Piezoelectric energy harvesting

One common use of energy harvesting systems is in those places where the access to conventional sources of energy is difficult due to availability, space constraints, environmental hazards or sealed equipment. This article explores the possibilities of piezoelectrics to extract electrical energy and store it in capacitors to supply power of ultra-low power microprocessors.

The piezoelectric under test is a Lead Zirconate Titanate PZT-5J with reference S128-H5FR-1808YB manufactured by MIDE. The tests I am going to conduct are aimed at a specific application in which the piezo has to extract energy at 100 Hz with an acceleration as low as 2 ms^{-2} or 0.2 g.

From right to left, the setup consists of a signal generator, signal conditioner and amplifier (top), signal amplifier (bottom), oscilloscope and vibrator or shaker with the piezoelectric (behind the oscilloscope).

Continue reading Piezoelectric energy harvesting

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

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.


Insulation design of low voltage electrical motors fed by PWM inverters

L. Lusuardi, A. Cavallini, M. G. de la Calle, J. M. Martínez-Tarifa and G. Robles, “Insulation design of low voltage electrical motors fed by PWM inverters,” in IEEE Electrical Insulation Magazine, vol. 35, no. 3, pp. 7-15, May-June 2019.

doi: 10.1109/MEI.2019.8689431


Abstract— This paper proposes a model to determine the partial discharge inception voltage of magnet wires, including the effect of elevated temperatures, and shows its applicability to the complete range of wire geometries considered in IEC Standard 60317-13.

For long, the insulation of magnet wires used in low voltage motors was mostly stressed by temperature and vibrations. In addition, moisture sometimes hastened thermo-mechanical stress by hydrolyzing the insulation leading to crack formation. The ultimate breakdown mechanism was an excessive leakage current throughout cracks and pinholes in the insulation. Within this framework, the thickness of the insulation was dictated mostly by mechanical considerations, to prevent crack formation during manufacturing and operation. Electrical stress did not play a key role in the aging process.
Power electronics changed this picture…

Keywords— inverter-fed machine, partial discharges, insulation design.

Multiple Partial Discharge Source Localization in Power Cables Through Power Spectral Separation and Time-Domain Reflectometry

G. Robles, M. Shafiq and J. M. Martínez-Tarifa, “Multiple Partial Discharge Source Localization in Power Cables Through Power Spectral Separation and Time-Domain Reflectometry,” in IEEE Transactions on Instrumentation and Measurement. doi: 10.1109/TIM.2019.2896553

Open access post-print version (ie final draft post-refereeing) available (Copyright 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works).

Early access available at http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8653470&isnumber=4407674



Abstract— Insulated power cables are becoming increasingly popular in today’s developing distribution and transportion networks. However, due to aging, deterioration, and various operational and environmental stresses, insulation defects may appear and so the cable needs to be monitored in a timely manner to avoid unexpected failures. Many of these defects are responsible for partial discharge (PD) activity. The localization of the sources of these discharges is a highly decisive facet in the condition-based monitoring of power cables. The techniques for the localization of single-PD defects in insulated power cables are well presented in the current bibliography. However, when several simultaneous PD sources are active, the localization of the sources becomes quite complex. This paper develops an efficient technique for the separation and localization of multiple PD sources in a medium voltage cable. The experimental results are obtained with single-end-based measurements using a high-frequency current transformer in a laboratory environment. The data processing based on the spectral characteristics of the signals is carried out by using the power ratios technique in order to determine the presence of different types of PD. Once the signals are separated, the PD sources can be localized with an individualized analysis of each source through time-domain reflectometry. The proposed methodology can be very valuable to improve the location diagnostic capability of the condition-based monitoring solutions, especially for underground cables.

Keywords— Condition monitoring; partial discharges (PDs); particle swarm optimization (PSO); power cables; signal characterization; signal propagation; spectral power ratios (PRs); time-domain reflectometry (TDR).

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 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.


20 puestos de especialización para jóvenes ingenieros y físicos aplicados en la 4ª convocatoria del Spanish Traineeship Programme, CIEMAT-CERN

En los próximos días, se abrirá la cuarta convocatoria del Spanish Traineeship Programme, FTEC-2018, un programa de especialización tecnológica en el CERN, Ginebra, Suiza, destinado a jóvenes ingenieros y físicos aplicados.

La convocatoria tiene como objetivo incrementar la presencia de investigadores y técnicos españoles en el CERN, así como consolidar un colectivo de ingenieros y físicos especializados en tecnologías de los grandes aceleradores de partículas, detectores e infraestructuras asociadas, con la finalidad de una futura incorporación a la industria e instituciones del sector.

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Online condition monitoring of MV cable feeders using Rogowski coil sensors for PD measurements

M. Shafiq, K. Kauhaniemi, G. Robles, M. Isa, L. Kumpulainen, “Online condition monitoring of MV cable feeders using Rogowski coil sensors for PD measurements”, Electric Power Systems Research, Volume 167, February 2019, Pages 150-162, ISSN 0378-7796,


Abstract— Condition monitoring is a highly effective prognostic tool for incipient insulation degradation to avoid sudden failures of electrical components and to keep the power network in operation. Improved operational performance of the sensors and effective measurement techniques could enable the development of a robust monitoring system. This paper addresses two main aspects of condition monitoring: an enhanced design of an induction sensor that has the capability of measuring partial discharge (PD) signals emerging simultaneously from medium voltage cables and transformers, and an integrated monitoring system that enables the monitoring of a wider part of the cable feeder. Having described the conventional practices along with the authors’ own experiences and research on non-intrusive solutions, this paper proposes an optimum design of a Rogowski coil that can measure the PD signals from medium voltage cables, its accessories, and the distribution transformers. The proposed PD monitoring scheme is implemented using the directional sensitivity capability of Rogowski coils and a suitable sensor installation scheme that leads to the development of an integrated monitoring model for the components of a MV cable feeder. Furthermore, the paper presents forethought regarding huge amount of PD data from various sensors using a simplified and practical approach. In the perspective of today’s changing grid, the presented idea of integrated monitoring practices provide a concept towards automated condition monitoring.

