Optical Ground Wire Research Articles

Review on fiber-optic sensing in health monitoring of power grids

Fiber-optic sensing technology is best adapted to health monitoring and evaluation of power grids because of its immunity of electromagnetic interference, capabilities of multiplexing and distributed sensing, and tolerance to harsh environments. We review key fiber-optic sensing technologies, including fiber Bragg gratings, fiber-optic interferometers, optical time domain reflectometries, and their applications in three main parts of power grids, transformers, power towers, and overhead transmission lines, during the past 20 years. In particular, optical fiber composite overhead ground wire and optical phase conductor applied in power grids are the areas of great potential to go further. The perspectives of an intelligent fault diagnosis subsystem for power grids based on a fiber-optic sensing network are discussed, and related on-going work is described. The review shall be of benefit to both engineers and researchers in power grids and fiber-optic sensing.

Insulation Reconstruction for OPGW DC De-Icing and Its Influence on Lightning Protection and Energy Conservation

In order to satisfy demands for DC de-icing of optical fiber composite overhead ground wire (OPGW) and solve questions such as those relating to circulating current loss and liability of suffering from lightning strike, the grounding method of OPGW must be changed from the current commonly used method of being grounded at every tower to being grounded at one tower. The OPGW would be connected to the tower by an insulator, which is often shunt connected with a protective discharge clearance. The recommended value of the discharge clearance is from 70 to 80 mm. The lightning impulse discharge voltage of such a clearance is generally not more than 100 kV. However, as the transmission line is struck by lightning, over-voltage on the clearance is 885 kV at least, even up to a few MV. The clearance can be broken down reliably. The influence of insulation reconstruction for OPGW on the induced current and the power loss of the AC transmission line was studied by means of theoretical analysis and simulation calculations. Results indicate that change of the OPGW grounding mode could reduce the induced current of the ground wire to below 1 A and reduce the power loss of the line to below 1 W/km. Power loss could be reduced by over 99%. Adoption of a suitable grounding mode for OPGW is of great significance for DC de-icing, lightning protection safety, and energy savings for UHV projects.

Analysis of Operation and Maintenance of Optical Fiber Communication System

With the development of the times, the use of optical fiber network communication is widely used in power communication, most power plants through optical fiber technology to improve the level of power transport and power security. ADSS (All-dielectric Self-supporting Optical Cable) and OPGW (Optical Fiber Composite Overhead Ground Wire) are the most widely used optical fibers in power systems.

Analysis of Short-Circuit Current Characteristics and Its Distribution of Artificial Grounding Faults on DC Transmission Lines

Grounding faults are common faults on dc transmission lines. Characteristics of the short-circuit current, such as amplitude and frequency, and its following distribution are very important for analyzing the influence of the fault. Based on the ±500 kV Yongfu dc transmission project in China, several artificial grounding short-circuit tests at the terminal or middle of the dc transmission line were carried out. This paper reports the measurement and analysis of the short-circuit current and its distribution in a dc system for the first time. The short-circuit current distribution includes currents in the ground wires of the fault tower and currents in ground wires, which are connected to the converter station grounding grid, such as the optical ground wire (OPGW) currents of ac outgoing lines, neutral point currents of different transformers, and the grounding electrode bus arrester current. In addition, the frequency components of the fault currents are analyzed. Based on the PSCAD/EMTDC software, the current distribution is simulated and discussed. The simulation results are in good agreement with the test results.

应用于光纤复合架空地线的光纤分布式振动的测量

应用于光纤复合架空地线的光纤分布式振动的测量

Optimal Design of a Wide Area Measurement System for Improvement of Power Network Monitoring Using a Dynamic Multiobjective Shortest Path Algorithm

Wide area measurement system (WAMS) usually contains three dependent infrastructures called management, measurement, and communication. For optimal operation of a power system, it is necessary to design these infrastructures suitably. In this paper, measurement and communication infrastructures in a wide area network are designed independently from a management viewpoint, considering an adequate level of system observability. In the first step, optimal placement of measurement devices is determined using an integer linear programming (ILP) solution methodology while taking into account zero-injection bus effects. In the next step, new dynamic multiobjective shortest path (MOSP) programming is presented for the optimal design of communication infrastructure. The best architecture design is introduced in terms of optical fiber power ground wire (OPGW) coverage for the suggested central control bus and the number of phasor measurement units (PMUs). The applicability of the proposed model is finally examined on several IEEE standard test systems. The simulation results show better performance of the proposed method compared with other conventional methods. The numerical results reveal that applying the proposed method could not only reduce the OPGW coverage cost, the number of PMUs, and the number of communication links but could also improve the system technical indexes such as latency as subsidiary results of the optimization process.

