In order to settle the problem of the exact fault placement on grounding grid

a new fault diagnosis method was brought forward based on the fuzzy theory.The two important principles of fuzzy theory

degree of nearness and furthest selection

were improved according to this specific problem of grounding grid fault diagnosis.Making use of the complex image method and Prony method

adopting the MATLAB program

the distribution of earth surface potential of the 10×10 intact and fault grounding grid were calculated

as the sample data-base.Adopting VC++ program

calculating the relation between the intact grounding grid sample and the fault grounding grid sample based on the improved fuzzy degree of nearness

the fault sample data-base were diagnosed.Subsequently

calculating the difference between the fault samples

the fault placement of grounding grid was diagnosed based on the principle of furthest selection.The result indicated that the accuracy is high.