Partial discharge (PD) measurements provide valuable information for assessing the condition of high voltage (HV) insulation systems, contributing to their quality assurance. Different PD measuring techniques have been developed in the last years specially designed to perform on-line measurements. Non-conventional PD methods operating in high frequency bands are usually used when this type of tests are carried out. In PD measurements the signal acquisition, the subsequent signal processing and the capability to obtain an accurate diagnosis are conditioned by the selection of a suitable detection technique and by the implementation of effective signal processing tools. This paper proposes an optimized electromagnetic detection method based on the combined use of wideband PD sensors for measurements performed in the HF and UHF frequency ranges, together with the implementation of powerful processing tools. The effectiveness of the measuring techniques proposed is demonstrated through an example, where several PD sources are measured simultaneously in a HV installation consisting of a cable system connected by a plug-in terminal to a gas insulated substation (GIS) compartment.

On-line partial discharge (PD) measurements have become a common technique for assessing the insulation condition of installed high voltage (HV) insulated cables. When on-line tests are performed in noisy environments, or when more than one source of pulse-shaped signals are present in a cable system, it is difficult to perform accurate diagnoses. In these cases, an adequate selection of the non-conventional measuring technique and the implementation of effective signal processing tools are essential for a correct evaluation of the insulation degradation. Once a specific noise rejection filter is applied, many signals can be identified as potential PD pulses, therefore, a classification tool to discriminate the PD sources involved is required. This paper proposes an efficient method for the classification of PD signals and pulse-type noise interferences measured in power cables with HFCT sensors. By using a signal feature generation algorithm, representative parameters associated to the waveform of each pulse acquired are calculated so that they can be separated in different clusters. The efficiency of the clustering technique proposed is demonstrated through an example with three different PD sources and several pulse-shaped interferences measured simultaneously in a cable system with a high frequency current transformer (HFCT).

Nowadays many researchers are focusing on on-line condition monitoring of high-voltage (HV) insulated cable systems to prevent failures. With the aim of reducing the voltage induced in the cable sheaths, cross-bonding (CB) grounding cable systems are used in long distance power transmission land lines. This paper proposes a new criterion for the detection and localization of defects that might occur in the cables sheath when a CB configuration is adopted. The criterion proposed can be applied at different levels of load current. For the application of the criterion, the cable system under evaluation is modeled using the ATP software. Various practical cases were studied showing the effectiveness of the criterion for the detection and localization of different types of defects in simulated cable systems. Furthermore, in order to validate the criteria adopted for the defect detection, based on the ATP model, a real defected case was evaluated. The results obtained proved that this criterion is suitable for the detection and localization of defects in the cables sheath, when on-line measurements are performed in monitoring applications.

No abstract

Power transformers are key electrical assets in power networks. Their lifetimes are estimated to be around 40 years if they are properly maintained. However, thermal, electrical and mechanical stresses can cause the apparition of partial discharge (PD) activity in the insulation system that can lead to its degradation. Thus, the presence of PD activity can be considered as indicator of failure. Conventional PD acquisitions can be done in accordance with IEC-60270 and IEC-60076-3 standards. In the last decades, unconventional methods, depicted in the IEC-TS-62478 standard, based on acoustic and electromagnetic measurements are being combined with the conventional ones for monitoring power transformers identifying and localizing PD sources. In this paper, the necessity of PD monitoring in power transformers is highlighted and a review of different methods for measuring PD is featured. Besides, sorne technological trends are depicted. Finally, PD modelling is presented as a promising compliment for PD diagnosis.