Muhammad SHAFIQ (1), Guillermo ROBLES (2), Kimmo KAUHANIEMI (2), Brian STEWART (3), Matti Lehtonen (4). Propagation characteristics of partial discharge signals in medium voltage branched cable joints using HFCT sensors. 3 – 6 June 2019, 25th international conference and exhibition on electricity distribution (CIRED 2019). Madrid – Spain
(1) University of Vaasa – Finland
(2) Carlos III University of Madrid – Spain
(3) University of Strathclyde – UK
(4) Aalto University – Finland
Abstract—Rapid proliferation of underground cables in today’s distribution networks need improved fault monitoring and diagnostic capabilities. Dielectric insulation is the most critical element of underground cables and exposed to various stresses. Cable joints and terminations are always needed and are the most vulnerable locations for insulation defects within the cable feeder. Partial discharge (PD) signals emerging during the progression of insulation faults, travel along the lines and split into connected branches at the T/Y splices. This makes the use of conventional diagnostics solution inappropriate as compared to straight cable section. This paper presents a study on the propagation behaviour of PD signals in a branched joint configuration. Experimental investigations are presented to study the PD propagation across the T/Y-splices. The presented study provides interesting outcomes that can be used for development of an efficient PD monitoring system to watchdog the cable feeder.
Keywords— Power cables, Partial discharges, Signal Propagation, Transmission lines.
Invited lecture at the International Workshop on Advanced Dielectrics and Applications (IWADA) 2019 – 26 April at the Universidade Federal de Campina Grande (UFCG) – Campina Grande, Paraíba, Brasil.
Slides in pdf.
This work has been done in collaboration with José Manuel Fresno during his PhD. thesis.
Guillermo Robles; Muhammad Shafiq; Juan Manuel Martínez-Tarifa, Designing a Rogowski coil with particle swarm optimization, November 2018, Proceedings of the 5th International Electronic Conference on Sensors and Applications session Physical Sensors (doi: 10.3390/ecsa-5-05721)
Open access at https://sciforum.net/paper/view/conference/5721
Abstract—Rogowski coils are inductive sensors based on Faraday’s and Ampère’s Laws to measure currents through conductors without galvanic contact. The main advantage of Rogowski coils when compared with current transformers is the fact that the core is air so they never saturate and the upper cut-off current can be higher. These characteristics makes Rogowski coils ideal candidates to measure high amplitude pulsed currents. On the contrary, there are two main drawbacks. On the one hand, the output voltage is the derivative of the primary current so it has to be integrated to measure the original signal; and, on the other hand, the transfer function is resonant due to the capacitance and the self-inductance of the coil. The solution is the use of a passive integration with a terminating resistor at the output of the sensor that splits the two complex poles and gives a constant transfer function for a determined bandwidth. The downside is a loss of sensitivity. Since it is possible to calculate the electrical parameters of the coil based on its geometrical dimensions, the geometry can be adapted to design sensors for different applications depending on the time characteristics of the input current. This paper proposes the design of Rogowski coils based on their geometric characteristics maximizing the gain-bandwidth product using particle swarm optimization and adapting the coil to the specific requirements of the application.
Keywords—Rogowski coils; particle swarm optimization; gain-bandwidth product; current
measurement; magnetic field measurement.
J.M. Martínez-Tarifa, G. Robles, J.M. Fresno and J.A. Ardila-Rey. Paper accepted in the International Conference on Dielectrics (ICD) 2018 — 2nd, 5th July — Budapest — Hungary
Abstract—Partial discharge (PD) detection using antennas has become a useful technique for condition monitoring of highvoltage equipment. However, one of its main drawbacks is the lack of knowledge for the quantification of the PD magnitudes, which is possible when conventional capacitive dividers or highfrequency
current transformers (HFCT) are used. This paper studies a possible relation between PD pulses measured in the HF and RF range. Different types of PD events were measured in the HF range using an HFCT and in the VHF/UHF range using two types of antennas. The peak value and the energy of each PD pulse have been studied for both HF and radio-frequency (RF) sensors, representing them in graphics. In addition, the possible
statistical dependence between variables (peak-energy; peakpeak; energy-energy) has also been quantified.
Keywords—Partial discharges, UHF measurements, HF measurements, Antennas, IEC60270, Correlation.
Department of Electrical Engineering. Universidad Carlos III de Madrid. Avda. Universidad, 30. 28911 Leganes. Madrid. Spain
* Author to whom correspondence should be addressed
The paper is open access and can be dowloaded here.
