Connecting to tubular copper bus 2

[HighPotter]

We have some 3000amp rated, tubular copper bus work. Any suggestion on a good way to cut out a ssection, then put it back in? A splice you might say, between tubular, 3"square x 1/4" thick copper bus.

Can copper bus be "welded" ? If so, what would be the best way? Or should "splice plates" be bolted or welded on all sides, equal to the amp rating?

Or should a piece, manufactured to be just slightly larger then the outside diameter of the bus be fabricated, and then bolted or welded together?

I'd like to hear peoples suggestions.
Let me know if you need anymore info.

HP

 

[Warpspeed]

Copper is usually silver soldered, any plumber can do it for you.

As for the other details, anything that provides sufficient cross sectional area of copper should work.

 

[bigbillnky]

Evening HighPotter,

My suggestion would be to contact the OEM, if that is possible. Out of curiosity, why is this "splice" necessary? If it is do to a failure, I would recommend replacing the entire damaged section instead of attempting a repair.

You did not mention the applied voltage of the bus. I would be even more cautious of a field repair of the type you mention if the equipment is rated for medium or high voltage. While it is true 3000 amps is 3000 amps, bus failures in medium and high voltage equipment are far more devastating and costly than low voltage equipment.

As far as the mechanics go, I personally would be more comfortable with bolted connections if I had to make such a call.

Bigbillnky,C.E.F.....(Chief Electrical Flunky)

 

[waross]

Hello HighPotter;
You probably know that tubular copper and aluminum bus is often manufactured to Iron Pipe Sizes. Hence the designation, "IPS bus"
If you must weld, check with your favorite refrigeration man. Refrigeration mechanics use a special type of silver solder that will weld copper without flux. It's stronger than copper and has a good wetting action. It is quite easy to use. You're probably going to need a large torch to get 3" IPS bus hot enough, but it's do-able.
If you decide to go with a mechanical joint, the web sites below may be able to supply ready-made, bolt together hardware.

https://portal.fciconnect.com/res/en/pdffiles/doc_search/electrical/ns.pdf

https://portal.fciconnect.com/porta...cur_label=NS&productID=NS2020&P=126448&FAM=NS

http://www.dossert.com/products/eproducts.htm

http://www.alcoa.com/global/en/products/product.asp?prod_id=837

http://www.hubbellpowersystems.com/powertest/literature_library/pdfs4lib/Anderson/AEC-39.pdf

https://portal.fciconnect.com/porta...cur_label=NS&productID=NS2020&P=126448&FAM=NS

respectfully

 

[HighPotter]

thanks everyone.

Wow, Waross, those links are great. I'll check them all out.


I can't see how just soldering this bus would be sufficient. But since you say the solder is actually stronger then the copper, I guess Im wrong. I am partial to a bolt together system, if rated properly.

Replacing the entire run is out of the question, it's a 300' run X 3, 30 off the ground in an enclosed busway

The piece might need to be taken out, to change the way it is fed.

The voltage is 7kv. Bus must be rated to 3000 amps


HP

 

[HighPotter]

And it is square, hollow, copper tubular bus.

 

[cuky2000]

There are several methods to joint a high conductivity copper busbar. The most popular are: welding, bolting, clamping or riveting.

Even though the welding joint is perhaps the most expensive process, this method provide the best results with minimum joint losses, virtually no maintenance and the most important, do not impair the current carrying capacity of the busbar, particularly for high current above 3000 A.

The preferred methods to weld copper busbars is using inert gas process with shielded arc, tungsten or metal inert gas.
<sub>COMMENT: Regardless the jointing method selected, the busbar system should have minimum electrical resistance and capable to withstand the maximum mechanical stresses produced by short circuit, wind, snow, seismic and any other load combination.
- Provision for thermal contraction and expansion should be considered in the design to avoid transmission of excessive forces over insulators and other fragile components.</sub>

 

[waross]

Hi HighPotter;
I understand that the joint used in refrigeration is brazing rather than soldering. I am under the impression that it actually alloys with the copper, and results in an alloy that is stronger than the copper. The name was Silfos or Silflos. It was similar to silver solder but would join copper without the need for flux.
I haven't used it for many years and the formulation may have changed.
The formulation that I used years ago took a higher temperature to melt than it did to form the original joint. The product is probably new and improved now.
I misunderstood you and thought you were trying to connect Rround tubular to 1/4' flat plates. My mistake.
I am with you on the bolt together system. My first choice would be a manufactured, approved connector, IF one is available. Will clearances be a problem or do you have lots of space?
respectfully

 

[Warpspeed]

Yes you are right. it is called silver brazing, or silver soldering, depending on which part of the world you live. The melting point varies with the silver content of the filler rod, several different percentages are available. Higher silver content has a lower melting point, and runs more freely, is recommended for this application.

It is used exclusively or joining copper pipe in the refrigeration and airconditioning industry, as well as most general plumbing work. It's main advantage is that the filler rod wicks readily into an overlapping joint, completely filling any voids. It makes a 100% leak proof joint, and is excellent for busbars too, because there will be no invisible voids within the joint.

