The IEC 60060-1 (2010) and IEEE 4 (2013) Standards establish the k-factor function to determine the test voltage value of lightning impulses (LI) with superimposed oscillations. The test voltage function is included in these Standards to enable a more accurate and consistent determination of the test voltage and the time parameters, of LI with superimposed oscillations of any frequency content. The experimental k-factor function was determined by five research European institutes, but no dielectric fundaments were given to justify the k-factor function. This paper presents a specific study that was performed to validate the k-factor approach by checking its compatibility with the disruptive physic phenomenon. The same testing data used for determining the k-factor function for the air dielectric medium were used to determine the disruptive effect area model proposed by Kind in 1958. The results obtained ratify the compatibility between the k-factor function and the disruptive effect area model. The results presented in this paper are considered a valuable information for future research related to the test voltage k-factor function to improve the current International Standards.

Usually, developers of partial discharge (PD) measuring systems have difficulties to test their new functionalities or the improvements made in the existing ones. Furthermore, when a new PD measuring system is acquired by an electrical company, the subsequent training period for qualified analysts may be particularly complicated. This is because on many occasions, demanding and costly laboratory assemblies or even real installations already in operation are required for the measurements of representative PD activity and background noise. Furthermore, when using laboratory or real installations, the performance of repetitive tests anywhere for comparison purposes is not possible, due to logistics problems and to the stochastic phenomena of the PD generated. In this paper, a solution to solve these difficulties is presented. This solution is based on the development of a novel scale test setup designed to simulate a three-phase cable system. PD activity and noise conditions are simulated in the test setup injecting, in a controlled way, signals using an analog generator. The setup is useful both, for testing PD measuring systems´ functionalities and for training analysts.

Currently, electrical company users of PD measuring systems face the difficulty of the lack of procedures, for the training and evaluation of their technicians' analytical capabilities. This same difficulty must be also afforded by companies developers of PD measuring systems technology. In this paper a benchmark method, useful for the comprehensive training and evaluation of PD analysts in a technically and economically feasible way, is presented. This method is focused on the issues faced by technicians of this field in real-life PD measurements and analysis. Various evaluation tests are proposed in the method, with which the technicians are challenged with practical cases of analysis. The measurements to be analyzed are related to real experiences when HFCT sensors are used. A practical example of the method application is presented, showing its effectiveness for the training and evaluation of PD analysts' capabilities.

Main text To reach the main text of this paper, click on Final Report . Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/ . The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Currently, the evaluation of partial discharge (PD) measuring systems and associated sensors, is of utmost interest to the companies of the electrical sector. The availability of accredited expert analysts is also of interest. The most efficient systems and analysts will be the most demanded. On the other hand, it is requested by these companies reference tests facilities where the systems and analysts can be evaluated in a complete and reproducible manner. On-site facilities are rarely available for testing and the use of laboratory facilities is often very complex and expensive. In this paper it is presented a technically and economically affordable scale modular tests platform, that allows the performance in a suitable way of PD tests, for the evaluation of measuring systems along with the analysts capabilities.

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.

Smart grid monitoring is growing with large scale deployments including technologies such as partial discharge sensors for assessing insulation condition. This paper describes the application of permanent monitoring solutions supplemented with artificial intelligence systems to generate reliable alerts for insulation defects based on partial discharge pattern recognition. Three different data models, initially with a high level of accuracy, have been implemented and compared using several types of architecture and training data sets. A characterization of the three models has been designed to show the performance in real conditions where data is: more complex than the training data set, noise is mixed with the defect, sensitivity is lost, and clustering techniques were needed to separate multiple defects. The analysis of the results is performed using a criticality matrix that helps assess which data models accurately identify which failures are true.

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.

A synthetic partial discharge (PD) calibrator has been developed to qualify PD analyzers used for insulation diagnosis of HVAC and HVDC grids including cable systems, AIS, GIS, GIL, power transformers, and HVDC converters. PD analyzers that use high-frequency current transformers (HFCT) can be qualified by means of the metrological and diagnosis tests arranged in this calibrator. This synthetic PD calibrator can reproduce PD pulse trains of the same sequence as actual representative defects (cavity, surface, floating potential, corona, SF6 protrusion, SF6 jumping particles, bubbles in oil, etc.) acquired in HV equipment in service or by means of measurements made in HV laboratory test cells. The diagnostic capabilities and PD measurement errors of the PD analyzers using HFCT sensors can be determined. A new time parameter, "PD Time", associated with any arbitrary PD current pulse i(t) is introduced for calibration purposes. It is defined as the equivalent width of a rectangular PD pulse with the same charge value and amplitude as the actual PD current pulse. The synthetic PD calibrator consists of a pulse generator that operates on a current loop matched to 50 Ω impedance to avoid unwanted reflections. The injected current is measured by a reference measurement system built into the PD calibrator that uses two HFCT sensors to ensure that the current signal is the same at the input and output of the calibration cage where the HFCT of the PD analyzer is being calibrated. Signal reconstruction of the HFCT output signal to achieve the input signal is achieved by applying state variable theory using the transfer impedance of the HFCT sensor in the frequency domain.

