Quieting Large "Dry Type" Transformer

cinematechnic · Mar 5, 2017

Now that I have my first workshop set up that will be the site of my machine shop, I was hoping I can get advice on the following:

I want to know any strategies that can reduce the noise level of a large dry transformer.

Here are the transformer specs:

DRY TYPE TRANSFORMER
12.5 KVA, Three Phase, 60 Hz, Type HT
Voltage 480 - 208Y/120
W(1) Electrostatic Shield
Insul Sys. 220ºC, 150ºC Rise, Cooling Class "AA"
Impedance 6.16% at 170º C

The transformer emits a substantial amount of hum/buzz noise. Here's what I've noticed:

It's loudest when there is no load on it.

When I connected a heater to a 120V outlet powered by the transformer it seems to get quieter.

When I run my Schaublin lathe unloaded on the low speed (1.1 HP), the transformer seems to get much quieter. It's difficult to know how much because you are listening for the sound of the transformer and trying to ignore the sound of the lathe motor/spindle spinning.

The lathe is currently the only load I can apply that equally loads all 3 phases.

I'm curious to know if a small noiseless load applied equally to all 3 phases might quiet the transformer. For example: 3 equal wattage incandescent light bulbs each connected to one phase and neutral.

Thanks in advance for your input!

cwilcox · Mar 5, 2017

If you end up putting it in a sound enclosure of some sort don't forget that it will overheat if this is not designed for.

cinematechnic · Mar 5, 2017

At this point to I am NOT considering an enclosure around the transformer due to cooling issues. Also not sure of the electrical code issues with that approach.

I do plan to try some sound absorbing panels surrounding the transformer which will absorb radiated sound while still allowing warm air to easily escape. But that approach can only go so far since any open enclosure allows noise to escape. It would only reduce the radiated sound somewhat.

I stil have a hunch that a small load, equal on all 3 phases, may reduce the sound considerably.

Monarchist · Mar 5, 2017

cinematechnic said:
At this point to I am NOT considering an enclosure around the transformer due to cooling issues. Also not sure of the electrical code issues with that approach.

I do plan to try some sound absorbing panels surrounding the transformer which will absorb radiated sound while still allowing warm air to easily escape. But that approach can only go so far since any open enclosure allows noise to escape. It would only reduce the radiated sound somewhat.

I stil have a hunch that a small load, equal on all 3 phases, may reduce the sound considerably.

Sound deadening panels will not help a great deal. Simply do the math @ 1100 fps in average air and find the wavelength of 60 Hz and its first-order harmonic want HUGE cells to work at the resonance points.

OTOH, any radiated sound decreases at an exponential rate with distance.

Wisest and least-cost route is to relocate it remotely, and the other side of a rather ordinary and already 'paid for' wall.

Better-built transformers may also be quieter. My UNpotted 3-P 15 KVA R. E. Uptegraff with its elliptical coil bobbins, or my 5 KVA's and smaller with full 'potting' compound for example.

I'm not one to suggest you 'get in there' with Bamboo splint wedges and a tin of red Glyptal, but getting laminations and windings tight, then well-braced against physical vibration IS one of the things that sets premium-priced transformers above the cheaper ones.

You needn't ask here if three incandescents as a light load will help. At about a buck three-fifty per ignorant Edison-base socket, lamps of your choice as can be re-used elsewhere, it is cheap enough, and nowhere near rocket insemination complicated. Just go and try it.

johansen · Mar 5, 2017

Connect it for the highest voltage you can get away with, if you have 480v available then connecting it for 504 will give you 114/197v on the output. Motor run capacitors connected across the output may work to reduce the noise far more cost effectively than a heater load, might also make it worse.

