Shape of Busbar Based on Current Rating

To make it difficult for you to copy.

Look up skin effect.

They're hollow so the can transport water at the same time as electricity?

for cooling?

Not as silly as it sounds.I have seen high frequency,high current carried by copper tubing that was internally cooled by water.50KHZ @300 amps for a cap-sealer application for instance.The same water was also used to cool the driver SCR's heat sinks.

Nobody understands me. Whine, whine................

I've had many hours of wet fun with water cooled cables. I'm sorry you can't make out the power cables too well in the picture. They're on the other side of all the cooling water hoses. They were rated at 4000A 1200V 50Hz.

Not only were the flexible cables water cooler the inductor coil was made of square section copper pipe so it could be cooled.

Now we expect a treatise on square/rectangular pipe, like your other one on round pipe.

Electrons are negative charges,and as such,repell each other.At low voltages,currents and frequencies,the result is not significant,but as currents and voltages,and frequencies increase,electrons tend to travel more on the surface of the conductor,rather than within the conductor.Therefor a hollow conductor,when properly designd,can carry as much current as a solid one.The so called "skin effect",as mentioned eleswhere on this page.

If the surface area of busbar is large heat radiated will be more & current rating increases. For example for 100mm^2 bus bar you can choose 2x50 or 4x25 or 10x10mm cross sections but 2x50 gives more surface area(104).

Skin effect as explained by others is the criteria for keeping it hollow - whether circular or sqaure cross section. As reegards the shape it may be because of fastening requirements. if there is no condition laid down for shape, Circular ( Tubular) conductor is most economical.
For out door use all hollow conductors are tubular.
Your classification is not clear of the duct. Am I to understand regarding duct for each phase and a combined duct???

Please visit the website of Copper Development Association (CDA) and download a publication called Copper for Busbars. You will get your answers.

Skin effect has been covered in other posts. If the middle of the conductor is not carrying any current, why go to the expense of having a middle. The other reason is for ease of mounting. Each segregated phase bar normally sit on top of a post insulator. Two channels mounted toe to toe or two angles mounted to form a diamond allow for a simple fixing with a single bolt and a pair of shaped brackets. The vertical slot created between the channels/angles helps with cooling. In isolated phase the currents tend to be much higher, so short circuits forces are greater and typically the fixing is three post insulators are mounted at 120º to restrain the additional force. Making the bar circular means that all three post insulators and bracket sets are identical reducing on price and stock holding.

Dear geeharamakrishna,

The current flows only in the outer pheriphery of a conductor and less at the centre for low frequency, and for higher frequency, above 20,000 cps current flow at the centre is zero. That is why bus bars are put in multiple rectangular size. For higher current value the circular shape of bus bar will have large diameter.

DHAYANANDHAN.S