Lei Jinyong

Effect of load on zero-sequence current in low resistance grounding system with complex grounding fault

The events that a single-line fault evolves into a multi-line fault are increasing recently in China Southern Power Grid. To make matters worse, zero-sequence current is closely related to the load in fault lines particularly when a complex multi-line single-phase grounding fault (SPGF) occurs in a low resistance grounding system. In this case, the load factor must be considered, otherwise it may result in unneglectable calculation errors. Therefore, a comprehensive theory analysis on the relation between zero-sequence current and load was carried out for complex multi-line SPGF firstly. On this basis, the influence mechanism of load variation on zerosequence currents was analyzed in detail, and some general rules were revealed at last. The conclusions summarized in this paper can provide a theoretical basis for improving the performance of zero-sequence current protection.

System stability and its influencing factors analysis of the isolated wind-solar-diesel- battery hybrid micro-grid

An isolated micro-grid system of wind-solar-diesel-battery hybrid power generation is suitable for remote areas and islands. Possessing qualities generally attributed to the isolated micro-grid are inadequate anti-disturbance ability and weak stability. Power system stability analysis is needed for providing some suggestions and advices to planning and design. This paper analyses system stability of an island isolated micro-grid at different operation modes. Based on the results, reasonable operation modes and system reserve demand are proposed for long-term, efficient, and stable operation of the isolated micro-grid. Sensitivity analysis has made to find critical factors which mostly affecting system ability, such as transformer selection, low voltage ride-through capability and so on.