Overhead Ground Wire Research Articles

Lightning Protection Improvement and Economic Evaluation of Thailand’s 24 kV Distribution Line Based on Difference in Grounding Distance of Overhead Ground Wire

This study determines the voltage across insulators after a direct lightning strike to an overhead ground wire on a 24 kV pole structure for different grounding distances of overhead ground wire, to calculate the maximum ground resistance required to avoid disruption of the distribution line system using ATP-EMTP software. The results show that when a 40 kA lightning current, the average lightning current in Thailand, strikes a 24 kV pole structure, the maximum ground resistance should not exceed 4 Ω for a 40 m grounding distance of overhead ground wire, based on an existing critical insulator flashover of 205 kV. However, because the average ground resistance in Thailand is approximately 10 Ω, this study proposes increasing the insulation level from 205 kV to 300 kV to reduce the likelihood of power outage. The cost-effectiveness of such an investment is assessed in terms of net present value (NPV), internal rate of return (IRR), profitability index (PI), and discounted payback period (DPP) using existing economic tools. Results show that when the critical insulator flashover is increased from 205 kV to 300 kV for a 40 m grounding distance of overhead ground wire, the project is likely to have a DPP of 15.12 years, NPV of 143,321.87 USD, IRR of 12%, and PI of 1.15. On the other hand, grounding distances greater than 40 m for overhead ground wire result in negative NPV, although the back flashover rate can be reduced by 1.51–5.71% with grounding distances of 80–200 m compared to the situation in the absence of grounding.

Detection for overhead ground wire by lines clustering

Detection for overhead ground wire by lines clustering

Phi-OTDR Based On-Line Monitoring of Overhead Power Transmission Line

The overhead power transmission line, as an important component of equipment for long-distance power transmission, is threatened by icing and galloping, which will lead to equipment troubles and cause huge economic loss. Thus, there is a great need for on-line monitoring for transmission lines. Because the photoelectric composite cable, such as optical fiber composite overhead ground wire (OPGW) is widely used, it is possible to introduce distributed optical fiber sensors (DOFS) into transmission line status monitoring. Common schemes based on DOFS usually offer low sensing density and are hard to realize global awareness, while phase sensitive optical time domain reflectometry (Φ-OTDR), as a DOFS that has the characteristic of distributed sensing, is hoping to address the limitation. In this paper, by establishing mathematical models, proposing analytical method, and building demonstration devices to analyze the dynamic strain characteristics of overhead power transmission line, an Φ-OTDR based on-line monitoring scheme of transmission line status is presented and experimentally proved for the first time. The estimation error of sag is less than 5.8% on centimeter scale, and the estimation error of ice thickness is no more than 10.84% on sub-millimeter scale, which gives an accurate description of transmission line status and provides strong support for early warning of transmission line failures.

Optical frequency-domain reflectometer-based experimental study on lightning strike temperature variation of overhead ground wire

An overhead ground wire is used for both communication and power transmission and is crucial for the long-term operation of power grids. The temperature variations in overhead ground wires under a lightning strike were analyzed using an optical frequency-domain reflectometer. During lightning, the relationship between the peak temperature and the time can be considered a double-exponential distribution. The temperature distribution over time for the overhead ground wire was considered a Gaussian distribution, where the R-squared coefficient was ∼0.95. Moreover, we used the −3 dB bandwidth of the temperature curve at each moment as the lightning temperature influence range for the overhead ground wire. The temperature influence was considered a quadratic function distribution, where the R-squared coefficient was ∼0.98. The characterization of the temperature variation of the lightning struck-overhead ground wire can provide a basis for distributed optical fiber measurement systems to accurately monitor the location and intensity of lightning strikes and can be potentially used to ensure the safety of transmission lines.

A Study on an Impact of Tower Surge Impedance Against Lightning Surge Phenomena

Lightning strikes creates damages to the electrical power system utilization and equipment. To reduce the effect of lightning strikes in the tower transmission, the ground resistance of the tower must be kept to a low value of less than 5 Ω. This research is a study of tower surge impedance using additional conductor line connected by parallel two overhead ground wire at the top of the tower transmission line. The additional of ground wire which is connected from the top of the tower utilizes copper and aluminium alloy for the simulation. Calculation of tower surge impedance using finite element method by COMSOL in 3D simulation based on traditional electromagnetism equations. Surge impedance values were calculated, and it was found that the calculation results obtained with less than 0.5 % error when using finite element method compare with conventional numerical method. Aluminium alloy conductor was found to have an effect on reducing the overvoltage magnitude of lightning strikes at the tower transmission line when compare with copper conductor.

