Thesis
Asymmetrical operation of EHV transmission lines
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2026
- Thesis identifier
- T18088
- Person Identifier (Local)
- 202051690
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- The increasing penetration of Renewable Energy Sources (RES) and Inverter-Based Resources (IBR) is changing the operational behaviour of modern power systems. As conventional synchronous generation is displaced, transmission networks are required to operate with reduced inertia, increased power-electronic interfacing, and greater sensitivity to major line outages. In this context, the complete disconnection of an Extra-High-Voltage (EHV) overhead transmission line following an asymmetrical fault may lead not only to the loss of load supply, but also to the disconnection of significant generation connected along the transmission corridor. Since single-phase and two-phase faults represent a large proportion of transmission-line faults, Asymmetric Operation (AO), in which a line remains in operation with one or two phase conductors open, may offer a means of maintaining partial power transfer during selected post-fault conditions. This thesis presents a simulation-based investigation of different forms of AO in long EHV overhead transmission lines, with emphasis on electromagnetic modelling, converter-based sequence-current mitigation, and safety-related voltage assessment. First, a high-fidelity three-phase simulation model of a long overhead power transmission line is developed. The model explicitly represents electromagnetic coupling between conductors, ground wires, tower structures, and earth return paths, allowing zero-sequence current distribution and transient behaviour during AO to be studied more accurately than with conventional simplified π-section representations. Second, a converter-based support strategy is developed using E-STATCOMs located at the line extremities. A filterless two-degree-of-freedom internal-model-control (2DF–IMC) approach is adapted for the detection and suppression of negative- and zero-sequence current components. The proposed control structure enables rapid sequence-current mitigation without relying on resonant filters or narrow-band signal processing stages, while preserving the nominal positive-sequence operation of the converter-interfaced devices. The proposed modelling and control framework is evaluated on a representative 500kV, 300km overhead transmission line under one-phase and two-phase asymmetric operating conditions. Simulation results indicate that, for the studied system and scenarios, AO can maintain controlled power transfer after selected asymmetrical faults when supported by appropriate converter-based sequence-current compensation. The results also show that negative- and zero-sequence currents can be substantially reduced, voltage profiles at the line terminals can remain within acceptable limits, and tower-tip voltages can satisfy the voltage-based safety criterion considered in this work. Cases with no pre-fault power restoration, partial restoration, and full restoration are also examined to assess the operational implications of different AO support levels. The findings strongly suggest that AO may provide a potential resilience-enhancing operating option for future converter-dominated transmission systems. However, the study also shows that AO is not a universally applicable solution and would require additional converter capacity, control functionality, protection coordination, operational procedures, and techno-economic justification. Therefore, the contribution of this thesis is not to establish immediate practical deployment of AO, but to provide a physically grounded simulation framework and control methodology for assessing its technical potential.
- Advisor / supervisor
- Campos-Gaona, David
- Resource Type
- DOI
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PDF of thesis T18088 | 2026-07-06 | Public | Download |