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 Post subject: Safely Opening Corroded Air Disconnect Switches
PostPosted: Tue Jan 09, 2018 12:38 pm 

Joined: Tue Jan 09, 2018 12:26 pm
Posts: 1
Hi All!

Just looking for any advice on the best methods to safely free a corroded air disconnect switch.. I am dealing with both single and gang operated switches. I obviously don't want to stick a metal can up there and cause an arc flash.

Any advice would be greatly appreciated!

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 Post subject: Re: Safely Opening Corroded Air Disconnect Switches
PostPosted: Sat Jan 13, 2018 8:44 am 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2178
Location: North Carolina
I have a lot of experience with these things.

First I'm going to answer your question directly. Look at a "typical" lineman. Line work is not for scrawny guys like me. Approach the disconnect switch accordingly. Whether it's hot stick operated or pipe operated there is nothing that my scrawny 180 lb. body can do by itself to damage it because I've tried. I've slammed into the handles and had them torqued almost 45 degrees and they snapped right back with no damage. Think like a lineman when you try to open it. The worst that you will do is more damage on something you will probably have to replace anyways...It's not as bad as it on and you'll understand why destroying it is not necessarily a bad thing.

Don't forget that no matter what you are electrically isolated from the business end of things. As far as arc flash goes, look at the label. Does it say any distance between 18 and 36 inches for a working distance? That is a clear indication that someone was not doing their homework. The actual incident energy is going to be MUCH less. It is cut in half with each doubling of the distance. I have almost never seen overhead switches with an incident energy over 1 cal/cm2 when the calculation is done with the proper working distance whether it is operated from an 8 foot hook stick or with a pipe operator that is at least 12 feet long.

Second step is to recognize that these things are extremely reliable when they are working but after about 10 years or so with NO use they will be corroded beyond use and even with routine operation 20 years is about the limit, and that they weigh a few hundred pounds so you aren't going to simply service one with a couple guys on ladders. That means you will in all likelihood be hiring yourself a line crew. Expect rates of around $500 per hour, more or less. You will be paying for at least 2 line trucks (one will have a jib crane, one will be a bucket truck), and at least a 2 man crew but usually more likely a 4 or 6 man crew. The prices are crazy high. My advice is don't argue with them....get a couple prices from the major names in your area and call it a day. They have a lot of insurance, windshield time, downtime, and very expensive tools and trucks to pay for so they charge accordingly. You're getting a mix of linemen, specialist technicians, riggers, and crane operators all rolled into one. If you don't know anyone call your local utility and try to talk to someone in the maintenance department. They can give you names and numbers of local contract crews that they use.

A good crew can probably have the old switch out and a new one installed in a half a day. "Two men and a line truck" will take probably all day and then some, if they can manage to do it right. They're OK for hanging transformers for houses or light poles but not for this. You will save money by gong with a line crew with a good reputation in the reduced time they will be on site.

Unless you are using it excessively and eroded the contact tips away (you said corroded so it doesn't sound like it) or it's actually a non-load break type and someone made the mistake of opening it very slowly where it welded the contact tips together, chances are that the bushings are all shot, too and there might even be some severe corrosion problems in the linkages and on top of that the rust often stains and contaminates all the insulators to the point where they are also shot and you can't get all the rust off them. On a 5 or 15 kV disconnect it is certainly possible to rebuild them and often utilities will do this. But on a 25 or 35 kV disconnect my experience is that you might get a couple more uses out of one if you try to rebuild it but then it will fail again. Just replace the higher voltage ones. But the point of all this is to suggest that realistically the majority of the costs are in the labor. Since the line crew costs are so high, you want to have ALL the possible parts that you will need on hand and then some to attempt a repair. Even one little part will blow any cost savings you might achieve by rebuilding one because the cost of having the line crew out a second time is more than the cost of a brand new switch. So my advice from experience is do not rebuild...replace. Once you replace it, THEN you might want to attempt to repair/rebuild the damaged unit when it can be done with lower cost labor and time is on your side depending on what is wrong with it. This is how utilities do it for the same reasons.

As to disconnecting it, this is best done with a bucket truck. IF there is another nearby disconnect, that's the safest and easiest way. If not (usually not), then remove the jumpers from the switch first to remove power. Then hook up the jib crane to it since they weigh several hundred pounds and remove the bolts so that you can safely lower it to the ground. Now install the replacement that you previously obtained. Or if you insist take everything apart, enough to verify that everything is working without binding up anywhere, that the insulators are all clean (now would be the time to apply silicone gels or Collinite), replace all the contacts, replace any bent or corroded linkages, and apply zinc cold applied spray galvanizing liberally (protect the insulators from contamination though with rags taped/tied on!). Then put it back up. You CAN do this off ladders and bucket trucks in place. I tried that with a very old motor operator South States unit. It lasted for I think 2 more open/close attempts that we needed to stretch it out for until the new one arrived. But we also simply took an old bus bar and drilled it to make it fit as a contact tip and a lot of other make shift things that were just getting by. I would definitely NOT recommend working off ladders and bucket trucks if you can possibly avoid it. It takes much longer to do everything this way since access is so much more difficult and it just increases the already expensive labor cost of the job. If all you can get is "2 men and a bucket truck" local line crew and it's an emergency, that's the best you can do. But if you are going to ever have a hope of doing it right, you need a crane, period.

I work all over the Carolinas and Virginia but I am NOT a lineman and never have been one. I'm too scrawny for that line of work. Mines often have dozens of these things though and almost every industrial plant has one or two at the service entrance (whether or not the utility owns them) so I've been responsible for maintaining them more than I care to think about. I've worked with and without line crews and tried all kinds of things trying to keep from paying big bucks either for the crews and equipment or avoiding the cost of replacement. In the end all my ideas (and those that I was forced to do) all ended up simply wasting time or money or both, over the outright replacement and rebuild later if it can be rebuilt strategy. I can maybe stretch out the life a few cycles to make time to get a replacement without a total rebuild/replacement as I'm recommending. But the prognosis here isn't good. It should tell you something when the catalogs from the manufacturers (Bridges and Chance are the most common) do NOT include spare parts, and you have to go through quite a bit of phone tag attempting to even get a spare part price from anyone other than a switchgear rebuild/recycle shop (and they often stay away too), even on a current model.

The contact tips are just that. On all models you will have a moving contact and a fixed one. Usually they will be made out of solid copper alloy and spring loaded with a lot of pressure so they melt fairly easily but are very corrosion resistant considering what they are exposed to during normal operation. On many there will be an arc quencher mechanism. This looks like a plastic box or horn. There will be a thin tungsten tipped spring loaded arm attached to the main contacts that moves into the plastic "box". During operation the main contacts open first and the springs retard the motion of the secondary contact. Then the secondary contact moves into the plastic box stretching out and finally cooling and quenching the arc. This design is more common on higher voltage (15 kV and higher) and high current switches. It will still work without it but the main contacts are eroded much faster. The main contacts can be replaced with home made parts and will probably work once or twice too but obviously this is makeshift territory and something I can't recommend except in an emergency. Chances are on the first opening the home made tips will melt and weld together. Bushings can be fabricated out of brass, too. If worse comes to worse though the way that the switch is isolated (remove jumpers) also works but not under load.

So...just my experience here. Good luck.

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