Single-Pole High-Resistance Grounding Protection for DC Distribution Lines Based on Current Integral Quantity Correlation

doi:10.11930/j.issn.1004-9649.202408060

Abstract

Abstract:

When a single-pole high-resistance grounding fault occurs in a DC distribution system, the transient current amplitude is small and the fault characteristics are weak, making it hard for the existing protection methods to provide reliable protection for the DC system. Therefore, a single-pole grounding protection method is proposed for the DC distribution lines based on current integral quantity correlation. According to the transient current characteristics of the high-resistance grounding faults, distinct polarity difference features of fault currents are identified between internal and external faults. The current integral sequence is calculated to highlight the overall change situation of the current. Pearson correlation analysis is employed to quantify the current correlation degree between the line terminals. Based on the correlation level, a fault detection criterion is constructed to achieve protection against single-pole grounding faults in DC distribution lines. Based on PSCAD/EMTDC simulation platform, the simulation results show that the proposed method can provide accurate fault protection under relatively weak fault features, with high protection sensitivity and reliability.

Key words: current variation characteristics, DC distribution network, distributed capacitance, current differential protection

JI Xingquan, MAO Huizong, YE Pingfeng, LIU Zhiqiang, ZHANG Xiangxing, HUANG Xinyue, NI Yachao. Single-Pole High-Resistance Grounding Protection for DC Distribution Lines Based on Current Integral Quantity Correlation[J]. Electric Power, 2025, 58(8): 12-22, 30.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202408060

https://www.electricpower.com.cn/EN/Y2025/V58/I8/12

Figures/Tables 22

Fig.1 Topology of two-terminal flexible DC distribution network

Fig.2 Current loop of capacitors distributed along the lines

Fig.3 Equivalent discharge circuit for capacitors distributed along the lines

Fig.4 Current direction under normal condition

Fig.5 Current direction during internal single-pole grounding faults

Fig.6 Current direction during external single-pole grounding faults

Fig.7 Protection processes

Table 1 DC distribution system parameters

设备	参数	数值
MMC换流器	电压变比	AC 10 kV/DC±10 kV
	容量/(MV·A)	10
	子模块数量	50
	子模块电容/mF	10
	桥臂电感/mH	5
直流电缆	L1长度/km	2
	电阻/(Ω·km^–1)	0.0111
	电感/(H·km^–1)	0.0033
	电容(μF·km^–1)	1.372
光伏	工作模式	最大功率点跟踪
	光照强度/(W·m^–2)	1000
	功率/MW	0.5
储能	功率/MW	1
风电	功率/MW	0.5
直流负荷	功率/MW	1

Fig.8 Current integral quantities of positive and negative poles during internal faults

Fig.9 Positive-negative pole correlation coefficient during internal faults

Fig.10 Current integral quantities of positive and negative poles during external faults

Fig.11 Positive-negative pole correlation coefficient during external faults

Fig.12 Positive-negative pole correlation coefficient in current sudden change method

Table 2 Fault protection in current integral quantity method

故障位置	过渡电阻/Ω	正极相关性系数	负极相关性系数	保护情况
区内	20	–0.9133	0.9779	动作
	70	–0.9863	0.9969	动作
	200	–0.9982	0.9996	动作
	500	–0.9374	0.9999	动作
	750	–0.8956	0.9998	动作
区外	30	0.9965	0.9887	不动作
	70	0.9992	0.9749	不动作
	200	0.9993	0.9776	不动作
	500	0.9997	0.9996	不动作
	750	0.9985	0.9989	不动作

Table 3 Fault protection in current sudden change method

故障位置	过渡电阻/Ω	正极相关性系数	负极相关性系数	保护情况
区内	20	–0.5976	0.3010	动作
	70	–0.5243	0.6461	动作
	200	–0.3987	0.6420	不动作
	500	0.8963	0.9152	不动作
	750	0.9489	0.9345	不动作
区外	30	0.7897	0.2115	不动作
	70	0.8458	0.6476	不动作
	200	0.8909	0.6248	不动作
	500	0.9876	0.9896	不动作
	750	0.9328	0.9420	不动作

Fig.13 Current integral quantities at both positive and negative poles during internal faults with 10 dB noise

Fig.14 Positive-negative pole correlation coefficient in current sudden change method with 10 dB noise

Fig.15 Positive-negative pole correlation coefficient during internal faults with 10 dB noise

Table 4 Fault protection with 10 dB noise

故障位置	过渡电阻/Ω	正极相关性系数	负极相关性系数	动作情况
区内	30	–0.9044	0.9790	动作
	70	–0.9947	0.9912	动作
	200	–0.9948	0.9968	动作
	450	–0.9180	0.9988	动作
	500	–0.9660	0.9982	动作
区外	30	0.9944	0.9776	不动作
	70	0.9970	0.9001	不动作
	200	0.9856	0.9776	不动作
	450	0.9985	0.9776	不动作
	500	0.9947	0.9953	不动作

Fig.16 Positive and negative voltages under different faults

Fig.17 Current integral quantities at both positive and negative poles on the AC side during single-phase grounding faults

Fig.18 Positive-negative pole correlation coefficient on the AC side during single-phase grounding faults

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