Lightning Withstand Research Articles

Joint diagnosis and validation of lightning risk for transmission lines by using multisource data

This study proposes an improved method for assessing lightning risk for typical 750-kV transmission lines in Northwest China. The method involves enhanced preprocessing of multisource parameters and a joint diagnosis of lightning risk; on the basis of the diagnosis results, a cause analysis is conducted to identify towers at high lightning risk. In this study, raw data on the following parameters were obtained and processed: line lightning withstand capability calculation parameters, lightning localization parameters, microtopography parameters, and distributed monitoring parameters. These data were then integrated into a comprehensive multisource database. Furthermore, this study established a model for calculating lightning withstand capability; the study considered the influence of altitude and optimized the classic electrogeometric model. The joint diagnosis method was validated using distributed monitoring data. Through this method, this study identified the characteristics of typical high-risk towers and the underlying factors contributing to the high lightning risk on transmission lines.

Influence of lightning current waveforms of cloud-to-ground lightning with multi-return strokes on the lightning withstand level of 500 kV transmission lines

The most common factor causing line tripping is lightning strokes, and it is necessary to conduct research on the lightning withstand level (LWL). The statistical results of lightning location systems (LLS) in various regions of China indicate that the total proportion of cloud-to-ground lightning with multi-return strokes in nature is 30% to 50%. The traditional method of lightning protection design for 500 kV lines based on the current waveform of single lightning strokes is no longer enough to effectively protect existing transmission lines. Therefore, in this paper an electromagnetic transient simulation model for 500 kV lines was established, to compare the LWL difference between single and multiple lightning strokes. The influence of the tower height, the grounding resistance, and the lightning current waveforms are all simulated and discussed. It is found that the back flashover LWL of 500 kV lines is significantly influenced by the lightning current waveforms. Meanwhile, reducing the grounding resistance cannot effectively increase the LWL of 500 kV lines when the tower is too high and the rise time of the lightning current is too short. It is proposed that the lightning current waveforms should be fully considered while calculating the LWL of 500 kV lines, both single and multiple lightning currents, providing a reference for practical engineering construction.

Study on the Lightning Protection Performance for a 110 kV Non-Shield-Wired Overhead Line with Anti-Thunder and Anti-Icing Composite Insulators

Due to micro landforms and climate, the 110 kV transmission lines crossing the mountain areas are exposed to severe icing conditions for both their high voltage (HV) conductors and shield wires during the winter. Ice accumulation on the shield wire causes excessive sag, which leads to a reduced clearance between earth and HV wires, and could eventually result in tripping of the line due to phase-to-ground flashover. Due to the lack of effective de-icing techniques for the shield wires, removing them completely from the existing overhead line (OHL) structure becomes a reasonable solution to prevent icing accidents. Nevertheless, the risk of exposure to lightning strikes increased significantly after the shield wires were removed. In order to cope with this, the anti-thunder and anti-icing composite insulator (AACI) is installed on the OHLs. In this article, the 110 kV transmission line without shield wire is considered. The shielding failure after installation of the AACIs is studied using the lightning strike simulation models established in the ATP software. The lightning stroke flashover tests are carried out to examine the shielding failures on various designs for the AACIs. Assuming the tower’s earth resistance is 30 Ω, the LWL of back flashover and direct flashover are 630.88 kA and 261.33 kA, respectively, after the installation of AACIs on an unearthed OHL. Due to the unique mechanism of the AACI, the operational voltage level and the height of the pylon have a neglectable influence on its lightning withstand level (LWL). When the length of the parallel protective gap increases from 450 mm to 550 mm, the lightning trip-out rate decreases from 0.104 times/100 km·a to 0.014 times/100 km·a, and the drop rate reaches 86.5%. Therefore, increasing the gap distance for the AACI to provide additional clearance is proven to be an effective method to reduce the shielding failure rates for non-shield-wired OHLs.

