Noisy Tranformer - Bad core laminations?
Noisy Tranformer - Bad core laminations?
(OP)
Hey all,
I have a 300kVA Marcus brand transformer with an excessively high sound output. The sound output has been metered at ~85dB, which is well over the rated 65dB. The transformer was only purchased and install a little over 1 year ago. It was physically inspected and is clean as a whistle. Runs very cool.
Here are the tranformer specs:
Brand Marcus
Model MK300A7-13-F
Power Rating 300kVA
High Voltage 600?347V
Low Voltage 416Y240V
Impedance 3.3%
Temp. Rise 115ºC
K-Factor K13
We had some test equipment install for approx 24 hours, which showed low power factor ~0.5, and elevated current harmonics %THD consistantly over 25% (between 27.5% and 30%). What should I make of these results?? I was told it could be bad core lamination. Any advice/comments are appreciated!
I have a 300kVA Marcus brand transformer with an excessively high sound output. The sound output has been metered at ~85dB, which is well over the rated 65dB. The transformer was only purchased and install a little over 1 year ago. It was physically inspected and is clean as a whistle. Runs very cool.
Here are the tranformer specs:
Brand Marcus
Model MK300A7-13-F
Power Rating 300kVA
High Voltage 600?347V
Low Voltage 416Y240V
Impedance 3.3%
Temp. Rise 115ºC
K-Factor K13
We had some test equipment install for approx 24 hours, which showed low power factor ~0.5, and elevated current harmonics %THD consistantly over 25% (between 27.5% and 30%). What should I make of these results?? I was told it could be bad core lamination. Any advice/comments are appreciated!






RE: Noisy Tranformer - Bad core laminations?
K13 is not a very high distortion factor. Do you have much non-linear loads? (Like VFDs and SCRs).
Gunnar Englund
www.gke.org
RE: Noisy Tranformer - Bad core laminations?
The loading on the transformer is part of a plastic extrusion line: an extruder motor (150kW DC), a melt pump (small), and heating elements.
RE: Noisy Tranformer - Bad core laminations?
Were the current harmonics on the load side or the line side? Did you check the opposite side? If current THD higher on the load side than I tend to think the load created the harmonics, if higher on the line side I would think lean more towards overexcitation.
Don’t rule out overexcitation based on a voltage measurement without looking at the tap settings. With the fairly low transformation ratio, is this possibly an autotrasnformer?
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RE: Noisy Tranformer - Bad core laminations?
It's not an autotransformer. It's a K-Factor 13 as described at http://www.marcustransformer.com/vw/fs/p017.htm
The Marcus site claims its design is aimed at non-linear loads. And it's 'features' are listed as:
§ Specifically designed copper windings with multiple conductors reduce harmonic high frequency 'skin effect' and increase efficiency
§ Low flux density wound cores reduce saturation
§ Oversized neutral conductors eliminate overheating
§ Double grounded electrostatic shielding minimizes electrical noise
I just don't know what to think about all this.
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
I still think it must be something electrically related because it buzzes loudly when under load, but not when the machinery is off-line.
RE: Noisy Tranformer - Bad core laminations?
Is the sound level the same if the extruder is lightly or heavily loaded?
Is the sound a typical "electric hum" or is it a "yelling" sound?
Are there line reactors for the thyristors? Or does the transformer serve as a combined line reactor/transformer?
In the latter case, sound is inevitable.
Gunnar Englund
www.gke.org
RE: Noisy Tranformer - Bad core laminations?
As for reactors or thyristors, my knowledge of the internals of the control cabinet is limited. I'll check in to it if I can.
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
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It is possible that these harmonics are at least partly responsible for the noise level in the transformer. However, I have spoken to several people about your problem and the general consenus is that the most likely culprit is the laminations in the transformer. Although there is likely nothing "wrong" with the transformer, our suspicion is that the iron in the laminations is simply not top quality - which is relatively indicative of a low cost Marcus transformer.
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It kind of makes sense that bad iron would result in greater hysteresis losses which in turn increases the THD.
Would anyone agree with this evaluation?