Distributed Transmission Line Ice-Coating Recognition System Based on BOTDR Temperature Monitoring

An optical fiber composite overhead ground wire (OPGW) distributed ice-coating monitoring scheme based on Brillouin optical time domain reflectometer (BOTDR) temperature measurement is proposed and demonstrated. The thermodynamic factors affecting the temperature of the OPGW cable are analyzed, and the temperature variation characteristics of the icing and non-icing sections of the OPGW cable with different icing thicknesses are analyzed via finite-element analysis. The results of an OPGW icing experiment indicate that when the ambient temperature changes, there is an obvious hysteresis characteristic between the temperature changes of the icing and non-icing sections of the OPGW cable, which is related to the thickness of the ice. Thus, we propose a distributed OPGW cable icing monitoring system based on BOTDR temperature monitoring.

Design of a Lightning Protection System for an Overhead 3 kV DC Electrified Railway Line: A Case Study from South Africa

A protection scheme is proposed for the 3 kV DC railway, in Kwa-Zulu Natal province, a region with a high lightning occurrence density. The surge protection was sought by implementing three metal-oxide surge arresters and an overhead ground wire. The purpose of these arresters is determined by their location in the circuit and the points that are vulnerable to adverse lightning effects: an arrester is installed to protect insulators between overhead lines and the supporting metallic mast, an arrester is installed to protect the point of contact between a stationary power supply wire and the train, and an arrester is installed to protect apparatus associated with the running tracks (return rail). An isolated earthing system is explored, and the effects of surge impedances and footing resistances are discussed. The voltage dropped across relevant vulnerable components and energy absorbed by the system components are determined by the simulation software Simulink. These results are compared with a railway system outfitted with the designed lightning protection mechanisms. Lightning currents are injected into the system using Heidler function where the parameters are in compliance with lightning protection standards. It is observed that the protection mechanisms defend susceptible components to a specified level. This demonstrates the success of the design in accordance with arrester protection levels (73.3 kV) and equipment withstand capabilities (a basic insulation level of 143 kV). This offers a protection margin of 95%. The largest percentage overshoot in the system is 39%, and this value is substantiated using reflection phenomena.

Calculation and Analysis of Induced Current in Optical Fiber Composite Overhead Ground Wire

In this paper, the mechanism of electromagnetic induction current of overhead ground wire is analyzed, the models of overhead ground wire with different voltage levels are established on ATP-EMTP, the electromagnetic induction current of optical fiber composite overhead ground wire (OPGW) is calculated, and the factors affecting the induced current on OPGW are analyzed, including the change in loads of transmission lines, the value of grounding resistance and the location of lines. The results of this paper provide a reference for the actual measurement and the use of this induced current for induction power supply.

On-situ monitoring of sleet-thawing for OPGW based on long distance BOTDR

With the absence of on-situ temperature monitoring of optical fiber composite overhead ground wire (OPGW) for the process of sleet-thawing, early temperature warning and safety control of direct current (DC) in sleet-thawing process is difficult. Here we propose a Brillouin optical time-domain reflectometry (BOTDR) with broadband receiving for fast measurement and with distributed Raman amplification for long distance measurement of about 100 km. A field experiment for on-situ temperature monitoring of sleet-thawing of OPGW is also reported, which shows uneven change of temperature along the OPGW. The difference between the maximum and the minimum temperature change can be greater than 40 °C.

Research on High Voltage Insulation Performance of Grounding Grid in Large Substation

The gap between overhead ground wire insulators is changed by external force or subjected to overvoltage, intermittent breakdown will occur, and continuous arcing will occur in severe cases. Real-time monitoring of the current change on the ground wire is of significance to the reliable operation of the overhead ground wire major. The article proposes a method to detect the surface contamination of composite insulators by measuring the ground current of the insulator. The ground current characteristics of composite insulators are studied, and the test loops of composite insulator ground current, body leakage current and surface leakage current are established respectively. The above three currents of the insulator were measured and compared and analysed. At the same time, the article focuses on the design and development of the hardware system of the DC grounding system insulation resistance tester with digital display and multi-channel inspection function based on the microcontroller.

