Jeff Gifford
New member
I am preparing to do some calculations to verify that a 115kV underground ductbank can pass 70MVA continuously after a new ductbank of 480V at 2000 amps is passed perpindicularly underneath it.
My calculation is to find the distance that the two sets of buried conduits must be kept separate to prevent the existing 115kV ductbank from overheating to the point that it limits the current from the mutual heating of the two sets of duct banks.
The problem was solved apparently by a couple of engineers back in 1957 named Neher and McGraph. The calculations are quite complicated, and several electrical calculation software manufacturers can perform this calculation utilizing the Neher/McGraph method.
The problem is though, that they have only solved the problem (to the best of my knowledge from the research I have done thus far) for a parallel set of duct banks. Intuitively, the parallel methodology will give you a worst case scenario since the mutual heating will take place along the entire lenth that they are in the parallel configuration. For a perpendicular configuration, it will almost be like a point calculation. I need to find the minimum distance the ducts can be place above/below each other, and intuitively the perpendicular calculation will give me this minimum value.
I have contacted two popular s/w providers - EDSA and ETAP, and both admit that there s/w will not do the perpendicular calculation. I also called SKM, another popular s/w for performing coordination / arcflash calcs. etc, and they are still working on being able to do the parallel configuration.
My question is, has anyone done these calcs and is there any software that you know about that you can reccommend to help me solve this problem.
Thanks,
Jeff
My calculation is to find the distance that the two sets of buried conduits must be kept separate to prevent the existing 115kV ductbank from overheating to the point that it limits the current from the mutual heating of the two sets of duct banks.
The problem was solved apparently by a couple of engineers back in 1957 named Neher and McGraph. The calculations are quite complicated, and several electrical calculation software manufacturers can perform this calculation utilizing the Neher/McGraph method.
The problem is though, that they have only solved the problem (to the best of my knowledge from the research I have done thus far) for a parallel set of duct banks. Intuitively, the parallel methodology will give you a worst case scenario since the mutual heating will take place along the entire lenth that they are in the parallel configuration. For a perpendicular configuration, it will almost be like a point calculation. I need to find the minimum distance the ducts can be place above/below each other, and intuitively the perpendicular calculation will give me this minimum value.
I have contacted two popular s/w providers - EDSA and ETAP, and both admit that there s/w will not do the perpendicular calculation. I also called SKM, another popular s/w for performing coordination / arcflash calcs. etc, and they are still working on being able to do the parallel configuration.
My question is, has anyone done these calcs and is there any software that you know about that you can reccommend to help me solve this problem.
Thanks,
Jeff