Science of Arc Flash & Engineering

[Eddie_T]

I appreciate the reply (maybe not the condescending le-sigh). I confess ignorance as I am not a lineman and have never watched them at work. While I know gloves aren't designed for 115Kv I thought they would be required as added protection even though at the end of a hot stick. Also the camera didn't reveal the real distances in play regarding their position. Thanks again.

 

[mbrooke]

I appreciate the reply (maybe not the condescending le-sigh). I confess ignorance as I am not a lineman and have never watched them at work.

It wasn't meant to be condescending. Nor was it really directed at you as much as it was internet commenters outside this forum. People will see something they know nothing about having no real world experience and then make factual sounding statements receiving endless recognition. Actual professionals then come in saying otherwise only to be put down/made dumb/banned by everyone because it doesn't reflect popular legend.


Please do not take this statement personally as it does not apply to you. I know you aren't a troll while simultaneously knowing where new knowledge begins. On the other hand expect to go bust commenting outside Mike Holt's.

While I know gloves aren't designed for 115Kv I thought they would be required as added protection even though at the end of a hot stick. Also the camera didn't reveal the real distances in play regarding their position. Thanks again

Gloves would IMO actually create a greater hazard due to reduced dexterity.

At 115kv they know the distance required ahead of time and most likely had a safety briefing before hand. They would never guess or risk such a thing. With MV/HV you never go into something unsure because there is nothing forgiving- the entire details of the procedure is known and rehearsed ahead of time. Its like surgery, years of school, residency and dummy practice guarantee that you are qualified to do the job.

 

[tersh]

I asked the following in a forum exclusively for arc flash discussions. But no replies yet. Maybe someone can answer this in detail. My questions are:

https://brainfiller.com/arcflashforum/viewforum.php?f=2

"Post subject:

Quantity of carbonized particles before Arc Flash Initiation

In panels or switchgears where a tool dropped can initiate a major arc flash. I'd like to understand the behavior if carbonized particles (say from previous short) get into the conductors causing a short. What quantity before they can initiate and chain react into a major arc flash?

Imagine there is little amount of carbonized particles between the two phases or conductors. Once it conducts. It can vaporize immediately. Would this be enough to establish a major arc flash. What is the carbon deposit threshold before this can occur?"
​

 

[romex jockey]

Possibly some studies exist tersh?

http://przyrbwn.icm.edu.pl/APP/PDF/116/a116zs38.pdf

~RJ~

 

[tersh]

Possibly some studies exist tersh?

http://przyrbwn.icm.edu.pl/APP/PDF/116/a116zs38.pdf

~RJ~

Arc flash was not mentioned inside the article.

My point is this. When you have a swimming pool full of aviation fuel. It won't flame up when you don't apply a cigarette butt or lighter flame to it. So in industrial switchboards with conductors with incident energy that can cause major arc flash. If a thin of layer of carbon suddenly appears in the conductors or connecting them to a plastic with thin layer of carbon. Would it light it up just like the swimming pool full of aviation fuel or gasoline?

 

[mbrooke]

Arc flash was not mentioned inside the article.

My point is this. When you have a swimming pool full of aviation fuel. It won't flame up when you don't apply a cigarette butt or lighter flame to it. So in industrial switchboards with conductors with incident energy that can cause major arc flash. If a thin of layer of carbon suddenly appears in the conductors or connecting them to a plastic with thin layer of carbon. Would it light it up just like the swimming pool full of aviation fuel or gasoline?

Well, fuel needs to be atomized first:


https://www.youtube.com/watch?v=7nL10C7FSbE


But regarding what Steve linked, he is referring to a carbon path being able to conduct electricity.

 

[tersh]

Well, fuel needs to be atomized first:


https://www.youtube.com/watch?v=7nL10C7FSbE


But regarding what Steve linked, he is referring to a carbon path being able to conduct electricity.

Originally I wrote "swimming pool full of gasoline" but changed the word gasoline to aviation fuel the last second to make it imaginatively more explosive. But you were right. Aviation fuel when not atomized is like kerosene as I was reading many links after your comment.