Evaluation of Fibre Lifetime in Optical Ground Wire Transmission Lines

Abstract In the research, measurements of polarisation mode dispersion of two OPGWs (optical ground wire transmission lines), in total four fibres, have been carried out, and the expected lifetime of the infrastructure has been assessed on the basis of these measurements. The cables under consideration were installed in 1995 and 2011, respectively. Measurements have shown that polarisation mode dispersion values for cable installed in 1995 are four times higher than that for cable installed in 2011, which could mainly be explained by technological differences in fibre production and lower fibre polarisation mode dispersion requirements in 1995 due to lack of high-speed (over 10 Gbit/s) optical transmission systems. The calculation methodology of non-refusal work and refusal probabilities, using the measured polarisation mode dispersion parameters, is proposed in the paper. Based on reliability calculations, the expected lifetime is then predicted, showing that all measured fibres most likely will be operational within minimum theoretical service life of 25 years accepted by the industry.

Field measurements of SOP transients in OPGW, with time and location correlation to lightning strikes.

We monitored the state of polarization (SOP) of polarized light in an optical ground wire (OPGW) link located in North America using a test method and apparatus that measured Stokes space angular velocity and geographic location of SOP transients. We observed transients up to 5.1 Mrad/s and were able to correlate these events in both time and location to lightning strikes documented by the United States Precision Lightning Network (USPLN).

A Programme to Solution the Problem of OPGW Substation Structure Grounding

OPGW with functions of lighting proof and communication is widely used in the construction of power network. For optical fiber composite overhead ground wire (OPGW), it is required to achieve the separation of wire and signal after the introduction of the substation structure[1]; at the same time, the grounding for lightning proof is also required because of the frequent occurrence of the burnout of the optical cable and short circuit due to the electric discharge and lighting as a result of the problems in the grounding device or construction. This paper analysis some common advantages and disadvantages of OPGW structure grounding methods. In combination with the practical conditions of the project, the solution “Enhanced the grounding method” is brought up and solve the practical problem.

Modeling and analysis of lightning effects in OPGW cables using the ADI-FDTD method

Current density distribution in optical ground wire cables hit by lightning strokes is numerically calculated and studied in time domain. For this analysis, two models for current source were considered, since atmospheric discharge has two major components which usually damage more severely the cable: the long and short duration current components. The analysis is performed by employing the Alternating Direction Implicit Finite-Difference Time-Domain (ADI-FDTD) method, which the presented formulation was especially developed by the authors to analyze this phenomenon. The convolutional perfectly matched layer (CPML) technique adapted for the ADI method, called ADI-CPML, is also developed in this work for truncating the ADI-FDTD computational domain.

The Way of Reducing Current Values in Optical Ground Wires at Asymmetrical Faults on Overhead Transmission Lines

Abstract Given the fact that the installing costs of an optical ground wire on overhead lines directly depend on its cross-section, which in turn depends on the level of fault current it should withstand, in order to reduce these current values in the optical ground wire, I suggested performing its isolated descents from the end towers of the line with its transition to an optical cable. The research was carried out on the example of a 500 kV overhead line in the National Electric Power Grid. The Method of Symmetrical Components for calculating asymmetrical fault currents was not used; therefore, calculations were carried out on the base of presenting the line as a multi-wire system for the considered case as a five-wire system (optical ground wire, steel ground wire, and three phase wires). Such approach allows taking into account the initial asymmetry of the line parameters and modeling any kind of asymmetrical faults. The analyses of calculated results were performed. The conclusive evidence that the optical ground wire isolated descents from the end towers of the line give the possibility of reducing the level of maximal fault current distribution values in it and therefore its cross section, is presented.

DC ice‐melting and temperature variation of optical fibre for ice‐covered overhead ground wire

To prevent atmospheric ice on optical fibre composite overhead ground wire (OPGW) from affecting the safe and stable operation of power system, applying the direct current (DC) ice-melting technology to remove ice from OPGW is a feasible option. If the selection of DC ice-melting current is unreasonable, the temperature of optical fibre can be extremely high which may shorten its operating life or even cause it to burn. Therefore, based on the finite element method, the ice-melting process of OPGW under glaze icing condition is simulated by COMSOL and MATLAB. The ice-melting time and temperature variations of optical fibre for ice-covered OPGW under different environmental conditions are obtained. Then, a series of ice-melting tests are carried out in an artificial climate chamber to verify the calculation results. Results show that the ice-melting and temperature increase of optical fibre gradually slow down during the entire DC ice-melting process. When ice sheds from the OPGW, the temperature of optical fibre reaches its maximum value. The ice-melting time is closely related to the ice-melting current, ambient temperature, wind speed, ice thickness and type of OPGW. The maximum temperature of optical fibre is significantly influenced by ice thickness and ice-melting current.

