Assessment of Partial Underground Cabling in EHV grid
Partners: ETHZ (FEN)
Duration: 03/2025 - 04/2025
Funding: SFOE
Project Leader: ETHZ (FEN)
Project Team: Dr. C. Yaman Evrenosoglu, Dr. Turhan Demiray
external page Final assessment report by FEN
Swissgrid report (FR: external page short, external page long, DE: external page short, external page long)
The analysis will enable the SFOE to check the plausibility of Swissgrid's analyses and proposals. In addition to a general statement on the study, the analysis will also propose ways of finding solutions to the problems mentioned in this study, in particular:
WP1. Reactive power compensation
a. Quantification of the reactive power to be compensated. Plausibility of Swissgrid's calculations
b. Location of the power-factor correction systems: critical analysis of the proposals made by Swissgrid
c. Alternative solutions (Statcom, larger inductors, etc.): FEN proposal with pros and cons (costs, space requirements, flexibility, etc.)
WP2. EMT studies
a. Plausibility of the calculations and the critical values defined by Swissgrid
b. Are the selected cases realistic (e.g. N-2 case, selected substations)?
c. Investigation of the amplification of harmonics: are alternative solutions possible? (filters, etc.)
WP3. Restoration / blackstart
a. Plausibility of Swissgrid's calculations
b. General alternative solutions for the problems arising from the “South” and “Center” reconstruction cells (from the grid reconstruction concepts).
c. If possible, assessment of the potential problems in the “East” and “West” restoration cells.
The potential of using underground cables (instead of overhead lines) in the Swiss transmission grid (NE1, 380 kV and 220 kV) is discussed and investigated each time a new transmission project is planned or when a renovation/conversion/retrofitting of an existing transmission line is considered. The interest for constructing the new transmission lines as underground cable has increased recently. Although this solution offers certain advantages, an increase in the number of underground cables in Switzerland could potentially lead to restrictions in operation of the transmission grid.
In order to analyze, identify and quantify these restrictions, Swissgrid recently performed a study entitled “Cabling Study Switzerland”, officially known as étude de câblage Suisse.
The first version of this study was recently presented and submitted to the SFOE and ElCom. It consists of 3 work packages (WP):
- WP1: Study on reactive power compensation (Compensation de la puissance réactive)
- WP2: EMT studies at system and equipment level (Études EMT au niveau des systèmes et des équipements)
- WP3: Study on grid restoration (Reconstruction du réseau après black-out)
Swissgrid has analyzed three scenarios for each WP, which are described in the documents which are shared with FEN. The SFOE has carried out an initial analysis of this study and is interested in receiving a critical analysis of these documents from expert.