基于等效负荷分支的配电网功率纵联保护方案

doi:10.19595/j.cnki.1000-6753.tces.251586

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Abstract With the large-scale integration of distributed generation (DG), traditional single-source radial distribution networks have evolved into complex multi-source power supply networks, resulting in significant changes in their fault characteristics. The sensitivity and reliability of traditional three-stage overcurrent protection are difficult to guarantee. Pilot protection, with its superior selectivity and sensitivity, demonstrates greater advantages in modern distribution networks. Considering engineering implementation costs, distribution networks permit loads to be connected as non-measurable branches in a T-configuration. Due to the current diversion effect of these non-measurable branches, traditional current or power differential protection faces a risk of maloperation during external faults or under normal operating conditions. Raising the protection threshold to account for the current of large-capacity load branches would significantly reduce protection sensitivity for internal faults. Therefore, to mitigate the impact of non-measurable branches on the protection scheme, this paper proposes a pilot protection method based on an equivalent load branch.
Firstly, the reasons for the reduced adaptability of traditional power differential protection following the T-connection of non-measurable load branches are analyzed, highlighting the dead-zone issue of conventional protection during metallic grounding faults at the line outlet. Secondly, by integrating the impedance characteristics of distribution lines and loads and based on the principle of star-delta equivalent network transformation, a network parameter estimation method with low data synchronization requirements is proposed using the phase voltage and current information from both ends of the protected line. The estimation error for T-connected nonlinear loads is analyzed, and an adaptive restraint setting method based on voltage variation characteristics is constructed. Then, by analyzing the difference characteristics between the calculated and measured power at both ends of the protected line under different voltage sag levels during internal and external faults, as well as the influence of fault output characteristics from external distributed generation sources on the protection, a protection initiation criterion based on the equivalent load branch is established. This effectively reduces the impact of non-measurable load branches on the protection. Finally, leveraging the differences in power factor characteristics between transition resistance and large-capacity loads, along with the difference characteristics between estimated and measured power under different fault types, a load switching identification criterion is introduced. This prevents protection maloperation and effectively enhances protection reliability.
Verified through PSCAD simulations and actual field fault recording data, the proposed protection scheme offers the following advantages: (1) It fully considers the influence of nonlinear load models, proposing an equivalent network parameter estimation method and a pilot protection criterion with low data synchronization requirements, thereby effectively reducing communication costs. (2) The protection scheme exhibits high reliability and sensitivity, featuring no dead zone for internal faults and no maloperation for external faults. With a protection threshold of 0.05 MV·A, it demonstrates a transition resistance withstand capability exceeding 250 Ω. (3) It fully accounts for the impact of load switching on protection. By incorporating a load energization identification criterion based on the active/reactive power difference ratio, it ensures the protection does not maloperation during scenarios involving high-capacity load energization. The effectiveness of this protection scheme has been validated in typical distribution network structures with varying distributed generation penetration levels, demonstrating considerable potential for engineering application.

Key words： Power pilot protection unmeasurable branches equivalent networks synchronism load switching

Received: 11 September 2025

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TM614

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	Articles by authors
	Li Ao
	Zhao Yufeng
	Xue Haoyue
	Wang Zengping
	Wang Tong

Cite this article:

Li Ao,Zhao Yufeng,Xue Haoyue等. Power Pilot Protection Scheme for Distribution Networks Based on Equivalent Load Branches[J]. Transactions of China Electrotechnical Society, 2026, 41(19): 6740-6752.

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https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.251586 OR https://dgjsxb.ces-transaction.com/EN/Y2026/V41/I19/6740

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