In order to settle the underdetermined and ill-conditioned equations in diagnosis system

the total least squares method based on Tikhonov regularization is conducted and the corresponding codes are compiled. Moreover

a 110 k V transformer substation in Chongqing is tested and three sets of faults are set up to simulate the corrosion of the ground network to reconstruct the field test conditions. The results show that the fault either undetermined or determined branch fault can be easily diagnosed with a relative error of 10%. In the case of concurrent fault of six branches

it can also be diagnosed easily after proper adjustments. Compared with the traditional genetic algorithm

this method avoids crossover and aberrance effectively and diagnostic efficiency is improved apparently.