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Load Sharing Problem KATO Generators on rig

Load Sharing Problem KATO Generators on rig

Load Sharing Problem KATO Generators on rig


Good Morning Everybody,

I am Michel. I have a question.

I am on a rig right now running 4 3516 engines with 600V Kato Generators.

I was running with 4 generators with Dual Exciter Coils and was able to load share perfectly.

Now I send one generator to be rewound and it returned with a Single Exciter Coil arrangement. I placed it in and we ran the load test on all engines.

Now below is what I see,

As we increase the load gradually from 0%, I see the load being shared equally, I am talking KW, KVA, Kvars.

As soon as I reach about 65% to 70%, I see the rewound generator not able to take more load,the amps, kva stands at its maximum point whereas the other 3 generators begin to share the increased load. I cant figure out the problem here because the system is designed to share the load equally.

I had taken the measurement of the exciter voltage at one point in between.

3 generators stood at 48 to 50V, whereas this particular rewound generator was at 82V.

Could you guide me as to where my problem lies, whether its to do with the coil arrangement or a bad coil or anything else?

Below is some info,

This generator details (#2 with single exciter coil) :

Model 1030-680361111

P/N 6p6-2700

1030KW- 1200 RPM-1240 AMP

Exciter field # 12090-42

Exciter ARM# 12058-42

Exciter volt 50/ 100

Exciter AMP 3.5/7

The other generators details (#1, #3 & #4 w/dual exciter coils) :

Model 1030-680361111

P/N 6p6-2700

1030KW -1200 RPM-1240 AMP

Exciter field # 12010-30

Exciter ARM# 12064-30

Exciter volt 100

Exciter AMP 2.7

Please do help, thank you.


RE: Load Sharing Problem KATO Generators on rig

Is the AVR capable of supplying 100 Volts to the exciter?
KW sharing problems are governor related.
KVA (current) sharing problems are voltage related (generally field strength related: AVR, exciter, diodes etc.).
The AVR may have to be changed.

"Why not the best?"
Jimmy Carter

RE: Load Sharing Problem KATO Generators on rig

Something seems a bit backwards in your information, usually "dual coil" exciters are dual voltage rated(reconnectable), single coil exciters are usually single voltage. Also need to clarify if your talking about the AC OUTPUT of the PMG or the DC INPUT to the exciter, since on KATO you can have both, although it is way more common for the PMG to be dual voltage rated. actually I have only seen dual voltage exciters on special military units, typically the oil field tail ends have single voltage exciters and dual voltage PMG's.

Also, what voltage regulator are you using?

Have you checked the field resistance at the F1(+) and F2(-) terminals (after lifting the wires)?

Have you megger tested the generator after install, lot can happen between the shop and the rig.

Can you post a copy of your KATO connection diagram/schematic, would help clarify exactly what you have on your rig.


RE: Load Sharing Problem KATO Generators on rig

Also, can you provide the serial numbers of your units, I may be able to dig up some more info.


RE: Load Sharing Problem KATO Generators on rig

Thank you guys for your response
@waross Yes, the avr is capable of giving 100V and they changed the AVR

@catserveng my knowledge is extremely bad about generators, so I might be providing incorrect info. the voltage readings I provided were the DC output to F1 and F2 though. The resistance my electrician got was 288ohms between F1 and F2.
When I said Single and Dual coils, mostly I see Gens with F1 and F2, F3 and F4. The two sets are connected in parallel. But on this particular rewound gen, there is only F1 and F2. So may be this gives an idea of what I was speaking about.
I will try to get you the serial numbers soon.
Also, the megger test has not been done recently. If you need any more info, pls do let know .

Thank you,

RE: Load Sharing Problem KATO Generators on rig

The field resistance reading seems way off, most Kato exciters are in the range of 30-40 ohms. Can you measure field resistance of one of the other units?

