Keraunic Level Research Articles

How can acoustic measurements help us understand severe weather phenomena such as lightning?

Lightning is an indicator for monitoring severe weather events like heavy precipitation, flash floods, hail… It is also a climate variable for monitoring global warming. Lightning emits light, sound and radioelectromagnetic fields, allowing remote detection and analysis. Acoustic measurements can be used to, for instance, track global warming over more than 70 years via the keraunic level (the number of thunderstorm days per year in a specific location), or detect and monitor severe weather events such as cyclones, e.g. the Medicanes, or characterize optical phenomena such as sprites associated with violent thunderstorms, or highlight temporal changes in the upper layers of the atmosphere, such as the semi-annual oscillation of stratospheric winds in tropical zones. At closer ranges, less than 30 km, acoustic network measurements complement electromagnetic observations to reconstruct the 3D structure of cloud-to-ground and intra-cloud discharges. Recently, it has been shown possible to provide the 3D structure of acoustic power within the lightning source. From flash to flash, this power shows four orders of magnitude variations, similarly to electromagnetism or optics. Moreover, it outlines that large variations of power also exist even within a lightning flash, reflecting heterogeneities in conductivity within the discharge.

Distribution Transformer Failure Prediction for Predictive Maintenance Using Hybrid One-Class Deep SVDD Classification and Lightning Strike Failures Data

The distribution transformer failure may be influenced by its maintenance history and risk index in a distribution network associated with keraunic level, average number of lightning strikes, and protection devices employed. Transformer failure is a rare event, and the number of "failed" labels is much smaller than that of "non-failed" labels in field monitoring data. Therefore, the transformer failure prediction can be formulated as an anomaly detection or binary classification with an imbalanced dataset, which is challenging to handle. In this paper, we propose a novel distribution transformer failure prediction method through a hybrid one-class deep support vector data description (SVDD) that uses the synthetic minority oversampling technique (SMOTE) to handle the data imbalance between minority and majority class labels. Minimum redundancy maximum relevance (mRMR) is used as a feature selection technique to improve the model's accuracy. The proposed method uses the current condition data of transformers and the distribution network to predict transformer failure for the next year. Real-world field data for 15,066 distribution transformers is used to train and validate the proposed method. It shows superior performance when compared against five benchmark approaches.

Analysis of the Influence of the Earthing Resistance of Pylones on the Performance of the HVAC Line Facing Electromagnetic Transitories Lightning

The roles of electrical energy no longer need to be demonstrated since the industrial revolution of 1740 based on the use of new sources of energy, of which electrical energy is considered to be one of the greatest revolutions in the world. Despite this, we must note that electrical energy is changing the habits of human activity and, on the one hand, has consequences on its transport, the large quantities of which are transmitted by power lines, forcing them to operate more and more. more within their limits and unplanned outages increase the risk of instability. Storms, industrial pollution, and lightning strikes are the main causes of these unscheduled outages. In regions with a high keraunic level, the reduction of insulation breakdown due to lightning is, therefore, a major concern for designers and operators of HV lines. It is possible to reduce the number of tripping of power lines due to lightning by the proper installation of ground wires and by the appropriate grounding of pylons. In this article, we focus our research on the analysis of the impact of the earthing of the pylons on the performance of HV lines against lightning strikes. Considering these parameters and using the oldest and simplest analytical model as a time-varying current wave whose model is a difference of two decaying exponentials, we brought into contribution Maxwell's equations, the law of Ohm, telegrapher's equations, transmission line theory, and the FDTD method to model lightning-induced voltages as a function of HVAC tower grounding. This study was carried out on the Liminga-Funa 220 kilovolt alternating line in the DRCongo, located in a region where storm activity and industrial pollution are very high. Thus, the results obtained by simulation show that the peak voltage on the components of the HVAC line is a linear function of the impedance of the earthing of the pylon. The impedance value of the pylon earthing less than or equal to 10 Ohm dampens the atmospheric overvoltage and ensures good coordination of the insulation of the line elements in the event of a lightning strike at the top of the pylon for the first bow. But for the return arc taken in this case, the bypass of the insulator is unavoidable. The fractal dimensions of the results of our programs have been compared with those of the figures obtained experimentally.

Lightning Performance Improvement Of 123 kV Line Ston – Komolac By Use Of Line Surge Arresters

This paper presents HEP - Transmission System Operator Ltd. Line surge arrester (LSA) application pilot project on the Ston – Komolac 123 kV line. This 44 km long single circuit shielded transmission line operates in the region with a high lightning activity (keraunic level about 70 thunder days). In addition, it was very difficult to obtain good footing resistance. For these reasons, considered line used to have very bad lightning performance. It was decided to install Line surge arresters for line lightning performance improvement. In order to optimize arrester installation configuration sigma slp software simulations were performed. LSA are installed according to the results of the software simulations. LSA are installed in summer 2007 (110 gapless, IEC-class II Line arresters). Sixty one LSA are equipped with Excount - II monitoring sensors (monitoring arrester leakage current and peak of the impulse current). Based on the 8-month experience, LSA installation has improved line lightning performance. New line performance is close to the targeted once (improvement by 50 to 60 %). Surge arrester monitors collect very interesting information. Collected info will be compared with the software simulations.

