The overhead transmission line system is one of the methods of transmitting electrical energy at a high voltage from one point to another, especially over long distances. The demand for electrical ...energy is increasing due to the increase in the world population, the evolution of transport technology, and economic expansion, thereby resulting in overloading to the overhead line (OHL) system. In building new infrastructure for transmission lines, several issues need to be addressed. Thus, optimizing existing power by increasing the ampacity of power line is a practical solution to meet energy demand issues. During long-term operation, the temperature of OHL conductors may increase beyond their rated temperature, which is typically 75 °C for conventional conductors such as aluminum-conductor steel-reinforced cable. This condition is defined as thermal stress, which results in lower sag vertical clearance, tensile loss, elongation and creep, and reduced life span of the conductors. This condition must be avoided to ensure that the line is not permanently elongated, which can disrupt the vertical ground clearance, and to expand the conductor's life. Other factors such as lightning, wildfire, aging, and degradation of the conductor can also cause thermal stress on the conductors and have thermal effects on the conductor's performance. Therefore, unwanted thermal stress needs to be examined and identified by monitoring the thermal effect and behavior of the lines. This paper presents the state of the art in monitoring technologies that can be used to identify thermal stress on OHL conductors, including the issues and challenges in monitoring. At the end of this paper, a few suggestions are included to address the occurrence and assessment of thermal stress in lines. Ultimately, this work may provide complete information to researchers and maintenance engineers to enable them to make better decisions on condition monitoring, operation, and maintenance of the system.
•The use of arresters can improve the lightning performance of transmission lines.•Placement based on the tower-footing impedance does not allocate arresters optimally.•Solutions use a minimum number ...of arresters to achieve a target lightning performance.•Transfer effect of the lightning surge due to arresters operation is rarely mentioned.•The number of arresters may be underestimated if the transfer effect is not included.
Installation of transmission line surge arresters (TLSA) is one of the solutions found to improve the lightning performance of overhead transmission lines (OHTL). This work proposes a new multi-criteria methodology for the optimal placement of surge arresters on OHTL based on a multi-objective optimization algorithm coupled with ATP (Alternative Transient Program) software. Lightning performance calculation is performed considering the transfer effect of the lightning surge due to arresters operation. This transfer mechanism that can lead the adjacent towers to flashover is rarely mentioned in the literature. A case study considering a 230 kV transmission line with 231 towers and 105 km long operating in Brazil is presented. Compared to the real performance data, the solution found with the best cost-benefit ratio allows a reduction of 68% in the line outages with the use of 90 surge arresters (i.e., 0.86 TLSAs/km of line). This is practically 50% of the number of arresters calculated using the classical placement method based on the tower-footing impedance value. Regarding the transfer effect of the lightning surge, the results show that the performance levels and, consequently, the number of TLSAs to protect the line may be underestimated if this effect is not considered in the modelling.
The operation reliability of the power grid and the stability of social production are seriously threatened by the icing of the overhead line. The equivalent ice thickness (EIT) is to convert ...different densities and shapes of ice into the uniform annular ice with density of 0.9 g/cm3. Although many methods for calculating EIT of transmission line conductors have been proposed, there are lack an effective monitoring method of EIT for 500 kV ground wire with tangent tower under the special terrain where “the virtual lowest point” of the ground wire appears in the condition of large height difference. Therefore, a calculation method of EIT for 500 kV ground wire with tangent tower under the special terrain based on vertical tension measurement technology is proposed. That is the iterative method is used to preset different EITs. Then the calculated vertical tension under the preset values are solved by the established ground wire state equation and vertical tension equation. The EIT can be obtained when the calculated vertical tension is equal to the measured vertical tension. The comparison between the artificial observed EIT and the calculated EIT is carried out for two practical cases of 500 kV ground wire in the mountainous area of southern China. The results show that the absolute error is less than 2 mm, which verify the two values are in strong agreement. The corresponding finite element simulation models are established. A comparative study between the simulated EIT and the calculated EIT is carried out. The results show that the relative error is less than ±10% under severe icing from 10 mm to 30 mm and the absolute error is less than 1 mm under mild icing of 5 mm, which verify the two values are highly consistent. Finally, the application effect of this method in practical cases is analyzed.
