How can a branch PTDF be greater than 100%?
Normally, we would not expect any branch PTDF for a transfer to be greater than 100%. However, values larger than 100% may occur on branches with negative reactance, such as series capacitors. The illustration below shows PTDF flows for a transfer between the right bus and the left bus. The line directly connecting these two buses has a negative reactance. The PTDFs flow back to the right bus on the parallel path through the bottom bus, which has a positive reactance. Note that if we create a “network cut” at the lines attached to the left bus or to the right bus, we still see a net 100% PTDF flowing from source to sink.
