Low Frequency Neutral Point Currents (GIC)

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

Currents with frequencies near 0 Hz, i.e. quasi DC, are undesirable in the high-voltage transmission network. These low frequency currents can lead to saturation of power transformers. Saturation increases the volume, reactive power consumption and power loss of the transformers. These effects can have a negative impact on system stability and thus on supply security.

Problem definition and approach
In the project, the behavior of power transformers is investigated in the laboratory, compared with simulations and conclusions are drawn about the behavior of the transformers in the transmission network. To verify the assumptions, star point measurements and phase measurements are carried out at 6 measuring points in the Austrian transmission grid. The own simulation program is used to calculate the low frequency currents in the transmission grid and to identify endangered transformers and to assess the grid status. Figure 1 depicts the different fields of research in the project.


Figure 1: Project organization and fields of research

Cause of the low frequency currents
The cause of the low frequency currents has already been identified as geomagnetic disturbances (GMD), which are caused by the interaction of the Sun with the Earth's magnetic field system. These induced currents are called geomagnetically induced currents, GIC. For this reason, magnetic field measurement data are also taken into account and used to calculate the network state in our own simulation program.
Further causes and sources of the low frequency currents are the subject of current research.

Power transformers
Within the project laboratory tests with power transformers (Figure 2) are carried out to investigate the influence of the switching group at different low frequency loads. For this purpose, two power transformers were modified (Figure 3) in such a way that the vector group on one side of the transformer is freely adjustable.

Figure 2: Transformers setup in the laboratory

Figure 3: Modified power transformer

Network effects
With the help of the simulation program (Figure 4) and the transformer neutral point measurements, the model for the geomagnetic influence on the transmission network is verified. Taking into account the local currents, the influences of the transformers can be calculated and thus an overall picture of the grid state can be generated. From this, action measures can be derived for the network operator to ensure a long-term stable network operation. .


Abbildung 4: Simmulation Program

Measuring systems
Currently, the neutral point currents are measured (Figure 5) at 6 transformers in the Austrian transmission grid and the phase currents (Figure 6) in a transformer station. Further measuring locations and measuring methods are in preparation. The measurement data in a 1-second grid allows the validation of the calculations from the software and the laboratory tests. The challenge in measuring the phase currents is the different measuring range. The low frequency currents to be measured have amplitudes of up to 25 A, while at the same time operating frequency currents of up to the single-digit kiloampere range act on the measuring system


Figure 5: neutral current point measurement


Figure 6: phase current measurement

Publications

2020
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 Sternpunktstroeme im Ubertragungsnetz - Ein Ueberlick ueber aktuelle und zukuenftige Forschung in Oesterreich
In 16. Symposium Energieinnovations (EnInnov), Graz, Austria, 2020, Conference Paper & Presentation

2019
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

2018
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

2016
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

2014
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 Theses, Graz University of Technology, Graz, Austria, 2014

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Prof. Herwig Renner

  • Austrian Power Grid
  • Siemens AG