Study of overvoltages and insulation coordination of the DMR

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Your tasks

Mission Build a reference EMTP case of a bipolar VSC-HVDC link with a cabled metallic return, and conduct a parametric study on the overvoltages along the DMR.

Internship Objective Build a reference EMTP case of a bipolar VSC-HVDC link with a cabled metallic return, and conduct a parametric study in order to identify the important parameters and constraints to be kept for the insulation coordination of the DMR.

Expected Work

• Analysis of CIGRE and external works on bipolar links with metallic return and on the insulation coordination of HVDC cables, in order to establish the study framework and the catalog of parameters to explore.
• Construction under EMTP of the bipolar VSC-HVDC link case with cabled DMR, starting from a base case: converter stations, pole and return cables, grounding, surge arresters, protections, operating modes and operating conditions.
• Parametric study of the effect of cable characteristics, the grounding concept, faults (type, location, clearing time), the protection level of surge arresters, and pre-fault conditions, on the overvoltages along the DMR.
• Extraction of peak values along the DMR and the stress experienced by the surge arresters, followed by a sensitivity analysis to prioritize influential parameters.
• Analysis of results and formulation of the constraints to be kept for the insulation coordination of the DMR.

Expected Results

• A documented and reusable reference EMTP case.
• Parametric results allowing for a better definition of the insulation constraints of a cabled DMR.
• A potential scientific publication if the results provide new elements.

Requirements

• Basic knowledge in electrical engineering and electrical networks.
• Notions of electromagnetic transients and practice of modeling (networks, cables, converters).
• Interest in HVDC links and associated insulation issues.
• Practice of simulation in the transient domain (EMTP or equivalent); experience with EMTP is a plus.
• Ability to read and synthesize technical and scientific documentation in English.
• Autonomy and an interest in physical modeling.

• Student in the final year of engineering school or in Master 2, with a background in electrical engineering, electrical networks, or electromagnetism.
• Experience in electromagnetic modeling or simulation in the transient domain is a plus, but not necessary.
• An internal training program is planned (mastering EMTP, HVDC cable modeling, insulation coordination).
• Good command of scientific English.

Other

Internship Subject Context Bipolar HVDC links can be equipped with a dedicated metallic return (DMR), an additional cable allowing part of the transit to be maintained in case of the unavailability of one pole. In this configuration, the DMR is normally very close to ground potential, but certain faults and changes in operating mode can apply significant overvoltages to it. Recent works (CIGRE B) show that the maximum can appear inside the link and exceed the voltage limited by the surge arresters placed at the ends. The overvoltage levels to be kept for the sizing of its insulation remain poorly documented. Available publications give a general indication of the phenomena, without detailing the parameters that govern them, and CIGRE recommendations relating to HVDC cable testing (TB 852) do not set a level for the return cable: they refer to client-supplier negotiation and system calculations. The quality of the study therefore directly conditions the specification of the DMR insulation.

Means The work relies on the EMTP electromagnetic transient simulation software and on the base case. The internship may lead to interactions with foreign partners (electricity transmission, manufacturers, working groups) on the insulation of HVDC links. The internship report will be written in English.