Earth Fault Location in Non-Radial Resonant Grounded Networks – Theory, analysis and methods
Doctoral thesis
Permanent lenke
https://hdl.handle.net/11250/3115908Utgivelsesdato
2024Metadata
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- Institutt for elkraftteknikk [2500]
Sammendrag
A common grounding scheme for medium voltage distribution networks and high voltage sub-transmission networks is the resonance grounding scheme. Resonant grounded networks have few interruptions and a high quality of supply, but an important drawback is the particularly challenging conditions for protection systems and fault location methods during earth faults. Specialized methods are required to detect and locate earth faults, and although many fault location methods have been proposed and developed over several decades, reliable earth fault location remains a challenge. The fault location process can often become a manual process of trial and error, and it may take several hours to successfully locate faults. Earth faults are accompanied by overvoltages which are harmful to components in the network, and permanent faults can lead to insulation failure and additional faults. The classical distribution network is radial in structure, and the conventional fault location methods have also utilized this property. The high voltage sub-transmission network is however meshed, and increased meshing of the medium voltage networks as well alters the conditions for fault location methods. This can create both challenges and new opportunities.
This thesis studies earth fault location in non-radial networks. The research methods used include modelling and analysis of networks using electromagnetic transient software, theoretical analysis and development of novel fault location methods, and laboratory tests conducted using physical relays and network models.
First, the application of transient earth fault relays in non-radial networks is studied. Being the only real alternative in the meshed, subtransmission network, these relays have been used extensively over many years. However, transient earth fault relays have gained a reputation for being unreliable among several network operators, and operators are often reluctant to fully trust the relays’ responses during faults. Understanding how well these relays really work in a non-radial network topology is therefore one important motivation behind the research presented in this thesis. Four different transient earth fault relays are analysed and tested in a laboratory setup with the goal of understanding their fault direction indication in non-radial networks. The results show that the lack of a clear forward/reverse direction combined with their inability to gauge fault distance can lead to inconclusive and contradictory responses in non-radial networks. Furthermore, as relays in different locations can have different operating conditions, it is concluded that each relay in the network should be analysed and set individually, contrary to what several relay manuals indicate. Changes made to the network topology in normal operation can also change the conditions for the relays in the network, so careful planning and analysis in advance is required to ensure selectivity and coverage for all faults. A lack of such planning is identified as the most likely cause of the problems experienced by network operators.
Second, the thesis presents novel fault location methods which contribute to more efficient fault location in non-radial networks. The research contributes to the development of methods aimed at precise distance to fault estimation in closed-ring networks, which are verified with promising results in simulations for both permanent and transient faults. The thesis also presents a method for detection, location and clearing of high impedance earth faults. This method consists of two independent earth fault indicators, one of which can be used to provide continuous fault indication throughout a sectionalizing process. As a result, the method can aid the network operator in narrowing down the estimate of the fault location. Laboratory tests demonstrate the feasibility of the proposed method, but the method’s sensitivity is ultimately limited by the quality of the current measurements. The two earth fault indicators function up to 15–20 kΩ and 50 kΩ in the laboratory, respectively, but further study of real current sensors is required to predict the sensitivity in real networks.
Består av
Paper 1: Treider, Thomas; Gustavsen, Bjørn; Høidalen, Hans Kristian. Analysis of transient earth fault relays in meshed resonant grounded networks. I: 16th International Conference on Developments in Power System Protection (DPSP 2022). Institution of Engineering and Technology (IET) 2022 ISBN 978-1-83953-719-6. s. 350-355. © The Institution of Engineering and Technology 2022.Paper 2: Treider, Thomas; Hoidalen, Hans Kristian. Polarity crossover regions of transient earth fault relays in non-radial resonant grounded networks. Electric power systems research 2023 ;Volum 223. Published by Elsevier B.V. This is an open access article under the CC BY license. Available at: http://dx.doi.org/10.1016/j.epsr.2023.109598
Paper 3: Zerihun, Tesfaye Amare; Treider, Thomas; Taxt, Henning; Nordevall, Lars B.; Haugan, Thomas Sagvold. Two novel current-based methods for locating earth faults in unearthed ring operating MV networks. Electric power systems research 2022 ;Volum 213. s. Published by Elsevier B.V. This is an open access article under the CC BY license. Available at: http://dx.doi.org/10.1016/j.epsr.2022.108774
Paper 4: Treider, Thomas; Hoidalen, Hans Kristian. Estimating distance to transient and restriking earth faults in high-impedance grounded, ring-operated distribution networks using current ratios. Electric power systems research 2023 ;Volum 224. s. - Published by Elsevier B.V. This is an open access article under the CC BY license. Available at: http://dx.doi.org/10.1016/j.epsr.2023.109765
Paper 5: Treider, Thomas; Gustavsen, Bjørn; Høidalen, Hans Kristian. Steady-state, iterative method for locating and clearing permanent high impedance earth faults in compensated networks. I: 16th International Conference on Developments in Power System Protection (DPSP 2022). Institution of Engineering and Technology (IET) 2022 ISBN 978-1-83953-719-6. s. 327-332. © The Institution of Engineering and Technology 2022.
Paper 6: Treider, Thomas; Høidalen, Hans Kristian. Implementation and laboratory verification of method utilizing phase and neutral quantities for detection and location of low-current earth faults in resonant grounded networks. IET Generation, Transmission & Distribution 2023 ;Volum 17. s. 5446-5457. Published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology. This an open access article under the terms of the Creative Commons Attribution License CC BY. Available at: http://dx.doi.org/10.1049/gtd2.13059