It is difficult to obtain path information in the supply and demand relationship between sources and flows of electric power network according to the basic electrical principles and laws. The supply and demand relationships are usually obtained by traditional power flow tracing methods which are mostly based on proportional sharing principle. In this paper， the union of AC branch and bus is extended to consider ordinary transmission line with charging capacitors and transformers， and the united electrical dissection relationships are presented which strictly satisfy the basic electrical principles and laws. Then， how to obtain path linkages between sources and flows of electric power network is analyzed by directed graphs theory. Finally， electrical dissection algorithms for different objects are presented. Examples prove the correctness of the proposed electrical dissection algorithms.