New Fault-Resistance Estimation Algorithm for Rotor-Winding Ground-Fault Online Location in Synchronous Machines With Static Excitation

This paper presents a new algorithm for estimating the ground-fault resistance value in rotor windings. This new algorithm is an improvement of an online ground-fault location method previously presented. This location method is suitable for synchronous generators with static excitation, whose excitation field winding is fed by controlled rectifiers through an excitation transformer. The estimation of the fault resistance is obtained through the comparison between the third-harmonic voltage measured in a grounding resistance placed in the neutral of the excitation transformer and the third-harmonic voltage calculated by the algorithm. This latter variable is obtained with the dc component of the output voltage of the controlled rectifier and the ac supply voltage of this converter. The fault resistance value is used in the novel technique of online ground-fault location, and it allows improving the accuracy of the location of the defect. This new algorithm, integrated in the complete location method, has been tested with satisfactory results in a 5-kVA laboratory synchronous generator and in a 106-MVA hydro-generating unit.