Breakage Mechanism Study of Overhead Ground Wire Under Lighting Stroke Based On Finite Element Analysis

Breakage of overhead transmission lines and distribution lines will lead to severe power outage problems, and clarifying the breakage mechanism of the overhead lines is of great importance and value for the reliability and stability of the power system. Taking overhead ground wire for example, this paper presents its breakage mechanism study under lighting stoke based on finite element analysis. A multi-physics analysis model is built first, which includes the model of contact points. The current density distribution and the temperature rise under the impact of short circuit current are analysed, and contact resistance effect is proved the primary cause for the breakage. Then some major factors that influence the contact resistance which in turn influence the temperature rise are discussed. Based on the discussions, some valuable suggestions are given for the protection of overhead lines.

Lightning Performance of Unshielded 220kV Transmission Lines Equipped with Metal-oxide Arresters

Overhead ground wires have been proved to be effective to protect conductors from direct lightning strikes, but breakouts of ground wires have been frequently reported. In order to prevent ground wire breakout incidents to happen, unshielded 220kV lines equipped with metal oxide arresters (MOAs) whole line have been proposed in this paper. After cancelling ground wire, lightning strike risk of transmission lines becomes much higher. In order to improve the anti-lightning abilities of unshielded transmission lines, it is necessary to obtain the lightning energy absorption ability of these MOAs. In this paper, simulation model of MOA equipped unshielded 220kV transmission line was built, the influences of lightning parameters, striking occurrence point and grounding resistance of transmission tower on the absorbed energy of MOAs were calculated, and the suggested energy absorption ability of MOA was given, which can give references for the improvement of power supply reliability of transmission lines.

Overhead transmission line performance with respect to grounding impedance on alpine terrain

The present paper shows a study case of transient effects of direct and indirect lightning discharges on overhead transmission lines with respect to actual grounding impedances of the transmission line system. The transient measurement data was gathered from two 400 kV double-system overhead lines equipped with an overhead ground wire. Additionally installed RC dividers are used to perform transient voltage measurements with high accuracy in amplitude and frequency. The pairing of electric, time and geographic parameters of the used datasets provides the basis for an analysis of the performance of the overhead lines and the high-voltage system influenced by lightning discharges. For this case study, a novel approach is presented where the actual tower-footing grounding impedance of the two systems is related to the transient effects of direct and indirect lightning discharges on the lines as new parameter. The topic, whether it be exposed overhead transmission line systems in the alpine area or line sections with high grounding impedances that show a higher probability of power system faults, is analysed and interpreted in this case study. The results show no correlation between tower exposure (mountainous or flat terrain) and lightning discharge frequency. For the correlation of the tower footing grounding impedance with the recorded transient measurements, no accumulation of transient effects at towers with higher grounding impedance can be observed either. Regarding the analysed dataset, a high reliability of supply can be expected for systems with a similar setup and comparable lightning parameters. Grounding concepts of existing overhead lines can be validated by these results.

Circuit Model of Vertical Double-Circuit Transmission Tower and Line for Lightning Surge Analysis Considering TEM-mode Formation

The electromagnetic fields, which are produced by lightning currents flowing into a transmission tower and into overhead ground wires, spherically expand with time, and propagate as non-transverse electromagnetic (TEM) waves at least within the round trip time of the traveling wave along the tower. In this paper, a distributed-parameter line model of a vertical double-circuit transmission tower with an overhead line struck by lightning is composed considering the non-TEM characteristics. The surge impedances of the tower, ground wires, and phase conductors increase with time and reach their TEM-mode or steady state values with time constants determined from the configuration. In addition, the significant wave attenuation along the tower is included in the circuit model according to the propagation characteristic determined by the tower configuration. The virtual inductive grounding impedance or damping circuits for approximately representing the wave attenuation is no longer needed. The proposed model is applied to four types of transmission towers. Waveforms of voltages across insulator strings computed by the finite-difference time-domain method, which are regarded as the reference, are well reproduced by the proposed model. Computation efficiency is drastically improved by the proposed model comparing to the numerical electromagnetic field analysis.

Study on lightning protection scheme of multi‐terminal MMC‐MVDC distribution system

Based on a ±10 kV three-terminal MMC-MVDC (medium voltage DC distribution system based on modular multilevel converter) system, in this study, the authors mainly study on the influencing factors and protection schemes of the lightning intruding overvoltage (including direct lightning and back-flashover lightning). Firstly, a lightning intruding overvoltage simulation model of the MMC-MVDC distribution system using overhead lines is established based on the PSCAD/EMTDC program. The influence of steady-state operating voltage and the number of converter stations on the simulation results are simulated and analysed. Meanwhile, the proper simulation modelling method of the lightning intruding overvoltage for multi-terminal MMC-MVDC system is proposed. Secondly, the lightning intruding overvoltage is simulated when the line is struck by the lightning stroke current that occurs once in 20 years and the different lightning protection schemes are proposed. Finally, based on the lightning impulse withstand voltage, lightning trip-out rate and the cost of the protection schemes, the lightning protection schemes in different scenarios are proposed. The simulation results show that if the cost of the system is prioritised, the protection scheme of increasing the number of parallel stacks of the DL arresters can be selected, and if the power supply reliability of the system is prioritised, the protection scheme of installing the overhead ground wire as well as reducing grounding resistance can be selected.

