Engine Diagram) indicated that the engine under test (Gen 4) was delivering 101% of rated power (2017 kW).

On the electrical side the readings were as follow:

kV A A A MW HZ KVA Cos fi
Gen 4 10.87 81 83 85 1.5 49.6 1586 0.95
Gen 6 10.87 56 58 55 0.9 49.6 1053 0.85
Gen 1 10.87 61 62 61 0.9 49.6 1153 0.78

How to solve this conflict when both parties seems to be right.

 

[TheBlacksmith]

Did you correct the readings to standard conditions? Most engines are rated at 20 deg C/68 deg F and 1 atmos/29.92 inches of mercury. Variation from this would cause the engine to "compensate" with increased rack position and airbox pressure.

Did you factor in losses? In addition to the electrical output, the engine has to overcome friction, windage, perhaps drive the lubricating oil pump, fuel lift pump, cooling water pump and radiator fan.

Blacksmith

 

[BJC]

Whats the BTU value of the fuel you are using?

 

[nawao]

Responding to TheBlacksmith and BJC Dec 11, 2001 posting.
I don’t have accurate data regarding the fuel BTU, but let me try to clarify the situation.
During the load test with the three identical generator in parallel we alternatively transfer 1.8MW load to Gen 1 and Gen 6 while Gen 4 only accept a maximum of 1.5MW.
In this case we can assume that the de-rating due to local conditions and the fuel BTU equally affect the three Generators.

 

[TheBlacksmith]

It sounds like the engine on Generator 4 is not making full mechanical output.

Are all the cylinders firing?
What are the compression readings of all cylinders?
What is the firing pressure of all cylinders? (If applicable)
What is the fuel pressure? (Fuel filter clogged, pump weak?)
What is the jacket water temperature? (Running cold?)

These may appear to be silly, but the engine is down on power and it’s easy to overlook one misfiring cylinder or a gradual degradation of all cylinders.


Blacksmith

 

[BJC]

Do the engines have thermocouples on each exhaust port?

 

[nawao]

Cylinder
1 2 3 4 5 6 7 8 9 10 11 12
Firing Pressure (bar)
103 98 98 97 101 97 103 102 99 101 103 99
Exhaust gas Temperature (°C)
360 375 365 360 395 370 370 390 360 375 380 360
Jacket water Temperature 79 °C
Fuel Pressure 2 bar
Obviously there are thermocuples on each exhaust port.
We did not measure the compression pressure, only the firing pressure on each cylinder as above

 

[TheBlacksmith]

From the numbers, it looks good, but how do these compare to the engine manufacturer specs and previous readings?

You say the fuel is the same, do they all draw from a common tank or could #4 being using old or contaminated fuel?
Are you measuring the electrical load with the same meter, or could there be a gauge calibration error?

I'm not seeing anything obvious, but there has to be something!


Blacksmith

 

[nawao]

Compared to the initial Acceptance Test Record the differences are as follow:
Cylinder
1 2 3 4 5 6 7 8 9 10 11 12
Firing Pressure diff. (bar)
7 2 2 1 5 1 6 5 2 4 6 2
Exhaust gas Temperature diff. (C)
-29 -34 1 -35 -5 11 -6 -15 -19 1 -34 -29
Charge air pressure after charge air cooler diff. (bar)
Bank A –0.138 Bank B –0.13
Regarding the fuel, The Bulk Storage and Intermediate tanks are common.
The daily tank is individual but during the refurbishment was totally emptied and cleaned. All filters renovated.
Regarding the electrical instruments each generator has its individual Control Panel and meters. The instrument panel readings have been compared with Fluke 87 III Multimeter.
Electrical readings are OK.
Nawao

 

[TheBlacksmith]

I really have nothing more to add. There are some differences in cylinder pressure and exhaust temperatures. How do these compare to the manufacturer's specs and to the other engines? If the pressures are all lower than before, that could be significant, the exhaust gas temperature spread may or may not be significant, depending on the make, but cylinders 1 and 11 in particular raise my suspicions, since they both show a big change in pressure and temperature. Cylinder 7 also has a big pressure difference, but not a corresponding temperature drop; can you check that temp again? You may need to get the engine manufacturer's tech rep on site.

Blacksmith

 

[nawao]

The engine manufacturer's tech rep is already on site.
Precisely, the conflict is with him.
Nawao

 

[jbartos]

Suggestion: The excitation of generator number 4 is supposed to be verified for its proper function. It may need its finetuning.

 

[genRman]

Just an observation, but you say that the fuel tank has been refurbished and fuel filter replaced. I once had a similar condition, where a day tank fuel filter ( built into the tank) was fitted with an undersized coupling bore & hence was providing a fuel restriction.
If you are scratching your head for ideas, this may be of some consideration. (My experience of fault finding is that you cannot rule out the refurbishment work as a route cause, just because the work has been done. Pepole do make mistakes and the work is worth double checking!)

On the generator excitation system fine tuning point, looking at your load figures, it would appear that your reactive component load sharing ( quadrature droop setting) is miss-matched between gensets,[Provided of course that your instrumentation is accurate]
For a final balanced system, each machine should be set at manufacturers rated power factor, and would be normally expected to maintain a drooping charactoristic, say from 10% load upwards to full load at rated power factor, such that reactive load sharing between gensets at their respective per unit loads is maintained.