Emergency power requirement at a distance of 2 KM 2

[eletest]

For our installation , we are planning a common emergency DG set (EDG) of 2000 KVA , 415 volts. However there is one location with anticipated requirement of 200 KVA which is approximately 2 km distance from the EDG. The location and the logistics do not allow a separate EDG set of 200 KVA to be placed there.Therefore we have considered 415 volts cables from the EDG to the location.Considering the distance , the size and no. of cables required are more.There are suggestions that installing transformers at both the ends, and taking the required power through 11 KV cables , would be much more economical. Which option should we go for ?

 

[Skogsgurra]

You would, as you already say, need an enormously thick cable if you are trying to supply 200 kW over 2 km distance. My tables say that a 240 mm2 Cu cable can be used up to 125 m at that power level. Two km is sixteen times longer. So, sorry, either a 6 or 11 kV cable with transformers or a separate genset at the remote location.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[Power0020]

@Skogsgurra,

can you please provide these tables? reference?

 

[oldfieldguy]

You might want to look at stepping up your emergency power voltage level to a higher voltage, then stepping it back down to the utilization voltage at the far end. We do that at several facilities at the 480-volt level here, using small 2300-volt transformers wher we have about a thousand meters of separation.. Somebody gave you good advice.

old field guy

 

[Skogsgurra]

My tables are in paper format and copied from a book that I don't have access to. Also, they are in Swedish...

A good site is this:

http://www.openelectrical.org/wiki/index.php?title=Cable_Sizing_Calculation

And there, you can find a table that is very similar to "my tables".
You find it at

http://www.openelectrical.org/wiki/index.php?title=File:Cable_waterfall.jpg

The results are not identical, but they clearly show that you cannot go much further than around 200 m with the 200 kW load.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Keep below 11kV if you can. 200kW at 2000m is easily manageable at 3.3kV or 6.6kV. At 11kV you will enter the world of partial discharge, more complex joints and terminations, more expensive hardware, and you don't want to be involved in any of that without good reason.

Use a Yd transformer at the source (delta makes things easier for the generator) and a Dy at the load (avoids difficulties with protection and earthing).

 

[eletest]

Thanks @Skogsgurra,@oldfieldguy and @ScottyUK for your replies.

 

[racookpe1978]

Will there be significant differences in the poles for a 11 KV and a 3.3 Kv vs a 6.6 KV?

That is, check poles and insulators + cross-bars, wires, transformer cost and control (breakers/switches) cost .. Prices may go up for one part, but down for another part of the installation.

 

[ScottyUK]

Probably not if it goes overhead. The OP said cables, as opposed to lines, so I assumed it was a surface or buried application rather than aerial. I doubt the conductors for an OHL would be much different at any of those voltages because mechanical strength would be the dominant requirement rather than current-carrying capacity.

 

[15thaugust]

What if we use multiple cables in parallel? Then the load current will be divided amongst them and cable size can also be reduced. I dont know which will cost less.

 

[Skogsgurra]

15th
You will need around 20 thick cables in parallel for each phase. That is 60x185 mm2 cables for the phases and probably the same number for the Neutral, depending on what load there is. Not practical. And very, very expensive. And very tempting for the Cu thieves.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[7anoter4]

In my opinion, the solution proposed by Scotty is less expensive [approximate only a half]. That means 2 transformers of 300 kVA 4% 3.3/0.415 kV and 2*3*240 sqr.mm 3.3 kV copper cables [my appreciation 160000 US$ total].
However, 5 parallel groups of 3 single core cables of 500 mm^2 copper could provide a same voltage drop [on my appreciation it could be more than 350000 US Dollars].

 

[ScottyUK]

Hi 7anoter4,

I think the HV cable would be more like 1x 3C/120mm² for a volt-drop on the HV feeder of about 2% (2% of 3.3kV being 66V, and the line current being about 53A). Could be a much bigger saving.

 

[7anoter4]

Thank you,Scotty.You are right!