Shielding Failure Flashover Rate Research Articles

Estimating the shielding failure flashover rate of single-circuit overhead lines with horizontal phase configuration via stochastic lightning attachment simulations

A methodology is proposed for estimating the shielding failure flashover rate (SFFOR) of single-circuit overhead lines with horizontal phase configuration. An application to a 66 kV overhead line is presented. A stochastic lightning attachment model is employed, based on the concept of fractal structures, to compute the probability of shielding failure to the line. Results of stochastic modeling are combined with those of an ATP-EMTP model for estimating the critical lightning currents causing flashover of the line insulation. Shielding failure results of the proposed methodology are compared and discussed with results obtained employing the methodology of the IEEE Std 1243. Innovation of this work lies in estimating the SFFOR of overhead lines by considering the stochastic nature of lightning attachment, physical criteria associated with leader discharges’ inception and propagation, as well as electromagnetic transient simulations to predict lightning-related flashover to overhead lines accurately.

OVERVIEW OF FACTORS AFFECTING THE ESTIMATION OF LIGHTNING SHIELDING PERFORMANCE OF OVERHEAD TRANSMISSION LINES

This paper examines the risk of lightning stroke to overhead transmission line. The estimation procedure for the lightning performance of overhead power lines is based on the selected lightning attachment model, available lightning parameter statistics, the transmission tower design and voltage levels, type of overvoltage and other characteristics. In this paper the overview of factors affecting the estimation of lightning shielding performance of overhead transmission lines was performed. Among the factors that can affect the estimation accuracy, one can list insufficiently accurate data on the ground flash density in the area of interest and lack of complete data on statistical distribution of lightning current magnitudes. The paper shows that the influence of wind on the increase in the horizontal exposed distance of the phase conductor is not also taken into account. In this research traditional electro-geometric model was used for estimation of lightning performance of 220 kV overhead power line. Results obtained suggest that swing of suspension insulator strings caused by strong winds may lead to increased risk of lightning shielding failure during thunderstorm. Calculation performed for 3 kA lightning current magnitude shows that at swing angle equal to –1 degree, the horizontal unprotected distance of phase conductor increases by 3.1%, that corresponds to 5.240 m uncovered width. When the swing angle is increased to –5 degree, the uncovered width is increased by 15.8% that corresponds to 5.885 m uncovered width. It is proposed that an increase in the risk of lightning shielding failure as a result of wind load can be accounted by applying an appropriate correction factor in expressions for calculation of shielding failure rate, shielding failure flashover rate, etc. Proposed correction factor should account frequency and strength of wind in the area of transmission line route and depend on transmission line voltage level and tower design. Further efforts should be focused on obtaining and justifying the numerical values ​​of this correction factor.

Research on the lightning shielding performance of strained angled tower for the [formula omitted]1100 kV UHVDC transmission project

Rigid jumper is usually used in the strained angled tower for the UHV transmission project, which makes the protection angle of the ground wire to the jumper end larger, thus the lightning shielding failure risk of the strained angled tower may increase. In order to study the lightning shielding performance of strained angled tower for the ±1100 kV ultra-high voltage direct current (UHVDC) transmission project, a numerical model for the simulation of lightning attachment to the strained angled tower was established based on the research results in the aspects of lightning downward leader, inception and propagation characteristic of upward connecting leader and so on. The maximum lightning shielding failure current and the shielding failure flashover rate (SFFOR) of rigid jumper were calculated under different line angles and overhead ground wire cross-arm lengths based on the proposed model. Results show that the lightning flashover of rigid jumper mainly occurs on the outer side while the rigid jumper on the inner side is in a good shielding state. When the cross-arm length of overhead ground wire on the outer side of J27104A1 tower with 90° line angle is greater than 21.7 m, the SFFOR of rigid jumper will be below 0.1 times/(100 km a), which can meet the operation requirement. The analysis provides technical references for the lightning protection design of strained angled tower for the UHVDC transmission project.

A Stochastic Model for Evaluating the Lightning Performance of a −400 kV HVDC Overhead Line

A stochastic lightning attachment model for evaluating the lightning performance of overhead transmission lines is introduced. The proposed model considers the stochastic nature of lightning attachment by taking into account the lightning discharge branched and tortuous behavior. It integrates physical criteria on leader inception by adopting the Petrov and Waters model, as well as leader discharge progression considering also the competing interaction of multiple upward leaders. A generalized methodology combining stochastic modeling of lightning incidence with an electromagnetic transients (EMT) simulation model is proposed so as to estimate the backflashover and shielding failure flashover rates of HVDC overhead lines; an application to a monopolar −400 kV line sheds light on the basic parameters that affect the lightning performance of HVDC lines. The probability of shielding failure is higher than that obtained by the deterministic lightning attachment models. The stochastic nature of lightning attachment and the effect of lightning peak current distribution should be considered for the design and evaluation of the lightning performance of the emerging HVDC systems.