Reduction of the double-circuit flashovers on a 400 kV overhead line

Double circuit flashovers may cause very severe system disturbances when taking place on some critical double-circuit lines of an electrical network. Line arresters offer an efficient solution to protect these specific lines against double circuit outages due to lightning. This paper will study, on a double-circuit 400-kV line, the protection provided by line arresters against double circuit outages due to lightning. The efficiency of several configurations of line arresters will be compared. For that purpose, the double-circuit lightning flashover rates of the line with and without line arresters will be calculated using a newly developed software which includes a three-dimensional electro-geometric model and is able to take into account the random nature of lightning. This software automatically launches EMTP-RV (restructured version of EMTP) for analyzing fast front overvoltages impressed on line insulation. The energy stressing the line arresters will also be calculated in order to evaluate the risk of failure of the line arresters due to excess energy absorption. Furthermore, the effects of several other parameters such as the tower footing resistances, the lightning withstand voltages of insulator strings as well as the protective levels of line arresters will also be investigated.

Lightning protection performance of quadruple-circuit 500 kV transmission lines on the same tower with composite cross arm

In recent years, composite materials cross-arm (CMCA) towers have been gradually used in 10 kV, 35 kV or other transmission lines with lower voltage level in China. However, it is rarely used in higher voltage level transmission lines, especially in multi circuit lines on the same tower. Because of its higher height, we should pay more attention to the lightning protection performance of high voltage level multi circuit lines on the same tower. In this work, the simulation and calculation analysis of Lightning stroke model of quadruple-circuit 500 kV transmission line is done to compare CMCA tower with steel tower. The research shows that the tolerance lightning level of CMCA tower is superior to conventional steel tower, The lightning withstand level of single circuit flashover is 45% higher than that of steel tower and the minimum shielding failure lightning withstand level is 47% higher than that of steel tower. The data can provide the theoretical basis for the construction and optimization design of high voltage CMCA tower.

Analysis on Management Strategy of Lightning Protection in Hunan Distribution Lines

The lightning activity is frequent in Hunan, and frequent lightning activities seriously affect the safe and stable operation of distribution network equipment. The statistical analysis of lightning trip-out in Hunan distribution line is made in this paper. According to the current situation of lightning protection in Hunan distribution lines, the differentiated lightning protection management strategy is proposed, which takes into account the ground flash density and special landform factors. And the field application in the past year shows that the effect of lightning protection is good. However, there are also corresponding management and technical problems in the implementation process. The corresponding solution ideas and suggestions are put forward in this paper based on the fully investigation and the experimentation simulation, which has the certain reference value for further improving the lightning withstand level of hunan distribution lines.

Study of high frequency transient overvoltage caused by cable-transformer quarter-wave resonance

When the substations are separated from the overhead line by an underground cable, surge arresters are usually installed at the junction between the overhead line and the cable. Typical insulation coordination studies are conducted in order to decide if another set of surge arresters is required at the entrance of the substation. In this paper, a less classic issue is investigated. It studies the conditions of occurrence of strong overvoltages due to the interaction between a quarter-wave underground cable and the HV/MV power transformer, following a lightning strike. These overvoltages may appear on the secondary side of the transformer even if at the primary side they are well below the lightning withstand voltage of the equipment. The theoretical background is presented and the high frequency models of the system's component are detailed. In particular, a high-frequency model of the transformer is developed. An EMTP-like program is used to simulate the time domain electromagnetic behavior of the system and to investigate the different resonance frequencies. It is shown that, in configurations where the transformer is unloaded, the cable exhibits a quarter-wave behavior at specific lengths and frequencies which leads to high overvoltages. The connection of the load modifies the frequency response of the system and eliminates the risk of appearance of these critical overvoltages.

Research on calculation model of Tower Impulse resistancebased on EMTP

Accurate determination of impulse grounding resistance of tower grounding body is the premise to improve the lightning withstand level of transmission line. The current research mostly ignores the nonlinear effect of soil spark discharge. Based on the analysis of the idea and conception of the equivalent model of grounding body considering spark discharge effect, two simulation models based on EMTP are proposed. The two simulation models can well simulate the inductance effect and spark discharge effect when lightning current flows through grounding body, and improve the grounding body model under impulse condition. The comparison results show that the simulation results are in good agreement with the field measurement results.

