I anm trying to figure out what is good utility practice for performing generator interconnection studies on distribution systems. I have a situation where there is so much generation on the distribution system that there is a concern about backfeeding to the transmission level and overloading the distribution transformer (115/33kV).

The utility is using spreadsheet to deteremine the loading on the transformer. They just totaled up the maximum capacity for all of the generators (no historical factor or diversity factor) and then subtracted the minimum load. They also did not include any losses or run a power flow analysis to include those losses in calculating the bank loading.

1) Please me know if you would include the losses and/or us a power flow program to do this analysis.

2) Would you use historical factors or diversity factors for the existing generation?

Thanks!

The interconnection studies should be rigorous enough to identify all of the impacts that the new generation will impose on the utility. The study should identify all of the costs that the developer needs to agree to before construction. If you miss some of the impacts, you will be on the hook for them later.

It's not clear what size transformer you are referring to, load (MVA) is important to know.

If the generation is high enough, then certainly losses and transmission/distribution power flows should be evaluated. I don't see anything particularly wrong with considering all of the generation and load to be coincident.

Might be worthwhile to Google "distributed generation interconnection requirements" to see how other utilites approach it.