socalelect
Member
- Location
- so. cal
stupid question i know , but what causes the humming in a tranny ?
causes of xfmr humming
- Thread starter socalelect
- Start date
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ptonsparky
Tom
- Occupation
- EC - retired
The rise and fall of the magnetic fields acting on the metallic components. Ther is another reason but I will wait for someone else to explain.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
It doesn't know the words? 
Sorry, couldn't resist. :ashamed:
Sorry, couldn't resist. :ashamed:
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Loose windings, over loaded, if fed from a Y and has the X/0 bonded on the primary when common core, last but least because it doesnt know the words to the song?:lol:
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
It doesn't know the words?
Sorry, couldn't resist. :ashamed:
H'mm scary an't it:happyyes:
ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
Why does it hum? Because it doesn't know the words.
Bad joke, but I had to say it.
Think of a guitar string or any reed instrument that produces a sound; a note on the musical scale that the pitch is proportional to the frequency of the vibrating material.
The changing AC magnetic field causes the winding and core of the transformer or any other electromagnetic device (relay, contactor) to vibrate at a certain frequency. In this case, 60HZ or 60 cycles per second. If there is high THD involved then the pitch can vary because of the different frequencies affecting the fundamental. Pieces of insulation wedged between the windings and laminated core are used to supress the loudness of the hum (and for impulse level rating) but it still gets thru.
I had a customer that had a 20yr old 2500KVA dry type (GE) that produced a very loud hum.
(BTW the loudness is directly proportional to the loading; amount of current flow in the windings.)
This one was loaded to the 80% NEMA limit. Every PM period we would perform all the NETA tests but could not find anything wrong. Customer (TELCO office) was worried about the cost of the downtime ($1 million/ minute) if it ever faulted and finally had it replaced; mucho bucks!!
BTW another transformer, same size & vintage, in the power room did fail years later due to an internal fault. It was a nasty sight!
The coil vibrating against the core is one reason. Depends on how loud they are. Also the many plates in the core expanding and contracting against one another because of alternating cycles. Look up "magnetostriction"
I have had area light ballasts that are loud enough that customers could hear them inside their house. I cut a wood edge and inserted it between the coil and core to quiten it down. I don't recommend that to an inside XF.
I have had area light ballasts that are loud enough that customers could hear them inside their house. I cut a wood edge and inserted it between the coil and core to quiten it down. I don't recommend that to an inside XF.
Transformers do hum. It's their nature. The incoming AC voltage/current must magnetize the core of the transformer in order to induce the AC voltage/current in the secondary windings.
Due to the magnetic fluxes which surround the core and coil those magnetic fluxes can cause and steel components in that area to vibrate. Should those components be slightly loose they can emit noise.
Also, noise is relative. Should a transformer be located in an area one expect to be quiet such as an office of library a transformers inherent hum could be considered noisy where that same transformer located in an area that is inherently noisier the hum would not be noticeable.
Transformer noise is measured in dB at I believe 3 meters form the transformer. There are noise standards for various groups of KVAs,
For example for typical DTDTs:
KVA Rating 600V Class 5KV Class
0 - 9, 40dB 45dB
10 - 50 45 50
51 - 150 50 55
151 - 300 55 58
301 - 500 60 60
501 - 700 62 -
701 - 1000 64
Where a transformer is installed and the way that a transformer is installed also cam amplify transformer noise.
A room that has all reflective walls will cause the noise t bounce around. A transformer next to or mounted on a wall can transmit noise into an adjoining quiet office area. Hard piping a transformer can cause the transformer noise to be transferred through the pipe where flexible conduit such as liquid tight would be a better choice.
'Also, check the core and coil to assure that any shipping supports are removed. Most transformer core and coil assemblies sit on "Korfund" pads to help isolate core and coil noise from the enclosure. One can add these pads under the feet of the enclosure which may help isolate noise.
But, again, noise is like heat. When one expected something to be quiets and sound emitted often is considered to be noisy as is something that is expected to be cool is warm often is considered to be hot.
With noise, the noise should be measured and compared with the published values keeping in mind that those measure at the factory are don't in a controlled environment where field measurement are not so sometimes they are hard to compare to the published values and/or standards.
Due to the magnetic fluxes which surround the core and coil those magnetic fluxes can cause and steel components in that area to vibrate. Should those components be slightly loose they can emit noise.
Also, noise is relative. Should a transformer be located in an area one expect to be quiet such as an office of library a transformers inherent hum could be considered noisy where that same transformer located in an area that is inherently noisier the hum would not be noticeable.
