Small wind energy systems. State of the art and new challenges

This paper is devoted to the analysis of small wind energy systems, including a review of the state of the art and new challenges

Stream data cleaning for dynamic line rating application

The maximum current that an overhead transmission line can continuously carry depends on external weather conditions, most commonly obtained from real-time streaming weather sensors. The accuracy of the sensor data is very important in order to avoid problems such as overheating. Furthermore, faulty sensor readings may cause operators to limit or even stop the energy production from renewable sources in radial networks. This paper presents a method for detecting and replacing sequences of consecutive faulty data originating from streaming weather sensors. The method is based on a combination of (a) a set of constraints obtained from derivatives in consecutive data, and (b) association rules that are automatically generated from historical data. In smart grids, a large amount of historical data from different weather stations are available but rarely used. In this work, we show that mining and analyzing this historical data provides valuable information that can be used for detecting and replacing faulty sensor readings. We compare the result of the proposed method against the exponentially weighted moving average and vector autoregression models. Experiments on data sets with real and synthetic errors demonstrate the good performance of the proposed method for monitoring weather sensors.This research was partially funded by Spanish Government under Spanish R+D initiative with reference ENE2013-42720-R and RETOS RTC-2015-3795-3

Problems derived from the simultaneous utilisation of different flickermeters in large electric networks

Power Quality assessment in distribution networks requires distributed measurements in order to verify the PQ state of the art. This process cannot simply be considered as an extension of a measurement at a given point because several variables need to be considered: number of PQM; election of optimal measurement location; synchronisation of instrumentation and management of captured data. This work focuses on the problems related with the simultaneous utilisation of different flickermeters in large electric networks. From a classical instrumentation point of view, several flickermeters from different customers are tested in the laboratory in order to determine the differences in the accuracy of the results. Both Pst and Plt are statistical parameters calculated using a large number of samples of the instantaneous flicker level IFL . The number of captured samples can vary from one instrument to another, so different flickermeters provide different values

Influence on power quality measurement of the simultaneous presence of different disturbances

Power Quality measurements involve not only problems related with the real use of recorders but also theoretical questions connected with functional and design aspects of the instrumentation. In addition, there are a rising number of standards covering topics from design to data analysis, so final users usually assume that they do not have to pay special attention to PQ instrumentation functionality when the device is designed according to approved standards. However, it is not unusual to find different disturbances at the same point and in the same time and standards do not say anything about their mutual influence on PQ index. The main aim of this research work is to show the influence that having different disturbances (flicker and sags) simultaneously has on the final results provided by the instrumentation for each individual disturbance. The paper proposes a test system and a methodology. The results of various tests using commercial and research instrumentation are presented and some possible solutions to these problems are considered

Alarma activada por control remoto selectivo.

La finalidad de esta invención consiste en disponer de una alarma que bien evite el robo de objetos ligeros y portátiles por el procedimiento que se conoce como "del tirón" --es decir, arrebatar algo y salir corriendo--, bien permita identificar un equipaje entre otros. La originalidad del dispositivo reside en la activación/desactivación del dispositivo de sonido por control remoto, así como la posibilidad de seleccionar el sonido de salida dependiendo de su finalidad. Se reivindica como de nueva y propia invención la propiedad y explotación de cualquier alarma caracterizada por la inclusión en su circuito eléctrico o electrónico del dispositivo que se ha llamado control remoto selectivo, capaz de activar/desactivar la alarma y/o emitir dos sonidos funcionalmente distintos. Puede instalarse en bolsos, portafolios, neceseres, ordenadores, radio-casettes y, en general, objetos ligeros o portátiles, que frecuentemente, son robados en la calle o establecimientos públicos; o en cualquier objeto a identificar entre un conjunto de equipajes.Solicitud: 9502265 (06.11.1995)Nº Pub. de Solicitud: ES2112778A1 (01.04.1998)Nº de Patente: ES2112778B1 (16.12.1998

A methodology for the calculation of typical gas concentration values and sampling intervals in the power transformers of a distribution system operator†

Predictive maintenance strategies in power transformers aim to assess the risk through the calculation and monitoring of the health index of the power transformers. The parameter most used in predictive maintenance and to calculate the health index of power transformers is the dissolved gas analysis (DGA). The current tendency is the use of online DGA monitoring equipment while continuing to perform analyses in the laboratory. Although the DGA is well known, there is a lack of published experimental data beyond that in the guides. This study used the nearest-rank method for obtaining the typical gas concentration values and the typical rates of gas increase from a transformer population to establish the optimal sampling interval and alarm thresholds of the continuous monitoring devices for each power transformer. The percentiles calculated by the nearest-rank method were within the ranges of the percentiles obtained using the R software, so this simple method was validated for this study. The results obtained show that the calculated concentration limits are within the range of or very close to those proposed in IEEE C57.104-2019 and IEC 60599:2015. The sampling intervals calculated for each transformer were not correct in all cases since the trend of the historical DGA samples modified the severity of the calculated intervals.This work was partially financed by the EU Regional Development Fund (FEDER) and the Spanish Government under RETOS-COLABORACIÓN RTC-2017-6782-3 and by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 864579 (FLEXIGRID)