If you have a 200 volt motor on your lathe then this will be no problem, but if you have a 240v motor then supplying 197 volts to it will significantly reduce the starting torque and breakdown torque, but unless you are running the motor beyond its nameplate ratings and also for a long enough time to get it hot, you should have no problems.

dkmc · Mar 5, 2017

You could try tightening up any and all screws/bolts inside the unit.
With the power off.......or on if you want it more exciting.

cinematechnic · Mar 5, 2017

Monarchist said:
...At about a buck three-fifty per ignorant Edison-base socket, lamps of your choice as can be re-used elsewhere, it is cheap enough, and nowhere near rocket insemination complicated. Just go and try it.

Already bought the parts for what you're suggesting. Going to rig it up Monday for a quick test. Since I'm in the PRC (People's Republic of California) I can't get incandescent Edison base bulbs larger than 72W. Going to try three of those (216W) and see if it has any effect.

If it shows promise then I can go to the local motion picture expendables supply store (one block away) and see if they have any bulbs larger than 100W for a higher wattage test. But I don't want to run huge wattage incandescents in the room due to heat issues. I'm hoping something in the 300W (total) range will do the job.

If it works I'll have to buy a supply of the bulbs for when the nitwits in Sacramento ban them altogether. I know that day is coming.

Another possibility would be three small quiet 120V fans that could help pull air from the HVAC system into the room.

Thanks to all for the input.

JST · Mar 5, 2017

Lots of things MIGHT help.

Monarchist is right to the extent that the low hum is hard to absorb. But if there is any higher frequency buzz to it, you CAN hope to absorb that. Put some absorbent material on the wall behind, and screen the front.

Your problem is partly due to the room, which has reflective surfaces all over it. It will probably sound like a loud cave when you start making noise in there. Hanging up some batts of fiberglass will do quite a bit of helping with that. You will probably want to cover them with some sort of loose cloth.

If you do hang up some absorbent material, it will help with ANY noise in there. Hum, machine noise, whatever. You may already be OK for low frequencies, anyhow.... The sheetrock walls are just about transparent to lows. Your issues are going to be with high frequency noises.

For a quick check, go in there and clap your hands while standing in different places. Count off the seconds with the old "one thousand one, one thousand two" deal. If the sound takes a full second or more count, you need absorptive material. If it seems to die out in noticeably under a half second, you are probably good.

Monarchist · Mar 5, 2017

cinematechnic said:
Already bought the parts for what you're suggesting. Going to rig it up Monday for a quick test. Since I'm in the PRC (People's Republic of California) I can't get incandescent Edison base bulbs larger than 72W. Going to try three of those (216W) and see if it has any effect.

If it shows promise then I can go to the local motion picture expendables supply store (one block away) and see if they have any bulbs larger than 100W for a higher wattage test. But I don't want to run huge wattage incandescents in the room due to heat issues. I'm hoping something in the 300W (total) range will do the job.

If it works I'll have to buy a supply of the bulbs for when the nitwits in Sacramento ban them altogether. I know that day is coming.

Another possibility would be three small quiet 120V fans that could help pull air from the HVAC system into the room.

Thanks to all for the input.

Well somebody in Gummint screwed the pooch on the banning of 100 W incandescents.

MY shop is so well insulated that wintertime I just screwed in 100W incandescent, left them on 24 X 7, put LED or CFL in the same Edison-base sockets rest of the year.

Now.. time came I could no longer find 'honest' 100W (for heating value) on the shelves, only higher-efficiency 70 W with alleged-same Lumens-as.

.. but COULD find bare-nekkid, no-foolin' 150 W & 200 W, both as clear envelope 'decorative' 1930's replicas and 'normal' soft-white etched!

Go figure..

cinematechnic · Mar 5, 2017

JST said:
Lots of things MIGHT help...

Thanks! The room has two concrete block walls (highly reflective of sound), and two drywall walls. The ceiling is drywall and the floor is concrete. So it's about 50% hard reflective surfaces and 50% medium reflectivity.

I've already put two sound absorbing panels that I had on hand behind the transformer. I could hear no difference. I think only a "shell" that confines the sound and absorbs it (like a motor cover on a boat) will make a substantial difference. The hot air could be vented out the ceiling like a clothes dryer.

