Analysis of submerged small punch test under static load for its employement in hydrogen embrittlement situations on high and medium strength steels

En este trabajo se analizan dos aceros de media y alta resistencia bajo escenarios de fragilización por hidrógeno, mediante el empleo de ensayos Small Punch (SPT) sumergidos bajo carga estática sobre probetas pre-cargadas en hidrógeno. Se llevan a cabo ensayos de tracción a baja velocidad (SSRT) normalizados, y los ensayos SPT anteriormente citados. Se comprueba para estos escenarios una propiedad indicada en el código de buena práctica más orientada a fluencia, que indica que el valor de la velocidad de deformación en un ensayo SSRT y de desplazamiento de punzón en un SPT tienen valores numéricos semejantes cuando el tiempo de rotura en ambas situaciones es similar. Finalmente se proponen metodologías para determinar las velocidades de propagación en ambiente agresivo mediante el empleo de ensayos SPT.In this work two steels, of medium and high strength, are analyzed under hydrogen embrittlement scenarios using submerged Small Punch tests (SPT) under static load, on specimens pre-charged in hydrogen. Standard slow strain rate tests (SSRT), and the aforementioned SPT tests are performed. For these scenarios, it was checked a property proposed in the code of practice, mainly focused on SPT creep tests. It indicates that the deformation rate in a SSRT and punch displacement in an SPT have similar numerical values when the breaking times in both tests are alike. Finally, practical methodologies are proposed to determine propagation rates in an aggressive environment using SPT tests.The authors of this paper would like to thank the Spanish Ministry of Economy and Competitivity for the support received for the development of the research projects MAT2011-28796, and MAT2014-58738

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)

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

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)

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

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

Power quality impact of a small wind energy conversion system connected to the LV grid

This research work is devoted to the study of the Power Quality (PQ) impact of small wind energy conversion systems (SWECS) connected to the low voltage grid. A common coupling point (CCP) has been monitored using a PQ meter that fulfils the standard IEC 61000-4-30 class A. The PQ survey has been conducted with and without the SWECS and the results were compared with the limits defined by the standard EN 50160.This research work was supported by the Spanish Goverment under grant number ENE2007-68032-C04-04, Cantabria Goverment under the R+D 2009 initiative and SONKYO Group

A comparison of transformer HF models and their application to PQ analysis

This research work is devoted to the comparison of some proposed high-frequency (HF) models of transformers and their application to power quality (PQ) studies. The models are classified according their structure, physical description and experimental methodology and set-up facilities needed to obtain the parameters

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)

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