Bus Tie Duct Voltage drop

Sounds like to need to balance your load....

http://ecmweb.com/power-quality/saving-energy-through-load-balancing-and-scheduling

Yep. Take ²/₃ of the single phase loads off the yellow phase, split them, and put half each onto the red and onto the blue phases.

Sir we have all load three phase, load already balance.

Good point...I would have thought this would be checked already....but if he hasn't, definitely would be the most likely cause and first thing to check, a loose connection....

Absolutely! Here's a similar photo. These were 3 very nearly equally loaded phases, 2 cables per phase (the bottom 3 of 5 visible cable pairs). Just out of the photo to the right are three 600 Amp fuses. It doesn't take a whole lot of expertise to see that there is a problem with the top phase. I had previously tightened the connections, so it was down to either the fuse or the fuse holder. It turned out to be a defective ageing fuse.

Somewhat confusing the image is the fact that there were Rogowski coils measuring the currents at the time the photo was taken.

It used to be that the IR cameras were several thousand dollars and up. This image was taken with a "FLIR One™" camera attachment on my iPhone. It cost $250, and has paid for itself MANY time over! A similar attachment is available for Android phones, so there is no longer the excuse that "We can't afford one". Anyone who can't afford a $250 camera, shouldn't be anywhere near 5000A busbars!

Flir... A great tool...

Connection checked 2 time within month , there is no any loosing with any joint plate. we have three transformers each 3000KVA, have same size BTD with 45m, 50m, 55meter, each BTD have voltage drop at yellow phase , distance between each phase bus bar 100mm.

If three different transformers all have the same problem, especially with different lengths of busbars, then the cause is not in the busbars or transformers, but in the supply that feeds those transformers.

WE check wit detail when load is 3000Amp , same time we check voltage at 1st end transformer side LV bushing, same time we check at 2nd end of BTD where connected with Main LT Panel, drop is between 1st end to 2nd end, at transformer lv bushing voltage are equal on red, yellow and blue but at 2nd end yellow have 20-25voltage drop.

If this is true on all three transformers, then there must be a design problem.

You say"Bus bar design II II II II II II II 1st two neutral 2nd 4 red 3rd four yellow 4th 4 blue"

Since the yellow bus bars are in between the red and blue ones, It's hard to imagine a magnetic problem, unless perhaps the louvers cut in the ducting were oriented such that a continuous strip of steel follows the yellow, while the louvers make the steel discontinuous near the red and blue bars.

Thermally, heat from both the red and blue bars will contribute to the heat in the yellow bars, while the red and vlue bars only have an additional heat source on one side, so it would be expected for the yellow bars to be a little warmer. Of course warmer bars have a higher resistance, so more voltage drop would be expected.

Again, an infrared camera image would show all this instantly. When (not if - this is imperative) you get some IR images, look not only at the temperatures of the bus bars, but also at the temperatures of the ducting. Hot ducting indicates magnetic losses.

temperature is not issue.

as we energize the BTD within 30s load reach at 3000A within 30s temperature cannot rise , as ampere start increasing from 1000A than voltage drop start at yellow phase.

i think when load increase red and blue busbar flux link with yellow, that is why yellow resistance increase and drop is happen.

its only my observation.

In that case, then you may need to add some crossovers, as is done in transmission lines, to simulate the twisting of standard cables. 45-55 m are long distances for parallel conductors. Whoever installed the busbars should have known about that...

Obviously I know nothing of your plant layout, but I get the impression that each transformer feeds a single large load. The best solution would probably be moving the transformers nearer to the loads, to get rid of most of the busbar lengths.

In fact probably the first question that should have been asked is: Is this a problem that was found when first commissioning a new facility, one that appeared when a new installation was added to an existing plant, or one that appeared in a system that previously had no problem?

If you can not locate a temperature increase within your 30 second window, operate the system for a longer length of time until you can observe a temperature rise. You will ,perform this procedure only to locate the higher impedance connection(s). Disassemble the faulty connections, clean and inspect. We often use a product called Cool-Amp (an electroless silver plating technology)to insure low impedance connections.

Thanks for bringing Cool-Amp to our attention! Do you have any experience using it (and/or Conducto-lube) on old (30-50 years) high current devices? My specific current point of interest is on the blades of 600 Amp fuses and the fuse-holder contacts that mate with them.

I prefer to use silver plating, but it is usually an electrolytic process that must be done in tanks. However the Cool-Amp process is done with a wet cloth and does a respectable job. It can also be used to refinish silver instrument dials. We have bus bars in our resistance welding machines that have been in place for more than 20 years with less than 1 micro-ohm of measured resistance variation. To get this kind of stability we sometimes use washers between our bus conductors stamped from 100 mesh woven silver wire. These washers deform and are crushed during bolting of the bus assembly. This forms a hermetic connection that is water resistant and gas-tight.

Thanks again. It sound like it's worth trying.

We also do a lot of resistance welding, but mostly welding thin foils to each other or to a thicker substrate.

What kind of instrument do you use to measure µΩ?

That mesh washer sounds like a great idea for appropriate applications.

A μΩmeter of course!

Thanks for the link! Very informative, although it was disappointing to note a glaring error on page 3:

They say:“6000 A across a 100 μΩ bus = 3600 Watts.
6000 A across a 1 μΩ bus = 36,000 Watts, which will result in excessive heating.”

But: P=I²*R = 6000² * 100µΩ = 36,000,000 A²* 0.000,100 Ω = 3,600 W (correct)

While: P=I²*R = 6000² * 1µΩ = 36,000,000 A²* 0.000,001 Ω = 36 W

(They moved the decimal point the wrong direction!)

Sorry I didn't see your reply 'till today 4/25.

We use an instrument manufactured by RoMan called an IM-91 Impedance Master. It is obsolete, but ideal for these measurements. We maintain a collection of NIST certified instrument shunts to verify calibration.

Thanks. I saw one on eBay for around $400... What is the chance that it is usefully accurate? I don't need precision; I can compare connections in various locations, and watch for high values that need cleaning/tightening/replacement.

I can't advise on the condition of a used one, but I do have a copy of the user manual that I'd be happy to send you.

It is important that we know the bus bar material. Copper, aluminum, or something else?

Copper

yet not received any suggestion which can resolve my problem.

So assuming the currents are equal and all joints are equal (and good), one thing left to consider is the busduct design itself. I have seen examples where the centre phase (L2, yellow) runs hotter than the outer phases, partly down to restrictions of ventilation for air spaced bars, or poor design and therefore increased impedance (volt drop). Have you considered a phase crossover along the run? What is the maximum length of run suggested by the busduct manufacturer?

Ventilation system is natural. only installed louvers for ventilation.

Bus bar design II II II II II II II 1st two neutral 2nd 4 red 3rd four yellow 4th 4 blue

Distance between phase to phase 100mm and phase to ground 90mm phase to neutral 90mm , bus bar insulation supporting sheet at 800mm.

Perhaps yellow phase is facing a back emf due to greater proximity to steel somewhere along its length, I don't know. Just a thought.

You should be seeing signs of that metal heating up inductively though.

Make sure your phases are indeed equal at point of entry to this plant location.

Sir Thanks for your answer.

can you explain how much distance required between phase to phase bus bar?

bau bar size 120x10mm, 4 bus bar for each phase.

please explain with calculation

Thanks