Enhancing Power Transformer Reliability: High-Frequency Modeling, Transient Interactions, and Overvoltage Protection Scheme
Farzad Nasirpour (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Behzad Behdani (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Amir Heidary (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Mohamad Ghaffarian Niasar (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Forooz Ghassemi (National Grid Electricity Transmission plc)
Maarten van Riet (Alliander)
Mark Wilkinson (Royal Smit Transformers B.V)
M.A.M.M. van der Meijden (TenneT TSO B.V.)
Marjan Popov (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
The evolution of electrical power systems demands an increasing reliance on unpredictable renewable energy resources (RES). However, integrating these resources poses challenges, as their intermittent nature introduces transient events that can significantly impact power transformers. These transient phenomena may initiate energy oscillations in the form of weakly-damped resonances between system elements, i.e., transmission lines and cables, transformers, and the grounding system. Such conditions may impose stresses beyond the tolerance of insulating materials, leading to fast lifetime degradation and, eventually, the failure of critical components in the network, such as the costly power transformers. The impedance of the grounding system can limit the dissipation of surges, hence, causing severe overvoltages upon transient phenomena. By employing detailed transient models of crucial system components, this research puts forward a comprehensive analytical study of the transient interactions. In this regard, an analytical high-frequency transformer winding model based on lumped elements, and wideband frequency-dependent models for cables and the grounding system derived by applying electromagnetic theory are presented. These models, integrated into electromagnetic transient software, enable the identification of vulnerabilities and examination of case studies involving lightning strikes and switching events. Furthermore, the details of a novel protection method applied to safeguard the transformer are discussed in this paper. The presented protection method consists of a ring toroid core and a resistive suppressor on the secondary side of the core. This protection component is connected in series with the transformer to decrease the harmonic content and magnitude of the transient signals. The design procedure of the series protection device against voltage transient signals is presented and elaborated.