Doug Kerr
Well-known member
Inspired (or provoked) by the comments on my recent photo of the voltage regulator, I thought I would exhibit some shots I took on a similar errand about two years ago - again to come to understand some apparatus I had seen but not understood.
The shots were taken at the White Rock electric substation in East Dallas. Carla and I had gone there to photograph a colony of Monk Parakeets that had built an elaborate community among the ironwork at the substation. I'll post those shots a little later (although we do get to see the little critters here).
While I was there, I was interested in some apparatus that was standing on the ground, evidently ready to be installed. I took some shots of nameplates and such, and after a bit of research came to understand the story. I'll summarize it for you here as I show the pictures.
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The disconnects used to isolate paths in high-voltage transmission lines essentially use a "knife switch" concept. They cannot be opened (shut of) while the line is energized. In such a situation, when they begin to open, an arc jumps the initial gap between the blade and the jaw. This arc creates a plasma path (conductive superheated air), which will gladly extend the entire distance of the gap to which the switch eventually opens, keeping the current flowing and generating enormous heat that can well destroy the switch and its supporting infrastructure.
Here we see two installations of these at the White Rock substation. The ones on the right are the traditional kind. Those on the left have a special attachment I will be describing shortly (the set to the right would have the same thing shortly, which is why there were pieces of apparatus on the ground). These power lines operate at a nominal voltage of 138 kV (phase to phase; the lines are three-phase).
Here we see one disconnect (the older type) close-up. We also see an outpost of the Monk Parakeet colony, evidently undergoing some reconstruction. The second insulating bushing from the right is turned to operate a mechanism at its top that lifts the blade to open the circuit.
The matter of a plasma arc if such a disconnect switch were to be opened with the line energized is amply illustrated by this video.
http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=1587733
This test was conducted on a disconnect on a 500 kV line. One leg was intentionally left "live". As we can see, as the disconnect opened (this kind opens to the side), the plasma arc formed, and continues as the switch reaches its fully open position.
The plasma arc rose into the air as a result of the hot plasma being lighter than air. This might have eventually actually extinguished the arc, but not before severe damage would have ensued.
(In fact for operation at only a few hundred volts, we depend on that behavior to solve the problem.)
The phenomenon was terminated by the test conductor by tripping off an interrupter at the source of the line (several miles away). Otherwise, both the test switch and the surrounding infrastructure would have probably been completely destroyed. One observer estimated the total path length of the arc just before extinction at over 100 feet.
[continued in part 2]
The shots were taken at the White Rock electric substation in East Dallas. Carla and I had gone there to photograph a colony of Monk Parakeets that had built an elaborate community among the ironwork at the substation. I'll post those shots a little later (although we do get to see the little critters here).
While I was there, I was interested in some apparatus that was standing on the ground, evidently ready to be installed. I took some shots of nameplates and such, and after a bit of research came to understand the story. I'll summarize it for you here as I show the pictures.
***********
The disconnects used to isolate paths in high-voltage transmission lines essentially use a "knife switch" concept. They cannot be opened (shut of) while the line is energized. In such a situation, when they begin to open, an arc jumps the initial gap between the blade and the jaw. This arc creates a plasma path (conductive superheated air), which will gladly extend the entire distance of the gap to which the switch eventually opens, keeping the current flowing and generating enormous heat that can well destroy the switch and its supporting infrastructure.
Here we see two installations of these at the White Rock substation. The ones on the right are the traditional kind. Those on the left have a special attachment I will be describing shortly (the set to the right would have the same thing shortly, which is why there were pieces of apparatus on the ground). These power lines operate at a nominal voltage of 138 kV (phase to phase; the lines are three-phase).
Here we see one disconnect (the older type) close-up. We also see an outpost of the Monk Parakeet colony, evidently undergoing some reconstruction. The second insulating bushing from the right is turned to operate a mechanism at its top that lifts the blade to open the circuit.
The matter of a plasma arc if such a disconnect switch were to be opened with the line energized is amply illustrated by this video.
http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=1587733
This test was conducted on a disconnect on a 500 kV line. One leg was intentionally left "live". As we can see, as the disconnect opened (this kind opens to the side), the plasma arc formed, and continues as the switch reaches its fully open position.
The plasma arc rose into the air as a result of the hot plasma being lighter than air. This might have eventually actually extinguished the arc, but not before severe damage would have ensued.
(In fact for operation at only a few hundred volts, we depend on that behavior to solve the problem.)
The phenomenon was terminated by the test conductor by tripping off an interrupter at the source of the line (several miles away). Otherwise, both the test switch and the surrounding infrastructure would have probably been completely destroyed. One observer estimated the total path length of the arc just before extinction at over 100 feet.
[continued in part 2]
