Lightning Shielding Research Articles

Estimation of the current peak value distribution of all lightning to the ground by electro‐geometric model

AbstractWhen we examine the lightning frequency and the lightning shielding effect of the electro‐geometric model (EGM), we need the current distribution of all lightning to the ground. The distribution of lightning current to structures is different from this distribution, but it has been used in EGM conventionally. We assumed the lightning striking distance coefficient related to the height of structures in order to obtain a result which corresponds to the observed frequency of lightning to structures, and estimated the current distribution of all lightning to the ground from data listed in the IEC 62305 series of EGM. The estimated distribution adjusted by the LLS detection efficiency agreed well with the distribution observed by LLS. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(3): 14–26, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22356

Experimental Research on Lightning Influence of 500kV Transmission Lines in Complex Terrains

This paper presents the lightning influence of complex mountainous terrains in 500kV transmission lines and the corresponding methods to improve lightning withstanding level for the safety and stability of power system. According to the general situations and space distributions of lightning activities in East China, that is, mountainous areas are more serious than plains. Four groups of discharging experiment are conducted by the construction of solid models that simulate transmission line routes in mountains. Meanwhile, some commonly used effective methods are studied in detail to reach a conclusion that the lateral rod can reduce shielding rate most efficiently. Then the operation principles and effect factors of lateral rods are analyzed theoretically through the establishment of Electro-geometric Model (EGM), and a large number of repetitive discharging tests are also executed to count and calculate the experimental shielding rates. Experimental results indicate that different terrains have a significant influence mostly on the lightning shielding rate of lines. The lateral rod can largely reduce the shielding rate and the protection effects are influenced by the rod length and angle. The conclusion obtained corroborates the theoretical analysis, which can be widely used as reference in practical applications and lightning protection transformation assessments

Underground Ground Wires for Transmission Lines: Electrical Behavior and Feasibility

Icing of overhead ground wires on transmission lines may result in faults and widespread power outages. This paper investigates the feasibility of an unconventional overhead line structure that is equipped with underground rather than overhead ground wires to prevent faults caused by icing. The underground ground wire is a buried bare conductor connected to the grounding of each transmission-line tower. To analyze the ground fault of the overhead line structure, this paper derives analytical equations to evaluate the current and potential distribution in the underground ground wire, earth surface potential around the wire, and grounding impedance of the faulted tower. The validity of the presented equations is verified by measurements. Based on the ground fault analysis, this paper evaluates the electrical safety of the discussed overhead line structure. Lightning shielding of overhead lines is not considered in this paper.

Examination of Height of Transmission Line and Lightning Striking Distance concerning Lightning Shielding Effect Prediction

Examination of Height of Transmission Line and Lightning Striking Distance concerning Lightning Shielding Effect Prediction

電気幾何学モデルによる大地への全落雷の電流波高値分布推定

When we examine the lightning frequency and the lightning shielding effect of the electro-geometric model (EGM), we need the current distribution of all lightning to the ground. The distribution of lightning current to structures is different from this distribution, but it has been used in EGM conventionally. We assumed the lightning striking distance coefficient related to the height of structures in order to obtain a result which corresponds to the observed frequency of lightning to structures, and estimated the current distribution of all lightning to the ground from data listed in the IEC 62305 series of EGM. The estimated distribution adjusted by the LLS detection efficiency agreed well with the distribution observed by LLS. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(3): 14–26, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22356

Improved method of calculating lightning stroke rate to large-sized transmission lines based on electric geometry model

The characteristics of the lightning shielding of large-sized transmission lines have been calculated based on an electric geometry model (EGM) proposed by Armstrong and Whitehead. However, the characteristics of lightning strokes to large-sized transmission lines observed in recent years differed from calculation results, hence the present study was conducted to improve the conventional calculation method. First, the relationship between the striking distance and the lightning current was reviewed. Specifically, the air gap discharge characteristics based on test data with complementing the large gap region were applied. In addition, the return stroke velocity distribution obtained by actual measurement was newly applied. Second, the distribution of lightning waveforms was reviewed; the distribution of peak values of lightning current with the distribution of front duration was used in this study. With these improvements, the calculated lightning stroke rate to power lines and ground wires differs less from actual observations than that calculated by the conventional method.

Analysis on Induced Lightning of a 22.9kV-Y Distribution Line Using a Reduced Model

This study fabricated a simulation facility which reduced the structure of a current distribution line to 50:1 in order to analyze the induced lightning shielding effect of a 22.9kV-Y distribution line according to ground resistance capacity, grounding locations, etc. When installing an overhead ground wire, the standard for grounding a distribution line with a current of 22.9kV-Y requires that ground resistance in common use with the neutral line be maintained less than every 200m span. The reduced line for simulation had 7 electric poles and induced lightning was applied to the ground plane 2m apart from the line in a direction perpendicular to it using an impulse generator. If induced voltage occurred in the line and induced current flowed through the line due to the applied current, the induced voltage and current of the 'A' phase were measured respectively using an oscilloscope. When all 7 electric poles were grounded with a ground resistance of less than respectively, the combined resistance of the line was . When an average current of 230A was applied, the average induced voltage and current measured were 1,052V and 13.8A, respectively. Under the same conditions, when the number of grounding locations was reduced, the combined resistance as well as induced voltage and current showed a tendency to increase. When all 7 electric poles were grounded with a ground resistance of less than , the combined resistance of the line was . When an average current of 236A was applied, the average induced voltage and current of the 'A' phase calculated were 1,068V and 15.6A, respectively. That is, in this case, only the combined resistance was greater than when all 7 electrical poles were grounded, and the induced voltage and current were reduced. Therefore, it is thought that even though ground resistance is slightly higher under a construction environment with the same conditions, it is advantageous to ground all electric poles to ensure system safety.

