A few towers supporting a high voltage line in Victoria got blown down yesterday. I'm speculating that it is due to the wind setting the lines swinging too much for them to handle the strain. Maybe even harmonics like that famous suspension bridge in the USA.
So is that a civil engineering problem which you don't deal with? Or maybe one of you knows how the wind risk is taken into account in places where extreme wind is a high probability like Tornado Alley. Do they put the towers closer together so there isn't so much metal swinging between them or make the towers stronger?

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Mr Milk said..
A few towers supporting a high voltage line in Victoria got blown down yesterday. I'm speculating that it is due to the wind setting the lines swinging too much for them to handle the strain. Maybe even harmonics like that famous suspension bridge in the USA.
So is that a civil engineering problem which you don't deal with? Or maybe one of you knows how the wind risk is taken into account in places where extreme wind is a high probability like Tornado Alley. Do they put the towers closer together so there isn't so much metal swinging between them or make the towers stronger?

There are a couple of wind effects that need to be considered. Aeolian vibrations in transmission lines are low amplitude, high frequency vibrations that will cause the conductor to crack over time due to stress fatigue. They are limited by the addition of 'dog bone' dampers that you will see attached to the conductor at each end of a span. The larger visible type is 'galloping' (e.g. the Tacoma Narrows bridge that you referenced). Transmission lines don't suffer from galloping because the conductors are round. When large transmission towers come down, it is generally just due to the huge force created by a massive wind gust, not some oscillatory or harmonic behaviour.

The civil engineer will design the tower to meet a specified wind speed. It's not practical or economic to design for the biggest possible gust. I don't know if they specify a higher wind speed in tornado areas because I've never designed a tower for one. The examples of tower failure that I have dealt with in NSW have mostly been related to microbursts. This is where a column of cold air falls from a great height and when it hits the ground, the falling air creates a blast of around 150 km/h or more. It's quite a sight....everything in a radius of a few hundred meters is flattened and you can see it pointing outwards from the middle.

You may be interested to know that there are two main types of transmission tower....tension and suspension. A suspension tower does just what the name suggests, it holds the vertical weight off the ground. Tension towers look much the same to the untrained eye, but have much heavier steel truss members and larger foundations. Tension towers can withstand the horizontal force that is used to tension the line. Therefore, you need a tension tower whenever the line terminates at a substation or the line changes direction. If you are unlucky enough to have a tension tower fall down, then you can have a cascading effect as the suspension towers fall like dominoes, since they aren't designed to pull against the line tension after a nearby tension tower falls down and the line becomes slack on just one side of the suspension tower. This actually happened a few years ago on the 132 kV line that runs along the side of the road to Kurnell and about half a dozen towers were affected, although it wasn't due to wind - it was due to a contractor disconnecting all the conductors on one side of a suspension tower instead of gradually removing one from each side at a time to keep the forces even. Also, the next time you're at Bungendore, head north about 5 km toward the southern end of Lake George and you'll find a transmission line section where the steel transmission towers have been replace by large wooden pole structures. These are emergency structures that were used to quickly get that line back in the air when a microburst took out a string of suspension towers.

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Mr Milk said..
A few towers supporting a high voltage line in Victoria got blown down yesterday.....

pffft, as if.

I heard that a fireman said they had been brought down by non-explosive thermite in an controlled explosion. Just look at the photos and do your own research. How is a tower going to collapse by wind alone under free fall unless column 79 has been taken out with a mini-nuke ? Can't happen. Its empirical.

How is steel going to be melted by the wind ? Think about it, it is so obvious.

Do you know the towers were insured for like their replacement value or something and that annual insurance had been renewed within the last 12 months ? You can't make this up. I am guessing there were atleast 10,000 people involved in this and all five of them have stayed silent.

Oh yeah, also did you see the wind originally came from a weather system that formed over Saudi Arabia and blew around the world via Russia whilst being tracked by NOAA. And they expect us to believe this is a coincidence !!!

I reckon Harrow is part of it, with that gobble-de-gook garbage he wrote. What would he know about it. I have actually seen electricity towers just like these when I drove down the road once.

If you all send me $100 a week for the next 27 years, I'll take this all the way to the high court and then you'll see.

I am right, you are wrong so don't reply.

I stand with Carantoc. I'm calling BS on Mr Milk and Harrow.

Carantoc. Gold.
Amd harrow thanks for sharing. I saw the OP and thought i bet harrow will be all over this.
So much knowledge on here.

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Harrow said..

Mr Milk said..
A few towers supporting a high voltage line in Victoria got blown down yesterday. I'm speculating that it is due to the wind setting the lines swinging too much for them to handle the strain. Maybe even harmonics like that famous suspension bridge in the USA.
So is that a civil engineering problem which you don't deal with? Or maybe one of you knows how the wind risk is taken into account in places where extreme wind is a high probability like Tornado Alley. Do they put the towers closer together so there isn't so much metal swinging between them or make the towers stronger?

