Е-Публикации
Технически университет - София

Abstract: The increasing penetration of inverter-based renewable energy sources and the growing share of underground cable lines significantly modify the frequency-dependent characteristics of medium-voltage distribution networks, increasing the risk of harmonic resonance. Existing resonance studies are often based on detailed electromagnetic models that are difficult to apply during routine distribution network planning and operation. This paper proposes an engineering-oriented methodology for the preliminary assessment of harmonic resonance risk using an equivalent lumped-parameter model that incorporates overhead and cable lines, transformer inductance, photovoltaic generation, and the short-circuit strength of the supplying system. The methodology is applied to a representative 20 kV distribution network to investigate the influence of cable penetration, photovoltaic capacity, transformer loading, and grid strength on resonance conditions. The results show that increasing network capacitance and reducing short-circuit power shift the resonance frequency toward lower-order harmonics, increasing the probability of harmonic amplification. The highest resonance risk is observed under the combined conditions of high photovoltaic generation, low transformer loading, and weak-grid conditions. Unlike detailed electromagnetic simulation models, the proposed methodology enables rapid engineering assessment using parameters readily available to distribution system operators, thereby supporting network planning and operational decision-making in medium-voltage distribution systems with high photovoltaic penetration.

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