So just to be clear, in with the dual coil exciter, you have F1 and F3 tied together and F2 and F4 tied together, right?

the 6P6 frames are really good tail ends, but available in LOTS of different configurations.

Another thing you need to check, what is the PMG voltage on both your old and new sets?

Details of the AVR would help, like model/type, rated power and sensing voltage, just to be clear on what you have exactly.


RE: Load Sharing Problem KATO Generators on rig

I am currently not able to work around the engines due to other work being carried out but I can tell you that on other projects with Kato generators, the resistance I have measured is 23.6ohms. And yes, F1 and F3, F2 and F4 are tied together.These are not PMGs is what I know.
These engine generators are installed on rig which Ross Hill systems, I am not sure if you have seen one of these systems. It has an AC module for each engine, it controls the engine and the generator. It gives the throttle and excitation signal. I will try to get you the info on the excitation card soon.
I know that the excitation volts what can be provided is 100.
Do you think the difference in the coil could be causing this problem?

RE: Load Sharing Problem KATO Generators on rig

As Catserveng mentioned the resistance 288 ohms is way off,and it not practical to have 82 VDC with 288 ohms that mean your excitation current is only 0.28 ADC. Check the kvars on the generator with the rewound exciter, this would give you an idea of what is happen with the excitation circuit.

RE: Load Sharing Problem KATO Generators on rig

Ah yes, Ross Hill, I'm very familiar with those systems, should have guessed but there are a number of rigs out now that don't use that system.

I tried checking with KATO, but until you get me a serial number(s) not really much I can do at this point. I'm thinking you have a problem in the field circuit, I went back thru a bunch of old KATO info and the highest field resistance I can find is 45 ohms. The drawing I have for a similar 6P6 frame static excited calls out 25 ohms nominal for the field. Have you measured at both the Ross Hill output terminals and right at the generator? Just to make sure you don't have a field wiring problem between the two.

Another bit of info that might be helpful, why did this generator get removed and repaired? And what was the extent of the repair, dip and bake, rewind, core damage, etc?

Based on all the info you've provided so far, sounds like you are either hitting the field output limit of the Ross Hill regulator module, or the maximum of what the currently installed exciter field coil can put out. Another possibility, although a bit remote is that you may have a bad diode or diodes, or a leaking surge suppressor. When the generator was repaired were the rotating rectifier components just checked or replaced? The least likely possibility is a main rotor problem, but a quick megger test would rule that out pretty quick.

In rereading your original post again I'm going to ask this question again, do you have the information right for the generators because it doesn't make sense to me
Exciter field # 12090-42
Exciter ARM# 12058-42
Exciter volt 50/ 100
Exciter AMP 3.5/7
You have this info listed for the "single coil" exciter, but only a dual coil setup would have dual voltage ratings based on being connected in series or parallel. This exciter is 350 VA, according to the info I have on hand, about the right size to a 6P6-2700 around 1000ekW

Exciter field # 12010-30
Exciter ARM# 12064-30
Exciter volt 100
Exciter AMP 2.7
This info you have listed under the "dual coil" machines, only one voltage, only one possible connection I would think, also this exciter is rated 270 VA. This smaller exciter is about the same size as exciters I can find for older frames on the back of G398's and G399's, rated 500-650ekW

If this is actually the case it appears you have a smaller exciter and may not have the capacity to handle the demand of the larger generator. But this is an assumption that you have the data listed wrong above.

Just because an exciter coil assembly will bolt up in the end bell doesn't mean its the right size. Have seen these kinds of problems with both exciters and PMG's over the years.

Hope that helps, MikeL

RE: Load Sharing Problem KATO Generators on rig

Hello Mike,
I have received a lil info about the module. The voltage output is rated 70V for the AVR.I wonder if the dissimilarity between the exciter coils is what is causing this. Coz one is a single exciter coil and the other a dual.

RE: Load Sharing Problem KATO Generators on rig

Thank you for all the help so far:)

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