This thesis investigated the AC insulation performance of a Fluoronitrile gas mixture with a varying amount of humidity in the gas. Also the AC insulation performance of a humid Fluoronitrile gas mixture at different operating pressures is investigated. Furthermore, the partial discharge (PD) behaviour of corona in a Fluoronitrile gas mixture is investigated. This is achieved by comparing the Partial Discharge Inception Voltage (PDIV), the Phase Resolved Partial Discharge (PRPD) pattern and some of the PD characteristics (e.g. rise time, fall time) of corona in a dry and humid Fluoronitrile gas mixture.

The fresults from this research confirm that humidity influences the electrical breakdown behaviour of a Fluoronitrile gas mixture. An increase in the amount of humidity in the gas results in a decrease of the AC insulation performance. This also applies to higher operating pressures, although the influence of humidity on the AC insulation performance decreases as the operating pressure increases. The PD behaviour of corona in a Fluoronitrile gas mixture is also affected by the presence of humidity in the gas. The PRPD pattern and PD characteristics of corona in a Fluoronitrile gas mixture differ with the presence of much humidity in the gas, as the charge of the corona discharges in a humid Fluoronitrile gas mixture are larger. The PDIV however did not change with the presence of much humidity in the gas.