Transferred Voltages due to Single Phase Earth Fault on Power Transformers

Abstract In the event of an earth fault in one of the two systems of a three-winding transformer, an increase in the star-point voltage occurs in the disturbed system. This voltage is transferred to the undisturbed systems due to capacitive coupling, to affected earth faulty system and to earth. As a result, three phase voltages to earth are different in magnitude and phase position compared to their undisturbed service status. In this paper the mesh analysis method is used to calculate the neutral point shift of the faulted winding necessary to obtain values of transferred voltages to the unaffected winding (the one which is not earth faulted). The results are analyzed to investigate the influence of winding and network neutral grounding (insulated, solidly grounded, grounded over impedance) on the results.