Partial Discharge Monitoring of C3F7CN/CO2 Mixture Retrofilled in Gas Insulated Busbar

<p dir="ltr">Condition monitoring of gas insulated high voltage equipment is important to ensure reliable operation of electricity networks. Partial discharge (PD) monitoring is well established for existing SF₆ equipment, but still in its infancy for the emerging SF₆ alternatives as the power industry transitions from SF_6­­. PD characteristics of 20% C₃F₇CN / 80% CO₂ gas mixture as a viable retrofill solution were extensively investigated over extended energization periods in a busbar demonstrator designed for SF₆ and rated to 420/550 kV. Protrusions of 3, 5, 10 and 15 mm needle lengths were used on the high voltage conductor for comparative PD investigations of SF₆ and 20% C₃F₇CN / 80% CO₂ gas mixture. PD activity was measured with IEC 60270 (apparent charge) and ultra-high frequency (UHF) detection methods. The PD patterns recorded for all needle lengths were representative of a protrusion-on-conductor defect and the two PD detection methods were comparable. For identical defect lengths, SF₆ showed a comparatively longer time-to-breakdown when compared to a 20% C₃F₇CN / 80% CO₂ mixture. Results obtained in a controlled laboratory environment demonstrate wider applicability to field measurements of C₃F₇CN based mixtures adopted for retrofill application in SF₆-designed gas insulated busbar.</p>