Increase Ampacity on existing bus 1

[cuky2000]

Does any one know if there a way to increase the ampacity capability of aluminum pipe hollow bus.

I am not sure if there is any significant increment in ampacity gained if additional ACSR or Aluminum cable runs inside the bus.

If some know any reference or experience in this matter, please let us know.

Thanks.

 

[jraef]

Cooling through the hollow tube? I have not done that personally but I saw it done at an aluminum smelter operation. They pumped a cooling oil (don't know what kind, but transformer oil would certainly work) through the bus and had a heat exchanger for it outside. Their purpose was to avoid losing bus capacity because of the high ambient heat of the pot lines, but theoretically the concept could work the same since bus ratings are mainly about heat rise.

Just an idea.

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[jghrist]

The cable runs inside the bus are for vibration damping, not to increase ampacity. They wouldn't increase ampacity unless you could figure out a way to make solid electrical connections inside the tube wherever current can enter the bus.

 

[swn1]

The problem with running cable inside the tube is that the heat dissipated in the cable adds to the heating of the tube. The cross section is increased but the ampacity does not increase proportionately.

You do not have to land the cable at every tap point but rather design it to "bypass" overloaded sections. However, if it isn't solidly bonded at every bus tap it needs to be insulated, further complicating the thermal problem.

With multiple source and multiple loads you have to look at the entire bus topology. A center-fed bus can handle more load than one fed at one end. A bus fed from 1/4 and 3/4 positions can handle more than a center-fed. Total amps flowing from sources to loads does not necessarily pass through any one segment of the bus.

Analysis by segment may allow you to install a bypass cable or to weld on "piggyback" bus tubing in a couple of critical places and accomplish what you need.

NOTE however, that ampacity and withstand rating are designed together for anticipated source and load combinations. If the system has grown so much beyond the design assumptions that ampacity is a problem you need to re-evaluate the available fault current against the momentary ratings of all the equipment connected.

If the gap between rated ampacity and the ampacity you need is smaller than the safety margin in the original rating you might consider using infrared to check for hotspots and "uprating" the bus by test. Not a very good option for metal-clad but exposed bus can be 100% IR scanned as-installed.

 

[apowerengr]

Cuky - what are the application and installation details? Can't you just upgrade the pipe bus? If you can modify it you should be able to upgrade it - at least if it's open-air and outdoors.

 

[cuky2000]

The application is for adding generation in small power plant (adding 2x25 MW for a total of 5 generating units)

DESCRIPTION:
The existing outdoor bus system is outdoor aluminum bus mounted in horizontal configuration with 5" rated for 3500A at 13.8 kV. There is 50 ft of collector bus connected to 600 ft of bus work from the plant to the nearby substation power transformer. The new modification called for upgrade the existing bus system up to 6500 A.

ALTERNATIVES:
a) The obvious choice is to replace the entire bus system with larger and ticker bus.

b) Cable probably increase the ampacity but not clear if can increase extra 3000 A.

c) What about adding an identical parallel bus to obtain 2-5" bus per phase reducing the clearance from 3 ft to 2.5 ft phase-to-phase?

_{NOTE: To simplify the discussion, assume that the propose parallel bus configuration will withstand the SC forces and other mechanical stresses.}

 

[RalphChristie]

Cuky:

Just a remark on point c. (my substation/buswork knowledge is very limited)

What about adding an parallel bus on top of each existing phase? Or is this a weird idea?

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[cuky2000]

Hi Ralph,

There is another idea to check. It is anticipated that the insulator will be exposed to additional mechanical stresses do to dead load (extra bus weight), horizontal wind forces (twice surface) and also during SC event.

Thanks.

 

[BJC]

There are combinations of aluminum channel and special extrusions that may work. a couple of them are shown in here.

http://www.hubbellpowersystems.com/POWERTEST/catalog_sections/Technical_Data.pdf

I don't have a reference here for 5" sch 80 copper pipe but I suspect it may be close.
As noted you have to check the strength of you insulators and support system.