Limitations and Performance of Pressure Relief Devices in On-Load Tap Changer Compartments Under Arcing Faults

An on-load tap changer (OLTC) is a key subassembly inside transformers. Pressure relief devices (PRDs) are widely installed on the top cover of OLTC compartments to mitigate internal overpressure. At present, the limitations and performance of a PRD under internal arcing faults have not been quantitatively determined, which is hampered in part by a lack of theoretical and experimental evidence. In this paper, a numerical method considering the interaction of internal oil pressure behaviors and transient PRD operation is developed and validated by arcing fault experiments conducted inside a full-scale OLTC compartment. Using this method, the arc current levels and time durations that the OLTC compartment can withstand are identified. To explore the improvement limit of the PRD performance, an optimal solution for the structural parameters is obtained via the surrogate-assisted approach, achieving an increase of 27.3% in the oil discharge capacity. The venting diameter is found to have the most significant impact on the evacuation volume, whereas the spring stiffness has the minimal impact. Moreover, the optimized PRD extends the permissible arcing duration by 28.6% under an arc current of 50 kA, but this effect decreases significantly as the arc current level increases.