T”4=temperature drop through the duct thickness T’4=temperature drop from bunch of 3 cables to inner part of the duct T1=Ri insulation thermal resistance of one cable only I^2*R=main conductor losses This is the sum of thermal resistances multiplied by losses-thermal flow passing through. The total temperature drop from a loaded conductor up to environmental medium it is as follows: Thank you very much! RE: Underground cables in Concrete Encased PVC ducts 7anoter4 (Electrical) 24 Nov 13 13:07 just to clarify a final point if i am calculating for the same cable and same ductbank for different number of loaded cables i only have to change the N in 2.2.7.3 from 287-2-1 and n in 1.4.1.1 from 287-1-1 and the d'pk/dpk product in 2.2.3.2 from 287-2-1 to correspond to the distances between the expected worst condition cable and the other cables.

However it wasnt clear for me the process of iterative calculation in 2.3.1 and i assumed losses of 10% coming from circulating current.ĥ. However isn't it more critical to calcualte current capacity for bonding at both ends? using 2.3.1 the eddy currents could be ignored. in your calculations you considered the eddy currents calculations as in 2.3.6.1 from 287-1-1 for single bonded or cross-bonded systems. should i always consider Wd in 2.2 from 287-1-1 in table 3 it is mentioned that this could be ignored for operating voltage under 63 kV for XLPE! for 13,8 kV and 24,5 kV operating voltage this could be neglected correct?Ĥ. in this case n should be 27 in case i have 9 ducts which have cables each having 3 loaded conductors for which we calcualted T1, T2, T3, R and all the other variables.Ģ.b we have the parameter N in in 2.2.7.3 from 287-2-1 this should be the number of ducts containing acables in service, example for a fully loaded 3 x 3 duct bank i will have N = 9ģ. when considering single-core cables in duct banks:Ģ.a we have the parameter n in 1.4.1.1 from 287-1-1 which is number of load-carrying conductors. when i am considering non-armoured cables lambda 2 in 1.4.1.1 from 287-1-1 and T2 in 2.1.2.1 from 287-2-1 are zero since there is no armourĢ. I made the calculations and have some questions. the sheets you sent helped me a lot in understanding the calculations. RE: Underground cables in Concrete Encased PVC ducts Adam1980 (Electrical) If the 3 cables in one duct of the upper row –first or last will be loaded with 175 A the ampacity of the rest of cables will drop to 161.5 A. The first way result was 166 A and the second-considering also equally loaded cables-163.5 A. There are slight differences between results. This way is difficult to transfer in Excel.

This is not a relation but a procedure in order to find the final temperature distribution and iterate the way until reach the maximum permissible. If we intend to load differently one or more cables then we have to follow ch.2.2.3.1 Unequally loaded cables. This way uses global formulae simplifying the calculation. We calculated the ampacity for 27 single core cables equally loaded following IEC 6 ch.2.2.7.3 External thermal resistance of the duct (or pipe) T4”’ connected with 2.2.3.2 Equally loaded identical cables. RE: Underground cables in Concrete Encased PVC ducts 7anoter4 (Electrical) 26 Oct 13 09:21 in PVC duct) to see what is the ampacity and compare with the one given by the manufacturer for laid direclty in ground.įinally, you said that you are using information from ABB for the 9 cables arrangement but is it valid to use the factors from IEC 502 when considering 3 x 3 configurations, the factors are for horizontal arrangement only! correct?

I am doing calcualtions only for one cable (3x1 300 mm.sq. I believe i have all data i need to calculate the ampacity using the equations in 287-1-1 and 287-2-1 but i am not getting a logical result. for a rough estimation is this valid?įor the duct in question it is a 3 x 3 configuration vertically and horizontally there is 50 mm spacing between the ducts (165 mm center to center)and 75 mm from the concrete encasing border to the duct order also vertically and horizontally. So if the rating for cable in ducts is 166 A and for directly buried is 184 A the factor in between is around 0,9 (assuming all other conditions are the same).

Concrete encased duct bank 12kv