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 Shielding Failure Analysis of UHVAC Transmission Lines with an Improved EGM

Lightning shielding failure is an important issue in addressing the lightning performance of HVAC transmission lines. In this paper, an improved electro-geometric model (EGM) is proposed to evaluate the shielding failure outage rate of UHVAC transmission lines. In the improved model, the striking distances to phase conductors, shielding wires and the ground are differentiated, respectively. Furthermore, the influences of ground obliquity, wind deflection and instantaneous operating voltage of phase conductors are taken into account. The proposed improved EGM is applied to calculate the lightning shielding failure outage rate of a UHVAC transmission line to be built in a demonstration project in China. The simulation results show that the maximal difference of shielding failure outage rate due to the phase angle change of the conductor voltage in a period can reach 0.12 times/100 km·a. The shielding failure outage rate increases monotonously with the increment of ground obliquity and wind speed. The shield...

Air-Gap Discharge Characteristics in Foggy Conditions Relevant to Lightning Shielding of Transmission Lines

The features of lightning shielding of transmission lines have been calculated using the electrogeometric model (EGM) proposed by Armstrong and Whitehead. Discrepancies, however, have been found in the case of ultra-high voltage (UHV)-designed transmission lines. UHV-designed transmission lines often pass through high-altitude mountain areas, where foggy or rainy conditions are common when there is lightning. While the electrogeometric model determines the striking distance based on the lightning stroke current, environmental conditions, and how they might affect lightning discharge paths, they are not considered. It is possible, therefore, that foggy conditions may cause differences in the performance of transmission-line lightning shielding. This study used scale models of transmission lines for discharge tests with a 1-m air gap and analyzed differences in discharge paths and locations in dry and foggy conditions. The results showed that the polarity of the discharge had a significant influence, but differences in dry and foggy tests were negligible.

Discharge characteristics of 5 m long air gap under foggy conditions with lightning shielding of transmission line

The electric geometry model suggested by Armstrong and Whitehead was used to calculate the performance of lightning-shielded transmission lines. However, since the ultra high voltage (UHV) designed transmission lines were brought into 500 kV operation, it has become evident that their actual performance is different from the calculated predictions in terms of their actual faults, lightning observation results, etc. It is thought that the UHV designed transmission lines are subjected to foggy or rainy conditions when lightning strikes, because they often pass through mountainous areas at higher altitudes. However, according to the electric geometry model, the striking distance is determined by the lightning-stroke current value only, and the model does not consider the environment of discharge path for the relevant lightning strokes. These considerations suggest that foggy conditions may affect transmission line lightning shielding performance. In this study, discharge tests were conducted using a scaled-down transmission line with a 5 m air gap. The discharge point to the simulated conductor was analyzed in both dry and foggy conditions. Tests were also conducted with a DC bias applied to the simulated power lines, to take the operating voltage of the lines into consideration. These experiments have shown that the effect of fog on the discharge ratio to the conductors is negligible.

Substation lightning shielding and risk assessment

AbstractElectric power installations are subject to lightnining, lightning overvoltages, and the associated risk of damage or disruption. The paper presents a probabilistic method for assessing the risk of damage and disruptions from lightning overvoltages. The proposed method has two components: (a) shielding analysis and evaluation using a probabilistic implementation of the electro‐geometric model and (b) a probabilistic assessment of lightning overvoltages at power equipment and control cables for a specific lightning shielding design. Both computational procedures are based on a 3‐D model of the entire electrical installation. Visualization techniques based on animated 3‐D graphics are used to demonstrate the computational methodology.

A computer program for designing the lightning shielding systems of substations

A computer program is presented for designing the shielding systems of substations. The program is based on the most up-to-date version of the electrogeometric model (EGM). The calculation method is made free from the conservatism of some earlier versions of the EGM by introducing rational revisions. Shielding designs for typical layouts are also presented. >

A Computer Program for Designing the Lightning Shielding Systems of Substations

A computer program is presented for designing the shielding systems of substations. The program is based on the most up-to-date version of the electrogeometric model (EGM). The calculation method is made free from the conservatism of some earlier versions of the EGM by introducing rational revisions. Shielding designs for typical layouts are also presented. >

Monte Carlo Determination of the Frequrncy of Lightning Strokes and Shielding Failures on Transmission Lines

The probabilistic approach of the Monte Carlo method has been applied to the electro-geometric model used for the analysis of frequency of lightning strokes and shielding failures on overhead lines. This approach has enabled theoretical studies to be made of how these parameters are influenced by conductor sag, variations in terrain, and the presence of trees surrounding the line route.

Lightning Shielding of Plastic Telephone Cable

Data are presented on the surge characteristics of various types and combinations of metals when applied as a shield for buried telephone cables. Surge currents were applied to the shield of 500-foot lengths of cable and the potentials developed between the shield and conductors were measured at selected points along the cable length in order to determine relative susceptibility to lightning influence. The shield metals included copper, aluminum, stainless steel, and low-carbon steel, and combinations of these metals. This program was begun and completed in the calendar year 1968. This program may have a substantial impact in the future designs of cable used in the Rural Electrification Administration systems.