Transformer noise is measured in dB at I believe 3 meters form the transformer. There are noise standards for various groups of KVAs,
For example for typical DTDTs:
KVA Rating 600V Class 5KV Class
0 - 9, 40dB 45dB
10 - 50 45 50
51 - 150 50 55
151 - 300 55 58
301 - 500 60 60
501 - 700 62 -
701 - 1000 64
Where a transformer is installed and the way that a transformer is installed also cam amplify transformer noise.
A room that has all reflective walls will cause the noise t bounce around. A transformer next to or mounted on a wall can transmit noise into an adjoining quiet office area. Hard piping a transformer can cause the transformer noise to be transferred through the pipe where flexible conduit such as liquid tight would be a better choice.
'Also, check the core and coil to assure that any shipping supports are removed. Most transformer core and coil assemblies sit on "Korfund" pads to help isolate core and coil noise from the enclosure. One can add these pads under the feet of the enclosure which may help isolate noise.
But, again, noise is like heat. When one expected something to be quiets and sound emitted often is considered to be noisy as is something that is expected to be cool is warm often is considered to be hot.
With noise, the noise should be measured and compared with the published values keeping in mind that those measure at the factory are don't in a controlled environment where field measurement are not so sometimes they are hard to compare to the published values and/or standards.
scootk70
Member
- Location
- Allentown, PA
Hummer
Hummer
My estimation.
Hystersis.
As current flows through a xfmr, the iron core is temporarily magnetized by the electromagnetic field created by the alternating current.
A primary magnetic field expands and collapses; every instance causes the core molecules realign themselves to a changing polarity of an electromagnetic field.
The energy required to realign the core molecules to the changing electromagnetic field is called the hysteresis loss of the core.
Hysteresis losses are directly proportional to the alternating current frequency.
The higher the frequency, the more times per second the molecules must realign.Installations involving high frequencies and nonlinear loads require a special type xfmr.
A small explanation for the hum.
Information courtesy of Mike Holt Motors and Transformers chapt. 4 NEC Exam Prep 2008.
Hummer
My estimation.
Hystersis.
As current flows through a xfmr, the iron core is temporarily magnetized by the electromagnetic field created by the alternating current.
A primary magnetic field expands and collapses; every instance causes the core molecules realign themselves to a changing polarity of an electromagnetic field.
The energy required to realign the core molecules to the changing electromagnetic field is called the hysteresis loss of the core.
Hysteresis losses are directly proportional to the alternating current frequency.
The higher the frequency, the more times per second the molecules must realign.Installations involving high frequencies and nonlinear loads require a special type xfmr.
A small explanation for the hum.
Information courtesy of Mike Holt Motors and Transformers chapt. 4 NEC Exam Prep 2008.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The fancy term is magnetostriction.
The hum primarily comes from the movement of the laminations of the core. While the windings do create the magnetic field, they are very rarely, if ever, the source of the noise.
The hum primarily comes from the movement of the laminations of the core. While the windings do create the magnetic field, they are very rarely, if ever, the source of the noise.
So... My wood wedge incident was a lie?:?
Here is a link from Federal Pacific:http://www.federalpacific.com/literature/drytrans/10transformernoise.pdf
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- Location
- New Jersey
- Occupation
- Journeyman Electrician
I've seen transformers that are shipped with the core tightly bolted to the enclosure and a note stating that the mounting bolts should be loosened to prevent vibration. Typically these have rubber pads between the two pieces of metal. Many sparkies actually forget to loosen the bolts. Here's one such note that claims to give "super-quiet" performance.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I don't believe I said 'absolutely never'. But according to your link, on page 3 of the pdf, it definitively says "Transformer noise is produced by the core".
Windings and movement of the entire core assembly cause vibrational noise much more than they cause a 'humming noise'. Reducing the vibrations themselves, such as using wedges, or their transmission, such as isolation pads.
zog
Senior Member
- Location
- Charlotte, NC
THe hum is caused by the constant realignment of the domains of the core material. I made a cool animated PPT to show this but it on my work computer which I hope to not see for a few days.
And for those that like dorky trivia, the pitch is nearly a perfect B Flat, back in my training days I used to carry a tuning fork to show that to my students, whack it on the transformer and hear the near perfect pitch match was always a crowd pleaser.
And for those that like dorky trivia, the pitch is nearly a perfect B Flat, back in my training days I used to carry a tuning fork to show that to my students, whack it on the transformer and hear the near perfect pitch match was always a crowd pleaser.
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