Members of our department professor Božidar Filipović-Grčić and assistant Franjo Vuković participated at the International Conference on Power Systems Transients (IPST) and EMTP International User Conference, which were held in Guadalajara, Mexico, June 7-12, 2025. It was a great opportunity to exchange ideas, share knowledge and connect with the global community dealing with power system transients! Bozidar and Franjo presented several papers at IPST conference which will be soon published in the Electric Power Systems Research (EPSR) journal:
- Nina Stipetić, Bozidar Filipovic-Grcic, Igor Žiger, Silvio Jančin, Bruno Jurisic, Dalibor Filipović-Grčić, Alain Xemard, “Verification of low-frequency signal injection method for earth-fault detection”
- Iva Radecic, Bozidar Filipovic-Grcic, Paul Akiki, Alain Xémard, Bruno Jurisic, “Investigation of Resonance between HVDC-MMC Link and AC Network”
- Iva Radecic, Silvio Jancin, Marijan Perković, Bozidar Filipovic-Grcic, Bruno Jurisic, Dalibor Filipovic-Grcic, “Superimposed Impulse Voltage Test on 525 kV HVDC Underground Cable”
- Franjo Vukovic, Joan Montanyà, Bozidar Filipovic-Grcic, “Lightning Flash Observations on a Wind Turbine in Croatia: Insights from Current Measurements, High-Speed Camera, LLS and Lightning Imager Data”
- Franjo Vukovic, Bozidar-Filipovic-Grcic, Nina Stipetic, Bojan Franc, “Electromagnetic transients and failed upward leaders observed during lightning activity in an onshore wind farm”
- Dominik Miloš, Viktor Milardić, Amir Tokić „Detailed EMTP wind turbine model for simulation transient phenomena during lightning strikes”
At EMTP International User Conference Božidar held presentation “Application of EMTP for Simulating Transient Phenomena in High-Voltage Laboratory Test Circuits” prepared in collaboration with KONČAR - Electrical Engineering Institute. This presentation deals with simulations of a new test on HVDC cables involving a superimposed impulse voltage test, where the EMTP model was validated against real measurements taken in an HV laboratory. Additionally, simulations of very slow temporary overvoltage (TOV) on HVDC cable are shown, aiming to verify whether the existing impulse generator provides sufficient energy, given the challenge of prolonged test duration. Another similar simulation example illustrates a combined heat and basic impulse level (BIL) test, used to assess the energy capability of the impulse generator. Beyond its application in validating new test requirements and configurations in the HV lab, EMTP can also be used for the development of novel testing methods, such as the low-frequency signal injection method for earth-fault detection, where the simulation results were also validated with real-world measurements. It was a great opportunity to share practical insights and connect with the global EMTP community!
More about papers can be found below in detailed news content!
- 📃 Nina Stipetić, Bozidar Filipovic-Grcic, Igor Žiger, Silvio Jančin, Bruno Jurisic, Dalibor Filipović-Grčić, Alain Xemard, “Verification of low-frequency signal injection method for earth-fault detection”
Abstract: Unearthed neutral is commonly used in networks which require continuous power supply. This is common in MV circuits of industrial and power plants. Unearthed networks can remain in operation during an earth-fault, but fast determination of the faulty line is key for prevention of further fault escalation. Signal injection is one of the fault location methods often used in LV unearthed networks. The possibility of applying this method in MV networks depends on how to inject the signal into unearthed phases. In such networks, it is possible to use a group of three inductive voltage transformers (IVTs) for signal injection. After the simulations have shown promising results of signal injection and earth-fault detection in MV network, an experimental test was performed. This paper describes the experimental setup and shows the measurement results of signal injection method at MV level supported by EMT simulations.
- 📃 Iva Radecic, Bozidar Filipovic-Grcic, Paul Akiki, Alain Xémard, Bruno Jurisic, “Investigation of Resonance between HVDC-MMC Link and AC Network”
Abstract: HVDC networks offer several advantages over traditional HVAC systems, particularly for long-distance power transmission and integration of renewable energy sources, such as reduced losses and enhanced stability and control, but also increase the risk of oscillations. This study investigates electrical resonant phenomena associated with HVDC stations through numerical EMT simulations. The findings indicate that electrical resonance is primarily pronounced in weak networks with long cables, as confirmed by the Nyquist criterion applied to frequency responses. Two real cases were successfully simulated in the time domain by introducing network changes, such as temporary faults and alterations in network’s power strength, to activate the identified resonances. Notably, in a strong network with short cables, electrical resonance occurred alongside interactions between the network and the converter's protection system. The analysis of voltage waveforms revealed that the amplitude of the induced resonant harmonic dissipates quickly, indicating sufficient damping in the network configuration. Furthermore, the study confirmed the network's sensitivity to changes in converter parameters modeled using available MMC model.