[I'll post the graphics they sent me so you can take a closer look]
RE: Noisy Tranformer - Bad core laminations?
Core lamination noise (called magnetostriction) is not load dependent since the flux remains almost constant from no-load to full load.
Did you check whether the frequency is as per name-plate (50 or 60 Hz) ?
* Algebra - The weapon of math destruction *
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
Here is a link to the data graphics. I welcome any and all interpretations.
RE: Noisy Tranformer - Bad core laminations?
of course, my comment is valid only for linear loads. Non-linear loads may id=nduce higher harmonic noise from the laminations.
* Algebra - The weapon of math destruction *
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
Considering that the 300 kVA transformer has only about 70 kVA of load and that it has a K-factor of 13, there does not appear to be a loading problem with the transformer. There is no voltage harmonic problem. The only problem appears to be the noise.
RE: Noisy Tranformer - Bad core laminations?
In most cases I believe transformer noise is electromagnetic in origin and unrelated to any looseness. Certainly it applies to motors (like fractional slot motors which are rich in harmonics and very loud).
It was suggested this is not electromagnetic since the flux does not change with load much. That may be true for sinusoidal current but I don't think it's true with so much harmonic content.
My vote (guess) is that it is most likely electromagnetic noise related to the load harmonic current. There isn't much you can do about that... unless maybe someone sells a filter for this situation?
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RE: Noisy Tranformer - Bad core laminations?
The current waveform is not typical for a bridge rectifier input current, there are usually two equally high current pulses. But given that there are also linear loads and that the transformer winding also influences the total curve form - current pulses added - I think that this is a very normal look for a transformer primary when a thyristor controlled DC motor is connected.
What I do not like at all is the phase relationship between the currents. There must bee a mistake when connecting the voltage CTs. Phase A current should be 180 degrees shifted.
The interesting thing is that the voltage waveforms are also shifted. Again, the phase A is 180 degrees wrong. I really hope that it is a measurement connection error and not a condition that the transformer is working under. That would certainly produce lots of interesting effects.
It is interesting that PF seems to be about right (assuming that the extruder was run at low speed). So the connection U vs I is probably right.
Anyhow. With that primary current, there is bound to be a lot of noise from the transformer. The thyristor commutation seems to take place in about 3 degrees electric so it looks like the transformer is also doing duty as a commutation reactor. That is probably why you get so high a noise level.
Gunnar Englund
www.gke.org
RE: Noisy Tranformer - Bad core laminations?
But that particular graph only shows current, not voltage.
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RE: Noisy Tranformer - Bad core laminations?
I also see what you are saying the current peaks do not appear in the same order as the voltage peaks which seems like just a measurement polarity.
You are right - this looks like a transformer input waveforms resulting from add together two phase currents of the FWR input such as would appear on the input of a delta-wye transformer feeding a FWR. See last waveform on page 2 here
http://home.houston.rr.com/electricpete/FWR.pdf
Why do you think it has to be a thyristor-commutated rather than a line commutated (diode bridge) rectifier?
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RE: Noisy Tranformer - Bad core laminations?
I'll try to collect a few more load specifications which might help us find a solution.
The puzzling thing is that we have 8 other similar extruders, a few with dedicated 175kVA tranformers, and they don't seem to make nearly as much noise. Of course, those ones aren't likely K13 rated. Is it possible the higher K-rating is trying to 'fight' (damp) the harmonics generated by the DC motor and is therefore working harder?
Addressing the graphical issues, I don't see the problem. It goes Ch.2-Ch.1-Ch.3 (Yellow-Red-Blue) in both cases; voltage and current. Do you think Ch.1 and Ch.2 should have been reversed? Does it really make a difference?
RE: Noisy Tranformer - Bad core laminations?
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RE: Noisy Tranformer - Bad core laminations?
The vector sum of the three phases should be zero. The red phase signal is definitely reversed on both the voltage and current traces. It is inverted in polarity on the image. The other two phases look normal. If the transformer really is wired up like this, and it isn't a measuring instrument error, then expect wierd things to happen. You can verify this by looking at the time axis on the images: there should be 5.56ms between each successive crest for a 60Hz system, where your sequence shows periods of 2.78 ms / 2.78 ms / 11.11 ms between crests.