Determination of transformer oil contamination from the OLTC gases in the power transformers of a distribution system operator

Power transformers are considered to be the most important assets in power substations. Thus, their maintenance is important to ensure the reliability of the power transmission and distribution system. One of the most commonly used methods for managing the maintenance and establishing the health status of power transformers is dissolved gas analysis (DGA). The presence of acetylene in the DGA results may indicate arcing or high-temperature thermal faults in the transformer. In old transformers with an on-load tap-changer (OLTC), oil or gases can be filtered from the OLTC compartment to the transformer?s main tank. This paper presents a method for determining the transformer oil contamination from the OLTC gases in a group of power transformers for a distribution system operator (DSO) based on the application of the guides and the knowledge of experts. As a result, twenty-six out of the 175 transformers studied are defined as contaminated from the OLTC gases. In addition, this paper presents a methodology based on machine learning techniques that allows the system to determine the transformer oil contamination from the DGA results. The trained model achieves an accuracy of 99.76% in identifying oil contamination.This work was partially financed by the EU Regional Development Fund (FEDER) and the Spanish Government under RETOS-COLABORACIÓN RTC-2017-6782-3 and by the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 864579 (FLEXIGRID)

A comparative between IEEE and EN in the transformer derating when supplying nonsinusoidal load current. A practical case

Nowadays, power quality is a challenge for the distribution companies since the new energy policies are directed to a distributed generation system with power electronic based technologies. The reduction of distribution transformers capability when supplying nonsinusoidal load currents has a major impact within capacity reduction in distribution networks produced by technical losses. IEEE Std C57.110-2018, EN- 50464-3 and EN-50541-2 define procedures to derate transformers when supplying nonsinusoidal load currents. The aim of this paper is to compare these procedures through a real case distribution transformer that suffers problems due to high levels of current distortion.This research was funded by the “Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación” grant number “RTC-2017-6782-3”, the European Union FEDER funds with name “LOcalización de averías, monitorización de estado y Control en redes de bAja TEnsión—LOCATE” and the Horizon 2020 Program by the European Comision with project reference No 864579, H2020-LC-SC3-2019-ES-SCC

A comparison of mechanical and ultrasonic anemometers for ampacity thermal rating in overhead lines

CIGRE TB601 guide for thermal rating calculations recommends the use of ultrasonic anemometers over mechanical devices [1]. This paper aims to compare the mechanical and ultrasonic wind speed measurement technologies for the purpose of dynamic ampacity rating. The comparison consists of applying the measurements of both anemometers (placed in the same spot) to the computation of ampacity in the same overhead line, and evaluating the diferences at different speed ranges.This work was supported by the Spanish Government under the R+D initiative INNPACTO with reference IPT- 2011-1447-920000 and Spanish R+D initiative with reference ENE2013-42720-R. The authors of this article would also like to acknowledge Viesgo for its continuous support to the dynamic ampacity rating line of investigation

Distributed vs. spot temperature measurements in dynamic rating of overhead power lines

The increase of global energy demand and new ways of electricity production are two of the main challenges for the power sector. The electric market has to address the addition of new and renewable sources of energy to the energy mix and to be able to integrate them into the grid, while maintaining the principles of robustness, security and reliability. All of these changes point to the creation of smart grids, in which advanced generation, information and communication technologies are needed. An accurate knowledge of the electric grid state is crucial for operating the line as efficiently as possible and one of the most important grid parameters to be measured and controlled is the temperature of the overhead conductors due to their relation with the maximum allowable sag of the line and its thermal limit (annealing). This paper presents the results of real-time monitoring of an overhead power line using a distributed temperature sensing system (DTS) and compares these results with spot temperature measurements in order to estimate the loss of accuracy of having less thermal information. This comparison has been carried out in a 30 km long distributed temperature sensing system with fiber optic inside a LA-455 conductor and 6 weather stations placed along the line. An area of influence is defined for each weather station corresponding to the orography of the surroundings. The spot temperatures are obtained from the DTS in the nearest point from the weather stations assuming these six locations to be the ones where the spot temperature measurement equipment would be located. The main conclusion is that, in the case of study, spot measurements are enough to obtain a good approximation of the average temperature of the line conductor