Excess Voltage Drop for Busway

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kshah

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Hi all,

I have a project I am designing where I am asked to provide power for a conveyor and screening equipment from a main electrical room (5,000 Amp main switchborad @480/277V) to a location which is over 1,000' away. In the past, for a similar project at the same facility, we utilized busway to span from the main electrical room to the project location. However, in the past, the distances was not more than about 600'. In this case, my load is approximately 4,000 Amps at 480/277V, 3P and I need to run the busway over 1,000'. This results in an excessive voltage drop at the distribution end at the project location. I have thought of providing a substation at the distribution end of the busway with common voltage on the primary and secondary so as to use the taps to bump up the voltage, but size and cost become a major issue. Does anyone else have any other possible suggestions on how to provide electrical service from a main electrical gear to a project location which is 1,000' away? Thanks for the help.
 
Jack up the voltage to 13.2 kV and transform it back down at the other end. You may save enough from the differential between the busway and the cable to partially pay for the transformers, equipment, and terminations. 15 kV class cable would only need to be about 2/0 Cu. or 4/0 Al. to carry the load but it would take a couple of 5,000 kVA transformers. The added advantage is the availability of taps if the voltage is too high or low. :)
 
kshah said:
Hi all,

I have a project I am designing where I am asked to provide power for a conveyor and screening equipment from a main electrical room (5,000 Amp main switchborad @480/277V) to a location which is over 1,000' away. In the past, for a similar project at the same facility, we utilized busway to span from the main electrical room to the project location. However, in the past, the distances was not more than about 600'. In this case, my load is approximately 4,000 Amps at 480/277V, 3P and I need to run the busway over 1,000'. This results in an excessive voltage drop at the distribution end at the project location. I have thought of providing a substation at the distribution end of the busway with common voltage on the primary and secondary so as to use the taps to bump up the voltage, but size and cost become a major issue. Does anyone else have any other possible suggestions on how to provide electrical service from a main electrical gear to a project location which is 1,000' away? Thanks for the help.
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For similar installations I have seen all bussduct and the inspectors fudged the numbers a little to get it to pass after install.
 
Do you have 13.2 kv available. Having to agree with Charlie again but would consider a 13.2 circuit to the from existing line to the proposed location and install transformer there. No 480 to 13.2 and back down again.
 
What about simply increasing the size of the cable / busduct to decrease the voltage drop?

Is the cost of these increased cable / busduct sizes an issue? Would this cost more than transforming to a different voltage and back?
 
mull982 said:
What about simply increasing the size of the cable / busduct to decrease the voltage drop?

Is the cost of these increased cable / busduct sizes an issue? Would this cost more than transforming to a different voltage and back?
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Roughly, it would take 13x500 CU or 8x2000 CU to get it done at 480 volts whereas one #12 would do it at 13,200 volts.
 
Yeah step up transformer then step down transformer. In a recent project we've been looking at transformers 480v - 12.47kv, cheapest was quoted at around 5 grand, though those were 150kva.
 
mivey said:
. . . whereas one #12 would do it at 13,200 volts.
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I like the idea of taking service at 13.2 kV, 13.8 kV, or 12.47 kV depending on the standard distribution voltage of the serving electric utility. I do have a problem with using a #12 for the circuit conductors though. I am not so sure the wire would hold the current without melting, even at 13.2 kV. :smile:

Follow the requirements of 230.6 and hit the service equipment and transformation to 480 volts at the area where the load is located.
 
charlie said:
I like the idea of taking service at 13.2 kV, 13.8 kV, or 12.47 kV depending on the standard distribution voltage of the serving electric utility. I do have a problem with using a #12 for the circuit conductors though. I am not so sure the wire would hold the current without melting, even at 13.2 kV. :smile:

Follow the requirements of 230.6 and hit the service equipment and transformation to 480 volts at the area where the load is located.
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Yeah. I got carried away with the vdrop and overlooked that minor detail.:smile:
 
Thank you all for the valuable insight.

Since the load is approximately 4,000 Amps at 480V, I would need a 3,750 kVA transformer to do the trick of bumping up the voltage. The downside would be that I would need two transformers, one to bump up the voltage and a second to step it back down. I was looking at using an autotransformer which is rated at 3,750kVA at the end of the run, which could then bump up te voltage by a maximum of 10%. I would then only need one substation style gear, since space is very limited. Unfortunatly, there is no medium voltage currenly available at the site, so I would need to boost the voltage on the secondary of the utility company or provide the autotransformer.
 
Little odd this one - main switchboard with 5KA supply, and then a 4KA supply required half a mile away. No MV on site with a 5KA main board.

I also have a worry about half a mile of busway - won't thermal effects cause expansion and contraction differentially in the copper bars and steel enclosure, so the whole lot ends up in stress conditions and then start to fail? Its an interesting solution, but I'd like the manufacturers take on it before speccing something like that myself.

Certainly MV and a tranny or two sounds a lot less like hard work :)
 
kshah said:
Thank you all for the valuable insight.

Since the load is approximately 4,000 Amps at 480V, I would need a 3,750 kVA transformer to do the trick of bumping up the voltage. The downside would be that I would need two transformers, one to bump up the voltage and a second to step it back down. I was looking at using an autotransformer which is rated at 3,750kVA at the end of the run, which could then bump up te voltage by a maximum of 10%. I would then only need one substation style gear, since space is very limited. Unfortunatly, there is no medium voltage currenly available at the site, so I would need to boost the voltage on the secondary of the utility company or provide the autotransformer.
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If you used an autotransformer then I would think that you would somehow need a way to adjust the taps so that when there is a light load on the circuit the voltage will not be too high.

Rather than using an autotransformer, why not just use a regular type transfomer with a 1:1 ratio and set the taps high as you mentioned in your OP. I still think that you would have the issue of needing to adjsut taps during light loading?
 
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