Lightning flashover characteristics of metro viaduct section with contact rail power supply system

A flashover of the insulation guardrail will lead to a ground fault of the contact rail, which will cause metro traffic interruption. In this paper, we study the lightning flashover characteristics of a metro viaduct section with a contact rail power supply system. The lightning protection zones of different lightning overvoltage types on metro viaducts are divided according to the rolling ball method, and it is found that it is very unlikely that lightning will strike the contact rails directly. The damage caused by lightning to the contact rail is induced overvoltage and back flashover. A simulation model of a metro viaduct was formulated using electromagnetic transient simulation software. Based on those models, a series of simulations are performed to study the lightning flashover characteristics of the contact rail power supply system. The study found that the lightning protection belt and trains are vulnerable lightning strikes. When lightning strikes a train, the lightning current required to cause the insulation guardrail to flashover is 118 kA. When lightning strikes the lightning protection belt, only 53 kA is sufficient to cause an insulation fence flashover. In addition, the influence of the pier grounding resistance is also analyzed. The result indicates that reducing the pier grounding resistance could improve the lightning withstand level of the contact rail power supply system.

Influence of lightning surges on wideband‐frequency model of LCC‐UHVDC converter station

One of the leading causes of power system outages is lightning surges. A precise calculation of lightning overvoltages across insulators has vital significance for the investigation of lightning outages. This study investigates the impact of different lightning surges for the analysis of transient frequency characteristics of line commutated converter (LCC) based ± 800 kV ultra-high-voltage direct current (UHVDC) converter station by developing a wideband (WB) model of the converter station. The influence of lightning flashover criterion (LFC) of double exponential and Heidler surges methods on insulator/gap for precise lightning withstand level is examined. An analytical comparison for LFC of insulator/gap installed at high altitude transmission lines by incorporating the IEEE volt/time curve, CIGRE leader propagation (LP) and improved LP methods is presented. The proposed WB model explores the novel attributes of high-frequency transfer characteristics and the coupling mechanism of transient frequencies passing through the converter station. Moreover, the effect of internal frequency dependant DC line faults on the WB model is examined. The analysis presented here aims to investigate issues like overvoltage, electromagnetic disturbance prediction, insulation design of the equipment and standardisation of sensitivity issues that are being faced by the present relay protection systems.

From the editors

This issue of the Magazine is entirely dedicated to outdoor insulation of electric power networks. We present articles written by authors from China, Sri Lanka, Ethiopia and South Africa illustrating the states of national awareness to pollution-related problems. We also have an article from Brazil that reports on research aiming to understand and model the lightning withstand of switches and cut-out fuses designed to operate on overhead distribution lines.

Lightning withstand of medium voltage switches and cut-out fuses considering standard and nonstandard impulse shapes

Lightning discharge activity causes overvoltages in the electric power system, which may result in damage to the equipment and apparatus of the system. The lightning incidence is divided into two types: direct strikes and side strikes [1-4]. Direct strikes are lightning discharges that directly hit the line, structure or equipment, resulting in overvoltages of higher amplitudes. However, they are less common than side strikes, which are discharges that occur near the electric system and induce overvoltages of lower amplitudes than direct strikes, but may also cause damage in the distribution network. In this way, many works have evaluated the effect of side strikes on the insulation of electric power system equipment [5-8].

