A method for three-phase fault lost directivity

When the electric power system of line has faults with transition resistor,the distance protection maybe lose direction or trip when the faults are outside of protection range.The paper analyzes the reason of losing directivity and overreach faults using resistance vectogram.And it also analyzes the effects of transition resistor on distance relay when using some different polarizing voltage on the voltage vectogram.It gives a method to resolve this problem,i.e.using power variation distance relay to avoid losing direction when memorization voltage lost.The vectogram tests and verifies this principle and dynamic analogies examination proves its feasibility.