As you say, it alloys with the copper and makes a corrosion proof joint stronger than the original copper. The silver has very good electrical conductivity, and it also has a suitably high melting point ideal for hot running components.

It is extremely easy to use, no flux being required. Just heat up the cleaned copper parts and apply the filler rod. It runs right into the joint.

 

[ScottyUK]

Yes, copper can be welded, but it is a higly specialised procress and probably not suited to on site work. TIG or electron beam welding are the two processes I am aware of - there are probably others.

Something you must consider when choosing a repair method is not the thremal rating, but the fault rating of the bar. The mechanical stresses which exist during a major fault are staggeringly large, and will show up any weakness in a joint. Failure of a joint during a major fault will almost certainly turn a recoverable problem into something altogether more serious.

waross' suggestion that a silver brazed joint can be stronger than the parent metal is not inaccurate, but requires tight control of tolerances between components to avoid the gap being filled by weak braze alloy.

Waross: is the 'IPS' you refer to possibly 'IPB', an abbreviation for Isolated Phase Bus? IPB is typically used for very heavy current applications where it is desirable to limit external magnetic field intensity while providing great mechanical strength and virtually guaranteeing that an interphase fault can not occur. The interconnect from a large generator to its associated GSU transformer is a very typical application. IPB essentially comprises of a conductive tubular outer shield mounted co-axially with a central conductor. The shield is grounded and is electrically contiguous throughout its length.

----------------------------------

I don't suffer from insanity. I enjoy it...

 

[waross]

Hi ScottyUK;
The brazing alloy we are discussing is very user friendly. It has very good wetting action, and very good wicking action. It is silver based and very strong and a good conductor. It does require a high temperature. You need Mapp gas, Air-acetylene or Oxy-acetylene. A propane flame is not hot enough.
A query in the refrigeration forum will probably be productive.
Re; IBP/IPS. If the busbar in question is square, it is not IPS. IPS is aluminum or copper bus manufactured to the same dimensions as listed in the National Pipe Standards for Iron Pipe. It is quite common in North America.
Thanks for the information regarding IPB. Is this a general description for high strength, wide spaced, busbars or are there standards listing the conditions to be met?
respectfully.

 

[bacon4life]

ScottyUK, how does IPB reduce magnetic fields? Aren't the conductors actually farther apart than standard buswork?

I can definitely see why preventing interphase faults on a large resistance/reactance grounded generator would be important.

 

[ScottyUK]

The outer shield of an IPB design carries an antiphase image current which is of very nearly equal magnitude to the busbar current, causing almost perfect cancellation of the external magnetic field. If you look closely at an IPB installation you will notice massive bonding bars connecting the ends of the three single phase IPBs. The ducts themselves will sit on insulated pads through their entire length and are mechanically and electrically decoupled from the rest of the plant by an airgap closed by a flexible rubber bellows to keep out moisture and contamination. The bonding bars carry image current as well as providng mechanical support, and are key to operation of the IPB. Equally important is the avoidance of any unintentional current-carrying path between shields other than through the bonding bars, hence the insulated pads and airgap. When IPB is installed correctly the image current cancellation is very good on long linear runs, but less perfect on discontinuities such as bends and tee's. The ends of IPB ducts beyond the bonding bars - e.g. at transformer or generator bushings - don't benefit from image current cancellation and can have very high local field strengths.

----------------------------------

I don't suffer from insanity. I enjoy it...

 

[subtech]

Hello Highpotter

I would be very careful about soldering or using any process which would involve heat to re-insert the piece of bus that you intend to cut out. My concern would be this.
Copper tubing, angle or even wire is "drawn" or heat treated so to speak when it is manufactured. This "heat treatment" or drawing process is what gives copper or any copper alloy its physical strength. Depending on the amount of heat applied to your bus tube during a soldering or welding process, you could very well anneal, or soften the copper and remove a great deal of its strength. Depending on where in the "span" your splice or tap was placed, you may build in a point of mechanical failure which may become evident during a most inopportune time. For this reason, I would strongly consider using a mechanical connection. There is a sytem available which I have seen used on tubular aluminum bus in substations that linemen refer to as "Deutsch" fittings or connections. I believe this system is equally applicable to copper bus. A google search for Deutsch connections will give you results that you may find very interesting.
Regards

 

[dpmac]

This sounds like a basic repair. You will probably find the size of the bus a bit tough to "solder" without special material or expertise. A mechanical repair seems pretty straight forward IMHO. Cut the section out, make up the appropriate "spiders" or devices that contain captive nuts (probably four per flat side on each end). Insert and attach inside each bus end. Attach the appropriate pre-punched silver plated copper plates. Probably .250" thick per side, .312 if concerned. Add a couple of spacers/standoffs inside the repair if splice length warrants the extra support for interrupting capability. Watch the finished spacing between phases and ground when complete. You may require additional insulation. Raychem or 3M shrink sleeving would work well.