h1

%0 Thesis
%A Penthong, Thanakorn
%T Towards automatization of distance protection coordination and interoperability testing for digital substations; 1. Auflage
%V 148
%I Rheinisch-Westfälische Technische Hochschule Aachen
%V Dissertation
%C Aachen
%M RWTH-2026-01676
%@ 978-3-948234-62-1
%B E.ON Energy Research Center
%P 1 Online-Ressource : Illustrationen
%D 2026
%Z Druckausgabe: 2026. - Auch veröffentlicht auf dem Publikationsserver der RWTH Aachen University
%Z Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2025
%X Motivation, Goal and Task of the Dissertation: Distance protection is a protection function widely used in transmission systems due to its selectivity and speed. Before field deployment, the distance relay (DR) must be set, and its setting must be coordinated with other DRs within the system. For configuring the DR settings and validating their coordination, path determination is fundamentally required to identify the electrical elements, such as lines, buses, switches, and circuit breakers (CBs), within the protection zones of DR to be protected. Conventionally, path determination is a manual process, same for DR settings and DRs coordination validation, error-prone procedures, especially in the case of complex network topologies (e.g., loop/multi-loop networks) and/or when many DRs are implemented in the grid. This is even more so when DRs from different vendors are employed, as they are characterized by different parameter settings with different functions, e.g., power swing, load encroachment, etc. Nonconventional approaches, such as those based on graph theory and graph search algorithms, e.g., Depth-First Search (DFS), can automate path determination; however, these methods are still susceptible to errors, especially in complex network topologies. Besides DR settings and DRs coordination validation, DR testing is a crucial activity to identify DR issues due to, e.g., setting misconfiguration, and firmware bugs, as well as to evaluate the effectiveness of the fault detection approaches. These test activities are done to ultimately prevent the disruptive effects of protection failures. For DR testing, the IEC 60255-121:2014 standard is an important reference, which specifies the minimum sets of requirements (zone characteristics, maximum deviation of operating time, etc.) for a limited set of functions. With such limitations, the performance of the DR in certain realistic fault characteristics and system behaviors during dynamic conditions remains untested and unevaluated. This ultimately results in DRs may misoperate, underreach, or trip unnecessarily, leading to system instability or blackouts, e.g., DR may trip during stable power swings (DR must not trip under stable swings and must be differentiate between fault and power swings, as well as stable and unstable swings), underreach due to fault resistances, etc. Therefore, the IEC 60255-121:2014 standard and existing methodologies are inadequate to test additional functions-such as power swing, fuse failure, fault location-, whose testing is left to the final users based on their specific requirements. Moreover, the one-at-a-time (OAT) testing approach for evaluating DR performance presented in the previous works cannot capture the interaction among factors (e.g., fault resistance, fault location, fault inception angle, etc.). Besides the OAT approach, a full factorial strategy recommended by the IEC 60255-121:2014 standard to test the factors potentially affecting the DR performance quickly leads to hundreds or thousands of tests; also, this cannot handle the constraints among factors. Fundamentally, a digital substation consists of a high voltage level as a transmission system and a medium voltage level as a distribution system. The medium voltage level acts as the intermediary between transmission infrastructure and local distribution networks, enabling the efficient delivery of electrical power to end-users across residential, commercial, and industrial sectors. Within this context, the protection of distribution feeders is therefore essential to maintaining system reliability and preventing wide-area blackout under abnormal operating conditions, e.g., feeder fault, multiple feeder faults (MFFs), etc. Among the available protection strategies, overcurrent relays (ORs) are most widely adopted as a primary feeder protection. This preference arises from their inherent simplicity, proven reliability, and cost-effectiveness compared to more complex alternatives such as distance or differential protection. However, the existing overcurrent protection function is vulnerable to MFFs even if the ORs within the substation can coordinate with each other at all fault current values. The MFFs cause the OR at the incoming feeder to operate faster than the faulted feeder ORs. This ultimately results in all feeders connected to the power transformer being de-energized, including the healthy ones. Furthermore, unlike conventional substations, digital substations are characterized by the deployment of standardized communication frameworks, particularly those defined in IEC 61850 to facilitate communication between devices coming from different manufacturers, and ultimately foster interoperability (IOP). The conformity of a device with the IEC 61850 standard does not guarantee IOP with devices from different manufacturers. Therefore, the use of relay compliance to the