There are a couple of wind effects that need to be considered. Aeolian vibrations in transmission lines are low amplitude, high frequency vibrations that will cause the conductor to crack over time due to stress fatigue. They are limited by the addition of 'dog bone' dampers that you will see attached to the conductor at each end of a span. The larger visible type is 'galloping' (e.g. the Tacoma Narrows bridge that you referenced). Transmission lines don't suffer from galloping because the conductors are round. When large transmission towers come down, it is generally just due to the huge force created by a massive wind gust, not some oscillatory or harmonic behaviour.

The civil engineer will design the tower to meet a specified wind speed. It's not practical or economic to design for the biggest possible gust. I don't know if they specify a higher wind speed in tornado areas because I've never designed a tower for one. The examples of tower failure that I have dealt with in NSW have mostly been related to microbursts. This is where a column of cold air falls from a great height and when it hits the ground, the falling air creates a blast of around 150 km/h or more. It's quite a sight....everything in a radius of a few hundred meters is flattened and you can see it pointing outwards from the middle.

You may be interested to know that there are two main types of transmission tower....tension and suspension. A suspension tower does just what the name suggests, it holds the vertical weight off the ground. Tension towers look much the same to the untrained eye, but have much heavier steel truss members and larger foundations. Tension towers can withstand the horizontal force that is used to tension the line. Therefore, you need a tension tower whenever the line terminates at a substation or the line changes direction. If you are unlucky enough to have a tension tower fall down, then you can have a cascading effect as the suspension towers fall like dominoes, since they aren't designed to pull against the line tension after a nearby tension tower falls down and the line becomes slack on just one side of the suspension tower. This actually happened a few years ago on the 132 kV line that runs along the side of the road to Kurnell and about half a dozen towers were affected, although it wasn't due to wind - it was due to a contractor disconnecting all the conductors on one side of a suspension tower instead of gradually removing one from each side at a time to keep the forces even. Also, the next time you're at Bungendore, head north about 5 km toward the southern end of Lake George and you'll find a transmission line section where the steel transmission towers have been replace by large wooden pole structures. These are emergency structures that were used to quickly get that line back in the air when a microburst took out a string of suspension towers.

Gee who'd have thought you could get such information on a water sports site
I just come here to get financial advice & if I should get the vaccine jab

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myusernam said..
Carantoc. Gold.
Amd harrow thanks for sharing. I saw the OP and thought i bet harrow will be all over this.
So much knowledge on here.

No wind needed in QLD to bring down a line. Your coastal towers are rusted to almost nothing!

Do a search on 'corrosion' in this document:
www.powerlink.com.au/sites/default/files/2023-11/TAPR%202023%20-%20Chapter%206.pdf

Aeolian vibrations in transmission lines are low amplitude, high frequency vibrations that will cause the conductor to crack over time due to stress fatigue.

So that's the hum that you notice sometimes near substations?

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Mr Milk said..
Aeolian vibrations in transmission lines are low amplitude, high frequency vibrations that will cause the conductor to crack over time due to stress fatigue.

So that's the hum that you notice sometimes near substations?

Inthink i know rhis one harrow can correct me if im wrong. Power here is 50hz. 50 hz is audible (50hz hum) power lines humming probably just a speaker effect of the lines moving or inducing energy (parasotic oscillations) into air or stuff that makes noise.. if u put a speaker close it would hum

The hum is the noise produced by the large power transformers as their cores vibrate due to the 50 Hz supply. However, the hum is actually 100 Hz, not 50, since there are two voltage peaks (+ve and -ve) within each 50 Hz cycle that each cause the transformer core to try and expand (magnetostriction).

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Harrow said..
The hum is the noise produced by the large power transformers as their cores vibrate due to the 50 Hz supply. However, the hum is actually 100 Hz, not 50, since there are two voltage peaks (+ve and -ve) within each 50 Hz cycle that each cause the transformer core to try and expand (magnetostriction).

Totally off topic, but reminded me of a similar phenomenon. If you get an arc over on a radio transmission tower, it demodulates the RF and acts as a speaker. Not very Hi Fi, not much base, but you can hear it for a long way.

I used to work at a very high power (biggest in oz) HF transmissiom site. The huge curtain antenna array were fed by 300 ohm feeders in a huge field in the middle of nowhere. If there was a fault in the transmission lines instead of the 300kw HF going out the curtain, you would get arc faults. The energy would ionise the air into whats called a corona and you would have these 6ft high green and blue flames on the lines. It would also demodulate the broadcast audio (i think because of the balanced audio on the lines now had a path to gnd through the air) and so you would hear bits of the transmission. Youd be out in total darkness at 2 am in the field and all of a sudden there'd be bizzare northern lights flames and tesla coil style arcing, with bits of indonesion or english religous speak (evangelical content) ringing out. Was quite an experience.

