Key Takeaways & Executive Findings
- •• • The adaptive distance protection setting is updated every 5 minutes, which reduces the impact of solar irradiance fluctuations on protection reliability; in contrast, prediction-based methods exhibit significant setting errors when actual irradiance deviates from forecast samples, increasing the risk of protection failure. • • The scheme relies solely on local measurements to iteratively solve the IIDG short-circuit current, eliminating the need for real-time data exchange between line ends; this cuts communication infrastructure investment, which is particularly advantageous for distribution networks with limited communication capabilities. • • The proposed protection remains immune to variations in IIDG-T connected capacity, fault location, and fault type (three-phase and two-phase short circuits), effectively resolving maloperation and failure issues caused by T-connected IIDG integration in active distribution networks. • • By dynamically adjusting the distance protection setting in response to IIDG output fluctuations, the scheme suppresses the negative effects of T-connected IIDG output variability on protection performance, thereby enhancing operational reliability under high penetration of renewable generation.
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Abstract
The proliferation of inverter-interfaced distributed generators (IIDGs) connected via T-taps in distribution networks degrades the reliability of conventional distance protection, causing maloperation or failure due to the low-voltage ride-through (LVRT) control strategy that dynamically adjusts IIDG output currents. This paper analyzes the fault output characteristics of IIDGs and the resulting impedance measurement errors in traditional distance protection. Based on fault equivalent networks, the evolution of electrical quantities in IIDG-T-connected distribution lines is derived. A complete adaptive distance protection scheme is proposed for three-phase and two-phase short-circuit faults. The scheme iteratively solves the IIDG short-circuit current using only local measurements, computes an adaptive setting coefficient, and dynamically updates the distance protection setting every 5 minutes. Simulation results on PSCAD/EMTDC demonstrate that the proposed scheme is immune to IIDG-T capacity, output fluctuations, fault location, and fault type. It eliminates the need for communication infrastructure, reduces costs, and maintains high reliability under solar irradiance variations, overcoming the limitations of prediction-based methods that suffer from large errors when irradiance deviates from forecast samples.
1. Introduction
Distribution networks are undergoing a fundamental transformation as inverter-interfaced distributed generators (IIDGs), particularly photovoltaic systems, are increasingly connected via T-taps. This configuration introduces complex fault characteristics that traditional distance protection cannot handle. The LVRT control strategy of IIDGs dynamically adjusts output currents based on point-of-common-coupling voltage, causing random offset in measured impedance and leading to protection maloperation or failure. Existing solutions, such as improved pilot differential protection, require high-bandwidth communication between line ends, which is economically prohibitive for many distribution networks. Adaptive current protection schemes avoid communication but struggle to accurately compute T-connected IIDG output currents, especially under varying solar irradiance.
This paper addresses the bottleneck by proposing an adaptive distance protection principle that uses only local measurements. The method first analyzes the IIDG fault output characteristics and the adaptability of conventional distance protection. Then, based on fault equivalent networks, it derives the evolution of electrical quantities in IIDG-T-connected lines. A complete protection scheme for three-phase and two-phase short circuits is constructed, with settings updated every 5 minutes to track IIDG output fluctuations. The scheme is validated on PSCAD/EMTDC, demonstrating immunity to IIDG capacity, fault location, and fault type, while eliminating communication costs and improving reliability under solar irradiance variability.
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DAI Zhihui, NING Zhiheng, LIU Meiyuan, LIU Junyi (2026). Adaptive Distance Protection Principle for Distribution Lines with T-Connected Inverter-Interfaced Distributed Generators. Acta Energiae Solaris Sinica. https://doi.org/10.19912/j.0254-0096.tynxb.202608_9695
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Frequently Asked Questions
How does the proposed adaptive distance protection handle the random offset in measured impedance caused by IIDG LVRT control?
The scheme iteratively solves the IIDG short-circuit current using local voltage and current measurements, then computes an adaptive setting coefficient that dynamically adjusts the distance protection setting. This compensates for the impedance offset, ensuring correct operation. Simulation results confirm immunity to IIDG-T capacity and fault type, with settings updated every 5 minutes to track output fluctuations.
What are the communication requirements and associated costs compared to pilot differential protection?
The proposed scheme requires no communication between line ends, as it relies solely on local measurements. This eliminates the need for high-bandwidth communication infrastructure, significantly reducing investment and operational costs, especially in distribution networks where communication networks are not well developed.
How does the scheme perform under rapid solar irradiance fluctuations that cause large deviations from forecast data?
The protection setting is updated every 5 minutes based on real-time local measurements, effectively tracking irradiance-induced IIDG output changes. In contrast, prediction-based methods suffer from significant setting errors when actual irradiance deviates from forecast samples, increasing failure risk. The proposed method thus maintains high reliability under variable weather conditions.
Is the protection scheme effective for both three-phase and two-phase short-circuit faults, and does it require different settings?
Yes, the scheme includes complete protection logic for both three-phase and two-phase short-circuit faults. The adaptive setting coefficient is derived for each fault type, and simulation results confirm correct operation without interference from fault type or location.
What are the scalability limitations when multiple IIDGs are connected via T-taps on the same feeder?
The scheme is designed for IIDG-T connections and has been validated under varying IIDG capacities. While the paper does not explicitly test multiple IIDGs, the local measurement-based iterative approach can be extended to multiple T-connected IIDGs by solving the network equations for each IIDG current. Further research is needed to confirm performance in such scenarios.
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