Comprehensive Evaluation of Toroid Ring Core Parallel Inductor and Resistor as a Transformer Protection Device

The energy transition involves integrating numerous pieces of equipment that undergo frequent switching operations and face the risk of lightning strikes. Consequently, power systems are exposed to fast transient switching and lightning surges, necessitating enhanced protection solutions for power equipment. Over the past decade, viable solutions have emerged to mitigate fast transients and safeguard transformers in the form of a ring-core parallel inductor and resistor circuit (R-PIR). Although this device effectively protects medium-voltage transformers from fast transients, a precise and comprehensive model for this component is still lacking, especially considering the importance of refining the R-PIR for broader applications. This paper introduces a detailed model of the R-PIR as a protective device, validated by electromagnetic transient simulations and finite element methods, which are also confirmed by experiments. The main goals of the research work are to investigate the performance and design features of the R-PIR comprehensively and demonstrate how the designed R-PIR protects transformers against fast transients. The research work is validated by experiments conducted in a lab environment. It is concluded that designing the R-PIR within an appropriate frequency range can considerably suppress transient overvoltages to which the transformer is exposed.