Research On Voltage Sags For Distribution Systems

Voltage sags reflect the compatibility issues between power system and sensitive equipments. Voltage sags caused by short-circuit fault will spread in the system, and caused a great impact on programmable logic controllers, AC contactor, AC variable speed drive devices, which are widely used in industrial production. Voltage sags will even cause serious damage to the entire production process, resulting in significant economic losses Therefore, the research on voltage sags for distribution system has important practical significance.Based on the study of the impact on sensitive equipment caused by voltage sag, a set of method is proposed to mitigate the voltage sags on sensitive load. A node impedance matrix based calculation method of residual voltage is given under the superposition principle and the impact of transformer wiring form to the residual voltage is analyzed. Considered the duration of different protection shemes, a voltage sag frequency assessment algorithm is proposed based on the relationship between residual voltage and fault proportional coefficient. PSCAD/EMTDC electromagnetic transient simulation verifies the effectiveness of the algorithm on a IEEE-30 bus system.Combined with the China Southern Power Grid project "Research of voltage sags impact on power users", the proposed method is used on the voltage sags of North Sea petrochemical. Finally, measures of mitigating the impact of voltage sags on the power systems and the user side are summarized and the specific steps to strengthen Lightning Protection, change protection method and install SSTS are illustrated.