Experimental analysis of the strands breaking characteristics of optical fibre composite overhead ground wire due to simulating lightning strike

With the increasing application of OPGW (optical fibre composite overhead ground wire) in power systems, the strands in OPGW are frequently broken due to lightning strikes. In this study, ten kinds of OPGW lightning-strike tolerance was tested according to the IEC standards. The influences of the following factors, such as transfer charge, tensile force, the diameter and material of OPGW outer layer strands, were analysed. The transfer charge and tensile force are positively proportional to the degree of lightning strike damage to OPGW. The diameters of OPGW outer layer strands are positively related to the lightning strike tolerance of OPGW. Compared with OPGW with aluminium alloy outer layer strands, lightning strikes tolerance of OPGW with aluminium clad steel (AS) outer layer strands is better. It suggested that the OPGW outer layer strands diameter >3.2 mm and with AS outer-layer strands shows good lightning strike tolerance. The mechanism of OPGW strands breaking was also analysed by the infrared detection, micro-morphology detection and energy spectrum. The experimental results of this study provide significant data support for OPGW type selection for lightning protection.

Breaking Cause Analysis on a 110 kV Overhead Grounding Wire (OGW)

An in-serviced 110kV overhead grounding wire (OGW) was found to be broken, and the fracture cause was then studied by means of macroscopic morphology and metallographic observations, fracture microanalysis and mechanical properties testing. The results revealed that the fracture of OGW was mainly resulted from the lightning stroke, which was mainly informed from the craters on the surface of the broken wire steel strand by fracture morphology observation results. The lightning currents led to a rapid temperature rise, which eventually caused the surface OGW to be broken by tension after fusing or partially fusing under high temperature. At last, it was advised that coarser steel strands should be used in areas with frequent lightning strikes to improve the thermal stability of OGW, and the metal technical supervision in the operation process of high voltage transmission lines should also be strengthened.

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.

Safety impacts of electric potential and electromagnetic fields as result of faults in electric distribution system

ABSTRACTThis article investigates the impacts of electric potential (EP) and electromagnetic fields (EMF) on human health, especially for those living or working near a distribution system, as a consequence of faults inside the distribution system supplied by an outdoor substation. A case study was carried out using a 115/22 kV substation and a 22 kV distribution system of Thailand’s Provincial Electricity Authority (PEA), with simulated faults injected at the top of a pole of distribution lines located at three different locations. Two methods were proposed for EP and EMF reduction: 1) bonding the ground grid of the substation and the ground rod of the riser pole, and 2) connecting the overhead ground wires of the substation and that of the distribution system. The study results confirm that the two proposed methods offer practically effective problem-solving solutions for reducing EP, and they are therefore able to mitigate the risk of equipment damage. The spatial distribution of EMF measured in the vicinity of the distribution system was found to comply with the threshold set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the International Radiation Protection Association (IRPA), indicating that those living or working outside the substation were safe.

Особенности расчета поражения молнией элементов воздушных линий электропередачи

The article presents the main principles and specific features of a procedure for calculating the lightning-induced damage inflicted to power transmission line elements based on a probabilistic approach. The procedure takes into account the modern concepts on how lightning strikes at ground objects. A model simulating the development of a downward lightning leader in a manner maximally close to the real negative stepped leader development process is proposed. A scheme illustrating how a leader is targeting at a ground object has been developed. By solving the problem within the framework of 3D modeling, the possibility of a connecting leader to develop not only from the phase wires and overhead ground wires, but also from the line supports can be analyzed. Based on experimental and theoretical studies, a probabilistic approach for conditions under which the streamer corona flash transforms into an upward leader is proposed. The possibility of taking into account the natural and climatic conditions, and topography in the line route regions is considered. The elaborated procedure and the software package developed on its basis allow the places of lightning strikes at overhead power line elements and their probabilities to be predicted in the most grounded manner, which will make it possible to set up reliable overhead power line protection.