Big radios. Drew 30 amps per phase at 11kv. Size of a small apartment. Some were cooled by steam.

Lol decrepi ddint see yr post till after i typed mine

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decrepit said..
Totally off topic, but reminded me of a similar phenomenon. If you get an arc over on a radio transmission tower, it demodulates the RF and acts as a speaker. Not very Hi Fi, not much base, but you can hear it for a long way.

That's super cool, I'd never heard of it before.

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Harrow said..
However, the hum is actually 100 Hz, not 50, since there are two voltage peaks (+ve and -ve) within each 50 Hz cycle that each cause the transformer core to try and expand (magnetostriction).

I remember hearing or reading this same thing, but I am not sure I agree. Maybe it was in a TAFE class many years ago.

Now you can get apps on your phone that use the mic to analyse audio frequencies. Maybe I should actually try this to see for myself.

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myusernam said..
Youd be out in total darkness at 2 am in the field and all of a sudden there'd be bizzare northern lights flames and tesla coil style arcing, with bits of indonesion or english religous speak (evangelical content) ringing out. Was quite an experience.

Big radios. Drew 30 amps per phase at 11kv. Size of a small apartment. Some were cooled by steam.

You had God speaking to you? What did he say?

can you cool things with steam?

yeah steam is a superheated gas. I didnt do chemistry but it probably takes 1 joule or energy unit (whatever it is) to heat 1 gram or kg of water by 1 degree. But once it reaches 100deg and turns into steam it is superheated and then instead of a linear scale it becomes logorithmic (i havent googled this is just what I was told years ago) and to heat steam for every degree over 100 deg it takes way more energy. so long as you are happy with the thing u want to cool being around 100degc then steam becomes a very good way to remove heat because it is so hard to make any hotter

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FormulaNova said..
I remember hearing or reading this same thing, but I am not sure I agree. Maybe it was in a TAFE class many years ago.

Now you can get apps on your phone that use the mic to analyse audio frequencies. Maybe I should actually try this to see for myself.

I could be wrong as it's been a few months since I last measured harmonic sound pressure levels in a substation.

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Harrow said..

FormulaNova said..
I remember hearing or reading this same thing, but I am not sure I agree. Maybe it was in a TAFE class many years ago.

Now you can get apps on your phone that use the mic to analyse audio frequencies. Maybe I should actually try this to see for myself.

I could be wrong as it's been a few months since I last measured harmonic sound pressure levels in a substation.

I am pretty sure I have heard the same thing though about 100hz. Probably from a TAFE teacher. I think he was talking about the whine from a fluoro at the time.

I just tried an online frequency generator and 50hz seems correct to me, but I am so used to hearing 50hz from different things, that maybe I am just tuned in for that frequency? When I was a kid, that hum was pretty common, but since switchmode supplies have been used in almost everything, you hardly hear it anymore.

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myusernam said..
yeah steam is a superheated gas. I didnt do chemistry but it probably takes 1 joule or energy unit (whatever it is) to heat 1 gram or kg of water by 1 degree. But once it reaches 100deg and turns into steam it is superheated and then instead of a linear scale it becomes logorithmic (i havent googled this is just what I was told years ago) and to heat steam for every degree over 100 deg it takes way more energy. so long as you are happy with the thing u want to cool being around 100degc then steam becomes a very good way to remove heat because it is so hard to make any hotter

Oh, that makes sense. I just never thought it would be used that way, but as you say, its for things that are already over 100c.

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FormulaNova said..
I am so used to hearing 50hz from different things...

Maybe you've been hearing 100 Hz from things all along and assumed it's been 50 Hz. What kind of things are you talking about?

An online tone generator won't have the same harmonic content as transformer vibration (which has a lot of even harmonics in it) so maybe not that useful for making a comparison.

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Harrow said..

Maybe you've been hearing 100 Hz from things all along and assumed it's been 50 Hz. What kind of things are you talking about?

Hit the 4th fret on the bottom E string. Yes that's it. 100hz. (Well 103.8 if you're exactly in tune).

So I'd guess 100hz has been driven into our subconscious audio processing since birth. There you go a million dollar riff. Down tune by 40 cents compose a ditty in G sharp. People couldn't help but hum along.

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Harrow said..

FormulaNova said..
I am so used to hearing 50hz from different things...

Maybe you've been hearing 100 Hz from things all along and assumed it's been 50 Hz. What kind of things are you talking about?

An online tone generator won't have the same harmonic content as transformer vibration (which has a lot of even harmonics in it) so maybe not that useful for making a comparison.

