Experimental Research of Asymmetrical and Nonlinear Traction Loads in 110 kV Electric Grids

Introduction. The paper analyzes the results of experimental studies of asymmetrical and nonlinear traction loads (ANTL) at substations of a 110 kV external power supply system. Regions characterizing the degree of asymmetry depending on the positive sequence current (PSC) are constructed and compared with similar regions obtained through mathematical analysis. Traction load nonlinearity due to the presence of static energy converters primarily generates odd higher harmonic components, which affect the operation of relay protection (RP). Dependences for the maximum values of 3rd, 5th, and 7th harmonic components of phase currents are obtained, which will allow use in selecting the parameters of RP measuring units and basing for the current signal filtering requirements. Goal. The study of STE modes to refine the methods for calculating the response parameters of relay protection measuring devices (RP) and the development of new algorithms for the operation of microprocessor RS. Materials and methods. The study is based on the analysis of the modes of external and traction power supply electrical grids. Results and discussion. Regions of possible asymmetric traction loads are constructed depending on the degree of their asymmetry. Mathematical relationships between the maximum relative values of odd harmonic currents and phase currents are obtained. The need to consider the components of the traction load due to the traction load factor and higher harmonic components when selecting the parameters of the protection relay is demonstrated. Conclusion. The ratio of the negative sequence current (NSC) to the TPP has been shown to reach 100%, not only when shoulder of the traction transformer is idle, but also when both shoulder of the transformer are loaded under various load conditions. Odd harmonic components in the phase currents of traction transformers are significant, reaching 6–14 % of the maximum (nominal) current of the traction transformer.

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