Fresno, J.; Robles, G.; Martínez-Tarifa, J. Planar localization of radio-frequency or acoustic sources with two receivers. In Proceedings of the 4th Int. Electron. Conf. Sens. Appl., 15–30 November 2017; ; doi:10.3390/ecsa-4-04892
Abstract— In the localization of electromagnetic or acoustic emitters, generally, when a pulse is radiated from a source, the wave will arrive to two receivers at different times. One of the advantages of measuring these time differences of arrival or TDOA is that it is not required a common clock as in other localization techniques based on the time of arrival of the pulse to the receiver. With only two sensors, all the possible points in the plane that would give the same TDOA describe a hyperbola. Using an independent third receiver and calculating the intersection of the three hyperbolas will give the position of the source. Therefore, planar localization of emitters using multilateration techniques can be solved at least with three receivers. This paper presents a method to locate sources in a plane with only two receivers reducing the number of acquisition channels and hence, the cost of the equipment. One of the receivers is in a fixed position and the other describes a circumference around the first one. The TDOA are measured at different angles completing a total turn and obtaining a periodic function, angle versus TDOA, that has all the geometric information needed to locate the source. The paper will show how to derive this function analytically with the distance from the fixed receiver to the source and a bearing angle as parameters. Then, it will be demonstrated that it is possible to fit the curve with experimental measurements to obtain the parameters of the position of the source.
Keywords— Time differences of arrival, localization techniques, radio frequency, ultra high frequency, antennas
J. M. Fresno, G. Robles, J. M. Martínez-Tarifa and B. G. Stewart, “A combined algorithm approach for PD location estimation using RF antennas,” 2017 IEEE Electrical Insulation Conference (EIC), Baltimore, MD, USA, 2017, pp. 384-387.
Abstract— To locate the positions of partial discharge sources in free space at least four RF antennas are arranged in a suitable
spatial geometry to detect the radiated electromagnet energy from the discharge. The time-difference-of-arrival (TDOA) between the signals from each antenna are then used within multi-lateration equations to determine the position of the source. The iterative Hyperbolic Least Squares (HLS) method and the non-iterative Maximum Likelihood Estimator (MLE) method are two common techniques used in the literature to solve the multi-lateration equations. This paper investigates the ability of combining MLE and HLS to improve location accuracy and maintain fast location computation time. To this end HLS, MLE and the combined MLEHLS method are evaluated in terms of location accuracy and computation performance for three spatial antenna configurations, namely Square, Pyramidal and Trapezoidal arrangements. The location accuracies for each method are evaluated for theoretical TDOA values and also for the case when a finite sampling rate of 10G samples-per-second is considered; the latter is implemented through appropriate rounding up of TDOA values by one sample time. It is shown that MLE-HLS produces improved location accuracy compared with HLS and MLE for both theoretical and finite sampled TDOA values. In addition, it is shown that MLE-HLS improves significantly the computation time over the iterative HLS method.
Keywords— Antenna theory; Mathematical model; Maximum likelihood estimation; Partial discharges; Position measurement; location algorithms; partial discharges; radio-frequency localization
CIGRÉ WORKSHOP: MONTORIZACIÓN DE LÍNEAS – COMITÉS DE ESTUDIO B1 y B2
UNIVERSIDAD DE CANTABRIA – 27 de abril de 2017
José Manuel Fresno, Guillermo Robles, y Juan Manuel Martínez-Tarifa. E-Mails: firstname.lastname@example.org, email@example.com y firstname.lastname@example.org.
Departamento de Ingeniería Eléctrica. Universidad Carlos III de Madrid, Avda. Universidad, 30, 28911, Leganés, Madrid, España
Enlace al póster.
- La medida de descargas parciales (DP) permite llevar a cabo un mantenimiento predictivo en instalaciones eléctricas.
- Las DP emiten una radiación electromagnética que puede ser medida con antenas para la localización de la fuente sin interrumpir el servicio de la instalación.
- Actualmente, se usan al menos cuatro antenas situadas en distintos puntos para la localización de la fuente de DP.
- Calculando la diferencia de los tiempos de llegada de la emisión a las antenas, y minimizando la función objetivo F se puede estimar la posición de la fuente de DP.
- Se puede localizar fuentes de DP con sólo dos antenas siguiendo el procedimiento propuesto en este póster:
- Para calcular la dirección (azimut y elevación) de la fuente de DP se deben orientar las antenas maximizando y tomar datos en varias posiciones.
- La distancia entre antenas se mantiene contante e igual a 2 m. Como la velocidad de propagación es m/s, el máximo es µs.
- La posición de la fuente de DP se define como la intersección de las direcciones calculadas en las posiciones donde se realizan las medidas.
- Sistema de adquisición de señales de dos canales basado en una FPGA con un ADC de bajo coste.
- Antenas monopolo omnidireccionales adaptadas para medir en la banda de frecuencias de las DP.
- La nueva metodología permite localizar fuentes de DP con un sistema de adquisición de dos canales en lugar de cuatro.
- La reducción de canales de adquisición reduce el precio y el peso del sistema de adquisición.
- Es posible localizar fuentes de DP con un sistema de adquisición de dos canales.
