Partial discharge characteristic of fixed protrusions in HVDC-GIS

Inhalt:
This contribution experimentally investigates the PD activity of fixed protrusions in SF6-insulated, commercially available coaxial DC-GIS components. Various defect parameters, such as length and position of the protrusion are investigated. The considered SF6 pressure is in the range of pSF6 = 0.1 ... 0.5 MPa. The applied DC voltage is increased stepwise from PD inception voltage up to UDC = ± 520 kV. Depending on the position of the protrusion, which is either fixed onto the inner conductor or the enclosure and the polarity of the applied voltage, four different defect configurations are considered. PDs are recorded simultaneously in time domain using three different electrical measurement principles. In addition to UHF-PD wideband measurements, the discharge current at the protrusion is measured using two methods: a high frequency current transformer (HCFT) at a bandwidth fbw,HFCT = 0.1 ... 3 GHz and a current shunt (fbw,shunt = DC ... 100 kHz). Moreover, the light emitted at the tip of the protrusion is detected by a photomultiplier tube (PMT). The observations are evaluated in terms of PD pulse magnitude and repetition rate in order to gain an advanced understanding of the defect behavior. As a result, three different discharge features are discriminated in order to categorize the defects: pulseless PD, PD impulse and superposition of pulseless PD and PD impulse. Due to the different physical discharge mechanisms of the features, the individual sensitivity of each considered measurement system requires an individual evaluation.