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This paper aims at the overview of the measurement, diagnostics and monitoring system of partial discharge (PD) of high voltage power equipment. The system is made up of hard ware such as sensors of PD and soft ware including controlling and communication function. The measured PD characteristics are used to identify and evaluate condition changes of the related insulation-system. Presently, the capability of this diagnosis method is mainly used in the field of the quality control and of condition-based maintenance. Considering the strategy of the diagnosis and the available external high potential sources, the PD-measurement is carried out on-line or off-line. On-line PD-Monitoring and Alarm Systems are increasingly installed in order to reduce the life-cycle-costs and to extend the reliability and safety of the equipment and system operation. The different latest sensor technologies to decouple the PD-signals on transformers, capacitive apparatuses and cables are presented and compared with respect to their field of application, the related diagnosis capability and the degree of complexity. It is proved that the analysis of the measurement and monitoring results is very successful when evaluating the characteristics of PDs. Although, during the evaluation and estimation process of the data, the influence of each specific test object, of the measurement system itself and of ambient environmental conditions has to be considered. The design of the insulation system, the characteristics of the measuring system as well as the noise conditions are of high importance and critical regarding the respective interpretation evidence. This is demonstrated with practical measurement examples. The analysis of PD-monitoring data is always as good as the assessment guideline and the strategy of acting when exceeding a predefined level is. Because there are presently no standards for PD on-line monitoring at all, some aspects to setup helpful measurement and monitoring conceptions - for trend and rating performance are discussed.