Today, online partial discharge (PD) measurements are common practice to assess the condition status of dielectrics in high-voltage (HV) electrical grids. However, when online PD measurements are carried out in electrical facilities, several disadvantages must be considered. Among the most important are high levels of changing electrical noise and interferences, signal phase couplings (cross-talk phenomena), and the simultaneous presence of various defects and difficulties in localizing and identifying them. In the last few decades, various PD-measuring systems have been developed to deal with these inconveniences and try to achieve the adequate supervision of electrical installations. In the state of the art, one of the main problems that electrical companies and technology developers face is the difficulty in characterizing the measuring system’s functionalities in laboratory setups or in real-world facilities, where simulated or real defects must be detected. This is mainly due to the complexity and costs that the laboratory setups entail and the fact that the facilities are permanently in service. Furthermore, in the latter scenario, owners cannot assign facilities to carry out the tests, which could cause irreversible damage. Additionally, with the aforementioned installations, a comparison of results over time in various locations is not possible, and noise conditions cannot be controlled to perform the characterizations in a correct way. To deal with the problems indicated, in this article, an affordable scale modular test platform that simulates an HV installation is presented, where real on-site PD measuring conditions are simulated and controlled. In this first development, the HV installation comprises a cable system connected at both ends to a gas-insulated substation (GIS). As the most common acquisition technique in online applications is based on the placement of high-frequency current transformer (HFCT) sensors in the grounding cables of facilities, the test platform is mainly adapted to carry out measurements with this type of sensor. The designed and developed test platform was validated to assess its features and the degree of convergence with a real installation, showing the convenience of its use for the appropriate and standardized characterization of PD-measuring systems.

In general, a high voltage (HV) substation can be made up of multiple insulation subsystems: an air insulation subsystem (AIS), gas insulation subsystem (GIS), liquid insulation subsystem (power transformers), and solid insulation subsystem (power cables), all of them with their grounding structures interconnected and linked to the substation earth. Partial discharge (PD) pulses, which are generated in a HV apparatus belonging to a subsystem, travel through the grounding structures of the others. PD analyzers using high-frequency current transformer (HFCT) sensors, which are installed at the connections between the grounding structures, are sensitive to these traveling pulses. In a substation made up of an AIS, several non-critical PD sources can be detected, such as possible corona, air surface, or floating discharges. To perform the correct diagnosis, non-critical PD sources must be separated from critical PD sources related to insulation defects, such as a cavity in a solid dielectric material, mobile particles in SF6, or surface discharges in oil. Powerful diagnostic tools using PD clustering and phase-resolved PD (PRPD) pattern recognition have been developed to check the insulation condition of HV substations. However, a common issue is how to determine the subsystem in which a critical PD source is located when there are several PD sources, and a critical one is near the boundary between two HV subsystems, e.g., a cavity defect located between a cable end and a GIS. The traveling direction of the detected PD is valuable information to determine the subsystem in which the insulation defect is located. However, incorrect diagnostics are usually due to the constraints of PD measuring systems and inadequate PD diagnostic procedures. This paper presents a diagnostic procedure using an appropriate PD analyzer with multiple HFCT sensors to carry out efficient insulation condition diagnoses. This PD procedure has been developed on the basis of laboratory tests, transient signal modeling, and validation tests. The validation tests were carried out in a special test bench developed for the characterization of PD analyzers. To demonstrate the effectiveness of the procedure, a real case is also presented, where satisfactory results are shown.

The insulation condition of HVDC grids consisting of cable systems, GIS, and converters should be monitored by partial discharge (PD) analysers using artificial intelligence (AI) tools for efficient insulation diagnosis. Although there are many experiences of PD monitoring solutions developed for the supervision of the insulation condition of HVAC grids using PD analysers, there are no standardised requirements for their qualification available yet. The international technical specification TS IEC 62478 provides general rules for PD measurements using electromagnetic methods but does not define performance requirements for qualification tests. HVDC and HVAC PD analysers must be tested by unambiguous test procedures. This paper compiles experiences of using PD analysers with HFCT sensors in HVAC grids (cable systems, GIS, and AIS) to define a qualification procedure for HVAC systems. This procedure is applicable to HVDC grids (cable systems, GIS, AIS, and converters) because the particularities related to the insulation behaviour under HVDC voltage are also considered. Representative PD sources are discussed in HVAC and HVDC positive and negative polarity. The PD pulse trend of representative insulation defects in HVDC cable systems is quite different from that of HVAC grids. Special attention should be paid to the acquisition of PD signals in HVDC grids since few pulses appear in solid insulations, mainly during voltage changes (polarity reversals or surges), but rarely in continuous operation with constant direct voltage. A synthetic PD simulator has been developed to reproduce trains of PD pulses or noise signals, similar to those that can appear in the power network. A set of three functionality tests has been developed for qualification of the diagnostic capabilities of PD analysers working up to 30 MHz addressed to HVDC or HVAC grids: (1) PD recognition test, (2) PD clustering test, and (3) PD location test. This qualification procedure has been validated by means of a round-robin test performed by five research institutes (RISE, FFII, TUDelft, TAU, and UPM) using commercial and in-development AI PD recognition and clustering tools to demonstrate its robustness and applicability. Applying this qualification procedure, two PD methods for electrical detection and prevention of insulation defects have been approved, one for HVAC and the other for HVDC grids.

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.