- Iva Radecic, Silvio Jancin, Marijan Perković, Bozidar Filipovic-Grcic, Bruno Jurisic, Dalibor Filipovic-Grcic, “Superimposed Impulse Voltage Test on 525 kV HVDC Underground Cable”
Abstract: One of the distinctive electrical tests for HVDC cables is the superimposed impulse voltage test. This paper investigates the development and validation of an Electromagnetic Transient (EMT) model for conducting this test on a 525 kV HVDC cable. The model incorporates the actual configuration and parameters of the high voltage (HV) laboratory test circuit. Given the technical challenges posed by the simultaneous application of DC and impulse voltages, the EMT model provides valuable insights into the test circuit's behaviour. Validation with real HV laboratory measurements confirms the model's accuracy and its potential to address these challenges.
- Franjo Vukovic, Joan Montanyà, Bozidar Filipovic-Grcic, “Lightning Flash Observations on a Wind Turbine in Croatia: Insights from Current Measurements, High-Speed Camera, LLS and Lightning Imager Data”
Abstract: This study presents a comprehensive analysis of lightning activity at a wind farm lightning observatory in Croatia, where lightning strikes on a wind turbine are monitored using synchronized current measurements, high-speed optical recordings, and lightning location system (LLS) data. With the recent launch of the Meteosat Third Generation (MTG) Lightning Imager (LI) in July 2024, continuous optical radiance data is also available. By leveraging precise timestamps, LI radiance data is correlated with ground-based measurements. During the period, the current measurement system detected nine events serving as ground truth and, for some events, being complemented by high-speed camera data for LLS and LI. Ground-based equipment consistently validates each other in stroke detection, and current measurements of continuing-type currents are further corroborated by HS camera data and extracted luminance profiles. The LI detected all nine flashes at the instrumented WT. In every flash, LI detections preceded the currents measured at the WT, suggesting that the leaders and strokes were triggered by in-cloud lightning activity. LI also confirmed the polarity of the involved lightning leaders, enabled more precise quantification of flash parameters such as duration and extension, and verified the presence of continuing currents.
- Franjo Vukovic, Bozidar-Filipovic-Grcic, Nina Stipetic, Bojan Franc, “Electromagnetic transients and failed upward leaders observed during lightning activity in an onshore wind farm”
Abstract: At a wind farm in Croatia, lightning activity is monitored across the entire site using a lightning location system, and on a single wind turbine equipped with a Rogowski-coil-based current measurement system and a high-speed camera, all independently GPS-synchronized. In addition to recording lightning flash currents on the monitored turbine, the system is frequently triggered by electromagnetic disturbances caused by nearby lightning flashes. These include direct flashes to two neighboring turbines that share the same cable connection to the substation and have interconnected grounding systems with buried bare conductor, as well as cloud-to-ground flashes to soil near cable routes, where the resulting electromagnetic fields couple onto the cables, causing surges to propagate to the monitored turbine. The camera occasionally captures failed upward connecting leaders from the monitored turbine during these lightning events. This paper presents three cases of flashes to two neighboring wind turbines and two cases of cloud-to-ground flashes to nearby soil, all of which induced electromagnetic transients that propagated to the monitored turbine. Failed upward connecting leaders were observed in some of these cases. This paper provides observational analysis, providing Rogowski measurements of electromagnetic disturbances and failed leader currents, complemented by high-speed camera and lightning location system data.
6. Dominik Miloš, Viktor Milardić, Amir Tokić: „Detailed EMTP wind turbine model for simulation transient phenomena during lightning strikes”
Abstract: Lightning strikes on wind turbine blades cause significant damage to the wind turbine. This paper presents a detailed description of the EMTP wind turbine model for transient analysis of lightning strikes to wind turbine blades. The main objective of this paper is to develop the EMTP simulation model that can be used to perform simulations and transient analysis of lightning current strikes on wind turbine blades. Another objective of this paper is to identify the waveform of the lightning current that strikes the wind turbine blades by comparing the simulated current waveform with the current waveform obtained from a prototype measurement system at the base of the tower. A prototype measurement system for direct lightning current measurement was developed by a research group at Faculty of Electrical Engineering and Computing, University of Zagreb. Basic functionality of prototype measurement system is described in this paper. In future research it will be possible to determine voltage and current conditions on wind turbine components based on the developed EMTP wind turbine model.
