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Phoenix-7
10-05-2009, 06:16 PM
Trouble call, arrestor ground blown off arrestor bracket, no other indication for a fault, found other two arrestors starting to track to 2/0 pole ground.
What causes this type of fault?

T-Man
10-06-2009, 07:20 AM
without being there it's hard to say what caused the high voltage, recent electrical storm?, maybe the 35Kv passes under a higher tramsmission voltasge on a right of way where they can get together?

The way arrestors were explained to me is, it's like having a sea wall and the ocean swells come crashing into the wall. The water shoots up the wall and sometimes over.
Now the end of the cable (the dead end ) is the wall and the voltage is the water. . .when higher voltage gets into the system it's like an ocean swell and it speeds to the end of the cable. When it hits the end it spikes up causing damage to whatever it gets into. Jumps across switches, blows holes in terminators, messes up padmounted equipment etc.

The arrestor is like drilling holes in the sea wall. As the voltage spikes it has a place to go thru the holes or to ground as it were. This drains off the damaging effects of the high voltage.

Now a days utilities are putting Lightening arrestors at all the open points OH and URD to defer the damage high voltage can cause.

So if the ground was blown off on the 35kv arrestor it's a good bet whatever caused the problem has done in the arrestor and the next high voltage event will spike and cause more damage to equipment that was protected by the arrestor the last time.

Pootnaigle
10-06-2009, 06:49 PM
If this arrestor was located on a normally open point between 2 feeds Its my understanding that the voltage can actually double. Its not uncommon to find a blown arrestor at open switches around here.

Fiberglass Cowboy
10-06-2009, 08:20 PM
Last time I changed out these style of arrestors, I wondered why. I think they (management) - tried to blame a critter and also an old faulty unitary porcelain bell right outside the sub, on the urd-oh feeder pole. The crew I was with did see the old faulty unitary porcelain bell, but no critter. :( This is one of those poles that has a double riser feed (like 1000 mcm double cable riser feeder - [or backbone as u might know it ] - underground) from the sub-switchgear right out & under the sub to feed the beginning of the overhead circuit. My company is/was famous for this. With the UNDERSTANDING of DIFFERENT CLASSES of ARRESTORS, like you speak of, these were station class arrestors....I think. ( Or maybe intermediate class). There are sub-station (station) class arrestors, intermediate class arrestors, and distribution class (separated by O.H. and riser style) class arrestors. Originally them dudes were ampacted solid, right to the line, by the sub-station construction linemen; long before the feeder was energized. I wound up shooting on stirrups, (bail clamps) and running jumpers with hotline clamps on them; then pickin' them dudes up at the far end of an 8' shotgun (graball) stick. Picking up new station class or intermediate class arrestors with load on the line made me a little nervous, as I haven't had much training on the installation of different classes of arrestors, besides distribution class arrestors. And like Edge said, always picking them up at the end of a hotstick, the same as how I was taught. Most of them are probably made in Mexico or some other country where employees are not happy, making $6 or $7 a day total; or here in the states by guys that get drunk before work and stoned on their lunch break. You never know. So we don't trust them (arrestors) one bit. So's anyway's .... good luck 'n' "stuff" down naren' Phoenix. :cool: Later there gator,...... :D :cool:

Edge
10-06-2009, 09:03 PM
Trouble call, arrestor ground blown off arrestor bracket, no other indication for a fault, found other two arrestors starting to track to 2/0 pole ground.
What causes this type of fault?

If the other 2 were tracking... I'd say old age... the elements can factor in and tear them up... they glass or poxy's? poxys seem to weather worse... the old glass ones last a bit longer and usually clear themselves... (like a fuggin granade...)

Fiber... good idea to stick them bad boys in... regardless of grade the arresters can be bad and go boom... why guys still put them on by hand is beyond me... and if the blow out charge dont work and the bitch locks out the string buss then your station tranny in gonna go down vvia the curciut switcher...curciut breaker...or high side fuses... not to mention your on the string buss in the staion max amps for the feeder all faulting in your face...if the damned thing don't clear it's self... I don't trust them... never will...

for what it's worth...

Edge

MI-Lineman
10-06-2009, 09:18 PM
Old glass arrestors tend to break down or weaken. We've hadem give up the ghost over time after repeated strikes or over voltage situations. Usually they breakdown just enough to trip line but you can't see any visual damage unless you're up close! We have a policy NOT to tap by hand anymore. Edge called it "GRENADES"! Get the other two outa there!:eek:

Phoenix-7
10-06-2009, 10:20 PM
If the other 2 were tracking... I'd say old age... the elements can factor in and tear them up... they glass or poxy's? poxys seem to weather worse... the old glass ones last a bit longer and usually clear themselves... (like a fuggin granade...)

Fiber... good idea to stick them bad boys in... regardless of grade the arresters can be bad and go boom... why guys still put them on by hand is beyond me... and if the blow out charge dont work and the bitch locks out the string buss then your station tranny in gonna go down vvia the curciut switcher...curciut breaker...or high side fuses... not to mention your on the string buss in the staion max amps for the feeder all faulting in your face...if the damned thing don't clear it's self... I don't trust them... never will...

for what it's worth...

