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

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.