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.
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.
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.
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).
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.
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.
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},
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.