Partial Discharge Measurement
This chapter is devoted to the measurement of partial discharges (PD) originating in weak spots in the insulation of HV apparatus and their components. As most HV equipment used to generate, transmit and distribute electric power are energized by high voltage alternating current (HVAC), this chapter focuses primarily on PD measurements under alternating voltage. However, specific problems which arise for PD tests under DC and impulse voltage will also briefly be considered. Sensitive PD measurements are often interfered by electromagnetic noises in the measuring surroundings. Therefore advanced features developed in the past to cancel disturbing noises will also be highlighted in this chapter as well as in the relevant sub-sections of Sects. 10.3 and 10.4. For a better understanding of the principles, procedures and instrumentation required for the measurement of electrical PD quantities, first some fundamentals of the PD occurrence will be presented, where also the PD quantities recommended in IEC 60270:2000 for the insulation condition assessment are considered. In the following section, the existing PD models proposed to estimate the PD charge transfer will critically be reviewed. Thereafter specific aspects of pulse charge measurements, as specified in IEC 60270:2000, are considered, which include the major components required to design PD measuring systems used to acquire and display the captured PD data and even the procedures employed to calibrate PD measuring systems. The following sections are dealing with the localization of PD faults, the visualization of PD events, and features developed to reduce or cancel electromagnetic noises interfering sensitive PD measurements. Finally, so-called non-conventional PD detection methods will briefly be highlighted, such as the measurement of electromagnetic PD transients up to the ultra-high frequency range as well as the detection of ultrasonic signals emitted from PD sources.