Geomagnetically Induced Currents (GIC)

Influence of low frequency currents on power transformers and the transmission grid

Cause of the low frequency currents
The cause of the low frequency currents (LFC) has already been identified as geomagnetic disturbances (GMD), which are caused by the interaction of the Sun with the Earth's magnetic field (Figure 1). These geomagnetically induced currents are also referred as GIC, which can be calculated by an in house programmed software-tool.

Figure 1: Principle of geomagnetic induction in the Earth

Other causes and sources of the low-frequency currents are the subject of current research.

Power Transformers
The low-frequency currents in the high-voltage network cause problems, especially in transformers. The currents cause increased noise, distortion of the voltage and heating of the transformer. This also negatively affects the stability and the transmission grid. In order to investigate the effects of the low-frequency currents in more detail and to better understand them, experiments with transformers are being carried out in the institutes own laboratory as part of the “Nf-Sternpunkt 2” project. For this purpose, two distribution grid transformers, such as those found on power poles in rural areas, were converted. The conversion allows the transformers to be connected in any vector group on the low-voltage side and makes the high-voltage neutral point accessible from the outside.

Figure 2: Laboratory at IEAN with modified power transformers

In the experiments, the transformers are connected to each other, e.g. on the high-voltage side, and a direct current is fed in via the neutral point. In this way, an arrangement comparable to that in the high-voltage grid can be tested in the laboratory.

Network Calculation
In the simulation program (Figure 3), GICs and their effects on transformers and transmission systems can be calculated. Magnetic field data, earth conductivities and the use of a plane wave method lead an electric field. With transmission network data, including the coordinates of the substations, voltages and subsequently the currents in transformers, lines and earth electrodes are calculated. Furthermore, constant electric fields can be specified for worst-case analyses.

Figure 3: GIC calculation tool

From these calculations, recommendations for the safe operation of transmission systems can be derived.

Measurement System
Currently, the neutral point currents are measured at 7 transformers in APG's Austrian high-voltage grid (Figure 4).

Figure 4: Austrian transmission grid with measurement locations

The measurement data in 1-second intervals allow the validation of the calculations from the software and the laboratory tests. The measurement system was developed specifically for these measurements at the institute (Figure 5, Figure 6). It allows automated measurement and remote access to the measurement data. All signals with a frequency greater than 0.5 Hz are filtered out of the measurement signal. Thus, only the low-frequency currents are recorded

Figure 5: Neutral point current measurement system with heating system

Figure 6: Installed measurement system at 220 kV transformer neutral point


Albert, D.; Maletic, D., Renner, H.
Measurement based transformer modelling approach
In: VDE ETG Fachtagung, Wuppertal,Germany, 18.05.2021, Conference Paper

Albert, D.; Achleitner G.
Sternpunktsgleichströme im Hoch- und Höchstspannungsnetz - aktueller Stand der Forschung
In: Sternpunktbehandlung in Netzen bis 110 kV (D-A-CH), Online-Veranstaltung, 22.09.2020, Präsentation

Albert, D.; Schachinger, P.; Renner, H.; Hamberger, P.; Klammer, F.; Achleitner, G.
Field experience of small quasi DC bias on power transformers A first classification of low-frequency current pattern and identification of sources

In: Cigre 2020 Session, 2020, Accepted Conference Paper

Schachinger, P.; Albert, D.; Renner, H; Bailey, R. L.; Achleitner, G.; Leber, G.
Niederfrequente Sternpunktströme im Ubertragungsnetz - Ein Überblick über aktuelle und zukünftige Forschung in Oesterreich
In 16. Symposium Energieinnovation (EnInnov), Graz, Austria, 2020, Conference Paper & Presentation

Bailey, R. L.; Möstl, C.; Amerstorfer, U. V.; Amerstorfer, T.; Weiss, A. J.; Hinterreiter, J.; Reiss, M. A.; Albert, D.
PREDSTORM and SOLARWIND2GIC: Forecasting of Space Weather Effects and GIC with Python

Machine Learning in Heliophysics, Amsterdam, Netherlands, 2019, Conference Poster

Albert, D.; Halbedl, T.; Renner, H. Bailey R. L.; Achleitner, G.
Geomagnetically induced currents and space weather - A review of current and future research in Austria
In: 54th International Universities Power (UPEC), Bucharest, Romania, 2019, Conference Paper

Halbedl, T.
Low Frequency Neutral Point Currents on Transformer in the Austrian power Transmission Network
PhD Thesis, Graz, Austria, 2019

Bailey, R. L.; Achleitner, G.; Halbedl, T.; Leonhardt, R.
Geomagnetically Induced Currents in Austria
In: EnInnov, Graz, Austria, 2018, Conference Presentation

Halbedl, T.; Renner, H.; Achleitner, G.
Geomagnetically induced currents modelling and monitoring transformer neutral currents in Austria
In: e&i, 2018

Bailey, R. L.; Halbedl, T.; Schattauer, I.; Achleitner, G.; Leonhardt, R.
Validating GIC Models With Measurements in Austria: Evaluation of Accuracy and Sensitivity to Input Parameters
In: Space Weather, 16, 887–902, 2018, DOI: 10.1029/2018SW001842

Bailey, R. L.; Halbedl, T.; Schattauer, Ingrid; Römer, Alexander; Achleitner, G.; Beggan, C. D.; Wesztergom, Viktor; Egli, Ramon; Leonhardt, R.
Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach
In: Ann. Geophys., 35, 751-761, 2017, Journal Paper, DOI: 10.5194/angeo-35-751-2017

Halbedl, T.; Renner, H.; Bailey, R. L.; Leonhardt, R.; Achleitner, G.
Analysis of the impact of geomagnetic disturbances on the Austrian transmission grid

In: 19th Power Systems Computation Conference 2016, Genoa, Italy, 20th-24th June 2016, Conference Paper, DOI: 10.1109/PSCC.2016.7540833

Halbedl, T.; Renner, H.; Sakulin, M.; Achleitner, G.
Measurement and analysis of neutral point currents in a 400-kV-network

In: 2014 Electric Power Quality and Supply Reliability Conference (PQ), Rakvere, Estonia, 11th-13th June 2014, Conference Paper, DOI: 10.1109/PQ.2014.6866785

Halbedl, T.,
Messung von Gleichströmen am Sternpunkt von Drehstromtransformatoren im Höchstspannungsnetz
Master Thesis, Graz University of Technology, Graz, Austria, 2014

Project Information


Prof. Herwig Renner





  • Austrian Power Grid
  • Siemens AG