Analysis of Corona and Surface Discharge Signals from Different Non-Intrusive Sensors under HVDC

The use of high voltage direct current (HVDC) transmission technology has increased significantly in recent years due to its numerous advantages over traditional alternating current (AC) transmission. The aim of the present work is to investigate the efficiency of different non-intrusive sensors for partial discharge measurement in medium or high voltage direct current equipment such as air or gas insulated switchgear. In HVAC systems, partial discharge detection and quantification are well understood. However, under HVDC, it is a necessary to evaluate the efficiency of classic techniques and commercial non-intrusive sensors. This work presents a study of three different sensors for partial discharge measurement under HVDC: high frequency current transformer (HFCT), ultra-high frequency antenna (UHF), and transient earth voltage (TEV). The signals of the different sensors for corona and surface discharge detection are presented and compared in both temporal and frequency domains. The Pulse Sequence Analysis (PSA) technique is used for apparent charge and repetition rate study and the effect of the discharge type on the PSA patterns is investigated. The results show that the PSA patterns are sensitive to the discharge type and conditions. The increase of the applied voltage of corona leads to the increase of the apparent charge differences and the time duration between successive pulses. The spectrums of the discharge pulses of the three sensors are different and the maxima of the TEV and UHF PD signals are dependent on the apparent charge.