Research, assessment and proposals on resolving power quality problem for the power supply system of Lam Dong alumina refinery, Vietnam

Alumina production is rather complex technological process of processing mineral raw materials that requires development of effective technological solutions, including in terms of efficiency of using electric energy. The paper is devoted to studying the power supply system of an alumina refinery in Lam Dong Province, Vietnam. The tasks that need to be solved for improving the power quality in the power supply system were analyzed. It was shown that non-linear loads significantly degrade the power quality that in turn leads to equipment damage, malfunction and decreasing the refinery productivity. Models of the refinery power supply system were developed and, using which, the quality of power was assessed at the 6 kV voltage utility bus of the power supply system, as well as at the 6 kV and 0.4 kV buses of distribution substations of individual refinery’s subdivisions. Analysis of the simulation findings showed that the nonlinear loads lead to significant distortions of sinusoidal forms of voltages and currents, and decreasing the power factor. Based on the simulation results, it was concluded that voltage harmonics and current harmonics at nonlinear load at the low voltage buses of 0.4 kV and at the buses of 6 kV exceed the permissible limits of the harmonics in accordance with IEEEST519-1992 international standard. Proposals were developed for improving the power quality in the refinery power supply system. For suppressing higher harmonics of current and voltage, it was recommended to use special power quality regulators in the alumina refinery power supply system. It was proposed to use active harmonic filters as the power quality regulators. The proposed solutions allowed obtaining practically sinusoidal forms of voltages and currents in the alumina refinery power supply system.