Abnormal sound on busduct

Without hearing the sound, It could be a number of things

Electrical sounds (small explosions) would be caused by arcing which could be a result of

• oxidization on the aluminum,
• loose connectors,
• Connections with resistive joints or insulator breakdown,
• Bolts that come too close to each other or the duct cover
• poor tining finish
• Dent in the duct

Here is a few installation check points

http://ecmweb.com/mag/electric_ensuring_good_bus/

Mechanical sounds, regular bangs such as the pluming noises in a hot water line.

Mechanical sounds are usually caused by heating and expansion which cause movements of the conductors or the ducts. Even external heating not related to the power or load can cause this, such as the sun coming in a window onto the duct at a certain time, or a heat source below the duct. An Infra red detector would be helpful in finding the heat source

If this is a long duct (>20M) you may think of installing a flexible bus-duct connector such as on page 4 of this link to prevent thermal expansion noises

http://library.abb.com/GLOBAL/SCOT/SCOT209.nsf/VerityDisplay/21623CC783BB59E8C2256DD000264696/$File/MDY_Brochure_English.pdf

Sir,

you have given the valid points to solve the proublem.We will attend this points during shutdown period.Thank you for your answer.Any doubt we will raise again.

Does the noise recurr each day? If so it is likely to be due to the ripple control frequency the supply authorities use for load control. It is typically about 1200hz.

Aluminium is much less denser than copper and it transmits sound from vibration to greater extent.

The noise could be something as simple as enhanced 50 Hz hum or possibly harmonics in the neutral assuming it s 415 v 4 wire - is there a lot of fluoresecent lighting the load?

On a more postive note if it was something more serious I suspect there would be other signs - smoke or smell, by now.

Sorry but unless you can post a sample of the noise on the forum, its difficult comment further.

Would you describe the nature of the sound in some detail? For example, is it a humming sound or more like (white or pink) noise? Popping sounds? Please describe. These all have different sources and knowing the nature of the sound will go a long way in determining its source.

Sir

It is humming sound only.Give me reply please.

This is a hunch only, but given the magnitude of the current flowing through the conductors, and if a conductor and its return path are in reasonably close proximity, the current will produce a substantial A.C. magnetic field. This field can cause the conductors to oscillate at points between their mounting points.

As an experiment, you could install additional insulated mounts between the existing ones to dampen the oscillations. Or, if it is convenient, move the conductors farther apart.

Alternatively, you could wrap the conductors in a sound-dampening, insulating material, such as Sorbathane (a trade name for a non-porous, ultra-soft polyurethane) sheet to minimize vibration. McMaster Carr is one supplier of Sorbathane.

A strip of Sorbathane along the length of the bus duct will also dampen vibration, as will a strip of lead sheet.

The foregoing assumes that it is the conductors that are vibrating, producing the humming sound. If you can record this sound to a file, there are a number of inexpensive (and free) spectrum analyzer programs available which can reveal the hum frequency and harmonics. Chances are that if the source of the hum is the A.C. magnetic field surrounding the conductors, the primary frequency will be some harmonic of the mains frequency in combination with the natural resonant frequency of the bus duct.

Please understand that as I can't be there to actually see your installation, this is mere speculation on my part. On the other hand, experimenting with dampening materials would be fairly inexpensive, and could reveal enough information about your hum problem to lead to a resolution.

If you try this, please contact me (or respond to this thread) to let us know how it goes.

-e

Surely i will give reply after taking experiment analysis.More over i can operate at full load from28th of this month, since this is the acadamic year opening date of our university.Thank you for your reply.