The medium voltage cable networks act an important role in electric energy distribution. Failures can cause unplanned outages at large number of consumers, considerable amount of financial loss. By using proper diagnostic methods it is hoped to recognize the developing failure, to provide scheduled maintenance or replacement. The second chapter of my thesis is a review of the most widespread diagnostic methods of the middle voltage cables.
According to statistics most of the unplanned outages are caused by cable terminations and joints. Usually the faults of these cable accessories are caused during construction. By using proper diagnostic techniques during the installation these faults are recognizable.
The failures of cable accessories are often caused by partial discharges (PD) which can locally age the insulation and finally PD can cause breakdown. The third chapter of my thesis reviews the theory of the partial discharges and some of the most frequently used PD diagnostic methods.
The acoustic PD measurement has the advantage that it can be used during the installation of the cable and during normal operation conditions (i.e. online measurements). The method is not sensitive to electrical noise which is an important feature. The fourth chapter summarizes the theory of the acoustic partial discharge measurement and introduces the acoustical instrument used during the laboratory measurements.
During the laboratory measurements I used acoustical and conventional partial discharge diagnostic methods and studied cables with typical mistakes committed during the preparation of the cable.
The reason of the measures was to determine the efficiency, the sensitivity and the limits of the acoustical method. The seventh chapter summarizes the results of the measures.