Metrological Qualification of PD Analysers for Insulation Diagnosis of HVDC and HVAC Grids

Abstract

On-site partial discharge (PD) measurements have turned out to be a very efficient technique for determining the insulation condition in high-voltage electrical grids (AIS, cable systems, GIS, HVDC converters, etc.); however, there is not any standardised procedure for determining the performances of PD measuring systems. In on-line and on-site PD measurements, high-frequency current transformers (HFCTs) are commonly used as sensors as they allow for monitoring over long distances in high-voltage installations. To ensure the required performances, a metrological qualification of the PD analysers by applying an evaluation procedure is necessary. A novel evaluation procedure was established to specify the quantities to be measured (electrical charge and PD repetition rate) and to describe the evaluation tests considering the measured influence parameters: noise, charge amplitude, pulse width and time interval between consecutive pulses. This procedure was applied to different types of PD analysers used for off-line measurements, sporadic on-line measurements and continuous PD monitoring. The procedure was validated in a round-robin test involving two metrological institutes (RISE from Sweden and FFII from Spain) and three universities (TUDelft from the Netherlands, TAU from Finland and UPM from Spain). With this round-robin test, the effectiveness of the proposed qualification procedure for discriminating between efficient and inappropriate PD analysers was demonstrated. Furthermore, it was shown that the PD charge quantity can be properly determined for on-line measurements and continuous monitoring by integrating the pulse signals acquired with HFCT sensors. In this case, these sensors must have a flat frequency spectrum in the range between several tens of kHz and at least two tens of MHz, where the frequency pulse content is more significant. The proposed qualification procedure can be useful for improving the future versions of the technical specification TS IEC 62478 and the standard IEC 60270.

Novel Reference Method for the Characterization of PD Measuring Systems Using HFCT Sensors

“…The authors of this paper presented in [ 15 , 16 , 17 ] methods for the evaluation of PD instruments or analyzers that are applied measuring simulated defects in small-scale systems [ 15 , 16 ] or measuring them directly with the acquisition units [ 15 , 16 , 17 ]. These methods are valid to characterize some measuring instrument or analyzer functionalities.…”

“…If the scale systems were not used and the characterizations were performed with an analog generator [ 15 , 17 , 19 , 20 , 21 , 22 ], injecting the signals that simulate defects and noise conditions directly into the acquisition unit would not be possible to perform the characterizations in a complete way with real sensors in a physical system and measuring in a non-limited number of points.…”

“…Concerning the first difficulty, although various researchers have presented interesting measuring methods and techniques to perform accurate diagnosis [ 11 , 12 , 13 , 14 ], very few studies are focused on a comprehensive characterization of the technical functionalities developed [ 15 , 16 , 17 ]. Moreover, in none of them a reference method is proposed to be applied for the complete and reproducible characterization of measuring or monitoring systems measuring in real conditions.…”