Contribution to Lightning Parameters Study Based on Some American Tropical Regions Observations

This paper presents a recent characterization review of three cloud-to-ground lightning parameters [lightning peak current, ground flash density, and keraunic level (KL)] used in engineering applications based on available data from studies conducted in some tropical countries of Central and South America (Brazil, Colombia, Costa Rica, and Venezuela), considering seasonal and spatial variation aspects. There are some differences between the behaviors of the analyzed parameters in tropical areas in comparison with those published in the literature for temperate ones. The most significant conclusion is that historical data suggest that the highest ground flash density are located between latitude of 8° and 10° north. This value is much higher than the highest values reported for countries located in temperate regions. It is seen from the KL analysis that this parameter varies depending on the latitude with values up to 200 thunderstorm days (TDs).

Monte Carlo method for estimating backflashover rates on high voltage transmission lines

This paper presents a novel Monte-Carlo based model for the analysis of backflashover rate (BFOR) on high voltage transmission lines. The proposed model aims to take into the account following aspects of the BFOR phenomenon: transmission line (TL) route keraunic level(s), statistical depiction of lightning-current parameters (including statistical correlation), electrogeometric model of lightning attachment, frequency-dependence of TL parameters and electromagnetic coupling effects, tower geometry and surge impedance, tower grounding impulse impedance (with soil ionization), lightning-surge reflections from adjacent towers, non-linearity of the insulator strings flashover characteristic, distribution of lightning strokes along the TL span and power frequency voltage. In the analysis of the BFOR, special attention is given to the influences emanating from the insulator strings flashover characteristic and lightning statistics. The model could be applied to the transmission line as a whole or some of its portions, e.g. first several towers emanating from the substation or several towers crossing a mountain ridge.

Estimation of lightning current amplitudes incident to wind turbines in exposed locations

AbstractThis paper proposes a novel and comprehensive methodology for estimation of lightning current amplitudes, which are incident to wind turbines (WT) at lightning‐exposed locations, i.e., hilltops. The proposed methodology takes into the account the following aspects related to WT lightning incidence: (i) site topology and keraunic level, (ii)statistical nature of lightning currents, (iii) WT effective height, (iv) dependence of lightning current amplitudes on the WT effective height, (v) influence of an upward‐initiated connecting streamers interaction with a downward‐propagating step leader on the WT lightning attractiveness, and (vi) both downward and upward lightning strikes and their relative contribution in relation to the WT effective height. This methodology could be perceived as beneficial in providing relevant lightning‐current amplitudes—particularly at lightning‐endangered locations and wind farm sites characterized by high soil resistivity—for wind turbine and wind farm overvoltage protection and backsurge studies, as well as the WT grounding systems transient analysis. Copyright © 2014 John Wiley & Sons, Ltd.

Ten year observations of gravity waves from thunderstorms in western Africa

AbstractA new study of gravity waves produced by thunderstorms was performed using continuous recordings at the IS17 (Ivory Coast) infrasound station of the International Monitoring System developed for the verification of the Comprehensive Nuclear Test‐Ban Treaty. A typical case study is presented for a large thunderstorm on 10–11 April 2006 lasting near 14 h. Comparison with cloud temperature measured by the Meteosat 6 satellite shows that wave activity is large when the cloud temperature is low inside convection cells located over the station. Statistics based on 10 year data show that the wave activity is intense throughout the year with peak periods in May and October and less intense activity in January, in good agreement with the local keraunic level. The seasonal variations of the wave azimuth highlight clear trends from northward direction from February to August to southward direction from August to December. Lightning flashes, observed from space, show a similar motion confirming that thunderstorms are the main sources of the gravity wave activity. The gravity wave azimuth follows the seasonal motion of the tropical rain belt partly related to the Intertropical Convergence Zone of the winds. The contribution of other possible sources, such as wind over relief, is weak because surface winds are weak in this region and only oceans are present south of the station. We conclude that the large observed wave activity is mainly produced by convection associated to thunderstorms.

Comparative Study on Substation Shielding Due to Direct Lightning Strokes

Malaysia is one of the many countries that experience high lightning related activities. In fact, according to Malaysian Meteorological Department the Ground Flash Density (GFD) in Malaysia, it is rated at the fifth place in the ten most lightning cities of the world, with a high keraunic level, which is 240 thunderstorm days per year, and in other words, a Ground Flash Density (GFD) of 48.3 flashes per square kilometer per year. In the power systems, high keraunic level would contribute to high possibility of power interruptions such as disruption, degradation, damage and downtime. These outages would ultimately lead to revenue losses and reduction of network reliability. These lightning related interruptions may be in terms of direct lightning strikes to the lines or to the equipments in the substation. By the use of Mat Lab GUI (Graphic Users Interface), this study presents a simple computer program which uses the electro-geometric model (EGM) for the designing of substation shielding systems. The EGM uses the concept where the protection zone of a lightning system lies within the radius where the upward channel initiates and propagates through the air terminal to meet the downward leader. This interception point is called “the point of discrimination” and is where the downward leader decides its final jump. The distance at which the last jump occurs is known as the striking distance. With the use of the striking distance and the mathematical equations developed by Young, Brown-Whitehead, IEEE-1992 (IEEE T&D Committee Equations) and IEEE-1995 (IEEE Substations Committee Equations). This project aimed to investigate, understand and analyse the substation protection by means of masts and shield wires. The analysis is extended to account for lightning protection provided by single mast to two masts as well as from single shield wire to double shielding wires. The outcomes of these four equations will be compared.