Maybe. I think when I was a teenager I was playing around a bit with power transformers and the TVs they came from. The frame rate is 50hz, so most TVs of the time would have some sort of tone from this as well.

Maybe I am also used to hearing it from arc welders, which is where you would hear the giant transformer in these buzzing.

It's a very subjective thing, which I could only answer if I had something with me to measure the frequency at the time. Maybe I should find an old fluoro batten and hook it up and hope it hums.

There is a youtube channel 'Adrian's digital basement' where he uses an app to pick up whether the line rate frequency of a CRT is present, to tell if the flyback transformer is operating. It's something I would have never thought of doing, but seems to be pretty impressive in doing so.

The worst thing about those frequency generating apps is that you find that high frequency hearing gets worse as you get older...

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FormulaNova said..
The worst thing about those frequency generating apps is that you find that high frequency hearing gets worse as you get older...

I tried to play a 50 Hz tone and virtually nothing came out of my laptop speaker due to its poor frequency response, so I'm just gonna assume that's the reason for me not being able to hear any high frequencies in the online hearing test I did either... it has nothing to do with my old age!

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Harrow said..

FormulaNova said..
The worst thing about those frequency generating apps is that you find that high frequency hearing gets worse as you get older...

I tried to play a 50 Hz tone and virtually nothing came out of my laptop speaker due to its poor frequency response, so I'm just gonna assume that's the reason for me not being able to hear any high frequencies in the online hearing test I did either... it has nothing to do with my old age!

If you used the same one I did, you can change it to a square wave, sawtooth, or triangle wave to get output. For some reason the sine wave doesn't output. Maybe a filter?

edit: onlinetonegenerator.com/

Maybe there is a filter and the harmonics are what makes it audible?

Mmmmm . Love all the answers but..:: it was really really windy. 50 km up the road from me it was 130 km wind gusts and trees were snapped 30 m off the ground. A bit of a mess and it will take a few weeks to sort it out.

FYI
A Structural Engineer would have designed the towers.
Civil Engineers deal with concrete and earthworks.

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FormulaNova said..If you used the same one I did, you can change it to a square wave, sawtooth, or triangle wave to get output. For some reason the sine wave doesn't output. Maybe a filter?

edit: onlinetonegenerator.com/

Maybe there is a filter and the harmonics are what makes it audible?

I'd guess it is just that your PC speaker has almost zero response at 50Hz. I can hear the 100Hz if I turn it right up, but it's very quiet. From 200Hz upwards it's okay.

I'd think the reason you can hear those other waveforms is that the 50Hz sawtooth, square and triangle contain harmonics of 100, 150, 200. 250, 300, etc, which your speaker does have a reasonable response for, so that would be what you are hearing.

Did you try this one, it starts at 150Hz and slowly drops. My speaker starts to really drop out below 70Hz and I think I'm imagining anything below 50 or 60Hz.

onlinetonegenerator.com/subwoofer.html

I tried listening at 50Hz.

You know what, now I am totally addicted to bass. Wow woah-woo, Wow woah-woo.

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Harrow said..

I'd think the reason you can hear those other waveforms is that the 50Hz sawtooth, square and triangle contain harmonics of 100, 150, 200. 250, 300, etc, which your speaker does have a reasonable response for, so that would be what you are hearing.

Did you try this one, it starts at 150Hz and slowly drops. My speaker starts to really drop out below 70Hz and I think I'm imagining anything below 50 or 60Hz.

onlinetonegenerator.com/subwoofer.html

I downloaded Spectroid, so I can at least see what the phone hears. The speakers don't seem to produce anything below 170hz or so.

It makes me wonder if the output would be better connected to external speakers. Given the tiny size of laptop speakers, I can understand if this is the case....

Oh hang on, I just realised I had some cheap headphones lying around, so I plugged them into the laptop's headphone output. I could hear down to about 30hz, but when I did it again in Spectroid, it showed unreliable readings at about that point anyway.

I don't know if low frequency hearing varies too much among people, but high frequency certainly varies a lot with age.

With the inbuilt speakers I couldn't hear any of that subwoofer test, but with the external headphones, no problem, at least until 30hz.

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oceanfire said..
FYI
A Structural Engineer would have designed the towers.
Civil Engineers deal with concrete and earthworks.

To be totally clear, Structural Engineering is a subset of Civil Engineering, albiet a highly specialised and regulated one.

Structural Engineers have a Civil Engineering Degree, usually with a major in Structural Engineering, but not necessarily, the Structural certification comes after the Degree is completed and you have to work within the field to gain your registration as a Certified Practicing Structural Engineer.Most Structural Engineers can also design the concrete if they desire, it is a complementary and necessary skill, but they leave the dirt to the dirt doctors.