During the last few decades, partial discharge measurement and analysis have been considered one of the most important test methods for evaluating the quality of electrical machines and insulating systems. Test methods based on potential free capacitive and/or inductive couplers have taken place as well as methods based on the galvanic circuit with measuring impedance. These potential free couplers detect the electromagnetic field that is generated by partial discharge activity. The partial discharge detection, with using of the capacitive coupler, was the main reason to perform the measurements. The conclusions of the test are presented in this paper. Furthermore, the analysis of partial discharge of several physical models was performed because of the coupler's calibration and sensitivity evaluation. The different methods and apparatuses were used for partial discharge detection with the aim of the accuracy and sensitivity of the potential free method determination. The diagnostic equipment consists of a wideband analog apparatus, a digital apparatus, couplers and measuring impedance. The measurement was done according to IEC 270 standard. The capacitive couplers have been used as well for performing the potential free test method measurement.