Assessment of lightning current parameters suitable for wind turbine overvoltage protection analysis

ABSTRACTA selection procedure for determining the lightning current parameters, suitable for wind turbine overvoltage protection analysis, will be presented in this paper. It will be based on the mathematical model that accounts for the wind turbine geometry, keraunic level, statistical distribution of lightning current parameters and correlation between statistical variables defining lightning current waveshape. Theoretical analysis will be backed up by the most recent propositions of parameters that define statistical distributions and thereafter applied on the concrete wind turbine example. Subsequently, obtained results would provide insight into the selection procedure for the lightning current parameters (i.e., amplitude, front duration, wave duration and polarity), associated with lightning stroke incidence to wind turbines. Emphases will be given to the modern new‐generation wind turbines. This selection procedure could be subsequently applied in the analysis (and design) of the wind turbine and wind farm overvoltage protection, with emphasis on the so‐called back‐surge phenomenon. Copyright © 2011 John Wiley & Sons, Ltd.

Wind farm grounding system design for transient currents

Wind turbines are often very high structures that are usually installed in high keraunic level areas. The keraunic level is the number of storm days per year. Therefore, wind farms are very vulnerable to lightning discharge. The damage due to a lightning strike can be reduced if the high current is quickly conducted to the ground. To date, wind turbine grounding system designs have been based on prior experience, without accurately studying transient grounding system behavior. In this work, typical wind farm grounding system geometries are analyzed in the context of lightning strikes.

Assessment of the backflashover occurrence rate on HV transmission line towers

SUMMARY An assessment of the backflashover occurrence rate on the high voltage (HV) transmission line towers is presented in this paper. It is based on a mathematical model that accounts for the transmission line geometry, keraunic level, statistical distribution of lightning current parameters, and correlation between statistical variables defining the lightning current waveshape. Furthermore, assessment of the backflashover occurrence rate on these towers accounts for the tower footing impulse resistance, lightning impulse insulation strength of the insulator strings and surge impedance of the tower itself. Proposed theoretical analysis is backed by the most recent propositions of parameters that define statistical distributions of lightning current parameters and then applied to the typical HV transmission line example. This analysis might be useful when scrutinizing the several first transmission line towers incoming to the HV substations. Hence, here presented analysis could be subsequently applied for the design of the HV substation overvoltage protection. Finally, a sensitivity analysis is provided, in regards to the parameters of the log-normal distributions defining lightning current amplitude and steepness, as well as in regards to the tower footing impulse resistance. Copyright © 2011 John Wiley & Sons, Ltd.

Parametric analysis of lightning stroke incidence to HV transmission line towers

A parametric analysis of lightning stroke incidence to high voltage (HV) transmission line towers is presented in this paper. It is based on a mathematical model that accounts for the transmission line geometry, keraunic level, statistical distribution of lightning current parameters and correlation between statistical variables defining the lightning current waveshape. Theoretical analysis is backed by the most recent propositions of parameters that define statistical distributions and then applied to the typical HV transmission line example. The results provide insight into the selection procedure for the lightning current parameters (i.e. amplitude, front duration, wave duration and polarity) associated with lightning stroke incidence to transmission line towers. This selection procedure could be applied in backflashover analysis as well as in the analysis (and design) of HV transformer station overvoltage protection. Copyright © 2010 John Wiley & Sons, Ltd.

Seasonal Variation of Soil Resistivity and Soil Temperature in Bayelsa State

Problem statement: Due to the climatic variation for the year and it's sever harmattan during the month of December to March with the high keraunic level (80-90) in the areas, it was necessary to know the seasonal variation of soil resistivity. The seasonal variation and the nature of soil have considerable influence on electrical characteristics and therefore affect the earthling system performance. Approach: Eighteen sites were chosen from three main soil divisions. The soil resistivity was taken in each of the site at depths of 0.5, 0.8 and 1.2 m using the four point test instrument (Wenner Method). From the selected sites in the three soil divisions the temperature was also taken at depths of 0.2, 0.5, 0.8 and 1.0 m. Results: The coefficient of seasonal variation at the depth of 0.5 m was high and reduced drastically at a depth of 1.2 m. The soil temperature was higher than the ambient temperature at the depth of 0.2 m during the months of December to March. From 0.8 m depth and below the temperature reduced even during the dry seasons. Conclusion: The coefficient of seasonal variation of soil at the depth of 0.8 and 1.2 m was small (1.8-3.0) throughout the year in all soil types. That indicates the high water level and or the permanent moisture table which gives an advantage to low soil resistivity for buried conductors and electrodes in the area.