- Ubicando este equipo y las dos antenas en un vehículo aéreo no tripulado, se podría mejorar la exactitud de las medidas y por tanto de la localización.
Fresno, J.; Robles, G.; Martinez-Tarifa, J.; Stewart, B.; Spatial study of the uncertainties in the localization of partial discharges for different antenna layouts. 2017 IEEE International Instrumentation and Measurement Techonology Conference, Torino (Italy), May 22-25, 2017
Abstract—The maintenance of high-voltage equipment is paramount to avoid blackouts or the interruption of electrical service. One of the most reliable methods to know the status of insulation systems is the measurement of partial discharges (PD). This phenomenon occurs when the dielectric presents imperfections due to ageing and degradation processes. Partial discharges are sudden releases of charge that can emit energy in a wide band of frequencies even in UHF. Therefore, antennas can be used, not only to detect the occurrence of PD, but to locate the source of emission and, consequently, the damaged asset. The localization can be done using multilateration measuring the time-differences of arrival (TDOA) of the pulses to an array of antennas. However, the onset of the signal is difficult to define due to numerous issues, from low signal-to-noise ratio, to lack of line-of-sight or errors in the positioning of the antennas. Then, the position of the source may have large uncertainties that even can prevent finding the asset at stake. The configuration of the antenna layout can help to minimize the effect of the uncertainties in the measurement of the TDOA. It has been found that there are configurations that favour certain bearings when locating the source giving more accurate results. This paper explores three type of antenna layouts and devises a method to determine what directions are best to orient the array.
Keywords—Antennas, Radio-frequency, Localization, Partial Discharges.
Fresno, J.; Giannetti, R; Robles, G. A survey of time-of-flight algorithms to determine bone positions in movement. 2017 IEEE International Instrumentation and Measurement Techonology Conference, Torino (Italy), May 22-25, 2017
Abstract—In biomechanical applications where an ultrasound signal is used to determine the position of a specific organ or tissue, like for example a bone, a so-called A-mode ultrasonography is used. A ultrasonic pulse is generated by a transducer, injected in the tissue to be examined, and then the echoes are received and processed. Echoes are generated by changes in acoustic impedance in the medium, like for example a change of tissue from muscle to bone. To determine the position of the reflecting interface, the time-of-flight is measured and, utilizing well-know values for the transmission speed, the distance or depth is computed. If the localization device is to be designed to be small, wearable, and low-power, it is expected that the signal will be of worse quality with respect to traditional ultrasonography systems, especially under the point of view of signal-to-noise ratio. In these conditions, the reliability of the algorithm that implement the time-of-flight calculation is of paramount importance. In this paper, a simulated soft tissue–bone interface (implemented with an ultrasound gel-pad) has been measured with intentionally low excitation signals and with the presence of imperfections similar to those expected in a physiological system. Several classic algorithms have been tested and benchmarked in this condition, and a new method with better reliability and repeatability is proposed.
Keywords—Time-of-flight, ultrasonic sensors, biomecanical systems, cross-correlation, kurtosis.
Open access: http://www.mdpi.com/2504-3900/1/2/12/
Fresno, J.; Robles, G.; Stewart, B.; Martinez-Tarifa, J. The influence of antenna positioning errors on the radio-frequency localization of partial discharges sources. In Proceedings of the 3rd Int. Electron. Conf. Sens. Appl., 15–30 November 2016; Sciforum Electronic Conference Series, Vol. 3, 2016 , E003; doi:10.3390/ecsa-3-E003
Abstract—Electrical insulation can have imperfections due to manufacturing or ageing. When the insulation is electrically stressed, discharges may happen in these inhomogeneous imperfect locations resulting in partial discharge (PD) which have very fast rise times and short time durations. Since charges are accelerated within PD activity, radiated electromagnetic energy across a wide bandwidth of frequencies can occur. The measurement of the radiated PD energy is widely employed to identify defective insulation within high voltage equipment. Based on assessment of the strength and nature of the emitted PD signals, determination is made to carry out predictive maintenance in order to prevent equipment breakdown. The location of emitted radiated PD signals may be determined using multi-lateration techniques using an array of at least 4 antennas. Depending on the relative position between the antennas and the PD source, the radiated emissions from the PD source arrive at each antenna at different times. The relative time differences of arrivals (TDOA) together with the antennas position are variables used to locate the PD source in 3D space. The effect on the location error of a PD source using TDOA calculations based on acquisition sample time errors is a topic which has previously been studied (see bibliography). This paper now investigates the accuracy on PD location as a consequence of error on the measured positions of the antennas. This paper evaluates the influence of positional antenna error on the possible accuracy of the localization of the PD source. This error is analyzed for 3 different antenna array layouts and for different vector directions from the arrays. Additionally, the least sensitive layout with regard to positioning errors is proposed to assist in improving the location accuracy of PD sources.
Keywords—Radio-Frequency Localization; Partial Discharges; Antennas Positioning; Measurement Error.