270KW KATO Generator problem
270KW KATO Generator problem
(OP)
We rewound the stator on a KATO 270 KW/300 KVA 460v 625amp 100HZ single phase 10 pole synchronous generator that is driven by a six pole 60HZ synchronous motor. The generator puts out the correct voltage and frequency and for all purposes, it functions as it should. The problem is that it now emits a noise that resembles a very loud, high speed jackhammer. Our vibration specialist insist that the noise is electrical and not being caused due to a mechanical issue.
There are 90 slots, 90 coils (30 groups of 3),7 turns per coil, 1-8 coil span, 5 wires in multiple used to make coils-4#15 AWG & 1#14 AWG. I have attached a copy of the internal connection drawing.
KATO will not release any information as it is proprietary. Does anybody have any idea as to what would be the cause?
There are 90 slots, 90 coils (30 groups of 3),7 turns per coil, 1-8 coil span, 5 wires in multiple used to make coils-4#15 AWG & 1#14 AWG. I have attached a copy of the internal connection drawing.
KATO will not release any information as it is proprietary. Does anybody have any idea as to what would be the cause?





RE: 270KW KATO Generator problem
The angular alignment may be critical to ensure a best fit between the torque pulses produced by the motor and the torque pulses demanded by the alternator. Also check that all mounting bolts are tight.
Bill
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"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
Muthu
www.edison.co.in
RE: 270KW KATO Generator problem
RE: 270KW KATO Generator problem
Muthu
www.edison.co.in
RE: 270KW KATO Generator problem
RE: 270KW KATO Generator problem
Have you looked at the output with a scope? Are the wavsforms clean, the output voltage balanced and the proper spacing between the phases?
Do you have any excitation data, field volts and amps from before the repair in "normal" conditions, and compared that data to what you are seeing now?
Along with the noise is the measurable vibration? If so, what order and magnitude.
I had a similar problem with a 400 Hz unit several years ago, turned out the core iron had been damaged during the burnout.
Mike L.
RE: 270KW KATO Generator problem
Walt
RE: 270KW KATO Generator problem
Otherwise, the winding looks symmetrical so I do not think that is the problem unless you have some shorted coils or unless the actual connection is different than the drawing due to a mistake. If you wanted to check for shorted coils you could do a surge test comparing one circuit to the other. To find a mistake in the connection you would have disassemble the unit and physically check it. One possibility is that the L1 and L2 are swapped on one circuit. You could check that with the unit disassembled by applying DC to the circuit with each L1 as positive and using a compass or flux meter in the stator bore to determine that the poles do alternate as you pass from one circuit to the next. Otherwise, I would guess that if the voltage and frequency are correct that the winding is correct.
Air gap or rotor problems as suggested by Edison123 would be a likely candidate but it would appear that you have ruled that out. Also, catserveng may have a good point about core damage but I have never seen that cause this type of problem myself. A core loss test using a thermal camera or temperature probe would reveal this problem if it exists.
waross has an excellent point with the suggestion of checking the coupling and the alignment. My vote is for that being the problem. Of course, we are assuming that this is a separate motor and generator instead of a single unit with both being in the same frame.
Finally, Strong is correct in suggesting that posting of the vibration frequencies may get you a second opinion of what vibration analysis indicates the problem actually is.
RE: 270KW KATO Generator problem
I've been working in this field for 35 years and I have never seen this type of issue with a generator.
RE: 270KW KATO Generator problem
We have two rings running around the outside at potential L1 and L2.
We have two rings running around the inside, let's call them A and B. A is the inner-most of the two inner rings, and B is the outermost of the two inner rings.
But what is connected to B? Only boxes (2 coils per box) that have their other end connected to A! So the current flows from A through the boxes to B and then where? It has no other path to flow but through another coil back to A , which is nonsensical. Either this winding is seriously screwed up, or I am seriously missing something.
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RE: 270KW KATO Generator problem
Muthu
www.edison.co.in
RE: 270KW KATO Generator problem
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RE: 270KW KATO Generator problem
I was wrong about the circulating currents... comparing those boxes connected between A and B, they do have alternating flux polarity, but they also have have alternating connection polarities which cancels out to create in-phase induced voltages among the parallel boxes with the result that no current flows.
But still these boxes (2 coils per box) connected between A and B seem to have no useful purpose if there is no current flow in them.
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RE: 270KW KATO Generator problem
Does this make sense?