But then I'd have to figure out how much heat the transformer emits and make sure I have enough convection to get that hot air out. And sound will escape through the air intake. Plus building and insulating the enclosure. A lot of work.

Going to run the light bulb experiment tomorrow. Hopefully that will help.

If it does work, I'll have to stock up on the halogen bulbs because the People's Republic will be banning them by next year...

JST · Mar 6, 2017

Go with general absorbing stuff, for not just the transformer. It will likely get really loud in there when you start working, otherwise.

Is the noise you get from the transformer a buzz or a low hum?

So.....

Yes drywall is reflective for higher frequencies, but not super lows, usually. PAINTED block walls are reflective. Unpainted vary, depending on the blocks. the more porous ones are somewhat absorbing, especially at "middle" frequencies. Do the hand clap and see what you get.

With a very reverberant room, noise anywhere goes everywhere. You often find that the noise does not get less as much as you would think it should, as you walk away from the source. That makes for a loud room that bombards you with any noise made anywhere on it.

By absorbing sound as it passes through the room and/or gets reflected, you can get to a point where noise is more local, more like it is in an open area. That is usually enough to make it livable.

If the transformer noise is an issue, what do you think will happen when you have machines in there?

Monarchist · Mar 6, 2017

JST said:
If the transformer noise is an issue, what do you think will happen when you have machines in there?

Dunno about the OP, but given time enough, one gradually goes f*****g deef and it no longer makes much of a damn what a sneaky little insect-hum of a transformer has gotten up to.

Had to buy a decent Sound Pressure Level meter last year that I can use with the 'scope to make sure I'm not rousting the neighbours without even knowing it.

Our OP may be in the wrong line of work for his own peace and well-being?

mike_kilroy · Mar 6, 2017

Don't forget adding rubber bushings between the Transformer and the housing it is mounted to we did that all the time in Transformers to quiet them. your Transformer enclosure might be making a lot of the noise put in the rubber isolation mounts.

Sent from my SM-G900V using Tapatalk

cinematechnic · Mar 6, 2017

JST said:
If the transformer noise is an issue, what do you think will happen when you have machines in there?

I usually spend 95% of my machining time on set-up and measurement, not much time making noise. I have a Wabeco bench top mill (1 HP) and a Schaublin lathe (2 HP). Not huge machines.

Plus I usually wear hearing protectors while machining. I just don't want to have them on 100% of the time I'm in the room.

mike_kilroy said:
Don't forget adding rubber bushings between the Transformer and the housing it is mounted to...

Interesting... To do that I will have to see where I could shut down power input to the transformer. I know that it is not located inside the building. There is a large electrical box just outside the building. Perhaps there is a cut-off switch in there.

mike_kilroy · Mar 6, 2017

cinematechnic said:
I usually spend 95% of my machining time on set-up and measurement, not much time making noise. I have a Wabeco bench top mill (1 HP) and a Schaublin lathe (2 HP). Not huge machines.

Plus I usually wear hearing protectors while machining. I just don't want to have them on 100% of the time I'm in the room.

Interesting... To do that I will have to see where I could shut down power input to the transformer. I know that it is not located inside the building. There is a large electrical box just outside the building. Perhaps there is a cut-off switch in there.

WHAT??? You have no breaker on that 12kva xfmr inside?????? Ignore my advice please!!! Do not mess with that xfmr!!! hire a professional electrician ASAP!!!

cinematechnic · Mar 7, 2017

mike_kilroy said:
WHAT??? You have no breaker on that 12kva xfmr inside?????? Ignore my advice please!!! Do not mess with that xfmr!!! hire a professional electrician ASAP!!!

No worries... I wouldn't mess with the inside of any transformer without verifying that it is powered down first. When the electrician is back I'll see if we can figure out where the disconnect is for that transformer.

I did make the three light bulb rig today (one bulb per phase). 120V per bulb to neutral. They lit up just fine. But I could hear no difference at all in the transformer noise with the 72W bulbs I was using.

