PD Diagnostics of Eco-Efficient Gas-Insulated Switchgear – Sensitivity Verification

Inhalt:
The paper describes measurements to define the most important factors that have to be considered when the results of different sensitivity verification measurements are compared. The comparability of the test results between different gases and gas pressures in the typical application range is presented and evaluated by the authors. The amplitude of the artificial defect was measured by different systems, a wideband system, as typically used for monitoring systems, and a narrowband system, which is often used for on-site tests. As broadband system a spectrum analyser with custom made preamplifiers was used. A full frequency sweep in the range up to 2 GHz was performed. The measured spectrum consists of the maximum amplitudes which have been determined for each frequency during 60 s of measurement time. Moreover, the average frequency spectrum was also recorded. A comparison with the spectra of different voltage pulses can be done directly or with the aid of statistical tools. Another essential parameter which does have a significant impact on the results of such a sensitivity verification test is the type of sensor that is connected to the measuring system. In this paper, the sensitivity of isolated electrodes in disconnector and earthing switches, which are not designed but can be used for UHF partial discharge measurements, is compared to the sensitivity of standard partial discharge sensors which are applied especially for this purpose. Also, different methods for the comparison of the obtained results in respect to their frequency spectrum are evaluated. To summarize, it can be concluded that the test results are not significantly different, whether SF6 or eco-efficient gas mixtures based on CO2/O2/C4-FN or N2/O2/C4-FN are used in the relevant pressure range. This ensures that the results of the laboratory tests on SF6 systems can also be transferred to SF6-free equipment based on C4-FN mixtures of similar geometry, even without checking all possible combinations for various sensor arrangements, pressures, and gases.