Analysis of shielding failure flash-over rate of collection lines of wind farms in mountainous areas

Aiming at the current situation of serious economic losses caused by lightning shielding on the collection lines of wind farms in mountainous areas. First, this paper uses the horizontal section location map of the collection line to extract the terrain parameters, Then use the catenary equation to determine the spatial position of the conductor and ground of any section of the collector line along the pitch direction, and obtain the height of the conductor and the ground to the ground. Finally, complete the modeling calculation analysis of the three-dimensional electrical geometry model (EGM) of the entire collection line. The calculation results show that, when the thunderstorm day, the arrangement of the collection line and the structure of the tower are the same, the SFFOR of the collection line of the wind farm in mountainous terrain is 0.487 times/100 km/year, and the plain terrain is 0.167 times/100 km/year, that is, mountainous area is 2.9 times of plain terrain; It is recommended to use double lightning protection poles with small protection angles on the collection lines of wind farms in mountainous areas, or install lightning arresters for poles that are prone to flashover to meet the design requirements of line lightning protection.

Analysis of Lightning Performance on 345 kV Transmission Lines Using Python Programming

One of main causes of interruption of electrical power supply is the lightning strike on overhead power transmission lines. The lightning performance of transmission line can be determined by value of shielding failure flashover rate (SFFOR) and back flashover rate (BFOR). The object of this study is to create a computer application to compute lightning performance on the transmission lines using Python programming. Pythons package tkinter used for program interface window. Application programming is done by using the concept of object-oriented programming (OOP) using Pythons keyword class. Validation shows that the application has applied the method correctly with a percentage error 0 % for SFFOR and 3.14 % for BFOR. The application can do analysis on the factors that affecting SFFOR and BFOR such as the effect of thunder day, tower foot resistance, and number of isolator disk. The results obtained in this study is computer application that can perform lightning performance analysis and analysis of factors that can affect it, such as thunder day, tower foot resistance and the number of isolator disk.

A Methodology for Optimal Design of Transmission Lines to Protection against Lightning Surges in Presence of Arresters

In this paper, a methodology for determination of the optimal value of protection design parameters, i.e. tower footing resistance, insulation strength, and surge arresters’ rating in the planning stage of transmission lines (TLs) is presented. This method calculates the shielding failure flashover rate (SFFOR) of TLs, based on Electro-geometric model (EGM) of TLs, and the back flashover rate (BFR) of TLs, based on the Monte Carlo method, in which the accuracy of the proposed methodology has been verified by comparing the resultant results with those obtained with the use of the IEEE FLASH program. The proposed method can be directly used to achieve the minimum lightning flashover rate (LFOR) of TLs by the minimum investment cost. Also, it can be used, indirectly, for determination of the appropriate value of the footing resistance, insulation strength and arresters’ rating to satisfy any target number of LFOR that might be specified by the utilities or standards.

Monte‐Carlo‐based simulation and investigation of 230 kV transmission lines outage due to lightning

Here, using the probabilistic evaluation based on the Monte Carlo method, back-flashover rate and shielding failure flashover rate of 230 kV overhead transmission lines in the western regions of Iran are evaluated. To such an aim, first, the number of thunderstorm days per year is collected from the reported weather information in order to determine the ground flash density. Then, using MRU-200 equipment, the tower-footing resistance of several towers is measured. Matlab® software is used in order to produce lightning surges considering its probabilistic nature and randomly distribution on the ground to evaluate striking distance based on the geometric model. Then, calculated parameters are transferred to EMTP-RV software by establishing a link to perform the transient simulation and report the results for modelled 230 kV transmission line. Finally, considering IEEE-1243 standard, it is shown that due to high ground flash density, using 230 kV tower with one shield wire is not sufficient to protect the line against lightning phenomena.

Research on effect of lightning shielding level of EHVDC transmission line by installing coupling ground wire

Lightning shielding failure is the main reason causing lightning flashover of Jiangcheng EHVDC transmission line because of the designed ground wire protection angle. Based on the electric-geometry model, a simulation model including the coupling ground wire is established by using MATLAB. The effect of the coupling ground wire at different height and horizontal position on lightning shielding failure flashover rate is analysed. Results show that coupling ground wire can reduce the lightning shielding failure flashover rate and the lightning shielding performance increases with the increase of the height of the wire and the horizontal distance between the axis of the tower and the coupling ground wire.

