Summary
   
   Nowadays the measure of partial discharges is a useful tool for the diagnostic of insulations. The present thesis is focused in the different methods for medium and high voltage partial discharge cable tests. Mainly, it has been studied the influence of the different test methods in the partial discharge charge evaluation in off-line tests (test performed with the cable isolated of the grid).
   The thesis analyzes the particularities of the conventional methods, and the new methods or non-conventional methods.
   The conventional methods, employed since the 60’s in high voltage laboratories, use bandpass filters as tool for the partial discharge charge evaluation.
   The non-conventional methods employ sensors with larger bandwidth than conventional methods, because it allows the pulse location in the cable by time domain reflectrometry, and also the use of mathematical tools to help the identification of partial discharge pulses.
   In this thesis it is analyzed the different methods for charge evaluation for the non-conventional methods, and it is established the limits of the uncertainty in these measurements according to the sensors bandwidth and partial discharge pulse lengths.
   The thesis deals with the analysis of the high frequency current transformers usually employed as partial discharge sensors in measurements coupled by magnetic field, and the analysis of partial discharge sensors coupled by electric field. The comparative of both sensors provides conclusions about the obtained bandwidth, the uncertainty for different pulse lengths, the methods for pulse charge evaluation, and the sensitivity of the measuring systems employing these devices.
   The experimental measurements have been done employing different prototypes of sensors coupled by magnetic field and electric field, measuring their frequency response and the partial discharge pulse response. The experimental and construction part culminates with the development and construction of a partial discharge sensor coupled by electric field that reaches sensitivities close to the physical theoretic limits of this kind of measurements, with a bandwidth covering from a few kilohertz to megahertz, which implies low uncertainties in pulse charge evaluation comparing with other type of devices.
   As a conclusion of the analysis done in this thesis, it is proposed a measuring circuit topology that allows broadband measurements causing minimum partial discharges pulse shape distortions. Furthermore, the proposed measuring circuit topology allows an identification of partial discharges coming from the cable ends by means of a pulse shape analysis, solving the indetermination produced by pure time domain reflectometry techniques.