Partial Discharges in typical defects of power cable systems at variable test voltage frequency – fundamental and practical considerations

Summary

Testing energy cable systems often implies the necessity to drive large capacitive loads. A test voltage supply that generates testing voltages with service frequency (50/60 Hz) is then bulky and heavy because of the high demand of reactive power. In addition, the reactive power is sometimes difficult to obtain, especially under on-site conditions, where the energy supply for cable test systems is limited. A common solution is the use of resonant test systems that operate at variable testing voltage frequency to meet the resonant frequency. Another solution is to significantly lower the testing voltage frequency e.g. to 0,1 Hz in order to lower the demand of reactive power as well. In both cases the question arises, how the preferably performed measurement of partial discharges is influenced by the testing voltage frequency. In this paper the models and the equivalent circuits for defects that cause partial discharges are examined on their properties regarding the testing voltage frequency. Measurements of partial discharges on typical defects of energy cable systems are presented and compared to the results that may be obtained from the models and equivalent circuits of these defects. It is shown in theory and from practical measurements, which parameters of the PD behaviour are influenced and in which way that influences can be explained from the models. Furthermore the limits of the models are evaluated. The paper contributes to a better understanding of the PD behaviour, the modelling of PD defects and gives answers to the question which kind of testing voltage is suitable for which kind of testing conditions. The influence of the testing voltage on the PD behaviour can even support certain testing strategies.

Additional informations

Authors

Phung Bao Toan, Nourirad Ghasem