Optical Fiber Bending Detection on Long Distance OPGW using OTDR

In Malaysia, thousands of kilometers of Optical Ground Wire (OPGW) have been installed by a utility company. For long distance fiber cable, there is a possibility of optical fiber to bend with very small radius especially in joint closures which caused optical power to attenuate. This attenuation is known as ‘bend losses. Bend loss increases the total power attenuation of optical fiber. In addition, for long distance fiber cable, it is important to avoid any extra loss as the fiber itself attenuates 0.2 to 0.35 dB/km and splice loss about 0.1 dB each. Hence, in this study, the method of detecting bend loss as well as optical fiber bending is presented. The result of this study is expected to allow fiber industry players to determine the exact location and proper rectification can be done to solve bend loss problem.

Design and analysis of a wireless monitoring network for transmission lines in smart grid

AbstractIn order to timely and precisely locate a problem over the power lines, the control center needs to monitor the status of the transmissionlines and the towers. In this paper, we design such a monitoring network by taking advantage of the existing optical fiber composite overhead ground wire (OPGW) alongside the transmission lines. Because it is not cost‐effective to have gateway access to the OPGW for every transmission tower, we propose to deploy a multi‐hop wireless sensor network in between two sparsely deployed neighboring OPGW gateways. We mainly study the power allocation for the data transmission of the wireless sensors because of the assumption that such sensors are powered by green energy and a battery with limited capacity for easy deployment and maintenance. Specifically, we propose several centralized schemes with different objectives, for example, the minimum power usage and fast computation. We also propose a distributed scheme so that the sensors can be even more energy efficient dealing with dynamic traffic in field operations. Moreover, we analyze the centralized schemes to study their pros and cons. We also conduct a case study for the distributed scheme to demonstrate its feasibility in field operations. Copyright © 2015 John Wiley & Sons, Ltd.

Direct current lightning tests on Optical Ground Wires

In the last 19 years, the Mexican Federal Electricity Commission (CFE), proprietary of the transmission lines in all the country, has proceeded to replace its conventional overhead earth wires by Optical Ground Wires (OPGW) which is expected to lead to a better incentive. Indeed, those wires include in addition to the traditional protection aspect against atmospheric discharges, the ability to remotely control and operate the grid as well as passing telecommunications. The OPGW's are designed based on the electrical and mechanical specifications required by the end user to fit a given application. Nevertheless, the position of the wire at the top of the transmission towers is to protect the power phases below against lightnings. Therefore, the designer should guaranty its physical integrity as well as its additional functionalities under any atmospheric conditions which can be realized through direct current lightning tests as defined by the national specification given in CFE E000-21-2011 and the international standard IEC 60794-1-2. In addition, it is necessary to define the polarity applied during the tests in order to obtain a representative level of damages found in the field. Implementations of the this specification and the international standard has been carried out and various tests have been conducted on OPGW's for the Mexican utility grid. The results have been compared to actual damages found in the field.

Experimental study on location of lightning stroke on OPGW by means of a distributed optical fiber temperature sensor

abstract An electric anode with high pulsed current and a negative electrode are adopted to form a lightning impulse system with duration time of 200 ms for simulation of the lightning stroke process. The lightning stroke on the optical fiber ground wire (OPGW) is considered to be a heat release process at the lightning stroke position, and a distributed optical fiber temperature sensor (DOFTS) is employed to locate the lightning stroke. In the experiment, simulated lightning strokes with the quantity of electric discharge of 100 C and 200 C are generated respectively, but in the inner part of the OPGW the temperature increase captured by the DOFTS is just several degrees Celsius because of the heat-insulating property of the grease and jelly filled into the OPGW and the limit from spatial resolution of the DOFTS. Experimental results demonstrate that DOFTS has excellent potential for the maintenance of electric power transmission line and it is important to enhance the spatial resolution for further applications of DOFTS in engineering.