Whenever I saw a tanker of aviation fuel in the street. I raced away or far from it fearing an accidental explosion that can take out the entire block. So it's not really flammable so I can my park car near it now Thanks for the video. Gasoline tanker then is the more dangerous. So let me changed the description back to "swimming pool full of gasoline" with cigarette lighter ignition source. I was wondering if a thin layer of carbon could act like ignition source to the conductors at industrial switch gear with huge incident energy. In high tension power lines with very high voltage. It's set more distant apart to avoid spontaneous arc flashes. So I wonder if conductors in industrial switch gears have the current wanting to embrace and any carbon layer can become the "ignition source".

 

[mbrooke]

Originally I wrote "swimming pool full of gasoline" but changed the word gasoline to aviation fuel the last second to make it imaginatively more explosive. But you were right. Aviation fuel when not atomized is like kerosene as I was reading many links after your comment.

Whenever I saw a tanker of aviation fuel in the street. I raced away or far from it fearing an accidental explosion that can take out the entire block. So it's not really flammable so I can my park car near it now Thanks for the video. Gasoline tanker then is the more dangerous. So let me changed the description back to "swimming pool full of gasoline" with cigarette lighter ignition source. I was wondering if a thin layer of carbon could act like ignition source to the conductors at industrial switch gear with huge incident energy. In high tension power lines with very high voltage. It's set more distant apart to avoid spontaneous arc flashes. So I wonder if conductors in industrial switch gears have the current wanting to embrace and any carbon layer can become the "ignition source".

All is good.


Regarding carbon and arc flash I only know about it in relation to AFCIs.... Carbon is conductive and can certainly cause electricity to pass through it- but often not enough to cause an arc flash at lower voltages. Here is putting it into perspective:

https://www.youtube.com/watch?v=-qCuXF9eDBM

 

[kwired]

All is good.


Regarding carbon and arc flash I only know about it in relation to AFCIs.... Carbon is conductive and can certainly cause electricity to pass through it- but often not enough to cause an arc flash at lower voltages. Here is putting it into perspective:

https://www.youtube.com/watch?v=-qCuXF9eDBM

But even if it does flash over a light amount of carbon may not make much of a flash and then the carbon has been consumed and the event is over.

Tersh keeps asking questions about how much of an arc flash is possible, but the answer keeps involving more than just the conditions he brings with the question. bottom line is the incident energy has several factors involved, change any one of them and the total incident energy can change, and quite a bit sometimes with one simple little thing.

When they do calculations to determine what PPE is needed they are assuming worst possible case may happen, this does not mean every incident that can occur will be as severe as what they calculated - but as a worker you don't know how bad it will be if it happens so must be prepared for the worst.

 

[tersh]

But even if it does flash over a light amount of carbon may not make much of a flash and then the carbon has been consumed and the event is over.

Tersh keeps asking questions about how much of an arc flash is possible, but the answer keeps involving more than just the conditions he brings with the question. bottom line is the incident energy has several factors involved, change any one of them and the total incident energy can change, and quite a bit sometimes with one simple little thing.

When they do calculations to determine what PPE is needed they are assuming worst possible case may happen, this does not mean every incident that can occur will be as severe as what they calculated - but as a worker you don't know how bad it will be if it happens so must be prepared for the worst.

I was just asking given maximum or worse case total incident energy. Whether the carbon can not just be consumed but the miniscule plasma grows in size until it consumes the total incident energy to produce a room size explosion. But it seems you have answered the carbon will be used up. Hmm... But in the concept of negative resistance. Once a trace was started. It can go bigger and bigger so I wonder what is the critical mass of the carbon before chain reaction can sustain the plasma explosion.

 

[kwired]

I was just asking given maximum or worse case total incident energy. Whether the carbon can not just be consumed but the miniscule plasma grows in size until it consumes the total incident energy to produce a room size explosion. But it seems you have answered the carbon will be used up. Hmm... But in the concept of negative resistance. Once a trace was started. It can go bigger and bigger so I wonder what is the critical mass of the carbon before chain reaction can sustain the plasma explosion.

What we run into in the US commonly is that 120 volts can't sustain an arc very easily. So if that carbon tracing is between 120 volts and a grounded object, it is even more likely to consume the carbon and then stop. Systems that are 277 volts to ground do tend to have longer duration arc flash events, incident energy involved still depends on several factors but time is also a factor.

