Sandwich Busduct

I would assume they are trying to save money by using less material. The lower reactance gained by using the sandwich construction may allow some engineers to pass this as acceptable (using less material).

Obviously this is not acceptable.

I second your opinion. Somehow, I too cannot accept this unusual 'shrinking' of the cooling space around the busbars. Let me try to talk to my peers and try to get an answer.

Both sandwich and air insulated answer to the same IEC standards, including in terms of temperature rise.

The design is done by succession of calculations, modelling, and actual certification tests.

Air insulation has its advantages , but is very sensitive to pollution, long term corrosion and deterioration of contacts, or foreign bodies intrusion in the air vents.

Sandwich needs more attention to the quality of the insulation material (usually mylar sheets, or epoxy coating) .

When it comes to Aluminium busways, a big difference can be found on the contact design. Some use nickel-tin coated plating, which will never be completely freeting corrosion free. Others use welded co extruded silver plated copper-aluminium bi-metal on joints to ensure a silver to silver contact, which allows higher temperatures and still guarantees excellent durability of the contact.

As worldwide levels of quality mastery raise, air insulation is slowly but surely disappearing from the market. High quality sandwich can be found produced locally in India, China , Europe and North America .

Try a query with these guys. Right around the corner from you. Good luck!

The sandwich bus ducts are provided with large heat sinks in the form of channel pieces at the edges or fins on the body. The heat transfer from busbars is better due to conduction through solids instead of convection through air in case of air insulated busbars. The failures could be mainly due to improper installation practices e.g not allowing for expansion of busbars thereby straining the insulation, blocking heat transfer from busbars to surroundings etc. A regular thermal imaging routine can prevent many failures.

Good morning every one,

Though the guiding factor for bus bar sizing is the temperature rise limit as per IEC, i believe the failures of such sanwhiched busducts in Indian envirinment is more owing to the following reasons.

1) The sizing of dwonstream equipment and the protection are not properlu made to restrict the short circuit levels. Secondly the No. of scu deadshorts in the downstream equipment are more since we do not take much care about safe and good enginering practices when doing cabling / wiring. Though the busbars made be designed for withstanding say 50 KA for 1 sec, practically the bus insulation weakens under frequent / repeated SC. This culminates in localised hot spot generation followed by puncture and failure of insulation.

2) The sandwhich busducts require specail care while erecting. These are to be treated as new bord babies while handling and erecting. The joints are especally the weakest link. Any form of physical impurity in the overalps can result in internal arc generation, what ever may be the tightness of the bolts.

3) These sanwhich bus bars work relatively well in air-conditioned enviorns like that in IT sector but are not suitable for hot, dustyand humid environs.

Hope my theroy is correct.

Ramesh.A

Most failures in chennai are due to overheating. Consequential insulation failure and Flash over. Overheating is primary due to undersized busbars. Why Airconditioned atmosphere is required when air insulated busduct can work with out any problem and air insulated busducts are much cheaper than sand wich busduct