13.8kv , 50MW distribution

[bipinsa]

a 50MW gen at 13.8kv will be located 1.5 km away from the load.
I was wondering if anyone has any experience running U/G and tray rated cables for that long distance. 50MW is a lot of current, about 2700A. The cables we could think are using 1000MCM single conductor aliminum. If we use these, we might need 15 or 18 cables burried in a duct. (the design will have partial burried and parting cable in the tray)
I would appreciate if anyone can recommend a better solution to minimize cable runs. We do not want to run O/H lines. Response appreciated. Thanks

 

[davidbeach]

Given enough money, anything is possible, but...

You really, really, really need a transformer between that generator and the load, so step the output up to 34.5kV or 69kV and back down to 13.8kV at the load. You could also go to 1500kcmil or even 2000kcmil copper conductors and reduce the number of conductors. Overhead will obviously let you use much smaller conductors.

 

[bipinsa]

we do not have an option to step it up. But after the 1.5km span we are upconverting to to 240kv. The cables have to be at 13.8.
MOre suggessition?

 

[Overvoltage]

Wow...I would not be surprised if between the cost of the cables and the additional losses that you wouldn't be able to pay for transformers to step up and step down the voltage at each end and the associated higher-voltage cables. Of course, if there's no place to locate the transformers then that may be another issue. Seems like it's just begging for a higher voltage at that load level, however.

 

[bipinsa]

We do not have any real estate for the transformers.

 

[bipinsa]

another thought. Even if we find space to locate transformers, the losses in the cables and losses due to double transformation at each end woudl be more. Running cables at 13.8 would be still less losses. thoughts?

 

[Overvoltage]

Hard to say...I'd be surprised if that was the outcome. The only reason that might happen is the relatively short distance (1.5 km). I'd still be surprised if the overall costs were lower at 13.8kV, however.

 

[waross]

How about field fabricating a bus duct using 6 inch or 8 inch aluminum Iron Pipe Size (IPS) bus. There may be enough money saved to cover solving the insulation and/or spacing and guarding issues and a one time approval.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

You say you cannot change the voltage, so there is no change in current. You do not want OH wires. So how do you expect to minimize cable runs? If you already made up your mind, stick with it or do a cost analysis of options and make an informed decision.

Rafiq Bulsara

http://www.srengineersct.com

 

[jghrist]

If you are transforming to 240 kV at the other end, then transforming to a higher voltage at the generators is not a double transformation. It will mean one extra transformation and a different transformer at the other end.

 

[slavag]

Its not only transformer, CB, DS, ES, CT, VT, control and protection for transformer and line are needed and its 220kV, not so cheap.
But, 13.8kV, 50MW to 1.5km not so good solution too.

Are you have load 13.8kV on the second end or only connection to grid?

 

[bipinsa]

It is connection to grid

 

[slavag]

Hmmm.
Is not simple decision.
You need a serious technical and financal evaluation and check a local grid options for connection.
For exapmle:
install step-up transformet in power palnt yard with two 220kV field or may be only one field and connect this field directly to 220kV line without additional bay, that menas T-connection and your trafo will be protected by line zone protection.