There are other voltage systems, but 120 and 277 to ground probably make up over 80-90 percent of what you are likely to encounter as the main supply to a building here.

 

[tersh]

What we run into in the US commonly is that 120 volts can't sustain an arc very easily. So if that carbon tracing is between 120 volts and a grounded object, it is even more likely to consume the carbon and then stop. Systems that are 277 volts to ground do tend to have longer duration arc flash events, incident energy involved still depends on several factors but time is also a factor.

There are other voltage systems, but 120 and 277 to ground probably make up over 80-90 percent of what you are likely to encounter as the main supply to a building here.

I was not referring to carbon tracing between 120 volts to ground, but carbon tracing between phase to phase of 240v. If there is no overcurrent protection (breakers) upstream of it and the transformers are 75kVA to 100kVA, and assuming minimal load impedance meaning it is very close to the transformer. Let's say incident energy is substantial or big. Would the carbon tracing between phase to phase 240v sustain an arc flash?

 

[romex jockey]

Would the carbon tracing between phase to phase 240v sustain an arc flash?

Sustain being the key term here Tesrh, which would lead us to >>

https://en.wikipedia.org/wiki/Paschen's_law

~RJ~

 

[kwired]

Sustain being the key term here Tesrh, which would lead us to >>

https://en.wikipedia.org/wiki/Paschen's_law

~RJ~

I agree sustain is the key term. 240 volts is low enough that it won't jump a narrow gap without some help, like from some carbon deposits. If you consume those carbon deposits and don't replace them with something else in the process that will help sustain the arcing, the arcing event will end, so what may be available to replace/replenish the carbon is critical to how long it may continue to arc.

Sort of like taking a welding rod and striking an arc, the rod is consumed by the arc but the arc continues if you keep feeding the rod into the work area. If you hold it steady there eventually is a big enough gap the arc can no longer be sustained. Carbon deposits between terminals of a breaker - first have to get to a point where an arc is started. Then if no material is introduced into the arc to help maintain it, that arc will go out once the gap becomes too far for the voltage applied to maintain an arc. Melting of metals at the terminals can introduce additional material (probably in vaporized form) to help sustain the arc.

 

[RumRunner]

Sustain being the key term here Tesrh, which would lead us to >>

https://en.wikipedia.org/wiki/Paschen's_law

~RJ~

OP is talking about environmental [ambient] conditions that is present that will cause an arc. This arcing conditions are highly dependent on the material of the two media that are creating the arc and the gas that is present in the surrounding.

Arcing is also supported by free electrons. Since the environment [ambient] is not quite supportive in the production of arcs due to lack of free electrons-- these arcs can not readily be created.

The reduction of molecules that will support arcing can be achieved by introducing noble gases like argon or helium.


That's why welders use these gases to achieved even heat to make bubble-free welds.


Paschen's Law is not valid in all situations.--especially when different external sources of electrons are present.

 

[kwired]

OP is talking about environmental [ambient] conditions that is present that will cause an arc. This arcing conditions are highly dependent on the material of the two media that are creating the arc and the gas that is present in the surrounding.

Arcing is also supported by free electrons. Since the environment [ambient] is not quite supportive in the production of arcs due to lack of free electrons-- these arcs can not readily be created.

The reduction of molecules that will support arcing can be achieved by introducing noble gases like argon or helium.


That's why welders use these gases to achieved even heat to make bubble-free welds.


Paschen's Law is not valid in all situations.--especially when different external sources of electrons are present.

That is one reason to use those gases, they are also shield gases to prevent oxidation of the metal being welded.

 

[tersh]

I agree sustain is the key term. 240 volts is low enough that it won't jump a narrow gap without some help, like from some carbon deposits. If you consume those carbon deposits and don't replace them with something else in the process that will help sustain the arcing, the arcing event will end, so what may be available to replace/replenish the carbon is critical to how long it may continue to arc.

Sort of like taking a welding rod and striking an arc, the rod is consumed by the arc but the arc continues if you keep feeding the rod into the work area. If you hold it steady there eventually is a big enough gap the arc can no longer be sustained. Carbon deposits between terminals of a breaker - first have to get to a point where an arc is started. Then if no material is introduced into the arc to help maintain it, that arc will go out once the gap becomes too far for the voltage applied to maintain an arc. Melting of metals at the terminals can introduce additional material (probably in vaporized form) to help sustain the arc.