This is a three phase wye connected winding, the inner ring is the neutral which is not brought out. The next ring is L3 and is not brought out. The coils connected to L1 are reversed. Then every second group of three is reversed.
Still guessing, but the vector diagram may be a wye with the polarity of one phase reversed.
Now, looking at the group labeled 12,11,10,9,8,7. If #10 were connected to #8 instead of to #11 we would have a zig-zag winding to produce single phase from three phase.
Then every second group of three would have to be reversed.
As it is the machine appears to be shorting itself out.
Another guess, the machine may not be connected as per the possibly faulty diagram particularly if it is putting out normal voltage.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
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RE: 270KW KATO Generator problem
We have the generator back in our shop now and the connections were lifted and verified to the print. Our initial thought was that the technician made an error when he connected the stator. This was not the case unfortunately. At least if an error was found we would have some hope of coming to a resolution.
RE: 270KW KATO Generator problem
Muthu
www.edison.co.in
RE: 270KW KATO Generator problem
We are left with 1/3 of coils that have no purpose other than possible damper winding.
You mentioned flux density was verified... was that at full load? And was excitation consistent with actual field circuit measurements at full load? Was just wondering whether the core might be getting pushed deep into saturation at full load in order to keep terminal voltage.
The other scenario for load related noise/vibration that comes to mind is of course spatial harmonic effects associated with stator slotting. Those would be load dependent. I guess someone could run through the equations to see if there is a low-spatial order harmonic that stands out.
fwiw - attached is marked up diagram to show coil polarities in red. It does form a symmetric 10-pole pattern with 6 coils per pole and 3 "unused" (or damper?) coils between poles.
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RE: 270KW KATO Generator problem
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RE: 270KW KATO Generator problem
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RE: 270KW KATO Generator problem
This is wye connected. The inner ring "A" is the neutral. Power is taken from "A" Phase and "B" Phase. The inner ring "B" is "C" Phase.
This is the "POOR Man's" single phase conversion of a three phase alternator. Simply take single phase from two phases and forget about phase angles. I see this most often at 120/208 Volts. In this instance the center tap is not needed so phase angles are not an issue.
The only issue would be 15% higher excitation (Flux actually) to develop the same voltage. In North America it could be described as pushing a 208 Volt winding up to 240 volts.
If saturation is a cause of the noise it should only be apparent at full excitation.
Is there noise at full voltage but no load?
Are there any shiny spots in the coupling?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
Good point. I agree if you hook up point B to a (non-existent) 3rd phase, it would be a valid 3-phase winding. That is a bizarre simplistic approach to convert to single phase!
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RE: 270KW KATO Generator problem
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RE: 270KW KATO Generator problem
I have talked to the engineers at EASA myself when I needed help and they are a smart bunch. Their idea that the dead coils may act as a damper winding is interesting. The coils will have voltage induced in them by the rotor and will produce currents that circulate through the inner two rings. However, I have never heard of the concept of a damper winding on the stator, it is usually considered to be on the rotor. But, of course, I've never seen this type of winding before.
For edison123, the innermost ring is the wye point for the active winding. This is obviously a two wye connection. The next ring in from the center is the connection point for the dead (damper) coils. This ring and the wye ring is the path where the currents circulate between the dead (damper) coils.
For electricpete, the flux density calculations accordlx refers to are theoretical and are based on the winding design (# turns, pitch, connection, etc.), the stator core dimensions (slot depth and width, bore diameter, back iron depth, etc.), and the full load current. Of course, I am not sure how to perform those calcuations on this unusual winding.
For accordlx, here are some things that have stumped us in the past over similar problems.
Have you checked to be sure that none of the rotor poles are loose on the rotor? Have you checked to be sure that the stator core is not loose in the frame? Is it possible that the stator core shifted away from center of the frame in the burnout oven (core burned while standing end up)? Is it possible that the rotor shaft is broken inside of the rotor core? Are the bearing housing and journal fits good? If they are sleeve bearings, are the saddle fits good? Are the rabbit fits good for the end brackets and are the end brackets square to the frame (no angular misalignment)? Finally, of course, the coupling and the alignment are suspect until proven otherwise. Make sure that these things are good and make sure for sleeve bearings that the alignment is made to the magnetic centers of the motor and generator. As I'm sure you probably know, to determine the magnetic center of the generator simply run it as a motor and mark the shaft.