EdgeThese arrestors are polymer approximately ten years out in field, so I replaced them for like for like,when I re-energized the riser feeding a recloser I had all my PPE on, covered my head, used two lengths of stick. Everything held, must be age, contamination, UV rays breaking down the insulation on the arrestors.

Trojan
05-21-2011, 01:25 PM
Trouble call, arrestor ground blown off arrestor bracket, no other indication for a fault, found other two arrestors starting to track to 2/0 pole ground.

Armchair troubleshhooting: Over voltage might have caused ground to blow off arrestor. Tracking can be caused by contamination (dirt) or an overvoltage that did not completely blow MOV arrestor.

Those MOV's can take a number of spikes of higher than rating before they blow. So you never know what condition they are in. We don't liven them with rubber gloves, either use a hotstick or close some switches. hey can explode violently. Grenade is a good name.

rob8210
05-23-2011, 07:09 AM
We quit energizing arrestors by hand 20 years ago. It wasn't very hard to convince me. I changed out 21kv distribution class glass type where pretty much all that was left was the mounting bracket, they certainly grenaded. I was on insulator washing once and saw a polymer flash over then clear, then line never even reclosed. I have heard of cases where a polymer type will go bad, take the line out but will not blow clear. Makes it real hard for a trouble crew to find the fault and clear it. Always use a gripall to energize la's

tramp67
06-16-2011, 09:50 PM
Can anyone on here working on National Grid property explain why the utility insists on bolted connections on the high side of their arrestors, thus requiring linemen to put them on line by hand, which is in direct violation of many other utility/contractor safety rules? I asked a Grid engineer and safety inspector about this once, they said they would look into it. Never saw either of them again. Does Grid greed decide a lineman's life isn't worth the expense of a hotline clamp?

Divemaster
06-16-2011, 11:27 PM
At our one sub that feeds a large meat packing plant, both 20 MVA transformers were ordered with poly bushings and arresters because they were suppose to be trouble free in the contaminated environment. Two years after firing the sub up, boom, had an arrester blow on the transformer. After inspecting the other arresters and bushings were showing signs of tracking. Replaced them all with porcelain and haven't had a problem since and they don't show any tracking after over four years.

tramp67
06-17-2011, 02:58 PM
It will be interesting to see how these new 345KV lines hold up with the code 2 steel Myers poles and polymer insulators. I would imagine it won't take too many years for the rust to coat the polymer skirts and start tracking, as they don't have the ridges that the undersides of the porcelain suspension insulators have. Could be a lot of reinsulating jobs coming up in the near future! Thank you, MR ENGINEER!!!:D

lewy
06-17-2011, 09:40 PM
We stopped changing arrestors live over 10 years ago, but when we did we always used a stick. The thought of doing it by hand is just asking for trouble, even changing them live, why? It is just an arrestor, make arrangements to kill the cct if they feel it has to be done.

tramp67
06-18-2011, 08:26 PM
I think National Greed would have issues with dumping several thousand customers to change an arrestor on a circuit. Why they insist on the bolted connections is beyond me. Obviously their engineers have never witnessed first hand an arrestor failing.

lewy
06-18-2011, 10:28 PM
If they only have 1 way of feeding all of there circuits they have bigger problems than bad arrestors. Again if they want these arrestors changed they should be able to isolate for mtce.

rob8210
06-19-2011, 06:49 AM
The trouble is the way the world is going, isolating a line is getting harder and harder to do. Companies are getting into penny pinching and outages during normal working hours are getting harder to organize. I experience it first hand everyday. Commercial and industrial customers do not want power outages. Even residential is getting a lot harder with many people working from home on their computer. We have to learn to adapt. Many jobs can be done alive safely if you spend the time to plan and take the time to do the job safely, sure it takes a lot longer but that is what many utilities and customers are demanding. Jobs like changing lightening arrestors can be done alive using the right tools and proper live line techniques. If need be arrestors can be cut clear using live line cutters and then installed using a hot line clamp. The biggest problem is safely getting a hand on the arrestor itself to change it out. I cannot see the point in using bolted connectors, live line clamps are bolted too!!

lewy
06-19-2011, 07:05 AM
This started out about station arrestors, so I would think if you can do mtce on the breaker you could also change the arrestor. As far as changing arrestors live I still do not get it, you are maybe a foot away from ground you are likely very close to a fused switch , we are talking about arrestors, there are plenty on most lines.

19jarhead91
06-23-2011, 11:33 AM
How bout putting a temporary jumper w/ hot line clamps on your riser, then after putting it on line, you could make your bolted connection. Then take your temp jumper off.

reppy007
10-26-2011, 12:22 AM
How bout putting a temporary jumper w/ hot line clamps on your riser, then after putting it on line, you could make your bolted connection. Then take your temp jumper off.

Really thought you guys had good answers,all i will say is you dont want to be around a 345kv or a 138 kv arrester in a substation.I was on a fire call a few years back,there was no fire when i drove up,But as i walked inside the sub,there was only like millions of pieces of porcelin on the ground.If anyone is near one of thase babies when they go south ,i dont think they will have a chance.AS far as working them hot,there has to be a safer way to pick one up through a switch.