Vibration Damping in Overhead Transmission Line Conductors

Fatigue is a common cause for failure of conductors near associated hardwares and attachment. Vibrations due to wind is a common cause for fatigue and frettingof conductors. Conductors under the effect of high frequency and low amplitude are more prone to vibrations particularly in India and other parts of the world. ACSR conductors have been a popular choice for overhead conductors due to advantages in both electrical and mechanical characteristics and these conductors are more prone to Aeolian vibrations. Vibration dampers are widely used to control Aeolian vibration of the conductors and earthwires including optical ground wires. In this paper the author presents the performance of vibration dampers on ACSR conductors. The author emphasizes the importance offor evaluating the suitability of a damper for a particular overhead line by choosing appropriate design tension, type, quantity and placement of vibration dampers to avoid failure of lines.

Performance Evaluation of Optical Fiber Ground Wire Cable During Short Circuit Condition

Optical ground wires (OPGW) are increasingly being used on overhead transmission lines throughout the world. OPGW conductors protect the power line against lightning or short-circuit and provide communication through optical fibers embedded inside the conductor. In case of conventional ground wire, the permissible instantaneous temperature is limited by the highest allowable loss of tensile strength of metallic materials caused by annealing and bird-caging. Since OPGW conductors are expected to give protection to the embedded optical fiber, they shall meet a further requirement; i.e. the temperature of the conductor shall not rise in such extent that it may cause degradation in the parameters of the optical fiber. The highest temperature that the conductor may reach during and after short-circuit depends on the conductor design. This paper describes the testing requirements and the performance evaluation of typical OPGW conductor during short circuit condition as per IEEE Standard 1138.

Induced Voltage of Overhead Ground Wires in 50 0-kV Single-Circuit Transmission Lines

General grounding method of overhead ground wires adopted in Chinese 500-kV transmission lines is usually optical fiber composite ground wire (OPGW) grounded at each tower while common ground wire (CGW) insulated with one point grounded. Energy loss of OPGW and high induced voltage of CGW is a problem to be concerned as to its values and control methods. Both field measurement and ATP-EMTP simulation of induced current and induced voltage of overhead ground wires in a 500-kV single-circuit transmission line are carried out in this paper. Quantitative data of induced current and energy loss show the urgent necessity to reduce the energy loss and change the grounding method of overhead ground wires. A no-loss method for ground wires is proposed by comparing advantages and disadvantages of three grounding methods of overhead ground wires, where both OPGW and CGW are insulated with one point grounded. Induced voltage is calculated in different transposition pitch and segment length of ground wires with grounding position at the end of the line or at the midpoint of transposition pitch and segment. It shows that induced voltage of ground wires grounded at the midpoint of transposition pitch and segment is half of which grounded at the end. Moreover, induced voltage of overhead ground wires can be reduced to 500 V or other limited values by choosing a reasonable transposition pitch and grounding position.

基于氮化铝的OPGW交流融冰效率的研究

输电线路覆冰事故严重威胁电网安全运行，抗冰防灾是电网建设的重点攻克技术之一，其中，地线融冰研究是常用的关键技术。基于复合光架空地线两层层绞式结构，采用无感双绞线作为融冰热源，实现对地线覆冰段交流融冰。本文采用高热导率半导体材料氮化铝填充导线层间空气气隙，提高融冰传热速度，缩短融冰时间，减少融冰热损耗，有效改进OPGW融冰效率。结合热路分析法，理论计算氮化铝提高融冰效率。制作OPGW交流融冰样品及氮化铝样品，实验得到两种样品融冰时间，对比分析氮化铝提高融冰效率是可行的。Ice accident on transmission lines influences the safe operation of power grid. Preventing ice dis-aster is one of the key technologies for the construction of power network. Ground wire ice-melt- ing technology is of great significance in conventional technology. Based on the layer stranded structure of Optical Fiber Composite Overhead Ground Wire (OPGW), a twisted bifilar wire fabricated by insulated wire is used as a heater for AC de-icing of ground wire. In order to enhance the heat transfer rate and shorten the ice-melting time as well as reduce the heat loss and improve ice melting efficiency, aluminum nitride, a semiconductor with high thermal conductivity, is used to fill in the gap among the conductor. An equivalent thermal circuit is established to calculate the de-icing efficiency of OPGW with aluminum nitride. With the samples of ice melting conductors, the ice melting time is analyzed based on de-icing conditions. It is confirmed that the ice melting efficiency of OPGW can be feasibly improved by filling the aluminum nitride.