Another idea that comes to mind. Are you sure that the problem is not with the drive motor??? Once mounted on a common base and coupled together, it may be hard to distinguish the source of the noise and the vibration between the drive motor and the generator.
Of course, you should still try to post the vibration spectrum making sure to get axial and radial readings on both the generator and drive motor. I am sure that someone here could use that to help to determine whether you are actually looking at an electrical problem or a mechanical problem, a generator problem or a drive motor problem. Unfortunately, I am an amatuer at vibration analysis but I'm sure that there are others here that are better versed at it.
RE: 270KW KATO Generator problem
I have seen 120:208V three phase generators used to supply single phase loads by simply connecting the load to two phases and the neutral. The third phase is unused. That is what we have here.
My comments re saturation, if the third phase was used in a zig-zag connection less excitation would be needed.
Bill
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"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
The same conclusion the rest of us reached.... much later in the thread.
My apologies Ray.
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RE: 270KW KATO Generator problem
1 - These coils won't work as damper windings since no current will flow in them even if the rotor phase angle fluctutates.
2 - The pattern matches a 3-phase machine (with one input phase unconnected).
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RE: 270KW KATO Generator problem
Here are the spatial harmonics expressed as fraction of the fundamental:
A3 := .5578486011e-9
A5 := .9491375323e-2
A7 := .2782589722e-1
A9 := .1241002310e-8
A11, A13, A15 and A17 are a mirror image of A9, A7, A5, A3, as expected for 18-slot fundamental pitch.
There can certainly be other tricky harmonic-related stuff going on (for example when we consider rotor as well... or low-magnitude harmonic happens to match a core modeshape which is resonant at 2*line frequency), but what is attached is the extent of my knowledge/ability for evaluation of spatial harmonics, and it doesn't suggest any obvious reason for a spatial-harmonic-related problem based on the stator winding configuration.
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RE: 270KW KATO Generator problem
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RE: 270KW KATO Generator problem
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
A1 := .9727345828 [this has no significance other than as basis for normalizing the others]
A3 := .02122065950
A5 := .1552431963e-1
A7 := .2236000840e-1
A9 := .1414710605e-1
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RE: 270KW KATO Generator problem
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RE: 270KW KATO Generator problem
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RE: 270KW KATO Generator problem
In my 12:59 post I said: "The dead coils do have opposite polarity (to each other) but I cannot determine the polarity of the active poles compared to the dead sets of coils." Now, considering the 'B' ring as the missing third 'C' phase, I can say that the the polarities of the dead coils do alternate with the live coils in the normal three phase arrangement of N-S-N.
That being said, we are going to generate voltages on the dead poles (coils) because they are exposed to the rotor's magnetic field just like the live ones. But, as electricpete pointed out much earlier in the thread, there should be no circulating currents. Of course, that is obvious to the rest of us now that we correctly see the dead coils as the 'C' phase with no external lead. There will be no circulating current between them any more that there will be circulating currents between the poles of the 'A' or 'B' phases (assuming that the rotor does provide a balanced and symetrical rotating magnetic field). It is also obvious now that they provide no dampening effect any more than the other two phases do. It is great how waross's observation of the 'B' ring being the 'C' phase lead simplifies everything.
I do still stand by my comment that the EASA engineers are a smart bunch of guys but, obviously, none of us is perfect.
Electricpete, about your 13:08 post; no apologies necessary. I probably helped your confusion by being lazy and saying "every third coil" instead of the proper term of "every third coil group." To clarify this for others, 60 coil groups with 3 coils per group equals 180 coils. Two coils sides per slot equals 90 slots.
So, all that is left for me is to wonder whether accordlx has found the problem. I sympathize with the poor guy since I have also spent many weekends at my shop stumped by similar problems. I hope he finds it and I hope that he lets us know what the problem was for future reference.
RE: 270KW KATO Generator problem
Do you remember seeing in the news about 6 months or a year ago where an anthropologist published some photos allegedly taken from a low flying plane that showed the settlement of a primitive amazonian tribe deep in the jungles of the rainforest? There were some natives pointlessly shooting arrows or throwing spears at the plane and there were some that were just standing there looking up with their arms at their sides and their mouths hanging open in the typical " OMG, what the hell is that" pose. Well, right now I feel like one of those natives standing there stunned and wondering "OMG, what the hell is that" upon seeing my first airplane.