Keywords—Condition monitoring; Rogowski coil; Dielectric insulation; Partial discharge; Medium voltage cable; Transformer.

Partial Discharge Signal Propagation in Medium Voltage Branched Cable Feeder

M. Shafiq, K. Kauhaniemi, G. Robles, G. A. Hussain and L. Kumpulainen, “Partial discharge signal propagation in medium voltage branched cable feeder,” in IEEE Electrical Insulation Magazine, vol. 34, no. 6, pp. 18-29, November-December 2018.


doi: 10.1109/MEI.2018.8507714

Abstract— Rising global and regional electricity use is accelerating the need to upgrade networks. The adoption of sustainable ways of energy generation (renewables energy resources) is the top priority of today’s grid, and these resources are predominantly embedded within the distribution networks that are mostly connected by medium voltage (MV) cables. Driven by urbanization trends, negative land value impacts, public safety, environmental aesthetics, and network reliability, the resistance to overhead lines in distribution networks is gradually increasing in many countries. Either choosing the proactive path considering the operational superiority of underground cables compared with overhead lines or following the ongoing legislative policies, the use of cables has been increasing rapidly over the past 30 years. This trend is likely to accelerate.

Keywords— Power cables; Partial discharges; Power cable insulation; Cable shielding; Current measurement; Voltage measurement; Medium voltage; Condition monitoring; Cables; Branch; Joint; Diagnostic; Sensor},


Energy harvesting for a smart sensor with NFC capability

Autor/Author: Javier Molina
Director/Supervisor: Guillermo Robles
Master Thesis Document in pdf.


Abstract – Modern life’s concerns regarding unnecessary energy wasting and the unstoppable development of electrical engineering gave birth to the concept of energy harvesting. All this, along with an overwhelming number of internet connected devices, make necessary new smart devices to make easier our lives not only at home but also in industrial environments. Throughout this project, the feasibility of using a Peltier cell as a thermoelectric generator is discussed in order to scavenge energy from a heat source. This project aims at using this system in dicult access locations to create a smart sustainable system that can keep track of relevant parameters such as temperature, pressure or radiation. By implementing this self-powered system, there is no need to replace batteries when fully discharged, it is only necessary collect the data when required. In particular, this Peltier cell supplies an energy harvester module that powers a standalone microcontroller to establish a communication with a NFC module. This device embedded with a NFC tag will store the parameters measured by a sensor. This novel approach is intended to allow any NFC enabled device such as any modern smartphone to access this data to be subsequently analised and take action when needed.


Resumen – Las preocupaciones de hoy en da con respecto al consumo abusivo energetico sumado al gran desarollo reciente de la ingeniera electrica y electronica han dado como fruto el concepto de energy harvesting. Ademas, el mundo en el que vivimos con un mayor numero de dispositivos conectados a internet hacen necesario dispositivos inteligentes para facilitar nuestras vidas, no solo en casa, si no tambien en el entorno industrial. En este proyecto se expone la viabilidad de usar una celula Peltier que es un dispositivo termoeléctrico para proporcionar energa a partir de una fuente de calor. Este proyecto persigue usar este sistema en sitios de difcil acceso y crear un sistema sostenible que lleve a cabo un sistema de recogida de datos, como temperatura o presion. La ventaja que ofrece un sistema como este es que no es necesario cambiar la batera, puesto que el sistema se autoalimenta. Concretamente, la celula Peltier suministra energa a un modulo de almacenamiento que establece una comunicacion con un modulo NFC. Este dispositivo contiene una etiqueta NFC que almacena los datos recogidos por un sensor. Este enfoque permite a cualquier operario con un dispostivo que permita la lectura de etiquetas NFC, como por ejemplo cualquier smartphone moderno, acceder a estos datos para analizarlos y tomar decisiones si es necesario.


Energy harvesting and NFC tag (LTC3108 -> STM32L433 -> M24SR)

The idea behind this work was to test the capabilities of using a near-field communication (NFC) tag to store the information acquired through an analogue input of a microprocessor powered by an energy harvesting source.

The setup includes these components:

  • Peltier cell
  • Energy harvesting system
  • Microprocessor
  • Dynamic NFC/RFID tag IC
  • Temperature sensor

Energy harvesting system

The capabilities of Peltier cells to harvest energy from differences of temperature between its two sides has already been studied in other posts starting with this link, so I will not develop this part of the work here.

The energy harvesting system used in this project is now based on the outstanding Linear Technologies (now part of Analog Devices) Ultralow Voltage Step-Up Converter and Power Manager LTC3108. This device can work with four selectable output voltages: 2.35 V, 3.3 V, 4. V or 5 V to power wireless transmitters or sensors and a low dropout voltage regulator output (VLDO) to power an external microprocessor. According to its datasheet it can start harvesting energy from voltages as low as 20 mV which is precisely indicated for applications that use thermo-electric generator (TEG) such as Peltier cells. The energy is stored in a bank of supercapacitors connected to two outputs of the LTC3108. Two 1 F supercapacitors in series are connected to VOUT and charged when VAUX has reached 2.5 V. Another two 1 F supercapacitors are connected to VSTORE supporting VOUT and preventing an unexpected drop of voltage due to a high power demand by the load. A picture of the setup for this integrated circuit (IC) is:

Continue reading Energy harvesting and NFC tag (LTC3108 -> STM32L433 -> M24SR)