Analysis And Research Of Three-phase Unbalance In Distribution Network

Unbalanced factors are made of fault and normal. It is focused on the subject of normal three-phase unbalance in this paper. It is illuminated to hazard of three-phase unbalance. It is modeled and studied to reason of three-phase unbalance through time domain simulation. There are several reasons as follows: 1. unbalanced distributed capacitance. Power frequency displacement voltage is created when system appears unbalanced direct-to-ground parameter. 2. effect of load. Single-phase load is used widely in the electrical network, especially electrothermal furnace, electrical locomotive and other single-phase electrical equipments. Although sing-phase loads are distributed equably on the three phases, three-phase unbalance still exists because of asynchrony of using in the course of operating. 3. ferromagnetic resonance of saturated voltage transformer. Direct-to-ground inductive reactance of system is unbalanced partly in general system. Because voltage transformer is saturated, direct-to-ground inductive reactance is unbalanced partly. 4. effect of extinction coil. The degree of three-phase unbalance is increased by adding extinction coil. The value of phase-voltage is maximum value when harmonic oscillation appears by adding extinction coil, which can damage electrical equipment. Through simulation of ATP-EMTP and MATLAB, it is get oscillogram of three-phase voltage and magnitude of voltage. It is listed flow process chart of three-phase unbalanced reason and parallel table of every reason.Three-phase unbalance to Northwest China power grid are carried on research in this paper.Through investigation and research, it is get to reason of unbalanced voltage and countermeasure in 35kV electric network based on theory analysis and parameters of field engineering. It is get to a new method of measuring capacitance, that is, external connection capacitance. This paper has a certain theoretical and practical meaning. It is expected to improve effectively systematic operation management level in certain meaning.