•A calculation method of equivalent ice thickness for 500 kV ground wire is proposed.•The comparison with the artificial observed equivalent ice thickness is carried out.•A finite element simulation is established to verify the effectiveness of method.•The application effect of the method in practical cases is analyzed.
Harvesting energy from the insulated shield wire with tuning is expected to be a possible solution to the problem of high power supply for online monitoring devices on high voltage overhead ...transmission lines. However, the randomness of meteorological conditions, such as wind and temperature, may cause fluctuations in the energy harvesting system's power and voltage. This paper presents an integrated energy harvesting reactor with both tuning and transformer functions, which can also consider the randomness of meteorological conditions. The statistical confidence interval of equivalent circuit parameters is numerically calculated based on meteorological data collected along a transmission line for a whole year from 2016 to 2020. On this basis, a combined magnetic circuit for the energy harvesting reactor is proposed to achieve a self-adaptive negative-feedback regulation, and parameter optimization is carried out and validated by field-circuit coupled simulation. Finally, an energy harvesting reactor prototype is developed and tested. The statistical analysis results on the equivalent circuit parameters show that they are approximately subject to Gaussian distribution. Besides, it is found from the experimental results that the maximum power under rated equivalent circuit parameters is 935 W, and the maximum power can reach 800–1000 W within the fluctuation range of equivalent circuit parameters considering meteorological randomness. Overall, the experimental results of the harvested power varying with load resistance conforms to the simulation results. Furthermore, compared to using a deeply saturated tuned reactor, the energy harvesting reactor shows better robustness to the randomness of meteorological conditions and the total harmonic content of output voltage is reduced by 64%. Therefore, the proposed energy harvesting reactor for high voltage overhead insulated shield sires shows more potential for a practical application than the existing methods.
•An energy harvesting reactor for high voltage insulated shield sires is developed.•The statistical confidence interval of equivalent circuit parameters is calculated.•A combined magnetic circuit for the energy harvesting reactor is proposed.•A field-circuit coupled simulation for the energy harvesting reactor is performed.•An energy harvesting reactor prototype is developed and experimentally validated.
High-frequency electromagnetic fields such as those associated with electromagnetic pulse (EMP) and intentional electromagnetic interference (IEMI) can couple to overhead power lines. Since the ...height of the overhead power lines can be comparable or even larger than the smallest wavelength of typical EMP and IEMI pulses, the classical transmission line approximation might not be suitable for evaluating the line response. On the other hand, a traditional full-wave solver (e.g., method of moments) is computationally inefficient, especially when dealing with long lines. To address these problems, we propose an efficient method to handle the high-frequency electromagnetic field coupling to overhead lines with nonlinear loads above a lossy ground. In the proposed method, the asymptotic approach is adopted and extended to the case of a lossy ground, which handles the problem in a semianalytical way and has a much higher computational efficiency in the case of long lines. Although the proposed method applies to the frequency domain, the case of nonlinear loads can be considered through a combination with the time-marching method. The proposed method is validated with several numerical examples.
•The power equipment has continuous and short-time overload endurance capabilities.•Overhead line is the weak point of overload capability on the transmission channel.•The heavy load warning strategy ...is based on the predicted bottleneck current.•The safety strategy provides transfer capability support for power system emergency.
The overload endurance capability (OEC) of transmission equipment in power system emergency not only relates to the safety of equipment itself but also affects the security of the power system. The action threshold of the existing backup protection (such as distance protection zone 3) reacting to the overload condition is determined by the static thermal rating. The action time is set according to the sequence coordination of upstream and downstream transmission lines. This strategy ineffectively adapts to the surge overload current after power flow transferring, may cause backup protection false trip and accelerate the cascading trip of power system. The parameters and their influential factors that represent the OEC of transmission equipment were clarified in this study. The dynamic OECs of the switchgear, current transformer, and overhead line on the transmission channel were analyzed. The heavy load warning method of the transmission section based on the predicted continuous overload endurance capability (COEC), and the load adjustment and overload protection strategy based on the short-time overload endurance capability (SOEC) were proposed. Finally, the feasibility and validity of the proposed methods were verified through a case study. The proposed safety strategy can effectively utilize the SOEC to protect the safety of the power equipment and provide transfer capability support for the security of power system in emergency conditions.
