Towards Series Arc Fault Detection in More Electrical Aircrafts

M. G. d. l. Calle, G. B. d. María, D. Izquierdo, R. Martín, J. M. Martínez-Tarifa and G. Robles, “Towards Series Arc Fault Detection in More Electrical Aircrafts,” 2020 IEEE 3rd International Conference on Dielectrics (ICD), Valencia, Spain, 2020, pp. 866-869, doi: 10.1109/ICD46958.2020.9342025.

Abstract – The trigger of an electric arc represents an unacceptable risk to the safety of the aircraft and a blocking point to certify the new high-voltage architectures. These high-voltage networks are required to cover the growing electric energy demand for new developments. Thus, the study of the electric arc phenomenon, its detection and the parameters affecting its behavior is needed to progress along the path to the all-electric aircraft.

Partial discharges measurement during under-damped steep-fronted overvoltages

J. M. Martínez-Tarifa and G. Robles, “Partial discharges measurement during under-damped steep-fronted overvoltages,” 2020 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), Dubrovnik, Croatia, 2020, pp. 1-5, doi: 10.1109/I2MTC43012.2020.9129294.

Abstract – Inverter-fed drives have become essential in most industrial processes nowadays to control the speed of rotation of electric motors. Unfortunately, the insulation of these electric motors show unexpected failures due to the appearance of partial discharges (PD). These type of discharges undermine the insulation along time creating weak spots than can cause total breakdowns. Thus, the detection of partial discharges is a challenge that must be faced by electric motor manufacturers and users. The problem of detection is intensified because the voltage supplied to the motors is based on steep-fronted pulses and PD are also very narrow pulses so it is quite complex to separate them from the electrical interferences created by the train of square pulses. In this paper, two different radio- frequency (RF) sensors will be used to detect PD in an insulation system subjected to square voltages with low rise-times. The response will be analyzed in the UHF range to select the best option for the detection of those hazardous under-damped pulses.

Piezoelectric Energy Harvesting System to Detect Winding Deformation in Power Transformers

Robles G., Febbo M., Machado S.P., García B. (2020) Piezoelectric Energy Harvesting System to Detect Winding Deformation in Power Transformers. In: Ball A., Gelman L., Rao B. (eds) Advances in Asset Management and Condition Monitoring. Smart Innovation, Systems and Technologies, vol 166. Springer, Cham.

Open Access available at

Abstract – One common use of energy harvesting systems is the installation on applications where the access to conventional sources of energy is difficult due to availability, space constraints, environmental hazards or sealed equipment. In this work, we propose an alternative use of an energy harvesting system based on a piezoelectric that takes the vibration of a transformer tank due to winding deformations and hence helps to monitor the condition of the equipment. The system consists on a cantilever piezoelectric beam with a mass tuned to the resonant frequency of the vibration. The output of the piezoelectric is connected to a quadrupler, a low-drop regulator and a capacitive storage. The harvested voltage is planned to supply a low power microprocessor that detects changes in the vibration measurements to determine an abnormal behavior of the transformer. This work introduces the causes of abnormal vibration of transformers, describes the installation of the piezoelectric on a model that generates the same acceleration as the vibration of a transformer tank and studies the capability of charging capacitors to determine the feasibility of the method.

Keywords – Condition monitoring, Energy harvesting, Piezoelectrics, Power transformers, Vibration analysis

Identification and Location of Partial Discharge Defects in Medium Voltage AC Cables

Muhammad Shafiq, Guillermo Robles, Amjad Hussain, Kimmo Kauhaniemi, Matti Lehtonen, Identification and Location of Partial Discharge Defects in Medium Voltage AC Cables. 5 August 2019. Proceedings of the 26th Nordic Insulation Symposium NORD-IS, Trondheim (Norway), pp 22-27. ISSN 2535-3969.

Open access available at

Abstract – The presence of partial discharge (PD) in electrical equipment is the confirmation or indication of an ongoing degradation of its dielectric insulation. PD study is a widely used tool for condition monitoring of medium voltage (MV) cables. The location of the defects can be considered as one of the most important tasks of diagnosis in underground installations of MV cables. A lot of references can be found on the location of single PD sources along the cable. However, several PD defects can be active simultaneously along a cable section. This paper presents an experimental study on a MV cable having two PD sources and noise. Adopting one end measurement technique, a high frequency current transformer (HFCT) is used to capture the PD current pulses. A simple approach of identification of the PD signals originated from different PD sources is presented based on wave-shape study along with a time domain reflectometry analysis. The presented measurement methodology and time domain analysis technique provides a convenient way for detection and location of more than one PD sources along a cable section.

Propagation characteristics of partial discharge signals in medium voltage branched cable joints using HFCT sensors

Available in open access here:

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.


Designing a Rogowski coil with particle swarm optimization

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

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.


Statistical correlation between partial discharge pulses magnitudes measured in the HF and UHF range

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.

Planar localization of radio-frequency or acoustic sources with two receivers

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



A combined algorithm approach for PD location estimation using RF 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.
doi: 10.1109/EIC.2017.8004695

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