IEC 61850 standard from multiple vendors within the digital substation poses a challenge in IOP to perform protection schemes at the bay level. Hence, IOP testing prior to field implementation is crucial for ensuring that relays from different vendors work seamlessly together based on protection schemes, e.g., detecting and identifying inter-bay faults. Within this context, the IOP testing focuses on the ORs for testing and validating the proposed protection scheme in addressing MFFs. Guidelines for IOP testing have been documented in previous studies. However, these references are not suitable for practical testing at a system level for testing the IOP to assess the performance of the protection scheme of multi-vendor bay-level ORs, e.g., breaker failure, arc detection, etc. Hence, such methodologies are left to the end users, who align them with their specific requirements. Overall, the following three main challenges and goals are identified:1. In the context of DR settings and DRs coordination validation, conventional techniques adopted by protection engineers require manual, prone-to-error intervention, which becomes time-consuming even for a limited number of single/multi-vendor DRs. When adopting sophisticated algorithms such as DFS, their applicability boundary is limited to simple topologies. Hence, the goal is to propose novel algorithms for automatizing the path determination, DR settings and DRs coordination validation, which can be applicable regardless of the network topology, can handle apparent impedance with/without multiple currents fed by generation units, without under- and over-reach issues of the protection zones, as well as the different fault detection setting parameters of multi-vendor DRs can be mathematically mapped and converted without losing selectivity, have better accuracy and lesser computational time than manual and DFS-based techniques.2. In the context of DR testing, the IEC 60255-121:2014 standard and existing methodologies can be used only in a limited set of impedance-based functions, and OAT cannot observe the key interactions among factors. Furthermore, the recommended full factorial strategy results in a large number of experiments, and this cannot handle the constraints between factors. Hence, the goal is to propose testing methodologies that allow testing a broader spectrum of functions and enable the optimal choice of the tests to reduce the experiment burden while constraining the experimental effort.3. In the context of MFFs and IOP testing for digital substations, the MFFs cause a wide-area blackout in the distribution systems, and the existing overcurrent protection function cannot prevent blackouts from the MFFs. Furthermore, the IEC 61850 standard does not guarantee IOP of ORs from different vendors, and available IOP testing methodologies are not suitable for practical testing at a system level. Hence, the goal is to propose an IEC 61850-based overcurrent protection scheme to support existing overcurrent protection functions in addressing MFFs, and a methodology that allows testing the IOP of multi-vendor bay-level relays to assess the performance of the protection schemes. Major Scientific Contributions: First, novel and more broadly applicable algorithms are developed to automatize the path determination, DR settings and DRs coordination validation, namely: (1.1) an extended version of the DFS algorithm-Modified Depth-First Search (MDFS)-for path determination within the DR protection zones which is applicable irrespective of the network topology complexity; (1.2) a MDFS-based algorithm for DR settings that is able to straightforwardly compute the apparent impedance seen by the DR more accurately, it is applicable for mapping parameters based on apparent fault impedance for multi-vendor DRs, and it has better performance in terms of path determination errors; (1.3) a MDFS-based algorithm for validating the DRs coordination with enhanced properties in terms of computational time and can highlight overlapping protection zones to facilitate intuitive verification of coordination. Second, (2.1) a test environment is developed based on a real-time digital simulator of a transmission system model and testing methodologies to assess the performance of the commercial DRs. This framework aims to overcome the limitations of state-of-the-art testing approaches (including the IEC 60255-121:2014 standard), that allows covering a broader spectrum of functions such as power swing, fuse failure, and fault location, etc.; and (2.2) the statistical design of experiments is introduced for DR testing to aid in the optimal choice of the tests and enhance experimental efficiency by focusing on impactful factors while retaining the efficacy, objectivity, reproducibility, and generalization of the testing activity. Third, (3.1) an IEC 61850-based overcurrent protection scheme is proposed for detecting and identifying multi-bay faults to reduce the outage areas caused by MFFs, and (3.2) the development of a test environment based on a real-time digital simulator of a distribution system model with the integration of distributed generation for the IOP testing of multi-vendor relays at the bay level to assess the performance of the protection scheme is presented.
%F PUB:(DE-HGF)11 ; PUB:(DE-HGF)3
%9 Dissertation / PhD ThesisBook
%R 10.18154/RWTH-2026-01676
%U https://publications.rwth-aachen.de/record/1028508