High Voltage Engineering

From Wikipedia:

At a guess, I would say it's to stop the electrodes coming into contact and causing expensive destruction!

In my experience at "our sub station" and on our high Voltage Transformers ( this was at a Mini Mill Steel Producing) ... WE DID NOT INSTALL any barriers in other than in PROVEN and Grounded Isolation. Then the barriers prevent Phase to Phase Shorting. We had switches and breaker capable of closed under load. HOWEVER, we conducted open and closing as if they were NO Load. Safer and even then the "Stabs" draw an arc. The idea is to control this rather than have it control us!

So back to the question.

In very humid weather and with the high concentration of heavy metals at the steel mill where this was we lost several High Voltage step Down transformers for the insulators at the termination ends of the leads cracking - The result was a phase to phase short and a VERY Expensive and Dangerous repair!

So.. to prevent major damage and injury in the event of that. There is also a NFPA or NEC requirement, I believe.

I agree with the other WAG that this barrier is probably there to lengthen the arc path through air. However, without a picture or manufacturer's part number to identify the barrier, electrodes, chassis, orientation, color, material, voltages or anything else that might be relevant, this barrier could be actually a drip shield for rain, a block for debris, an attempt to prevent vermin from nesting where they will get zapped, or almost anything.

Yes, in hind sight I concur. It could very well be there for a number of issues. All of which I assume would be more positive than negative.

They are for insulation purposes. Air, especially foggy or rain is too good a conductor and will arc if sufficient insulation is not provided. The solid dielectrics increase the equivalent length of the separation. An example of this is high voltage transmissions lines. With a dry atmosphere they are quiet. Put some rain or snow in the air and they begin to make a crackling noise. Can be heard easiest with 250KV or 500KV. There is a 250KV and 500KV switching station in my town that sounded like a bowl of Rice Krispies during a snow storm. Crackling is from the air trying to fail and let an arc start. This is also why some power lines slightly glow blue/white under the right conditions. What you see is the beginning of arcing to adjacent wires on a different phase.

Sometimes these dielectrics fail and bad things happen. 2 weeks ago at a local switching station a 250KV transformer failed. Arc was so bright it lit up the dark for over a mile radius. Fire had flames over 100' and a huge plume of smoke from the mineral oil within it. Smoke was seen 10 miles away. Noise of initial explosion could be heard over 3 miles away. Electric company wouldn't let us put fire out for 4 hours. Finally used copious quantities of foam and water. Whole station was live except in the immediate area of the fire, a very nervous situation.

As previously posted, Teflon has a higher dielectric rating than most others. This is why many electronic devices in critical applications mostly use Teflon insulated wire.

Good Luck, Old Salt

Thank U for replying.It was very helpful.

Beside its electrical characteristics, it also serves a mechanical function, (like a physical support) for the intended application!

To prevent incidents like these from occurring:

Electrical explosions and arcing

This is the 250KV transformer referenced in answer #6. This picture was taken 3-1/2 hours after the initial explosion and fire. At that time the flames were averaging 40 ft with up 50ft. The material burning is Mineral Oil from the inside of the transformer. It started by a breakdown within the transformer. Other identical transformers were approx. 25-30 ft high without wires. This is why when engineering dielectrics and insulation materials you over engineer, not skimp. It took 2ea 1,000gpm nozzles with foam operating 100-150 ft away to put it out. As noted before, all of this was done while the rest of the switching station (250KV and 500KV) was still live. They wouldn't shut it down because several states would loose power. Needless to say we were very cautious, like EVERYONE should when dealing with high voltage from 60 volts up to 500KV. Note the picture was taken from 300ft away.

Good Luck, Old Salt

Basically a plasma, flames are electrically conductive (I've seen loudspeakers based on this - the sound emanated from the flame itself), and so was there arcing from the live parts of the substation through the flames? Toward the end of the video segment in the link I gave, where you see that Florida substation in flames, there's a flash & bang above the transformer as the flames lick around a high-voltage bushing, providing a conductive path. I suspect the arc didn't continue because of a breaker tripping upstream.

Wish I could provide more "electrical" information on the incident. Last week I saw one of the power company's loss prevention managers and all he would say is that it was "a fault inside the transformer".

I was operating one of the engines feeding water to a nozzle rated at 1,000 gal/min at 100 psi. In actuality we were at the limit of the apparatus capacity. We were rated at 1,500 gal/min and were pushing at 195psi.

Good Luck, Old Salt

Thanks...I love watching those videos.

what is the electrical conductivity of brass, aluminium, mild steel and air?

The value should be in siemens?

please reply.

52, 94, 76 and 4.

The unit should be S/m.