Shielding failure analysis of a hybrid transmission line with AC and DC systems on the same tower

Hybrid AC/DC transmission lines have different systems on the same tower and combine HVDC transmission over long distances with common HVAC transmission. Evaluation of the risk of lightning stroke outage of high power transmission lines is very important because lightning strokes cause mainly outages. The present paper illustrates how to combine efficiently different methods to support insulation coordination studies. Maximum lightning current amplitude that does not cause flashover across insulator string is estimated in response to first and subsequent lightning strokes with three different flashover models using several electrogeometric models and simulations in EMTP-ATP. Characteristic quantities like Shielding Failure Rate (SFR) and Shielding Failure Flashover Rate (SFFOR) are calculated for different shielding configurations.

Estimation of the shielding performance of transmission lines considering effects of landform, lightning polarity and stroke angle

Lightning is the main cause of transmission system outages, affecting reliability of power supply and resulting in economic losses. Shielding failure is an important issue in addressing the lightning performance of overhead transmission lines. In this paper an improved method based on the electro-geometric model is proposed to evaluate the shielding failure flashover rate (SFFOR) of transmission lines, considering the influences of landform, lightning polarity and stroke angle. In the improved method, the striking distances to phase conductors, shield wires and ground are properly differentiated by using recent equations developed to take into account other factors not only magnitude of lightning strokes. These factors include height of wires as well as lightning polarity. To reflect the effects of changes in terrain and height of wires on SFFOR, a method for identifying the topography and the relative position among the wires and ground is proposed. A 400-kV double-circuit transmission line section in complex terrain area was taken as example, and the results show that this method can reflect changes of the SFFOR along the span and can be useful to figure out which towers are easy to be struck by lightning along the entire transmission line. This research is helpful for the design and operation of overhead transmission lines.

The effect of wide band modeling of tower-footing grounding system on the lightning performance of transmission lines: A probabilistic evaluation

This paper presents a probabilistic evaluation, based on Monte-Carlo method, to estimate back flashover rate (BFR) and shielding failure flashover rate (SFFOR) of overhead transmission lines (TLs). In the proposed approach, as opposed to the conventional methods, a wide band model of the tower-footing grounding system is adopted assuming the soil electrical parameters to be either constant or frequency dependent. The statistical parameters affecting the TLs’ outage rate are taken into account in the probabilistic studies. Simulations are done for a typical 400-kV transmission line which is modeled in EMTP.RV. From the simulation results, it is found that the BFR of transmission lines is markedly affected by the tower footing grounding system model. This effect is more pronounced when the soil electrical parameters are frequency dependent. It is also found that the SFFOR of the transmission lines is not significantly affected by the wide-band model of the tower-footing grounding system.

Effects of Considering A Stroke Angle Distribution on Estimating the Shielding Performance of Overhead Transmission Lines

The shielding analysis method recommended by the IEEE Working Group on Estimating the Lightning Performance of Transmission Lines is based on the Electrogeometric Model and the concept of striking distance. The simplistic assumption of a vertically descending leader is adopted, although a statistical distribution for the stroke angle has been previously proposed in the literature. This paper aimed to investigate the influence of assuming both vertical and non-vertical flashes on the evaluation of the shielding failure flashover rates of overhead transmission lines. The study is based on a modified Electrogeometric Model built in a procedure implemented by the authors in MATLAB, in a comparative perspective with the well-known IEEE Flash program. Parametric studies are performed to determine the sensitivity of the outage rates with respect to the parameters of the transmission line, the striking distance equation and leader angle distribution.

Estimation of the minimum shielding failure flashover current for first and subsequent lightning strokes to overhead transmission lines

ATP-EMTP simulations are performed to estimate the minimum shielding failure current causing flashover in overhead transmission lines with operating voltage in the range of 66kV up to 735kV. This critical current, affecting shielding failure flashover rate, is of great importance for assessing the insulation coordination of overhead transmission lines and the connected substations. The minimum shielding failure current causing flashover of line insulation is highly dependent upon insulator string flashover modelling and, also, markedly higher than that calculated according to the relevant IEEE Std 1243-1997 simplified expression. A modification of the latter is suggested by using multiplication factors of 1.5 and 1.65 for first and subsequent lightning strokes, respectively, so as to account for the increased dielectric strength of line insulator strings under non-standard lightning overvoltage surges. Alternatively, the critical currents can be respectively estimated by using average negative breakdown gradients per unit length of insulator string of 680kV/m and 750kV/m. The shielding failure flashover rate of the overhead transmission lines, being greatly influenced by insulator string flashover modelling, is lower than that obtained based on the critical current according to IEEE Std 1243-1997.

