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staggerlee
12-06-2006, 10:27 AM
I was wondering if anyone has any thoughts on how to deal with these. We have the "Booty" to cover suspect arrestors that is installed by stick but there can still be a lot of danger if it suddenly falls apart. We also go up in the bucket and visually inspect the arrestor for cracks tracking etc before attempting anything. Seems a bit drastic to go to an open point to change out an arrestor on a Tx simply because Thermal shows some heat tracking. How is everyone else dealing with this. thanks

topgroove
12-06-2006, 12:27 PM
have you thought about cutting the hot arrestor lead with a pair of hotstick bolt cutters? Or if it is the gap type arrestor slipping a rubber blanket between the arrestor and TX bushing?

loodvig
12-06-2006, 03:02 PM
have you thought about cutting the hot arrestor lead with a pair of hotstick bolt cutters? Or if it is the gap type arrestor slipping a rubber blanket between the arrestor and TX bushing?

Frig that! Kill it! If it showed up hot and tracking kill it!

topgroove
12-06-2006, 05:36 PM
Sometimes to kill it you have to open a large part of the feeder. I can't see taking out a couple thousand customers just to change out an arrestor. If I can hotstick 115KV I'm sure I can cut an arrestor lead with a pair of hotstick bolt cutters. How many times have you put a jumper across a burning 600 amp disconect switch or lifted a hotline clamp on a burning transformer?

OLE' SORE KNEES
12-06-2006, 07:59 PM
If you can find them, I saved a pair before they cleaned the old tools up that we "did"nt need anymore", crabs, hot-sticks,lever-lifts.....you know the stuff we used to do line-work with....anyway that is the next best method to killing it,I 'm glad I have a pair from time to time with safety rules we're not supposed to cut any arrestor gloving at FPL...........:)..these put you at a reasonable distance away.
Here's a link to one brand
http://www.hfgp.com/images/catalog/E-7-1h.jpg

old lineman
12-06-2006, 08:29 PM
I would never profess to be an expert about all of the causes of failures but do you really appreciate the forces your dealing with?
Heres a couple of instances that may make you hesitate.
1. When I was just new in the industry we went to a substation outage and found that a primary bushing had exploded on one of the station transformers. The flying porcelian flew in all 360 degrees. It took out other equipment and most astonishing is that a piece perforated the explosion chamber pipe. That pipe was about 1/4 inch thick steel.
2. Many years later I saw the damage a distribution arrestor did when it exploded. Two cars parked beneath it had holes in their tin roofs.
3. A crew had to open an air break the lift taps to work on the system. All was fine until they tried to re-install the taps to pick up a couple of spans of conductor. One intermediate lightning arrestor exploded.
We concluded that the arrestor was defective and likely was heating up. Once the power was off the cooling down drew in moisture which caused the failure.
These things can be bombs and I don't believe a person even at the end of a live line tool would be totally protected from a porcelian explosion.
As for the best way to go about, I'll leave that alone but don't take this lightly.
The Old Lineman

Orgnizdlbr
12-06-2006, 08:42 PM
I would never profess to be an expert about all of the causes of failures but do you really appreciate the forces your dealing with?
Heres a couple of instances that may make you hesitate.
1. When I was just new in the industry we went to a substation outage and found that a primary bushing had exploded on one of the station transformers. The flying porcelian flew in all 360 degrees. It took out other equipment and most astonishing is that a piece perforated the explosion chamber pipe. That pipe was about 1/4 inch thick steel.
2. Many years later I saw the damage a distribution arrestor did when it exploded. Two cars parked beneath it had holes in their tin roofs.
3. A crew had to open an air break the lift taps to work on the system. All was fine until they tried to re-install the taps to pick up a couple of spans of conductor. One intermediate lightning arrestor exploded.
We concluded that the arrestor was defective and likely was heating up. Once the power was off the cooling down drew in moisture which caused the failure.
These things can be bombs and I don't believe a person even at the end of a live line tool would be totally protected from a porcelian explosion.
As for the best way to go about, I'll leave that alone but don't take this lightly.
The Old Lineman

Amen brother, I have seen porcelain pieces across 4 lanes of hIghway and break a few windshields in a parking lot across the street from a pole where a distribution arrestor failed. I'm killing it! I will limit the impact to as little customers as possible, too old a dog and too long in linework to eat a load of hot porcelain now!

OLE' SORE KNEES
12-06-2006, 09:13 PM
Amen brother, I have seen porcelain pieces across 4 lanes of hIghway and break a few windshields in a parking lot across the street from a pole where a distribution arrestor failed. I'm killing it! I will limit the impact to as little customers as possible, too old a dog and too long in linework to eat a load of hot porcelain now!


