Overhead transmission lines BUZZING

[bdn2004]

I just started working at an industrial plant and every morning I walk underneath some large open wire, 3-phase lines that buzz fairly loudly considering they are in the air 50' or so. I think they are 15kV. They are on transmission towers, and look like about 500 kcmil ACSR open conductor on porcelain insulators.

What is the buzzing? And is this a symptom of anything? Is there anything that can be done about it?

 

[davidbeach]

Corona. At 15kV you probably have dirty insulators. At 230kV and above it just happens.

 

[Arevaengineer]

Never heard of 15kV transmission lines.Must be at least 33kV.By a rule of thumb you can determine the voltage level of a transmission line by counting the insulator discs supporting the line.Each disc is about 10kV. The buzzing sound as explained by David is corona due to dirty insulators.

 

[cranky108]

Could be 15kv class distribution lines. And they can make noise.

 

[alehman]

If a 15kV line is making noise, I'd be concerned that something bad is likely to happen soon.

Above 230, audible buzzing seems to be common.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[bdn2004]

Something bad is likely to happen soon....like what?

 

[davidbeach]

Letting out the magic smoke. About the only thing that ever goes wrong, the smoke gets out. If really 15kV the smoke release will come in the form of an insulator flash over.

 

[msquared48]

Check for bees nests in the insulators.

Seriously, I worked for years in substations and hydroelectric projects, and the buzzing is just part of the game.

FYI, 15kv is a common transmission line voltage after being stepped down at the main distribution substation, at least here.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[davidbeach]

No, 15kV is not a transmission voltage. Really common as a distribution voltage, but unheard of as a transmission voltage.

 

[msquared48]

OK... terminology.

We have 512, 230, 115 feeding to the distribution subs and fed out at 26, 15 or 13, and 4 in the distribution system.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[davidbeach]

For anybody outside the utility business it is probably just semantics. For those of use who deal with it all the time there is a big difference between transmission and distribution.

 

[cranky108]

The big difference being who works on it. Distribution engineers work of 15kv. Transmission engineers work on the higher voltages.

 

[bdn2004]

I just walked under these lines again and noticed the sound seems to be coming mid span, not at the insulators. I started to bring this up to somebody in maintenance based on the dirty insulator reply, which implies that the sound would be at the insulators - but I didn't.

Also, these open wires are paralleled 2 per phase. The paralleled conductors are very close to each other. Could this be the issue?

 

[marks1080]

It's unusual to see parallel 15kV phase conductors. Are you sure the voltage is 15kV?

 

[alehman]

Magic smoke, magic light and magic kaboom. Buzzing at 15 kV is usually indicative of advanced insulation breakdown, which usually leads to a fault after a short amount of time. I don't understand why it would occur at mid-span.

Multiple conductors per phase is common at transmission voltage ( > 69 kV). That should not be the source of the buzzing.

Yes, I'm wondering if this isn't 115 kV. Can you count the knobs on the insulators?

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[Arevaengineer]

If its really 15kV then a single conductor should be very heavy for a transmission line to carry.Perhaps that is the reason 2 conductors per phase could have been used.
At a height of 50' with an approximate pole spacing of 60m, you cannot judge the source of sound. It is, coming from the insulators but seems to you that its coming from midspan.

 

[jghrist]

If it really is 15kV, then as Arevaengineer pointed out, the bundling is to carry a lot of current. Perhaps there is some loose hardware on the bundle spacers that is vibrated by the magnetic forces from heavy current.