Arrangement of cables for transformer

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Marius

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Between a 2 MVA generator and the transformer, there will run 15 ea. 750 MCM single wires.

The distance is less than 10’.

It is my plan to connect the shield of the wires to ground in each end of the wires (closed loop).

But how in the world can I arrange the wires so they will have a minimum of magnetic disturbances?

(The current running is approximately 2,500A, the voltage is 480 V, and the width of the only cable-tray is 24”)


All ideas are so welcome.

Best Regards
Marius
 
Shield wires for 480V? I am thinking that is more typically a Medium Voltage (2400 and up) thing?

But you are talking about (3) x 5 = 15? So (3) sets of Parallel?

You can do this with (5) 4 inch conduits, right? But you want to use cable tray?

Saves on fittings, etc.?
 
Marius said:
Between a 2 MVA generator and the transformer, there will run 15 ea. 750 MCM single wires.

The distance is less than 10’.

It is my plan to connect the shield of the wires to ground in each end of the wires (closed loop).

But how in the world can I arrange the wires so they will have a minimum of magnetic disturbances?

(The current running is approximately 2,500A, the voltage is 480 V, and the width of the only cable-tray is 24”)


All ideas are so welcome.

Best Regards
Marius
Click to expand...
You bundle them in the tray in groups that have A, B, C, and N in each group, as required by 392.20(C).
Like others, I question the shield for 480 volt systems.
 
If this arrangement will be according to NEC 2017 art. 392.22 (B) (1) b [that means for 24” wide cable tray - Ladder or Ventilated Trough Cable Trays-maximum 28 sqr.in -and you have only 25.46] and according to

Table 310.60(C)(69) for copper conductor 90oC rated 900 A ampacity.

Then 75% will be 675. You need 2500/5=500 A continuous load.

If you will ground both ends of the shield the shield losses will reduce the ampacity. I don’t know what kind of the shield you have but however if you ground only one end for 10 ft long cable, I don’t expect high voltage at the other end.5 set single in tray.jpg
 
I am sorry: from my above post the introduction is missing.

At first, I think the cable 1kV insulated [EPR or XLPE ] jacked and shielded overall diameter it is 1.47”.So you may arrange your 5 -three phases-parallel single core cables as in attached sketch.

The problem it is the unbalance between cables due to magnetic flux unbalance so this it could be a good arrangement in order to avoid this.
 
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