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Join Date: Mar 2019
Posts: 29

Noise

05/01/2019 11:50 AM

dear all

we have outdoor panel this panel consist of 6.6kv circuit breaker ,busbar ,CT and

PT the normal load is 30MW ,but now the load is 15 MW because when the load

increase above 15MW the buzz noise will appear .we tight all screw then we change

the breaker but the noise still appear please can any one help me to know the

possible reasons of this buzzing.

thanks

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#1

Re: noise

05/01/2019 11:58 AM

..."The cause of this sound is alternating voltage and currents that make a transformer's steel core extend and contract. The result is the familiar vibrating hum. This phenomenon is scientifically referred to as magnetostriction."...

http://www.acoustiguard.com/blog/419-transformer-noise.html

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Guru

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#5
In reply to #1

Re: noise

05/01/2019 10:30 PM

So check the tightness of your PT lamination bolts, may have stretched due to higher nearby heat load from higher load operation, now at lower load, bolts might not be so tight. Also check current transformers for iron core noise

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#2

Re: noise

05/01/2019 12:10 PM

Try viewing the panel box under load with an infrared camera or viewer.See if there are any junctions heating up.Many possibilities for the noise,including a bad CT,PT,a junction termination breaking down.Do not ignore this issue,it could potentially be very dangerous

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#3

Re: Noise

05/01/2019 12:50 PM

30MVA @ 6.6kV = 2624A, magnetic reaction between busbars will cause vibration unless they are well restrained, even the housing will vibrate.

I changed the feed in point to one of our main boards which meant the main current on the board was fed through a longer section of the boards bars, the vibration was horrendous.

Worth looking at.

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#4
In reply to #3

Re: Noise

05/01/2019 2:37 PM

Current creates a magnetic field. AC current creates a vibrating magnetic field which generates a vibrating force on other current carrying conductors and ferrous metals. The force is stronger at close proximity. Anything loose will allow this vibrating force to generate vibration (sound). If the length and mass of the vibrating object cause resonance at the power frequencies, production of sound will be particularly efficient. Try restraining your busbars at different points if you think they might be resonating at the power frequencies. Just a thought.

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#6

Re: Noise

05/02/2019 3:32 AM

Choose between a corona 'buzz' sound or a vibration 'buzz' sound.

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#7
In reply to #6

Re: Noise

05/02/2019 4:55 AM

A Corona discharge is usually accompanied by an ozone odor,sort of like a bleach odor.This is a very dangerous sign,and remedial action must be taken immediately. A corona "buzz" sounds like an arc welder when the arc is too long. If you ever hear it,you will always know the sound and the smell.

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#8
In reply to #7

Re: Noise

05/02/2019 6:30 AM

Does he know the difference?

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#9
In reply to #6

Re: Noise

05/02/2019 11:32 AM

Some corona has a crackling overtone on the base ‘buzz’ frequency....

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#10
In reply to #9

Re: Noise

05/02/2019 12:17 PM

Some good pork has crackling on it with overtones of orange. I shall get a regular frequency and a buzz with the beers.

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#11
In reply to #6

Re: Noise

05/02/2019 12:19 PM

Corona would depend on voltage and presence of moisture. At increased load, the voltage is likely to be a bit lower and moisture also is likely to evaporate due to heat produced by current.

Hence, it seems more likely cause is inadequate busbar supports. Was the noise there right from the day of installation??

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#12
In reply to #11

Re: Noise

05/02/2019 12:24 PM

Corona is inoized air, not water/moisture.

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#13
In reply to #12

Re: Noise

05/02/2019 12:30 PM

I am aware of it. Thanks any way.

What I meant by moisture is that in presence of humidity in air, possibility of corona discharge increases. I have seen this in 400kV switchyards just after a rain.

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#15
In reply to #13

Re: Noise

05/02/2019 12:37 PM

shubh raatri

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#14
In reply to #12

Re: Noise

05/02/2019 12:31 PM

And Yes, indeed, air does contain moisture, my apologies. The ozone is burned air which contains minute particles of moisture, however any heat built up will not evaporate the moisture from a cable. It will make matter worse and increase ozone.

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#17
In reply to #6

Re: Noise

05/03/2019 12:54 PM

thanks for your reply

its a vibration 'buzz' sound.

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#18
In reply to #17

Re: Noise

05/03/2019 9:08 PM

I say laminations, if no loose mounting bolts. Without information on bus supports, etc, it will be hard to differentiate types of mechanical noise

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#19
In reply to #17

Re: Noise

05/04/2019 1:30 AM

Henry98,

Thanks for posting the feedback.

Suppose the vibration is from busbars. Appreciate your confirmation.

One of the main objectives in these fora is learning. The feedback from the OP always is valuable.

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#16

Re: Noise

05/02/2019 7:12 PM

I nudge the breakers a bit and see which one/s buzz. That sometimes does it.. but this is a whole other level.. food for thought.

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