Transformer must be a delta-star (or star-delta) type as noted above to produce the current waveform displayed. Not much inductance in the load either.
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Sometimes I only open my mouth to swap feet...
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
First, if it is a DC motor for an extruder, it has to be a speed controlled one. And that means thyristor control. The commutation is when phase B takes over from phase A etc. That means a momentary short between the phases and that's what normally produces the sound, either in the line reactors or in the transformer - as seems to be the case here.
Second, the angle between the phases shall be 120 degrees. You have 60, 60, 240 degrees in the recordings. That's why I think there is a polarity error in phase A (the one that sits between B and C).
Gunnar Englund
www.gke.org
RE: Noisy Tranformer - Bad core laminations?
Brand: Thrige-Scott Ltd.
Type: Shunt Motor
Power: 150kW
RPM: 2000
Armiture: 460V - 350A
Exciter: 360V - 6.1/4.85A
Again, the control cabinet also powers some small melt-pumps and heats.
I checked the power factor stated by the switchgear and it said 0.77 (with the extruder off-line). How is this related to the ~0.5pf displayed in the graphs? I didn't think the pf on the switchgear bus and the transformer primary would be different considering they're directly connected.
RE: Noisy Tranformer - Bad core laminations?
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RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
I'm not surprised by the difference even if the two metering points are being monitored simultaneously. Your PQ metering is looking at true rms values that include higher order harmonics. Your switchgear metering is probably only looking at fundamental quantities.
RE: Noisy Tranformer - Bad core laminations?
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Sometimes I only open my mouth to swap feet...
RE: Noisy Tranformer - Bad core laminations?
The thing is, I remember when he hooked them up, he said "the tester won't allow them to be backwards, it'll beep or something". Haha, as a skeptic I believe everything can be hooked up wrong!
I've already emailed the guy, so I'm hoping he'll get back to me soon, maybe tomorrow.
RE: Noisy Tranformer - Bad core laminations?
Calculating the power factor from the phase displacement also gives around 0.42 pf. Yellow phase voltage peaks at about 5.6 ms, yellow phase current peaks at about 8.6 ms, 3 ms lag or 65°, cos(65°) = 0.42.
These two measurements are within the margin of error of picking up points from the graphs. It wouldn't appear that the distortion contributes significantly to the low power factor. This is to be expected with very low voltage distortion.
The transformer var loss would not account for the difference. It is only 60% loaded and the impedance is only 3.3%. I still think the difference can be explained by the fact that the switchgear bus measurement was with the extruder off-line.
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
"Yes, it looks like the PT may have been reversed. Hard to say for sure, but it is either that or you have a more serious power problem that we first thought! <G>"
I'm not sure what the "<G>" means.. but it looks like I might not get much help out of this guy.
So you think besides the waveforms that the other data is correct? I find this a bit hard to believe.
RE: Noisy Tranformer - Bad core laminations?
The <G> probably means "Grin" - a way of saying "Sorry, but what can I do about it?"
I have studied your waveforms in detail. Except the phase error in A voltage and current, I think that the data are correct. The low PF is typical for a thyristor controlled DC motor running at low speed. In fact, there is an almost linear connection between percent rated speed and power factor.
As I said earlier, the commutation between phases seem to take about 3 electrical degrees. That is a rather typical value. Perhaps on the low side. And that indicates that the transformer with its low impedance is the only impedance in the thyristor/motor path. That makes the transformer noisy - nothing to do about it. It won't fall apart.
Gunnar Englund
www.gke.org
RE: Noisy Tranformer - Bad core laminations?
RE: Noisy Tranformer - Bad core laminations?
Thanks again to everyone who offered info and advice.
If I see any further conclusion to these issues I'll be sure to post back with the results. THANKS!
RE: Noisy Tranformer - Bad core laminations?
The power factor is a phase shift between the voltage and the current. If there are any other loads on the switchgear bus, then the phase angle of the switchgear current will be the vector sum of all the load currents. This current and the resulting phase angle and power factor may easily be different than the current, current phase angle and the power factor in the transformer.
respectfully