Fault Mechanism Analysis and One-terminal Protection Method of Flexible DC Transmission Line under the Influence of Multi-type Faults

doi:10.11930/j.issn.1004-9649.202404004

Abstract

Abstract:

Multi-terminal flexible DC transmission line protection faces various fault types and is susceptible to factors such as transition resistance and noise. To address this, a fast-action protection method for the entire flexible DC line using single-ended voltage gradient energy values is proposed, which can protect the entire length of the line based solely on single-ended measured voltage. The voltage fault characteristics inside and outside the flexible DC line are analyzed, and an improved voltage gradient algorithm is introduced to construct a protection initiation criterion. Furthermore, a full-line fault protection criterion based on energy value comparison is constructed, and fault pole selection is achieved based on the different ranges of positive and negative energy ratios under unipolar or inter-pole faults. Simulation verification shows that the proposed method can quickly identify faults inside and outside the zone, determine the fault pole, and exhibits good noise immunity and high resistance tolerance.

Key words: flexible DC line, single-ended protection, improved voltage gradient, fault zone identification

CLC Number:

TM733

Zongjun MU, Junhong QIU, Zhenxing LI, Weidong WANG, Dengxin LIU, Bin HU. Fault Mechanism Analysis and One-terminal Protection Method of Flexible DC Transmission Line under the Influence of Multi-type Faults[J]. Electric Power, 2025, 58(1): 107-114.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202404004

https://www.electricpower.com.cn/EN/Y2025/V58/I1/107

Figures/Tables 10

Fig.1 The transmission system of four-terminal MMC

Fig.2 Voltage gradient energy value of positive grounding external fault

Table 1 Transmission line parameters of Zhangbei four-terminal flexible DC transmission

MMC	额定容量/ MW	额定直流电压/ kV	桥臂电感/ mH	平波电抗器/ mH	子模块电容值/ mF	单桥臂子模数/ 块	交流侧线电压/ kV
MMC1	1500	500	75	200	10	200	330
MMC2	1500	500	75	200	10	200	330
MMC3	3000	500	75	200	10	200	330
MMC4	3000	500	75	200	10	200	330

Fig.3 The voltage gradient value is when the positive grounding faults

Fig.4 Positive metal grounding fault at F3

Fig.5 The inter-pole metallic grounding fault at F3

Fig.6 The negative metallic grounding fault at F3

Fig.7 A 700 Ω resistance grounding positive fault at F3

Table 2 Simulation results of multiple external faults

故障类型	故障位置	E_P/kV²	E_N/kV²	判断结果
正极接地	F₄	3.327×10⁴	5656	区外正极
正极接地	F₁₂	3.061×10⁴	4500	区外正极
负极故障	F₄	5607	3.039×10⁴	区外负极
负极故障	F₁₂	4067	3.097×10⁴	区外负极
极间故障	F₄	2.979×10⁴	3.146×10⁴	区外极间

Fig.8 Current fault component similarity method

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