I know that you are wondering what I am talking about. Well, here it is. I just got around to looking at your harmonic analysis and I am standing here stunned and wondering what the hell I am looking at like the native who just saw his first airplane. I think the last time this happened was during a discussion about odd groups in motors when you whipped up an Excel spread sheet calculating phase balance coil by coil, group by group. I did eventually get a handle on your spreadsheet but I am still clueless to how you came up with it. Now there is the harmonic analysis worksheet and I look at it and it might as well be in Chinese. I am guessing that you did include the spatial harmonic effect of the dead phase since that is one of the points we are talking about but if you did, I don't know how and I can't see it because what you did is Chinese to me.
Maybe one day you can tell me what I am looking at. Until then, just let me say good job Pete. You never cease to amaze me.
Ray
RE: 270KW KATO Generator problem
If you will forgive me talking a little bit more about these spatial harmonics...
I attached here a final version that makes the final correction that I discussed before, and also adjusts the plotting range 0..90 so you can eyeball verify that the mmf waveforms are in fact periodic with a period of 90 slots.
The math I think is straightforward, but the reason it starts to look Chinese is more a result of the "Maple" programming language. That is a tool that makes it easier to do the math, but harder for someone else to figure out what the heck you did. But I think the graphs tell the story.
The approach that I used takes advantage of a unique aspect of single-phase winding (compared to 3-phase).....the single-phase winding creates a "standing wave" flux pattern around the airgap... it doesn't rotate or travel like a 3-phase winding. So all we have to do for a single-phase winding is look at the mmf at a snapshot in time, and we know the shape for all time (which is the basis for the spatial harmonic analysis). In contrast, we couldn't do it like this for a 3-phase winding where the shape changes over time (the slot boundaries are stationary, but the fundamental moves).
Each conductor creates a step in the mmf.
If you look the graph of mmf_profile1, you can recognize the pattern 6 slots stepping up, 3 steps constant and 6 steps down. The flat spot on top/bottom of the sinusoid is the result of those 3 unused coils.
mmf_profile1 only represents one half of each coil (let's say the half that falls in bottom of a slot). To get the other half, we create mmf_profile2 which is the same as mmf_profile1, but inverted (current flows in opposite direction in the other half of the coil), and shifted by 7 slots (coil pitch 1-8).
We add them together to get the total mmf – I personally was expecting that it would be very choppy with spatial harmonics at 3rd, 5th 7th which might have contributed to noise (a cause/effect which would have been worthy of its own discussion). But in fact the short coil pitch did a great job of smoothing out the flat spot and creating a sinusoidal mmf (look how much more sinusoidal the graph of the total looks than the two graphs before it).
The final results is a fourier transform of the total stator mmf waveform (with position around airgap circumference as the independent variable)
A1 := .9945006841
A3 := .4868941122 e-9
A5 := .008331740666
A7 := .02140225834
A9 := .1118970159 e-9
An interesting thing I would pause to observe is that the 3rd and 9th harmonics are virtually zero. I don't know why but I have to think that is not just a coincidence but instead somehow a result of the symmetries present in the winding (the number 3 shows up in many ways in this winding).
While it's not exactly the same thing, it reminds me of a vaguely similar mysterious thumbule about eliminating 3rd harmonic based on slot size.
http:
I have the feeling maybe I have beat this aspect of spatial harmonics to death. I'll move on unless someone else has comments.
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RE: 270KW KATO Generator problem
Reg that winding diagram, let me see if I can get my mind around it today, Ray. I am convinced it's an electrical problem and not a mechanical one like misalignment, loose poles etc. But loose stator core is another probability.
Muthu
www.edison.co.in
RE: 270KW KATO Generator problem
I can't follow your math. That is my problem not yours. Short term memory is shot to "What were we just talking about??"
There is a point that concerns me when you mention single phase windings.
This is a combination of two of three phase windings. If each winding has a flat spot, those flat spots may manifest themselves as hard to spot deviations from a true sine wave centered at about 90 deg and 270 deg of the resultant wave form.
Put another way, we are taking a line to line voltage similar to taking 208 Volts from a 120:208 Volt system. This would be a 139:240 Volt system.
Question, does the noise sound like a 60 Hz hum or is it lower pitched?
It is hard to imagine (but if I'm wrong I expect a quick education) any electrical noise at less than the well known 120 Hz. or a multiple. I would first look for a mechanical issue if the noise is pitched lower than 120 Hz.
Electrical noise from the alternator would be expected to be at 200 Hz.
