Experimental evaluation of differential voltage protection scheme based on a coherence function applied to AC machine stator windings

A coherence algorithm is used to detect and classify electrical faults in the stator windings of the induction machine in this paper. The approach can definitely define turn-to-turn and internal shunt faults that occur on the three-phase machine windings. It can also distinguish between the diverse types of the internal shunt faults. The approach requires the acquisition of three-phase voltage measurements at the midpoints and complete terminals of the stator windings of the induction machine. The function of the numerical differential voltage relay can be performed using cross-coherence and auto-coherence coefficients quantified for the voltage measurements to determine and categorize the various faults. A modified configuration for the three-phase stator windings of an induction motor is used to test the technique; in which, each stator winding of the equipment is re-wounded to obtain 20 taps per phase. This configuration aims to construct voltage transformers at the midpoints and complete terminals for the machine stator windings, and to facilitate making comprehensive tests to ensure the effectiveness of the coherence technique. The testing results demonstrate the effectiveness and efficiency of the advanced protection. The experimental findings indicate that the protection's dependability and security percentages are greater than 98.0%, and the protection's reliability and accuracy rates are nearly 97.0%. The coherence measure has the ability to discover winding faults, particularly those occurring from turn to turn, differentiate between fault locations, and categorize shunt faults located within the machine protection zone. Additionally, the proposed approach has a high-speed response that is adjustable, and new tripping curves are created.