Analysis of fault current and overvoltage at the neutral point of ±800 kV High-Voltage DC converter transformer

• Published in: Energy reports Vol. 8; pp. 292 - 300
• Main Authors: Fu, Jiaqing, Han, Yang, Yang, Ping, Wang, Congling, Zalhaf, Amr S.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2022; Elsevier
• Subjects: Converter transformers; Fault current; Grounding overvoltage; HVDC; Neutral point; Grounding overvoltage; Neutral point; Fault current; Converter transformers; HVDC
• ISSN: 2352-4847; 2352-4847
• DOI: 10.1016/j.egyr.2022.05.195

In order to enhance the security of ±800 kV High-Voltage DC (HVDC) system, it is needed to consider and analyze the grounding mode of the neutral point of converter transformer. Different neutral grounding modes have different inhibitory effects on the current of transmission lines when faults occur, and also produce different overvoltages at the neutral point. Therefore, this paper first analyzes the influence of converter transformer on fault current and neutral point voltage in three cases of ungrounded, direct grounding and via small reactance grounding. Through the analysis, it is known that the neutral grounding via small reactance is the most suitable for the HVDC transmission system. Then the model of ±800 kV bipolar HVDC transmission system is built in PSCAD/ EMTDC simulation software and analyzed under two typical conditions of grounding overvoltage and breaking overvoltage. By comparing several cases of converter transformer neutral point grounding directly, via 5Ω, 10Ω, 17Ω, 20Ω and 25Ω reactance grounding, it is found that grounding via small reactance can effectively suppress fault current. However, with the increase of the resistance value, the inhibitory effect will gradually weaken and cause the increase of the neutral point overvoltage.