M.A. Thesis:

Comparison of Superconducting Fault Current Limiter and Dynamic Voltage Restorer for LVRT Improvement

Abstract Power system networks are growing and changing rapidly. The continuous increase in the interconnection of various grids to form a central grid and the ever growing power demand has led to an increase in fault current levels. This increase in the fault current has led to a simultaneous increase in the current interrupted by the circuit breaker also which makes it to break fault currents which are out of its rated breaking capacity. Currently, conventional and superconducting power devices have been utilized to improve the LVRT capabilities of power grids. The adoption of a dynamic voltage restorer (DVR) or a super-conducting fault current limiter (SFCL) has been receiving more and more attention. When using a DVR, it is usually necessary to consider the series transformer, converter, control system as well as energy storage at the DC side, and there may be a tradeoff among the capacity, cost and size. Nevertheless, when using a SFCL, especially coordinating with a superconducting magnetic energy storage (SMES) system, it is able to help the renewable power source smooth the output power fluctuations and enhance the LVRT capability. Based on the theoretical analysis, simulation study which is done by MATLAB/Sinulnk, this thesis carries out the comparison of the SFCL and the DVR for enhancing the grid’s LVRT capability, and the following conclusions can be obtained. 1) The SFCL and the DVR can both assist the grid to reduce fault current level. 2) Regardless of the full-compensation or non-full-compensation DVR, its total cost is more than the SFCL. 3) DVR not only reduce the fault current level but also can compensate voltage power quality issues like voltage sag. 4) Power losses of SFCL is higher than DVR.

Keywords: Key words: SFCL, Fault current limitation, dynamic voltage restorer, power quality