I was not asking if the arc would sustain (for long period), I was only asking if such an arc would at all formed when there were carbon between the phase to phase terminals of breakers for example. The following as I explained was an actual case that occurred in 2015. The electrician simply connected the live wire to the right terminal, and there was a flash. Not only was the chassis torched. He suffered 2nd degree burn to a large rat size area in the arms. Imagine a rat size part bubble over. Not just blister.

There was a first short before the incident above between live wire and chassis which may have caused carbonization in the breaker casing. Many hours later, the above occurred. I was just asking if the carbon deposited was enough to initiate an arc flash. The key word is "initiate", not "sustain". I know when it sustained, it can cause a classic switch gear level arc flash that can throw the electrician to the floor. But it didn't happen or I could be injured too. So what I wanted to know whether it can "initiate" it just by carbon deposition between the 2nd and 3rd terminals of the breakers. Then I can imagine the arc flash forming higher up explaining why the plastic in between them is not scorched.

The supply is 3 phase open delta composed of two 75kVA tranformers. The CoPo even let me paid the two transformers because it was to serve only my office building and a one-storey office beside it. So the incident energy was large considering we didn't have much load that day and there were no breakers upstream of it. So the terminals were exposed to the full blunt of the energy. So could it "initiate" arc flash due only to the carbon deposit? If you or others will say the electrician short the two phases. I was sure it didn't happen that way because of the earlier short and hence we were very careful the second time with 3 or 4 people double checking everything like the breaker in off position and all the chassis were covered, etc. and of course he wouldn't connect the last remaining live terminal to the 2nd filled up terminal but the last empty one (as we clearly saw with our own eyes).

 

[romex jockey]

Tersh, was this.....

3 phase open delta composed of two 75kVA tranformers

groundED at all?

~RJ~

 

[tersh]

Tersh, was this.....



groundED at all?

~RJ~

Yes. I could see the ground rod in the pole just 2 to 3 meters from that service panel in the office building. In fact. I was discussing this at length with an electrical engineer last year learning about the 3 phase open delta supply but I forgot to ask the following question.

With two 75kVA open delta transformers. Do you get 150kVA total in one phase or just 75kVA? Just double checking although its logical to think it's only 75kVA for any single phase of the 3 but it's still 5 times the current served in US residential and my office building take the full blunt of the current should there a short circuit current (caused by the carbon deposits and not dead short).

 

[mbrooke]

Yes. I could see the ground rod in the pole just 2 to 3 meters from that service panel in the office building. In fact. I was discussing this at length with an electrical engineer last year learning about the 3 phase open delta supply but I forgot to ask the following question.

With two 75kVA open delta transformers. Do you get 150kVA total in one phase or just 75kVA? Just double checking although its logical to think it's only 75kVA for any single phase of the 3 but it's still 5 times the current served in US residential and my office building take the full blunt of the current should there a short circuit current (caused by the carbon deposits and not dead short).

I'd wager a bet its open delta for two reasons:

1) A closed delta secondary - wye grounded primary turns the bank into a "grounding transformer", meaning faults on the primary line will cause nuisance fuse blowing on the bank. The solution to that is a delta or ungrounded wye primary (which is great) but susceptible to ferroresonance during single pole switching at voltages over 12kv.

Which leads me to ask, how many volts is your primary system? 34.5kv by chance?

2) Being that in your area everything is connected phase-phase on the LV, you would need a 138 volt transformer to get 240 volts on a wye secondary. This is the ideal solution- but such are rare in the US and really unheard of in many places. Thus the only way to get 240 volts from standard US pole pigs is to connected the secondary in delta.



Anyway- This is a good read:

Sometimes the power delivered by an open delta transformer is compared to that of an equivalent three winding transformer. Typically figures like having 57.7% of the capacity of an equivalent three winding transformer or 87% of two transformers (same winding size) are quoted. While you can think of the transformer in this manner, it is more fruitful not to consider comparisons but to the necessary calculations on the open delta transformer.

https://myelectrical.com/notes/entryid/254/what-is-an-open-delta-transformer





at voltages above 12kv can produce ferroresonance