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The measurement of partial discharges (PD) in HV installations by means of high-frequency current transformers (HFCT) is being extended progressively in recent years, as they are affordable non-invasive sensors that can be easily installed. Several manufacturers provide in their data sheets the technical characteristics considered most relevant. However, there is no formal definition of these characteristics and/or minimum requirements to be met for such type of sensors, nor objective procedures to measure and quantify them. A new European EMPIR Project [1] aims to develop a characterization procedure for PD measuring systems. The main objective of this article is to analyze some of the most relevant characteristics of an HFCT sensor and to present testsetups to be used for obtaining them, especially its frequency response, as well as its EMC immunity, and their impact on the measured PD signals.

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.

La monitorización y medida de las descargas parciales en las redes eléctricas e instalaciones de alta tensión para evaluar el estado del aislamiento de los activos es un tema de gran actualidad, sin embargo, no existen criterios ni procedimientos para evaluar las características técnicas de estos sistemas de medida y diagnóstico. Los sistemas de cable se monitorizan con sensores de tipo HFCT por tener alcances de medida de varios kilómetros cada sensor. En las instalaciones GIS, los sensores invasivos de tipo UHF son ampliamente utilizados, al presentar alta sensibilidad para detectar pequeñas DP pese a su corto su alcance de pocos metros y para los transformadores de potencia se utilizan las capacidades de las bornas capacitivas, como condensador de acoplamiento acoplado a una impedancia de medida. Aunque aparentemente no existe una solución universal para resolver el mismo problema “detección del defecto del aislamiento eléctrico”, en realidad no son bien conocidas las capacidades que tienen las diferentes técnicas de medida convencionales, en HF, VHF y las de UHF. En este artículo se presenta un procedimiento de ensayo desarrollado con motivo del proyecto europeo “FuturEnergy” dentro del programa EURAMET que utiliza un banco de ensayo monofásico de alta tensión (20 kV) compuesto por una GIS y un sistema de cable que permite realizar pruebas de caracterización de sistemas de medida que utilicen sensores de tipo convencional, HFCT, VHF y de UHF. Las descargas parciales son generadas por un conjunto de probetas de referencia diseñadas al efecto o por un generador de trenes de pulsos de DP de referencia utilizado como calibrador.

Nowadays, many researchers are focusing on on-line condition monitoring of high-voltage 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 cable sheath when a CB configuration is adopted. The proposed criterion can be applied at different levels of load current. For the application of the criterion, the cable system under evaluation is modeled using the alternative transient program (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 cable sheaths, when on-line measurements are performed in monitoring applications.

Periodic calibrations of Energy Measurement Systems (EMS) installed in locomotives must be carried out to demonstrate the required accuracy established in the EN 50463-2 standard according to European Parliament and Council Directive 2008/57/EC on the interoperability of rail systems within the Community. As a result of the work performed in the “MyRailS” EURAMET project an AC calibration facility was developed consisting of a fictive power source was developed. This fictive power source can generate distorted sinusoidal voltages up to 25 kV-50 Hz and 15 kV-16.7 Hz as well as distorted sinusoidal currents up to 500 A with harmonic content up to 5 kHz or phase-fired current waveform stated in EN50463-2 standard. These waveforms are representative of those that appear during periods of acceleration and breaking of the train. Reference measuring systems have been designed and built consisting of high voltage and high current transducers adapted to multimeters, which function as digital recorders to acquire synchronized voltage and current signals. An approved procedure has been developed and an in-depth uncertainty analysis has been performed to achieve a set of uncertainty formulas considering the influence parameters. Different influence parameters have been analyzed to evaluate uncertainty contributions for each quantity to be measured: rms voltage, rms current, active power, apparent power and non-active power of distorted voltage and current waveforms. The resulting calculated global expanded uncertainty for the developed Energy Measuring Function calibration set up has been better than 0.5% for distorted waveforms. This paper is focused on presenting the complete set of expressions and formulas developed for the different influence parameters, necessary for uncertainty budget calculation of an Energy Measuring Function calibration.

This paper describes the Direct Current Injection (DCI) tests, in both Low and High levels, performed on a full scale aircraft cockpit with hybrid construction (carbon fiber composite and metallic parts). Additionally, some electromagnetic simulations carried out to optimize testing and analyze test results are also described.

Very fast transient overvoltages (VFTOs) due to switching operations can appear between the gas-insulated substation (GIS) enclosures and the cable sheaths and between these grounding parts and the substation Earth structures. These VFTOs achieve hundreds of kilovolts, provoking hazardous disruptive discharges for human safety. This paper includes a sensitivity analysis of the different parameters in order to establish criteria to be adopted in the grounding system design of the GIS structures and the cable connection to mitigate transient overvoltages. The use of bypass surge voltage limiters (SVLs) between the GIS enclosure and the cable sheath is also needed to avoid uncontrolled discharges. The selection of these SVL according to insulation coordination rules is presented in this paper, ensuring electrical safety without affecting the current mode of exploitation of the 220-kV GIS or the cable.

The new IEC 60060-1 standard establishes the k-factor function to determine the test voltage value of lightning impulses with superimposed oscillations, but no rule is given to determine experimental k-factor values. Testing methods, testing setups, and formulas to determine k-factor values are some crucial issues to obtain good results. This paper describes the two procedures used in the investigation funded by the European community and referenced in the Annex D of the last edition of IEC 60060-1 standard to determine experimental k-factor for air gaps, one for nonhomogenous fields and other for quasihomogenous fields. Both procedures were implemented using a setup with only 1 generator and a setup with 2 generators. Compatibility of new experimental k-factor values determined for air gaps up to 900 kV in quasihomogenous field with the factor function stated in IEC 60060-1 is shown by means of several examples, but additional examples show a significant discrepancy for air clearances of a sharp rod-plate configuration in the voltage range 250 to 800 kV.

A transient analysis software for high voltage cables has been developed as an aid to partial discharge measurements carried out to assess the insulation condition of installed cables. Knowledge of the transient behavior of cable systems allow to know if a specific measuring PD system is sensitive enough to detect partial discharge pulses that can occur along a high voltage cable. Series impedances of a high voltage cable are analyzed considering its semiconducting layers using Bessel functions. The influence of semiconducting layers is also taken into account to determine the parallel impedance of a high voltage cable. A Gaussian pulse is considered as a PD pulse traveling along the cable and the inverse Laplace transform is used to determine the resulting pulse at the end of a cable length. The results presented in this paper show that attenuation and distortion of PD pulses traveling along any cable system depend largely on the resistivity and the permittivity relativity of semiconducting layers of the high voltage cables.

Partial discharges phenomenon (PD) is one of the most relevant degradation modes that affects in the gradual deterioration of the insulation elements in high voltage (HV) electrical systems, thus PD measurement is essential for their condition assessment. In the last decades on-line PD measurements have become a common technique for assessing the insulation condition of installed HV installations, although in on-line tests it is difficult to perform accurate diagnoses due to the existence of high levels of background noise and in many cases of more than one source of pulse-shaped signals. In order to overcome the difficulties mentioned, this paper proposes a method for the classification of PD signals based on a mathematical modeling. With the proposed model, representative parameters associated to the waveform of each pulse acquired are calculated so that they can be separated in different clusters. Furthermore, this mathematical model enables the reconstruction, generally with a reasonable accuracy, of the measured signals in HV installations. This approach permits to save the pulse data of a test with a low requirement of memory capacity in comparison with other approaches, that need to save all samples of each recorded pulse to visualize them and for further analysis or post-processing.