Lightning Flashover Rates of Overhead Distribution Lines Applying EMTP and IEEE Std.1410

This paper calculates the lightning flashover rates of 22 kV overhead distribution line. In order to calculate the backflashover rate (BFOR), the performance of line which related to the insulator backflashover has been modeled and analyzed using Electromagnetic Transient Program (EMTP). The flashover models, volt time curve (VT), disruptive effect model (DE) and leader progression model (LPM) have been compared. The shielding failure flashover rate (SFFOR) and induced voltage flashover rate (IVFOR) have been calculated follow equations given in IEEE std 1410-2010. Finally the total numbers of flashovers of line have been determined. The lightning flashovers rates of BFOR, SFFOR and IVFOR have also been compared with the data taken from the line outages recorder. From the system being studied shown that, the total numbers of flashovers from simulation and calculation is closed to the data from the line outage recorder.

Analysis of Lightning Shielding Failure for 500-kV Overhead Transmission Lines Based on an Improved Leader Progression Model

An improved leader progression model (LPM) for analyzing the shielding failure performance of overhead transmission lines is established, and implemented in calculating the shielding failure rate and shielding failure flashover rate of 500-kV transmission lines. This paper discusses the inadequate parts of the existing LPM and presents improvements to meliorate the model for applications on extremely high voltage (EHV) transmission lines. The model is improved mainly in three aspects: 1) the background electric field produced by the lightning cloud is simulated by multielectrode configuration, 2) different inception criteria of upward leaders for shielding wires and phase conductors are chosen, and 3) the impact of power frequency operating voltage on the shielding failure flashover rate is considered. The improved model is applied to analyze the shielding failure performance of 500-kV transmission lines in China considering the flat and hilly terrain conditions. The shielding failure flashover rates by existing models and the improved model are calculated and compared with the operating data of 500-kV transmission lines. It is shown that the predicted result of the improved LPM is in accordance with the operating experience. The improved model is suitable for the lightning shielding assessment and applicable in the design of EHVAC transmission lines.

Lightning Performance Analysis of an Overhead Transmission Line Protected by Surge Arresters

In general, the main causes of unacceptable lightning flashover rates of overhead transmission lines are a bad shield design or too high footing impedances. The first reason will cause unacceptable shielding failure flashover rates (SFOR); the second one can cause high backflashover rates (BFOR). The lightning flashover rate of a shielded transmission line can be reduced by installing surge arresters. In fact, the rate can be reduced to zero by installing arresters at all phases and all towers of the line, but even if arresters are not installed at all phases, a significant improvement of the lightning performance can be achieved. However, arresters have to be selected to withstand the energy stresses caused by lightning strokes; otherwise, failures could be caused by an excess of energy absorption. This paper is aimed at analyzing the lightning performance improvement of a shielded transmission line that can be achieved after installing metal oxide surge arresters as a function of the number of phases at which they are installed and at estimating the energy absorption capability of the selected arresters.

Shielding failure flashover rate under conditions of complex landscapes in mountainous areas

Based on the field investigation, a new Monte-Carlo method, combined with the improved Electro-geometric model (EGM), which can properly reflect the characteristic of random processes with good precision is developed to calculate the lightning flashover rate of transmission lines. Using this calculation system, this paper studied the influences of different landscapes in mountainous area, such as mountain peak, hollow, slope, ditch, etc., on the shielding failure flashover rates (SFFOR) of transmission lines. The decrease of the shielding effects of ground is the main reason of the SFFOR increase. As the increase of the ditch depth and the tower height, the SFFOR increases significantly. The same phenomenon appears when the slope gradient is larger than 20°. Ditch under lines often is ignored in the previous design. But according to the research result, it will apparently influence the ground shielding effect, and therefore lead to shielding failure flashover. This research is helpful for the design, reconstruction and operation of transmission lines.

An improved leader progression model for the analysis of the shielding performance of 1000 kV UHVAC transmission lines

AbstractThis paper presents an improved leader progression model (LPM). The model uses the proposed leader inception criterion for the analysis of lightning shielding performance of UHVAC transmission lines. It focuses on the discussion of the leader inception voltage of bundle conductors. The improved LPM is validated on 500 kV EHV transmission lines. The shielding performance of a UHVAC transmission line to be constructed in a Chinese Test Line Project is then evaluated. The results indicate that the power frequency operating voltage and the bundle conductor configuration have a greater influence on the shielding failure flashover rate (SFFOR) of 1000 kV UHV lines than that of 500 kV EHV lines. It is found that the UHVAC line to be built will not cause trip accidents due to shielding failure in flat terrain. In broken terrain, the SFFOR is only 0.0012 times/100 km·year, which is less than the design limit. Copyright © 2008 John Wiley & Sons, Ltd.