The Analysis And Resolution Of The Problem That Existed 66kV Three-phase Voltage Unbalance In Dalian

There is three-phase voltage unbalance both in normal and fault power system. It is focused on the analysis of unbalanced three-phase voltage phenomenon during normal operation in this paper. It is elaborate the damage of power transformer, motor, generator, distribution line with three-phase voltage unbalance in power system. Through the formula, calculation the loss of power transformer capacity and distribution line with three-phase voltage unbalance.There are several reasons of three-phase voltage unbalance after research and analysis:1. When the power system is basic for overhead lines without exchanged, there will be neutral displacement voltage because of unbalanced distributed capacitance, then unbalanced three-phase voltage appeared.2. In neutral point extinction coil grounding system, extinction coil will enlarge degree of unbalanced three-phase voltage. And harmonic oscillation appeared with distribution line and bus, Cause the violent fluctuation of three-phase voltage which can damage electrical equipment.3. It is ferromagnetic resonance of saturated electromagnetic voltage transformer, while switch on, Single-phase grounding etc disturbances in less compensation power system, then unbalanced three-phase voltage appeared.4. Unbalanced three-phase load is ubiquitous, especially of electrified railway traction locomotive, steelmaking, electrolytic aluminum and lots of impact load in Dalian area. Although take into account as far as possible the three-phase load balanced distribution, but the impact load is random and not at the same time, resulting in unbalanced three-phase load, and unbalanced three-phase voltage.5. In the single-phase grounding fault, line breaking and resonance occurs in power system will occur three-phase unbalanced voltage.The 66kV system in Dalian power grid is carried on research in this paper, whose degree of unbalanced three-phase voltage beyond the national standard. Through the simulink toolbox of the MATLAB software, according to the actual parameter, establish the simulation model. Put forward the method of installing capacitors at the end of the line whose voltage minimum to reduce the degree of three-phase voltage unbalance. Through the simulation analysis, verified the possibility of the method. Methods and results obtained in this paper provides a simple method to improve the three-phase voltage unbalance for Dalian, also can improve the management level of dispatch departments in power grid.