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 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

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

CO2 footprint reduction and efficiency increase using the dynamic rate in overhead power lines connected to wind farms

Since the first wind farms began operating in the early 1980s, several important factors have changed in the overall picture of energy politics worldwide. The total renewable wind energy capacity of Spain currently accounts for more than 20% of the total installed capacity, which makes integration into the grid challenging for wind farm owners as well as electricity transportation and distribution companies. The smart-grid concept, which focuses on real-time monitoring and dynamic rating operation of power lines, is an important component in the solution to these new challenges. This paper explains how a more efficient operation of energy-generating activities via dynamic rating of the electric grid due to a better knowledge of the main parameters contributes to more clean, renewable energy and decreases the CO2 footprint. The dynamic rating operation of a Spanish overhead power line is analysed, and different scenarios are studied. The dynamic rate achieved in 2015 has saved more than 1100 tonnes of CO2 and has generated over 240,000 € of extra income. This dynamic rating operation also increased the actual annual energy generated from 231.5 GW h to 834.7 GW h with only a 2% greater loss along the line due to Joule and magnetic effects.This work was supported by the Spanish Government under the R+D initiative INNPACTO with reference IPT-2011-1447-920000, the Spanish R+D initiative with reference ENE-2013-42720-R and RETOS RTC-2015-3795-3. The authors also acknowledge support from Viesgo

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

Thermal behaviour of medium-voltage underground cables under high-load operating conditions

The dynamic management of electric power distribution lines has become a topic of great interest at present. Knowledge of the ampacity of cables is fundamental to carrying out dynamic management. In this study, the ampacity of buried cables in different soil resistivities and depths was calculated. A small-scale model was built in the laboratory to simulate the operating conditions of a buried cable. With the experimental results, a numerical model based on the finite element method was validated to evaluate the ampacities calculated by two standards. A comparison was made between the ampacities calculated from the IEC 60287-1 and UNE 211435 standards and those obtained from the simulated model. In addition, a comparison was made regarding the steady-state temperatures obtained at each calculated ampacity. The results obtained from the simulated model design show that the ampacity calculation method of the IEC 60287-1 standard where drying-out of the soil occurs is the most accurate, and has the least risk of exceeding the maximum permissible cable temperature.This work was financed by the EU Regional Development Fund (FEDER) and the Spanish Government under ENE-2013-42720-R, RETOS-COLABORACION RTC-2015-3795-3 and SODERCAN/FEDER Proyectos Puente 2017 and by the University of Cantabria Industrial Doctorate 19.DI12.649. The authors also acknowledge support received from Viesgo

Acoustic noise-based detection of ferroresonance events in isolated neutral power systems with inductive voltage transformers

Power-quality events and operation transients in power systems (PS) with isolated neutral can saturate inductive voltage transformers (IVT), which, when interacting with the overhead and underground cable capacitances, can cause ferroresonance events in the local PS. This abnormal operating mode can partially or totally damage the transformers and switchgears within the affected PS. Distribution system operators (DSO) can minimize these effects by detecting ferroresonance events accurately and fast enough and changing the mode of operation accordingly. Direct detection methods, i.e., based on voltage measurements, are reliable, but the massive deployment of this solution is relatively expensive; i.e., power quality analyzers cost thousands of USD. Alternatively, indirect detection methods are also available, e.g., IVT vibration measurements with accelerometers costing hundreds of USD, but their reliability depends on the installation method used. This manuscript proposes using the acoustic noise caused by magnetostriction forces within the IVT core during ferroresonance events to detect their occurrence. Compared to other indirect methods, electret condenser microphones with preamplifying stage cost less than USD 10 and are less sensitive to the installation procedure. The proposed method is validated experimentally, and its performance compared to IVT vibration measurements one by using the same detection methodology.This work was partially financed by the EU Regional Development Fund (FEDER) and the Spanish Government under RETOS-COLABORACION RTC-2017-6782-3, the Spanish Ministry of Science and Innovation under project PID2021-128941OB-I00, and by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 864579 (FLEXIGRID)

Dynamic rating management of overhead transmission lines operating under multiple weather conditions

Integration of a large number of renewable systems produces line congestions, resulting in a problem for distribution companies, since the lines are not capable of transporting all the energy that is generated. Both environmental and economic constraints do not allow the building new lines to manage the energy from renewable sources, so the efforts have to focus on the existing facilities. Dynamic Rating Management (DRM) of power lines is one of the best options to achieve an increase in the capacity of the lines. The practical application of DRM, based on standards IEEE (Std.738, 2012) and CIGRE TB601 (Technical Brochure 601, 2014) , allows to find several deficiencies related to errors in estimations. These errors encourage the design of a procedure to obtain high accuracy ampacity values. In the case of this paper, two methodologies have been tested to reduce estimation errors. Both methodologies use the variation of the weather inputs. It is demonstrated that a reduction of the conductor temperature calculation error has been achieved and, consequently, a reduction of ampacity error.This research was funded by the Spanish Government AND FEDER funds under the R+D initiative RETOS COLABORACIÓN 2015” with reference RETOS COLABORACIÓN RTC-2015-3795-3 and Spanish R+D initiative with reference ENE2013-42720-R

Desarrollo de una plataforma virtual de simulación de sistemas eléctricos (DEVISI)

RESUMEN: Uno de los problemas de las pequeñas actividades de seguimiento o evaluación a realizar en casa por los alumnos es la facilidad con la que estas actividades pueden ser copiadas. El principal motivo es que normalmente todos los alumnos deben de resolver el mismo ejercicio. Una solución inmediata a este problema es que el docente prepare ejercicios individualizados para todos los alumnos, pero esta estrategia puede llegar a significar una carga de trabajo inasumible para el profesor. Este documento resume el funcionamiento de un sistema que genera automáticamente ejercicios de análisis de circui- tos individualizados para cada alumno y corrige automáticamente los resultados sin apenas interven- ción del profesor. El sistema genera variantes del mismo ejercicio y, por tanto, sigue siendo susceptible de copia, pero ahora esta copia no es tan inmediata y requiere un mínimo de entendimiento de lo que se está copiando por lo que, incluso copiando, el alumno terminará adquiriendo conocimiento. Ade- más, esto no es solo útil para la evaluación, sino que gracias a este desarrollo se pueden proporcionar fácilmente ejercicios para trabajo personal del alumnado desde su propia casa y con opción de verifi- cación de resultados. Por último, y en una situación de pandemia como la que se ha dado, el sistema permite examinar en remoto a los alumnos de forma simultánea dificultando la copia entre ellos.ABSTRACT: One of the main problems of the small monitoring and evaluation exercises to be completed out of the lecture room is the easiness to copy the results from other students. The main reason for this easiness is the fact that it is common for all students to face the exact same exercise. An immediate solution for this problem is for the teacher to prepare individualised tasks for every pupil. However, this solution may imply an unaffordable amount of work for the lecturer. This document describes a system that can generate individualised circuit analysis exercises for every student and allows for automatic verification of the results with minimum effort from the teacher. The system generates variants from the same exer- cise and so they can still be copied, but now copying them requires a minimum understanding of what is being done. This requirement means that the students will acquire some knowledge even if they do not resolve the task by themselves. Moreover, this system is not only useful for evaluation but also for easily providing exercises for personal work out of the classroom and with the chance of automatic co- rrection. Finally, given a situation like the pandemic, this development allows for remote simultaneous exams with barriers to cheating.Este proyecto ha sido dotado con fondos del plan de innovación docente de la Universidad de Cantabria