Identify overloaded transmission lines in TTC and ATC determinations

This paper presents a method to identify the potential overloaded transmission lines for single or multiple power-trading paths. Before making available transfer capability (ATC) determination, this technique can classify those lines are potentially reaching the bottleneck for single or multiple source-and-sink trading. The proposed method is used DC load-flow model technique to calculate the line factors of each line for each possible power-trading path. In fact, the calculated line factors are the actual line-flow solutions of the system DC model. The number of the possible power-trading paths is the product between the number of generators and loads in the system. To handle a large power system, a simple program is written to calculate the line factors of each line in each possible generator-load path. First, the program inputs the system bus and branch data to form a primitive reactance matrix and to construct a specific tree, with arbitrary branch orientation, using the depth-first search (DFS) algorithm. An element-node incident matrix (A) is obtained and the bus admittance matrix (Y_Bus) of the system is calculated by a singular transformation. For each possible generator-load path, the generator bus will be used as a reference bus of the system during line factor calculations. Finally, these sets of line factors can be used to forecast the potential congested lines during single or multiple power-trading paths. This can be setup a list of critical lines to reduce the computation time during ATC evaluation.