Here's me cringing in case I have made a mistake here.
Bill
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"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
I agree with you the lowest frequency for consideration of an electrical problem would be 2*electrical frequency. (In this case, that would be 2*100=200hz for the generator).
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RE: 270KW KATO Generator problem
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
So, only two phases are loaded, which is a severely unbalanced loading that will overheat the rotor. But why that would create vibration and noise beats me. I am not sure if this was the OEM winding design.
As for EASA's damper winding claim, I think it's hogwash. It's the rotating component that needs the damping (which, I am sure, is taken care of in the rotor with its own damper winding), not the stator.
Muthu
www.edison.co.in
RE: 270KW KATO Generator problem
If you tried to describe/analyse it as a 3-phase winding, you could describe those equal forward/reverse components as equal positive and negative sequence fields, which you could also be interpretted as severe unbalance in the three-phase sense.
Yes, that reverse-rotating field component travels at twice rotating speed relative to the rotor and tend to cause some surface currents on the rotor. (It also causes torque pulsations at twice electrical frequency.) This behavior would be the case for any single phase stator winding. I *assume* (point of clarification for OP) that this winding was single phase from the OEM?
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RE: 270KW KATO Generator problem
When a standard three phase to single phase reconnection is done by the manufacturer, the kW load is not balanced. With either a zig-zag or a double delta connection "A" phase produces the same kW as "B" phase and "C" phase combined (assuming a balanced single phase load).
each phase develops the same KVA but for unity PF the current is in phase with the voltage on one phase, the current leads the voltage on one phase and the current lags the voltage on the third phase.
The poor mans single phase conversion is to leave a gen-set connected at 120/208 Volts and use two phases at 120/208 Volts and tape up the third phase.
This may cause rotor heating but the rotor is usually able to reject the heat safely.
When a 60 KVA set is reconnected for single phase the rating drops to 40 KVA. The simple sum of the KVA of the individual windings is still 60 KVA but KVA cannot be added without reference to the phase angles. The phase shifts in "B" phase and "C" phase account for the apparent loss of 20 KVA of apparent power.
What's the point? Just that taking single phase power from two phases of a three phase set in this size range does not cause any issues such as the noise issue with this set.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
http:
Muthu
www.edison.co.in
RE: 270KW KATO Generator problem
Only L1 and L2 are brought out. All other connections including L3 and L0 are buried.
Note on dedicated single phase windings. These are factory wound and are not common above about 20 KVA at 1800 RPM or 25 KVA at 3600 RPM.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
RE: 270KW KATO Generator problem
Muthu
www.edison.co.in
RE: 270KW KATO Generator problem
I am not familiar with the idea that the range of allowable amps/circ.mil (or in your case amps/sq.mm) varies according to rotational speed. I have always seen it given as a fixed value without reference to speed. Can you tell me more about this since I am still on the uphill side of the learning curve (and always will be!)?
RE: 270KW KATO Generator problem
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
accordlx:
The torque transferred through the air gap of a single phase synchronous generator is not constant, like in a three phase machine, but pulsates with twice the rated frequency. The stators of large single phase units therefore are mounted with spring elements between stator housing and foundation.
I assume that you've rewound the stator exactly the way it was wound before. I also assume that you mounted the rewound unit in your test field before delivery. You should check the conditions at site: Condition of foundation and how the single phase generator was coupled with the drive motor. Especially the last point is of paramount importance in order to avoid a coupling failure.
How did the unit behave at site before it was rewound? Ask the owner.
Regards
Wolf
www.hydropower-consult.com
RE: 270KW KATO Generator problem
accordlx:
Just noticed that my last post was not transmitted completely.
I assume that you've rewound the stator exactly the way it was wound before. I also assume that you mounted the rewound unit in your test field. You should check the conditions at site: Condition of the foundation and how the single phase generator was coupled with the drive motor. Especially the last point is of paramount importance in order to avoid a coupling failure.
Regards
Wolf
www.hydropower-consult.com
RE: 270KW KATO Generator problem
RE: 270KW KATO Generator problem
By the way, i see in the Marathon information on single phase connections, that they suggest 50% KW and KVA for single phase connections. Any information that I have seen from other manufacturers allows 67% KVA loading and often 83% KW loading.
Bill
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"Why not the best?"
Jimmy Carter
RE: 270KW KATO Generator problem
RE: 270KW KATO Generator problem