Study on the Influencing Factors of Insulator on the Back-Flashover Lightning Withstand Performance of ±800 kV UHVDC Transmission Lines

The current research results indicate that the insulator’s insulation performance has a very important influence on the back-flashover lightning withstand performance of UHVDC transmission lines, especially for ±800 kV voltage level. However, it is not clear which factors will influence the insulation performance of the insulator, and the influencing mechanism is also not clear yet. To figure out this problem, the insulator’s insulation performance under different conditions has been deeply analyzed and considered to reveal the influence mechanism in this paper, such as the surface hydrophobicity, pollution degree, and the string type. Firstly, the insulator’s model is established using COMSOL software, and the lightning impulse voltage of insulator is calculated and verified with the corresponding experimental data. Then, the ±800 kV UHVDC transmission lines model is constructed using PSCAD software, and back-flashover lightning withstand level and back-flashover rate are calculated by considering the above lightning impulse voltage as the threshold of flashover. Finally, the back-flashover lightning withstand performance of ±800 kV UHVDC transmission lines is deeply analyzed based on different insulators. The simulation results demonstrate that the back-flashover lightning withstand performance of ±800 kV UHVDC transmission lines is obviously weakened with the increase of the pollution degree and slightly weakened with the decrease of the surface hydrophobicity. Considering the same pollution degree, the V-type string insulator has the least influence, while the II-type string insulator has the greatest influences on the back-flashover lightning withstand performance of ±800 kV UHVDC transmission lines. The research results are beneficial for providing theoretical basis for stable operation and reliable power supply of ±800 kV UHVDC transmission lines.

The Simulation Analysis of Factors Affecting Lightning Withstand Level of the Distribution Lines in Oilfield

Simulation analysis is an important method to study the lightning withstand level of distribution lines and conduct the design of line lightning protection. In the process of simulation, the components of the overhead line and the selection of the specific model of lightning current should be taken into account. All the work can be used to get the simulation results which are more consistent with the actual results. Based on the investigating the parameters of oil field lines, insulators and earth resistances, a lightning protection simulation model for typical distribution lines in oil field is built by using ATP-EMTP electromagnetic transient analysis program. By simulation analysis, the influence of line insulation level, earth resistance, layout parameters of arrests and lightning conductor on the lightning withstand level are studied. The results provide a scientific basis for the proposing of the comprehensive lightning protection measures of the distribution lines in oil field.

Lightning Protection of ± 500 kV Three-circuit Direct Current Overhead Transmission Lines on the Same Tower

The three-circuit flexible DC transmission line in the same tower has great advantages in saving transmission corridors, but its lightning protection design is obviously different from single-circuit or double-return overhead lines. Especially in the case of forming a DC grid, the striking flashover rate should be strictly controlled. For this reason, the lightning withstand performance of ±500kV three-circuit flexible DC transmission lines arranged on the same tower is analyzed by using electrical geometric model and traveling wave method. With such method and model the effect of polar line arrangement, grounding resistance, tower height on the lightning protection are analyzed. The computational results prove that when the lightning protection angle of overhead ground wire is designed to be -14° and the recommended E layout scheme is adopted for the pole conductor, the striking flashover rate can be controlled to be less than 0.1 times/(100km·a). The research results lay the foundation for the lightning protection design of the ±500kV three-circuit flexible DC lines arranged on the same tower.

The Research of real-time identification system of types of lightning failures of UHV transmission lines based on UV detection technique

Egineering running experience shows that with the increase of the operating voltage of the transmission line, the lightning trip rate is increasing. According to theoretical calculation ， UHV transmission lines should be provided with full lightning protection characteristics；however，running experience shows that the lightning withstand level of UHV transmission lines is high，not completely lightning protection; it puts forward higher requirements for lightning protection design of UHV transmission line in China. UHV transmission line is mainly against direct lightning stroke characteristics， one is caused by lightning counterattack trip，the other is the shielding failure of lightning around the line to strike the wound caused by the wire. The lightning fault type identification is based on the micro topography of UHV transmission tower，accumulation of historical data，the development of a more targeted and high voltage transmission line lightning protection scheme is of great significance. In this paper, a real-time identification system based on UV detection technology, which has high accuracy and fast response time, is proposed for lightning fault types of UHV transmission lines, the systems use ultraviolet light to realize online detection of high-voltage transmission line tower nearby lightning, can effective observation tower near lightning discharge, and it has the characteristics of continuous detection, longdistance, no power supply, no contact and no disassembly, it provides an advanced technology for the detection of lightning discharge in UHV transmission line.