I agree , That's why I said the next best thing to was the hotline cutters, the best being a dead line.I tell you what ....poly arrestors are just as crazy when they blow,also saw primary voltage on many blown arrestors on the ground side(bottom) before , almost as bad as a cap. bank but that is still number 1 on my list for a bomb !!

loodvig
12-07-2006, 10:23 AM
I keep forgetting that not everyone fuses every transformer. We do that's why I said kill it. Then I would use the hotline cutters to clear it.

BigClive
12-07-2006, 10:34 AM
What about open lightning arrestors like the old Jacob's Ladder style? Are they still used?

(Metal vee mounted on insulators. Overvoltage arcs across at the base and the arc is then extinguished by rising up the wires, making it wider until it breaks.)

CenterPointEX
01-18-2007, 09:25 PM
Suprisingly not a lot of Lineman know how a lightning arrestor works. The top side of the arrestor is hooked to the energized line and the bottem is hooked to a ground. The arrestor is a tube either made of porcelian or polymer. Inside the tube are donut shaped pieces of semi conducter stacked between conductive washers. When the voltage rises above a certain level it conducts through the semi conducters and flows to ground. Then when the voltage drops down again the flow is shut off. In this way a lightning strike is bled off to ground and the system is uninterupted. An arrestor fails when the flow does not shut off and the primary voltage keeps going to ground until the arrestor blows. It the arrestor gets dirt and or moisture inside of it this causes it to conduct primary voltage to ground and fail. It does not necessarly need to be lightning. A charged cloud passing over a line will induce over voltage on a line to the level that would operate a lightning arrestor. I have seen multiple arrestors blow at the same time under these conditions.

BigClive
01-19-2007, 06:03 AM
If the arrestors are made of layers of MOV (Metal Oxide Varistor) then they only have a capacity to shunt a certain amount of energy before they start getting a bit too conductive for their own good. In this case Ferro resonance or "ringing" on a line could nibble away at their lifespan with a continuous series of small high voltage spikes, and cause early failure. If they are indeed MOV's then the usual failure mode is heat then complete failure.

Is this how they are composed?

Ever seen the little mains surge arrestor adaptors for plugging your computer into? They have some MOV's inside to clamp any spikes between feed and return. There's also a little light that either comes on or goes off to show that the unit has failed. The failure detection is just a thermal fuse mounted next to the MOV that trips permanently if the MOV starts to fail and gets hot.

If the lightning arrestors work this way then a small flag held in by meltable wax might be a good failure indicator.

graybeard
01-20-2007, 09:32 AM
Clive
At work they now stock a hot line type clamp that scews to the top of the arrestor. I don't know how you hook yours up but we go from the line to the arrestor to the cutout. So with this clamp you can open it with a shotgun and lift the jumper out with the shotgun also. It at least it gives you alittle room to work and leave it hot. My first choice would be to KILL it; but I know that thats not allways possible. Let me know if you want any info on the clamp.

byjuvc
01-20-2007, 11:04 AM
Suprisingly not a lot of Lineman know how a lightning arrestor works. The top side of the arrestor is hooked to the energized line and the bottem is hooked to a ground. The arrestor is a tube either made of porcelian or polymer. Inside the tube are donut shaped pieces of semi conducter stacked between conductive washers. When the voltage rises above a certain level it conducts through the semi conducters and flows to ground. Then when the voltage drops down again the flow is shut off. In this way a lightning strike is bled off to ground and the system is uninterupted. An arrestor fails when the flow does not shut off and the primary voltage keeps going to ground until the arrestor blows. It the arrestor gets dirt and or moisture inside of it this causes it to conduct primary voltage to ground and fail. It does not necessarly need to be lightning. A charged cloud passing over a line will induce over voltage on a line to the level that would operate a lightning arrestor. I have seen multiple arrestors blow at the same time under these conditions.

In our Utility we had many incidents of Porcelain Arrestors blasting . So recently we have replaced all these with Polymeric Arrestors of make TYCO . It has been 3 months till now not even a single LA has failed. Is it possible that Polymeric LA also explodes or if it doesn't explode then what is the mode of failure ..may be melting ....has any body experience with these kinds of arrestors...for it will be helpful for us to look for those symptoms whenever they fail..thanks.

CenterPointEX
01-20-2007, 11:19 AM
The bottem blows off and remains hanging from the ground.

Usually the catostrophic failures are from intense lightning strikes that raise the temp of the porcelean to the boiling or exploding point. The more typical failure just blows the bottem off and the guts fall out.