arXiv subjects

Bozidar Filipovic-Grcic

Publications and source records attributed to Bozidar Filipovic-Grcic.

4 recordsLinked to original sources

arXiv2025

Investigation of resonance between HVDC-MMC link and AC network

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.

eess.SY↗

arXiv2025

Verification of low-frequency signal injection method for earth-fault detection

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.

eess.SY↗

arXiv2025

Electromagnetic transients and failed upward leaders observed during lightning activity in an onshore wind farm

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.

physics.ins-det↗

arXiv2025

Investigation of lightning effects on solar power plants connected to transmission networks

The increasing integration of solar power plants into transmission grids has raised concerns about their vulnerability to disturbances, particularly lightning strokes. Solar energy, while offering significant environmental and economic benefits, faces challenges when connected to transmission lines that are prone to lightning discharges. This paper investigates the impact of lightning events on solar power plants, focusing on overvoltage effects. Lightning stroke simulations were conducted at various distances from the solar power plant along the transmission line, considering scenarios with and without surge arrester. Key lightning parameters such as peak current, front time, and tail time were varied to simulate different lightning strokes. The study also includes a Fourier transform analysis of the resulting overvoltages with and without a surge arrester, along with the Hilbert marginal spectrum of these overvoltages. The results provide insights into the effectiveness of surge arresters in mitigating lightning overvoltages and highlight the importance of proper protective measures for enhancing the reliability and safety of solar power plants connected to transmission networks.

eess.SY↗