Blown Transformer Cutout

[mivey]

Right. So why does lightning still kill transformers?

Nothing is perfect. And we protect for near strikes. Not much you can do about direct strikes unless you put in a lot more protection which is normally not worth it.

 

[mbrooke]

this shows lack of experience and a bigger lack of “listen” to what we are “telling” you...

You are seriously trying to tell me fuzzing a line is a good idea? Relying on that has gotten linemen killed from what I've read.

 

[mbrooke]

not really. The arc will ignite cold oil too. Adding water/steam makes the situation worse. Fighting an already flaming open tank of oil with water is not so smart.

Good to know! Thanks for this info

 

[mbrooke]

Then don't do it. Simple. Use what works. Don't use it if it don't. I know you can buzz 7.2 kV.

I really don't remember about 2.4 kV but I doubt it. It would just lay on the ground and burn so not very strong.

Don't forget ungrounded delta...

 

[Hv&Lv]

In relation to what though? Remember that 15-50kva pole pigs are often overloaded to 200-300% capacity during peaks.

Fuses reflect that, and their time current curves start at around 200% of the link rating.

Nothing stop the oil from getting hot- fuse pops- then linemen sends it in with hot oil.

You've never seen CSP units with their red signal lights lit up all over town when the units are under 10 years old? The bulb burns out before anything else.

I’m not saying oil doesn’t get hot in a normal installation. I’m talking about almost hot enough to boil.
Add in fuse pops with insulation breakdown or worse, doesn’t blow.
If it doesn’t blow and there is an arc inside due to dielectric breakdown or installation breakdown, then there is pressure rise, blows the lid off. Air rushes in helping to ignite the oil once it is blown around in the oxygen rich air. (Richer than the inside of the XF anyway)

 

[mivey]

You are seriously trying to tell me fuzzing a line is a good idea? Relying on that has gotten linemen killed from what I've read.

You can read anything on the internet. Relying on that alone might get you killed. It is another tool, not the only tool.

Buzzing a line verifies it is on, not that it is off.

 

[mbrooke]

They don’t “stop” it. A surge arrester is a voltage variable resistor. As voltage exceeds the MCOV it quickly changes from megaohms to ohms or less. BUT a much bigger factor is cable inductance which increases impedance way more than the arrester. So they definitely work but the idea that if you use say a 15 kV arrester on a 13.5 kV line then you will not get above say 20 kV is not true. There is a way to calculate if I have a surge of say X Volts the resulting surge is Y. On top of that the probability of getting a strike of X Volts or larger is well known. Each individual strike can vary a lot but we know the likelihood of how bad it might get. Voltage is unlimited just that higher voltage strikes become less likely.

Plus a lot of grounds are not as low impedance as we think they are. The rod to ground coupling might be 1 ohm but the souil resistance also plays a factor. In some parts of the country it doesn’t matter how good your ground grid is. You can ground every pole and have arresters on every pole but if the ground conductivity is garbage it doesn’t matter.

Agree- though I'm tempted to argue bonding helps.

 

[Hv&Lv]

You are seriously trying to tell me fuzzing a line is a good idea? Relying on that has gotten linemen killed from what I've read.

It’s done everyday and still taught at lineman’s schools around the country.
relying on it for what? To take your gloves off and work like a rookie? That’s dumb.
But to rely on it to verify if the line is hot is perfectly acceptable.
Before grounds are installed you use something else anyway.

 

[mbrooke]

You can read anything on the internet. Relying on that alone might get you killed. It is another tool, not the only tool.

Buzzing a line verifies it is on, not that it is off.

Not internet, an IEEE PDF and incident reports.

Buzzing a line should not be used to verify anything in my view.

 

[mivey]

Don't forget ungrounded delta...

What about it? Doesn't change what we've said. You can't rely on just what you read on the internet as it is not comprehensive.

 

[mbrooke]

It’s done everyday and still taught at lineman’s schools around the country.
relying on it for what? To take your gloves off and work like a rookie? That’s dumb.
But to rely on it to verify if the line is hot is perfectly acceptable.
Before grounds are installed you use something else anyway.

Of course! So why even fuzz looking for on or off?

 

[mbrooke]

What about it? Doesn't change what we've said. You can't rely on just what you read on the internet as it is not comprehensive.

Ungrounded delta is a lot less likely to give results when fuzzing.

 

[Hv&Lv]

Of course! So why even fuzz looking for on or off?

Ungrounded delta is a lot less likely to give results when fuzzing.

??

 

[mbrooke]

I’m not saying oil doesn’t get hot in a normal installation. I’m talking about almost hot enough to boil.
Add in fuse pops with insulation breakdown or worse, doesn’t blow.
If it doesn’t blow and there is an arc inside due to dielectric breakdown or installation breakdown, then there is pressure rise, blows the lid off. Air rushes in helping to ignite the oil once it is blown around in the oxygen rich air. (Richer than the inside of the XF anyway)

I can agree on this.

 

[mbrooke]

??

4.8kv ungrounded delta vs 12.47kvY. Doubt fuzzing will be identical between the two.

 

[mivey]

Not internet, an IEEE PDF and incident reports.

Buzzing a line should not be used to verify anything in my view.

That's because it is a topic you don't know much about. Your view is based on very little knowledge and experience. You can't extrapolate a specific set of circumstances and broad brush the whole canvas.

 

[mbrooke]

That's because it is a topic you don't know much about. Your view is based on very little knowledge and experience. You can't extrapolate a specific set of circumstances and broad brush the whole canvas.

Hence why I'm asking. But I still can't see fuzzing being a legit tool worth using.

 

[mbrooke]

Nothing is perfect. And we protect for near strikes. Not much you can do about direct strikes unless you put in a lot more protection which is normally not worth it.

I'll agree with this. Direct hits aren't the same as near strikes.

 

[Hv&Lv]

Real world scenario.
We are working on a regulator bank out on the line with a headway.
Dispatch calls and asks if we have knocked the line out. I say “No” and ask my lineman to buzz the line. He tells me the line is dead. He knows this because he has heard it all morning.(buzz when he touches it) We immediately stop all work to assess why the line is out. My relays are set with 50 pickups in the HLT equation. We patrol the line, find problem, remove headway and re-energize.. (it wasn’t really that fast. Problem was behind a fuse).
Once all that’s done, we have to start over. Job briefing, headway on, resume work..

 

[mbrooke]

Real world scenario.
We are working on a regulator bank out on the line with a headway.
Dispatch calls and asks if we have knocked the line out. I say “No” and ask my lineman to buzz the line. He tells me the line is dead. He knows this because he has heard it all morning.(buzz when he touches it) We immediately stop all work to assess why the line is out. My relays are set with 50 pickups in the HLT equation. We patrol the line, find problem, remove headway and re-energize.. (it wasn’t really that fast. Problem was behind a fuse).
Once all that’s done, we have to start over. Job briefing, headway on, resume work..

Why not a hook meter?

I know you won't like my answer- so please forgive me for what I'm about to say- but to me fuzzing is the equivalent of HVAC techs shorting across the terminals of 24 volt transformers with a screw driver to test for power. It doesn't seem like an accurate, refined approach. Just looks cringy.

Of course I'll admit I'm biased by 600 volt and under practices... I've never been up in a bucket truck- I'll give you that.