Direct Buried DC cable ampacity calculation for solar farm
Direct Buried DC cable ampacity calculation for solar farm
(OP)
I am designing the cable trench for 24 direct buried cables (12 circuits) for a solar farm project. Each cable carries 168A dc current, continuously. Both "+" and "-" carry the same amount of current, which is obvious for DC.
Question 1: How am I suppose to size the cables with optimum arrangement and spacing between each cable, that guarantees each cable will carry 168ADC minimum?
Question 2: is there a code that talk about DC cable direct buried?
thank you all.
Question 1: How am I suppose to size the cables with optimum arrangement and spacing between each cable, that guarantees each cable will carry 168ADC minimum?
Question 2: is there a code that talk about DC cable direct buried?
thank you all.






RE: Direct Buried DC cable ampacity calculation for solar farm
For the derating due to grouping, refer to the vendor's catalogue. The optimum arrangement will depend upon the number of cables per group. It is a tradeoff. You increase the number of cables per group which will result in reduced ampacity.
RE: Direct Buried DC cable ampacity calculation for solar farm
For 24 cables- that means 3*8- another derating factor of 0.65 is to be applied. The load factor considered by the above standard is only 70%.
Then the total derating factor will be= 0.7*.65*.9=0.4095
Now 482*.4095=197.4 A it is admissible for 24 single core cables arranged side by side. The minimum clearance between two adjacent cables has to be 7 cm [3 inches approx.]
You may calculate the permissible ampacity following "The Calculation of the Temperature Rise and Load Capability of Cable Systems", by J.H. Neher and M. H. McGrath. or IEC 60287 also.
RE: Direct Buried DC cable ampacity calculation for solar farm
RE: Direct Buried DC cable ampacity calculation for solar farm
I took it into consideration [in a modest way, may be]. If using only a clean sand backfill, well compacted and the water content of minimum 3% the thermal resistivity could be 60 K.cm/w. If the water content will decrease up to 0.1% the resistivity will be still 100.But if the water content will decrease below the critical the resistivity could be 400!
The compaction degree is an important factor also. I think a thermal resistivity test of the backfill will be required, any way.