Impact of Adding Fast Switching Fault Current Limiter (FSFCL) to the Neutral Point of 220 kV Transformer

Abstract

In recent years, as the power grid continues to expand, the issue of asymmetrical short-circuit currents exceeding limits on the 220 kV medium-voltage side has become increasingly severe, and traditional current-limiting methods have certain limitations. Therefore, this paper explores the potential benefits and feasibility of installing a Fast Switching Fault Current Limiter (FSFCL) at the neutral point of a 220 kV transformer to effectively limit asymmetrical short-circuit currents on the medium-voltage side. The paper first analyzes the current-limiting performance of the FSFCL under different installation configurations, transformer operating conditions, and fault conditions through theoretical calculations. Subsequently, through simulation studies, the impact of different limiting reactance values on the overvoltage effect at the neutral point is discussed. The results show that the installation of the FSFCL has a significant effect on suppressing the asymmetrical short-circuit current on the medium-voltage side of the transformer, but this measure has also led to an increase in the voltage at the grounded neutral point. Finally, taking the No. 2 main transformer of a certain 220 kV substation as an example, to achieve the expected current-limiting effect, the limiting reactance value of the FSFCL needs to be at least 4 ohms. At this reactance value, the overvoltage level at the neutral point remains well below the withstand limit of its insulating material. Additionally, given the existing overvoltage protection devices at the neutral point, no further overvoltage protection measures are required.

Keywords

• asymmetrical short-circuit fault
• transformer neutral point
• fast switching fault current limiter
• neutral point overvoltage
• relay protection
• short-circuit current calculation