PhD project – Calculation methods for power systems facing large uncertainties

The power system is facing a number of changes, including a large scale integration of renewable energy sources (RES), changes in the grid such as the introduction of more cables at higher voltage levels, and changes in load composition, such as an increase in energy-efficient appliances and the addition of PV panels. These changes will affect the power system in different ways; one consequence being the occurrence of resonances at lower frequencies. Another consequence is the increased uncertainty regarding the frequency and damping of those resonances.

Uncertainties, e.g. in the operational conditions of the system, or in the modelling of components, can be addressed in several ways. A common approach is to perform Monte Carlo simulations, but depending on the scale of the problem (the model extent, the number of uncertainties and their characteristics, etc.), this may not be practical or even possible. At the other end of the spectrum are deterministic methods, which often use some kind of “worst-case” conditions. In case of significant uncertainties, such methods may give overly pessimistic results, resulting in the use of large design margins and high costs.

The overall objective of the project is to contribute to the development of a robust, secure and flexible power system, without limiting the amount of renewable energy that can be connected. This will be achieved through the development of new calculation methods that can be used to study insulation coordination and power quality in networks under large uncertainties.

The project is carried out by Independent Insulation Group in cooperation with Luleå University of Technology. Math Bollen (LTU) is the main supervisor with Jan Lundquist (I2G) as the co-supervisor.

List of main publications

List of additional publications

  • T. Karmokar, O. Lennerhag, “Simplified approach for investigating overvoltages in DC cables in a ±320 kV Symmetrical Monopolar HVDC System”, International Symposium on High Voltage Engineering (ISH), 2019, Budapest, Hungary
  • O. Lennerhag, A. Dernfalk, P. Nygren, “Harmonics and Supraharmonics in the Presence of Static Frequency Converters Feeding a 16 2/3 Hz Railway System”, International Conference on Harmonics and Quality of Power, 2020
  • O. Lennerhag, R. Rogersten, S. Råström, “A Parallel Resonance Investigation in Stockholm’s Future Cablified Transmission Grid: A Prospective Study on Transformer Energization”, IEEE PES Transmission and Distribution, 2020
  • J. Lundquist, O. Lennerhag, “Minimum Voltage-Current Characteristic for Calculating Surge Arrester Energy Dissipation in Temporary Overvoltage Conditions”, IEEE Transactions of Power Delivery (Early Access), 2021
  • D. Schwanz, M. H.J. Bollen, O. Lennerhag, A. Larsson, “Harmonic Transfers for Quantifying Propagation of Harmonics in Wind Power Plants”, Energies, 14(18), 5798, 2021

Power system model for resonance studies
As part of the project, a power system model suitable for resonance studies has been developed. The model is partially based on an existing grid and the line types, tower configurations, cables, etc., are also based on what is typical in the existing power system. The example grid covers voltage levels from 400 kV to 400 V, with all relevant parameters included. The benchmark model is included in PowerFactory as a built-in example case. It is used within CIGRE WG C4.46 – Evaluation of TOVs in Power Systems due to Low Order Harmonic Resonances. An overview of the 400 , 220 and 130 kV voltage levels is given in the figure below.

The publicly available report “Power System Model for Resonance Studies” (ISBN 978-91-7790-213-3), describing the model and all parameters, is available on the following link:

Power System Model for Resonance Studies

A list of revisions can be found on the link below. Revisions are listed by date. The latest revision was performed 2020-03-04.

TM18-1001-01 Power System Model for Resonance Studies – list of revisions

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