IV. CONCLUSIONFor PD in LN2, UHF me

IV. CONCLUSION
For PD in LN2, UHF measurement gives higher temporal
resolution allowing finer details of the discharge event, such as a pulse train, when compared to conventional methods.
Results from the UHF sensor show that PD events from a point cathode consist of a train of single pulses which cannot be resolved by the lower bandwidth of standard capacitive coupling circuits. The pulse sequence pattern depends on streamer propagation mode, bush-like or filamentary. For bush-like modes, an increase in magnitude of the pulses is observed, which is due to a step wise process of bubble expansion due to discharges in its gaseous phase. Filamentary negative streamers can grow from a bush-like structure which suggests that streamer propagation mode is also dependent on the electric field at the streamer tip. Mechanisms behind filamentary positive streamer are less well understood but in all cases only a single pulse is observed.