Distribution system operators apply online partial discharge (PD) [1] monitoring to diagnose insulation condition of HV and MV cables, power transformers, GIS and MV cabins belonging to the distribution grid. There is a large number of infrastructures to be assess with this predictive maintenance method and with different levels of criticality where periodic or permanent PD monitorization strategies could be applied. In this article it is introduced the way that EDP Redes España in collaboration with the PD monitoring solutions manufacturer Ampacimon and University Polytechnic of Madrid, are developing new solutions integrating artificial intelligence (AI) and adapting the hardware to the distribution grid needs.

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.

Driven by the voltage increase in high-voltage direct current (HVDC) gas-insulated substations (GISs), novel methods are needed for partial discharge (PD) detection and monitoring. This article shows a PD calibration method for very-high-frequency (VHF) magnetic and electric sensors in GIS. The calibration method uncertainty is tested in three laboratories using a low-voltage (LV) test bench and a high-voltage (HV) full-scale GIS. In the LV test, the calibration method’s linearity, signal-to-noise ratio (SNR), and pulsewidth were compared against a reference charge, resulting in an error of around ±10%. The HV test consisted of different artificial defects introduced in a full-scale GIS, resulting in errors of around ±30%. The uncertainty is attributed mainly to random noise, which is critical in the charge estimation method. The electric and magnetic sensor combination showed better results, especially in the full-scale GIS, where reflections play an important role. This research has been performed in the framework of the project Future Energy 19ENG02 of EURAMET, resulting in a calibration method with the potential to measure PD pulses and discriminate impulse interferences, giving an advantage over conventional and ultrahigh-frequency (UHF) methods.

Main text The supplementary comparisons of national standards of ratio error and phase displacement of AC voltage of power frequency have been performed among the following national metrological institutes (NMIs): VNIIMS, MIKES-TKK, SP, CMI, LCOE, BIM and SE “Ukrmetrteststandard”. The description and measurement results are presented in the present report. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Dataset for publication named: "Effects of coaxial cables on high-voltage lightning impulse measured parameters: A comparative between measurements and simulations".

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.

Traditionally, high voltage (HV) laboratories have required different measuring instruments to measure alternating voltages 50/60 Hz (AC), using peak voltmeters, lightning impulses, through peak voltage meters or oscilloscopes and the apparent charge, by means of partial discharge (PD) measuring instruments. All of them with very different technical requirements stablished in applicable hardware and software standards (IEC 61083 series [1], IEC 60060 series [2, 3] and IEC 60270 [4]). However, the technological evolution of measuring instruments has allowed these measurements could be carried out through highperformance digital recorders. This article describes a new universal measuring instrument, developed by the LCOE for high voltage quantities, known as UMU (Universal Measuring Unit), for the five typical measurements to be carried out in any high voltage laboratory: AC 50/60 Hz, DC, Lightning impulse 1.2/50 μs (LI), Switching impulse 250/2500 μs (SI), partial discharge measurements, Radio Interference Voltage (RIV) measurements, transmitted overvoltage in secondary winding of voltage and current measuring transformers.A new software package has been also developed in the framework of 19NRM07 HV-com2 project [5].

Tradicionalmente los laboratorios de alta tensión (AT) han precisado diferentes instrumentos de medida para medir las tensiones alternas 50/60 Hz (AC), mediante voltímetros de cresta, impulsos de tensión tipo rayo, mediante medidores de tensiones de cresta y osciloscopios y la carga aparente, mediante instrumentos de medida de descargas parciales (DP). Todos ellos con requisitos técnicos muy diferentes recogidos en normas aplicables al hardware y software (normas de la serie IEC 61083 [1] y norma IEC 60270 [2]). Sin embargo, la evolución tecnológica de los instrumentos de medida ha permitido que estas medidas se puedan y deban realizarse a través de registradores digitales A/D de altas prestaciones. En este artículo se describe el nuevo sistema de medida desarrollado por el LCOE “Registrador Universal de Alta Tensión”, denominado como “RUAT”, capaz de ser utilizado para las cinco medidas típicas de alta tensión en un laboratorio: AC, DC, impulso tipo rayo (1,2/50 µs), impulso tipo maniobra 250/2500 µs) y DP.

When partial discharge (PD) activity is detected in a high-voltage (HV) installation, those responsible for their reliable functioning want to know the criticality of the defect or defects with the aim of taking the appropriate corrective actions. In order to assess the criticality of a defect and decide when the red light on the alarm should be activated, a thorough study of the defects evolution over time is required. Although in recent years various companies have acquired valuable knowledge from on-site monitoring applications, the study over time of defects in controlled laboratory test cells can significantly strengthen this knowledge. In the research presented in this paper reproducible test cells, each containing a reference insulation defect, have been developed, tested and aged for the improvement in PD diagnosis. The temporary study of the insulation defects evolution provides valuable information for adopting adequate criteria when evaluating their criticality in the electrical assets. In addition, the information gathered in this research is useful to train the learning processes of artificial intelligence systems, which are developed to perform assisted or automatic PD diagnoses. Finally, it is worth mentioning that as a result of this research the reproducible test cells developed have proved to be useful to perform long lasting laboratory tests with real insulation defects, which results interesting not only for scientific purposes but also for didactic issues.