Optimization of third harmonic ground-fault protection systems of unit-connected generators grounded through neutralizer

Abstract

In this paper a method of optimizing the operating conditions of a ground-fault protection of the generator stator windings excited by the ratio of third harmonic voltage to ground in the neutral and at the generator terminals is presented. The influence of a ground-fault neutralizer (GFN) grounding the generator neutral on the operating conditions of a ground-fault protection scheme excited by 3rd harmonic voltage for different values of the additional capacitance to ground of the generator breakers and different ratios of the voltage transformers installed in the generator neutral and at the generator terminals was determined. It has been found that the parameters of the ground-fault neutralizer and of the voltage transformers and the additional capacitance to ground of the generator breakers have a marked influence on the voltage feeding the starting element of the protection. Parameters values for which optimum operating conditions of a ground-fault protection scheme excited by 3rd harmonic voltage occur were determined.