The thesis consists of 7 chapters. The first chapter will explain the background, motivations and the general overview of the thesis. Chapter 2 is a literature review describing the physics behind the creation of PDs. The conditions necessary for the occurrence of PDs are covered in addition to an analysis of the different types of PD in GIS ranging from corona, internal, surface and discharges due to electrically floating components for both AC and DC voltage. Chapter 3 presents the equipment available at TUDelft HV laboratory to create the set-up used for applying AC and DC voltages to the test object. The PD monitoring configuration are covered categorizing conventional and unconventional methods. Chapter 4 deals with signal processing of the PD data for classification of PD sources. Some quantities on which the analysis can be based, are discussed. Furthermore a distinction of quantities which are directly measurable by detection systems as direct data and the quantities or derived data derived through combinations or data analysis, will be made. In chapter 5, PD measurements using the conventional method of created defects in the HV laboratory are discussed. The defects are used to simulate insulation defects and the measurements in DC are analysed resulting in recognition graphs used for differentiating between the possible defects. Chapter 6 discusses the results of simultaneous measurements of PDs using the conventional method and RF techniques. The combined PD measurements on multiple defects are used to create plots of RF quantities to apparent charge. These plots are used for quantification of the relationship between the different techniques. Lastly, chapter 7 concludes the study and suggests future research related to the measurement of PDs in HVDC GIS using electrical partial discharge detection.