Development of a ±660 kV DC transmission line arrester

In order to improve the lightning withstand level of ±660 kV DC transmission line in China, the authors had begun to develop the ±660 kV DC line arrester since 2014, which was developed successfully in 2016. The structure, technical parameters, protection performance, and installation of line arrester are analysed in detail. The arrester adopts the structure of polymer housing with an external series air gap and a four-section body. The technical parameters and protection performance are designed and calculated according to the relevant standards. The results show that the arrester has good electrical and mechanical performances, and it meets the requirement of insulation coordination. Pillar insulator supporting installation is used in the arrester application. Up to now, the ±660 kV DC line arrester has been used in the ±660 kV DC transmission line in China, which works safely and reliably over a long time. The successful operation can accumulate operating experience and provide a basis for the large-scale application of the line arrester on the ±660 kV DC transmission line in the future.

Optimal Installation Scheme of Surge Arrester on Distribution Network

Surge arrester is an effective measure to protect distribution lines from lightning strikes. But high costs will be spent on the maintenance of a great many surge arresters in 10kV distribution line. Taking the relationship between reliability and economical efficiency into consideration, aiming at installation density of surge arrester, this paper established the effective simulation models of direct lightning stroke overvoltage and induced overvoltage by ATP-EMTP. Finally, this paper presented the optimal installation scheme of surge arrester on the basis of the simulation and analysis of the lightning withstand level. The simulation results provide references for the optimal installation scheme of surge arrester on the distribution network.

Influence of lightning flashover criterion on the calculated lightning withstand level of ±800 kV UHVDC transmission lines at high altitude

The operation experiences of power transmission lines show the lightning outage is still the main part of the total outage rate. So it is very important to calculate the lightning overvoltage across the insulators precisely and evaluate the lightning outage of the transmission lines correctly. Lightning flashover criterion of the insulator/gap is one of the most important factors that influence the precise calculation results of the lightning withstand level of transmission lines. In China, several ±800 kV ultra high voltage direct current (UHVDC) power transmission projects have been set up in recent years, and the altitude of the regions that the transmission lines across ranges from 0-3650 m. The paper mainly analyzed the influence of the modelling methods of insulator/gap on the lightning withstand level of ±800 kV UHVDC transmission lines by PSCAD/EMTDC program. The compared lightning flashover criteria of insulator/gap include the leader propagation model recommended by CIGRE, the volt/time curve recommended by IEEE and an improved leader propagation model, which is proposed based on the lightning flashover experiments of the ±800 kV UHVDC line insulators carried out at an altitude of 2100 m. Meanwhile, the influences of lightning current waveform and insulator structure were also considered and compared. The simulation results show that the calculated back-flashover lightning withstand level is much lower when using the improved leader propagation than that using other flashover criterions in the paper, it is lower under the 2.6/50 μs double exponential lightning current than that under the 2.0/50 μs Heidler function lightning current, and it is higher when using V-string than that using I-string insulator. Besides, the influences of the lightning current waveform and the insulator structure on the calculation of shielding failure lightning withstand level are little, but the flashover criterion has obvious influences on the shielding failure lightning withstand level.

Analysis on Lightning Withstand Level of Back Striking Flashover for Double-Circuit Transmission Line

The double-circuit transmission lines have already been the significant component of power system. Because of the symmetric insulation of the two circuits, the case that both circuits trip out often happens when the tower suffer lightning strike. And it harms the stability of power system and causes serious impacts to power equipments. In this paper, an electric-magnetic transient simulation model was established. Using this model, combining the analysis of physical mechanism of back striking trip-out, the influences of earth resistance, height of tower and length of insulator on the lightning withstand level of back striking (LWLBS) were clarified. The LWLBS of high tower is much low, therefore the relative high tower should be paid more attention to defense the back striking. Reducing the earth resistance and increasing the length of insulator can both upgrade the LWLBS observably. Especially, reducing the earth resistance can enhance the effect of upgrading the LWLBS by increasing the length of insulator.