This paper proposed a novel noncontact technology of operation-state monitoring based on magnetic-field sensing for high-voltage transmission lines, which can simultaneously measure both electrical ...and spatial parameters in real time. This technology was derived from research on the magnetic-field distribution at the ground level when the transmission lines operate in different states, including sagging, galloping, and current imbalance. Two typical models of high-voltage three-phase transmission lines were simulated, and the resulting magnetic fields were calculated. The correlation between the magnetic-field variations and the operation states were analyzed. Based on such correlation, a source reconstruction method was developed to reconstruct the spatial and electrical parameters from the magnetic field emanated by the overhead transmission lines. The reconstruction results for the 500-kV and 220-kV transmission lines verify the feasibility and practicality of this novel noncontact transmission-line monitoring technology based on magnetic-field sensing.
Harvesting power from ground wires is a promising solution for the power supply problem of online monitoring device on the overhead transmission lines. Nevertheless, this method is more likely to ...suffer lightning overvoltage or overcurrent due to the position of power harvesting device. In order to promote the reliability of harvesting power from ground wires, this paper studies the ground wire voltages under different lightning strike situations with different ground wire connection methods. Meanwhile, the influence of lightning current waveform, span and tower impulse resistance is also studied in this paper. The results of this paper can guide the design of overvoltage protection module of the power harvesting device on the ground wire.
•Application of Beam Spectral Element into the overhead transmission line vibrations,•Influence of hysteretic and aerodynamic damping in vibration of transmission line.•Analysis of the dispersion ...diagram due to the change of cable tension force.•Indicated overhead transmission line model by comparing with experimental tests.•Wittrick–Williams algorithm application to estimate the natural frequencies.
The paper treats a new approach of dynamic analysis of a conductor cable of an overhead transmission line under the theoretical background of spectral element method (SEM). The methodology relies on the analytical solution of the displacement wave equation in the frequency domain; moreover, it both enhances the accuracy of model predictions and reduces the computational efforts when compared to a finite element (FE) model. Two numerical models based on SEM are built for transmission lines taking into account hysteretic and aerodynamics damping and whose analyses consider dispersion diagrams and frequency response functions (FRFs). As SEM leads to a transcendental eigenvalue problem, to obtain the natural frequencies of the conductor, it is used the Wittrick–Williams algorithm. The results presented in the paper show the sensitivity of the response conductor changes according to the tensile load and damping parameters. Finally, the numerical models have compared with the analytical solution of the cable and experimental tests performed at CEPEL’s (Electric Power Research Center) laboratory with the overhead conductor Grosbeak cable. The results show outstanding accuracy in both experimental measurements and analytical analysis aspects.
As the key equipment in power system, the running state of overhead transmission lines is affected by various complex and random factors, and the maintenance workload of the line is too heavy to ...overhaul regularly. Therefore, it is very necessary to build a refined condition assessment system to improve the diagnosis accuracy and maintenance efficiency of overhead transmission lines. Recent years, State Grid Corporation of China (SGCC) has recorded mass of monitoring reports of transmission lines. The natural language processing (NLP) with deep learning model provides an effective way to extract the key defect information from the monitoring reports. In this paper, the joint model of intention classification and slot filling (ICSF) based on bidirectional encoder representation from transformers (BERT) is introduced. To improve the precision of defect information extraction, two optimization models of BERT are presented. The results show that Robustly Optimized BERT Pre-Training Approach (RoBERTa) has achieved better effects on ICSF with the extraction accuracy of 92.22%. Then, the hierarchical weighted scoring method is introduced to score the status of overhead transmission line based on the results of ICSF-RoBERTa. And the assessment results of the overhead transmission line state and the corresponding maintenance strategies are provided according to the scores. Finally, the feasibility of the proposed method is validated by practical cases of line inspection reports.
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