Running the Schaublin's motor however does seem to have an effect. The noise of the motor may be masking transformer noise a bit, but I noticed that once the motor was shut off, the transformer noise seemed to fade back in. It took about a second from motor shutoff to full transformer noise.

So why is a small (0.8 kW) 3 phase motor running with almost no load (just spinning the countershaft) so effective at quieting the transformer, but 216W of incandescent lamps had zero effect?

Anybody got any ideas?

Monarchist · Mar 7, 2017

cinematechnic said:
No worries... I wouldn't mess with the inside of any transformer without verifying that it is powered down first. When the electrician is back I'll see if we can figure out where the disconnect is for that transformer.

I did make the three light bulb rig today (one bulb per phase). 120V per bulb to neutral. They lit up just fine. But I could hear no difference at all in the transformer noise with the 72W bulbs I was using.

Running the Schaublin's motor however does seem to have an effect. The noise of the motor may be masking transformer noise a bit, but I noticed that once the motor was shut off, the transformer noise seemed to fade back in. It took about a second from motor shutoff to full transformer noise.

So why is a small (0.8 kW) 3 phase motor running with almost no load (just spinning the countershaft) so effective at quieting the transformer, but 216W of incandescent lamps had zero effect?

Anybody got any ideas?

Soitenly.

David Clark, Telex, better-yet Bose "noise cancelling" pilot's headset, gel pads, boom mic bringing you max volume limited audio from your surroundings, but with a passband that ignores all below about 300 Hz.

Works a treat at chatting-up cute barmaids in crowded and rudely noisy Sports Bars on the way home from the Airport, too.
DAMHIKT.

DDoug · Mar 7, 2017

cinematechnic said:
So why is a small (0.8 kW) 3 phase motor running with almost no load (just spinning the countershaft) so effective at quieting the transformer, but 216W of incandescent lamps had zero effect?

Anybody got any ideas?

"ELI the ICE man"...?
Your lights are purely resistive load, the motor is very much inductive.

I have a potted xformer, 15 kva (single phase) so maybe you need to do some
shopping for a potted model, it's pretty quiet.

Monarchist · Mar 7, 2017

digger doug said:
"ELI the ICE man"...?
Your lights are purely resistive load, the motor is very much inductive.

I have a potted xformer, 15 kva (single phase) so maybe you need to do some
shopping for a potted model, it's pretty quiet.

'Potted' is serious-rare in 3-P, even at half his 12 KVA.

Nor needed, usually.

As covered arredy - 'the better makers' use splints, wedges, camps, varnishes, Glyptal, isolators & cousins to reduce induced movement in their products.

Not really about perceived noise, that.

Most transformers live out their working lives multiple yards if not multiples miles away from human ears.

Unwanted movement shortens component life as well.

Uptegraf's elliptical coils are meant to greatly improve the life over squarish-cornered bobbins as a transformer's conductive windings actually compress, expand, lengthen, and shorten under the effects of the electromagnetic field they create and deal with. Fatigue cracks can occur, and at sharpish bends most of all. Goal was a 40-year transformer life in a utility world that required but 20 dead-reliable years, cared not a fig about what followed, because 'the grid' is always under maintenance and revision.

Uptegraf just may have created a thousand-year transformer. I'll not be around to care, either way. But, yes.. a transformer actually DOES Violate Arthur C. Clarke's highly advanced technology postulated as a directive in "Diaspar" AKA "The City and the Stars", to wit:

"No machine may have ANY moving parts".

DDoug · Mar 7, 2017

Monarchist said:
'Potted' is serious-rare in 3-P, even at half his 12 KVA.
.

Well darnit.

I have some 3p xformers but they all the open air "dry type" I figured he might be able to find a potted
one, based on my 15 kva single phase one.

However, I have seen (3) separate potted small ones linked by short pieces of conduit.
so that may be an option.

If the OP doesn't want to mess with glyptal/varnish etc. he could take it to a motor shop and let
them do it.

Quieting Large "Dry Type" Transformer

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