During their lifespan, high-voltage (HV) electrical systems are subjected to operating conditions in which electrical, mechanical, thermal and environmental-related stresses occur. These conditions over time lead to unforeseen failures caused by various types of defects. For this reason, there are several technologies for measuring and monitoring the electrical systems, with the aim of minimizing the number of faults. The early detection of defects, preferably in their incipient state, will enable the necessary corrective actions to be taken in order to avoid unforeseen failures. These failures generally lead to human risks and material damage, lack of power supply and significant economic losses. An efficient maintenance technique for the early detection of defects consists of the supervision of the dielectrics status in the installations by means of on-line partial discharge (PD) measurement. Nowadays, there are numerous systems in the market for the measurement of PD in HV installations. The most efficient with a reasonable cost will be those that offer greater security guarantees and the best positioned in the market. Currently, technology developers and users of PD measuring systems face difficulties related to the lack of reference procedures for their complete characterization and to the technical and economic drawback of performing the characterization tests on site or in laboratory installations. To deal with the previous difficulties, in this paper a novel method for the complete and standardized characterization of PD measuring systems is presented. The applicability of this method is mainly adapted for the characterization of systems operating in on-line applications using high-frequency current transformer (HFCT) sensors. For the appropriate application of the method, an associated and necessary scale modular test platform is used. In the test platform, the real on-site measuring conditions of an HV insulated distribution line are simulated in a controlled way. Practical characterizations, showing the convenience and advantages of applying the method using the modular test platform, are also presented.

In this thesis research related to the characterization, in a complete and reproducible way, of the systems for measuring and monitoring the state of high voltage (HV) electrical networks is carried out. The research is mainly focused on the approach of new developments, suitable for the characterization of systems used in the monitoring of the dielectrics status by measuring the activity of partial discharges (PD). The research can be extended to the possibility of characterizing systems that monitor the occurrence of insulation faults leading to intermittent or permanent short circuits. The study covers the characterization of PD measuring and monitoring systems operating both on-line, i.e. under normal operating conditions of the installations, and off-line, with the installations out of service. In these two cases, non-conventional measurements are carried out and the IEC-62437 technical specification serves as a reference. The performance of characterizations is also envisaged when the measuring and monitoring systems operate in laboratory tests. In this case, the measurements are performed according to the normative method being the IEC 60270 standard the reference. Fundamentally, for each system, the aim is to characterize both the measuring technique implemented and the processing and analysis techniques or functionalities with which the diagnostics are carried out. Special interest has been devoted to providing solutions to the problems faced by companies of the electricity sector, given the need to characterize measuring and monitoring systems when considering their operability in on-site installations. In this sense, the main objective of this thesis is to provide the necessary resources to characterize the systems in a controlled way, when they operate under the same technical conditions they face in industrial environments. To address this objective, several solutions are proposed and mainly a new characterization method associated to a scaled modular test platform. The implementation of the method using the test platform enables the characterization of the systems in a complete and reproducible way. Furthermore, the method is useful to support the training tasks of specialist technicians in the diagnosis of dielectrics. An adequate characterization of the systems and a quality training of specialist technicians will make it possible to carry out more accurate diagnoses and, consequently, will lead to more robust and efficient electrical systems. In this regard, the research presented here contributes significantly to the technological progress of the smart supervised networks of the future, known as smart grids. Part of the approaches developed in this thesis to carry out the characterization of the measuring systems are focused on the measurement and prior analysis of real insulation defects, for their subsequent controlled reproduction and measurement in the same conditions as in on-site installations. For the test or practical validation of the contributions of this thesis, laboratory assemblies, test cells and scale platforms with and without real defects were designed and developed, with which the necessary experimental measurements were performed. Most of the developments and experimental measurements were carried out at the High Voltage Laboratory of Polytechnic University of Madrid (LAT-UPM) and at the High Voltage Technological Centre (CTAT) of the Official Central Laboratory of Electrical Engineering (LCOE), of the Foundation for the Promotion of Industrial Innovation (FFII). Experimental measurements were also carried out at the High Voltage Laboratory of University of Delft (The Netherlands). RESUMEN En esta tesis se realiza una investigación relacionada con la caracterización, de forma completa y reproducible, de los sistemas de medida y monitorización del estado de las redes eléctricas de alta tensión. Principalmente la investigación se centra en el planteamiento de nuevos desarrollos, útiles para la caracterización de los sistemas empleados en la supervisión del estado de los dieléctricos, mediante la medida de la actividad de las descargas parciales. La investigación se puede hacer extensible a la posibilidad de caracterizar los sistemas que supervisan la aparición de faltas de aislamiento conducentes a cortocircuitos intermitentes o permanentes. Meter en las líneas futuras. El estudio abarca la realización de caracterizaciones de sistemas de medida y monitorización de DP que operan tanto on-line, es decir en las condiciones normales de operación de las instalaciones, como off-line, con las instalaciones fuera de servicio. En estos dos casos se realizan medidas no convencionales y sirve de referencia la especificación técnica IEC-62478. También se contempla la realización de caracterizaciones cuando los sistemas de medida y monitorización operan en medidas de laboratorio. En este caso, se realizan medidas de acuerdo al método normativo y sirve de referencia la norma IEC 60270. Fundamentalmente, para cada sistema se pretende caracterizar tanto la técnica de medida utilizada, como las técnicas o funcionalidades de procesado y análisis con las que se realizan los diagnósticos. Se ha dedicado especial interés en dar solución a los problemas que tienen las empresas del sector eléctrico, ante la necesidad de caracterizar los sistemas de medida y monitorización cuando se considera su operatividad en instalaciones de campo. En este sentido, el objetivo principal de esta tesis es facilitar los medios necesarios para poder hacer la caracterización de los sistemas de forma controlada, cuando éstos operan con las mismas condiciones técnicas a las que se enfrentan en los entornos industriales. Para abordar este objetivo, se proponen varias soluciones y principalmente un nuevo método de...