Part Of Transmission Line Research Articles

Insulator Abnormal Condition Detection from Small Data Samples.

Insulators are an important part of transmission lines in active distribution networks, and their performance has an impact on the power system's normal operation, security, and dependability. Traditional insulator detection methods, on the other hand, necessitate a significant amount of labor and material resources, necessitating the development of a new detection method to substitute manpower. This paper investigates the abnormal condition detection of insulators based on UAV vision sensors using artificial intelligence algorithms from small samples. Firstly, artificial intelligence for the image data volume requirements was large, i.e., the insulator image samples taken by the UAV vision sensor inspection were not enough, or there was a missing image problem, so the data enhancement method was used to expand the small sample data. Then, the YOLOV5 algorithm was used to compare detection results before and after the extended dataset's optimization to demonstrate the expanded dataset's dependability and universality, and the results revealed that the expanded dataset improved detection accuracy and precision. The insulator abnormal condition detection method based on small sample image data acquired by the visual sensors studied in this paper has certain theoretical guiding significance and engineering application prospects for the safe operation of active distribution networks.

Experimental study on anti-loosening technology of transmission line bolts

Bolts are widely used in transmission lines and are key connecting parts of transmission lines. Transmission lines have been affected by the natural environment for a long time, and bolts are prone to frequent vibration leading to loosening or falling off. Bolt loosening endangers the safe and stable operation of transmission lines. This paper analyses the loosening mechanism of the transmission line screw connection, carries out the transverse vibration contrast test of the common bolt anti-loosening measures, and develops the integrated self-locking double nut for the hidden danger of the transmission line bolt loosening, which has good anti-loosening performance, convenient installation, and the conditions for engineering popularization and application.

Holding Force Characteristics of Preformed Helical Fitting Based on Finite Element Method

As an important part of transmission lines, preformed helical fitting plays an indispensable role in the safe and stable operation of electronic circuits. However, due to the poor service environment of transmission lines, preformed helical fitting can often slip, scatter, and detwist. This paper explores variations in the holding force of the preformed helical fitting under different geometric parameters. First, the geometric structure of preformed helical fitting is analyzed, and the secondary development is conducted using the ABAQUS finite element software. The script program is written in Python language to realize the parametric modeling. Based on the experimental results, the changing trend of the holding force is consistent, which confirms the correctness of the finite element model. In addition, the preformed helical fitting is studied under different values of molding aperture, pitch length, pitch number, and armor rod diameter, and changes in the holding force under different parameters are analyzed. The results show that the holding force of the preformed helical fitting increases with the decrease in the molding aperture and pitch length, and the molding aperture has a negative linear correlation with the overall holding force. The holding force increases linearly with the pitch number; so, reducing the pitch length can increase the holding force of preformed helical fitting. Moreover, the results indicate that the holding force increases with the armor rod diameter. The research results presented in this study have important guiding value for the design of performed helical fitting.

Analysis of Transient Response of Jointless Track Circuit Based on Multiconductor Transmission Lines Theory

In order to ensure the train operation safety, it is necessary to analysis the transient response of track circuit in complex electromagnetic environment. According to the distribution characteristics of transmission lines in traction electric network and the structure of ZPW‐2000 jointless track circuit, the multiconductor transmission lines model of the traction electric network combined with the track circuit is established. The model cannot be calculated directly due to the presence of parallel or terminated nonlinear lumped elements in the track circuit. For this problem, the new analytical method is proposed, which is based on finite difference time domain (FDTD) method to solve the transmission line part, Thevenin's theorem with state variable method to solve the equations of the terminated nonlinear track circuit. The solution equation of multiconductor transmission line system is obtained by combining the two parts. The relevant parameters of the model can be calculated by finite element method. In ATP‐EMTP, the simulation results verify the correctness of the expression. In addition, through the transient response experiment of track circuit, it is confirmed that the transmission characteristics of transient signal on rail are consistent with the calculation results in this paper. Finally, the influence of signal frequency, ballast resistance on track surface voltage, and the influence of interline coupling voltage by the conductivity (σ) and the permittivity (ε) are studied. It provides theoretical reference for the anti‐interference analysis of track circuits. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Image Detection of Insulator Defects Based on Morphological Processing and Deep Learning

Insulators are an important part of transmission lines; failure may threaten the operation of these transmission lines. For insulator defect detection, an optical image detection method based on deep learning and morphological detection is proposed. First of all, the Faster RCNN is used to locate the insulator and extract its target image from the detection image. In the second place, a segmentation method of insulator image is proposed to remove the background of the target image. In order to simplify insulator defect detection, an insulator shape transformation method is proposed to unify all types of insulator detection. Finally, a mathematical model is established in the binary image to describe the defect of the insulator. Experiments show that our proposed Faster RCNN can accurately detect the insulators in the image. Its AP is as high as 0.9175, and its Recall rate is as high as 0.98, which is higher than the common insulator recognition algorithm. The accuracy of the proposed defect detection method is 0.98, which can accurately locate the defect position of the insulator. In order to prove the efficiency of the proposed method, we compared several common detection methods.

Cascade Modeling of the Measuring System Used to Assess S-Parameters of Anchor Rods on Power Transmission Lines Guyed Towers

The structural condition of the cable-stayed towers anchorage on power transmission lines requires constant monitoring. Maintenance routines must be able to identify faulty anchor rods and substitute them to avoid tower collapses and power delivery interruptions. Modern statistical diagnostic systems based on machine learning requires the generation of several distinct rod sample signals to be trained, which is a time-consuming process in typical electromagnetic solvers. Aiming to generate samples in a feasible time span, this paper presents a modeling strategy based on the cascade analysis of the transmission line composed by the anchor and the reference rods, interconnected by a dedicated high-frequency connector. Each distinct transmission line part is modeled by a quadrupole as a partial ABCD matrix. The complete response for each experimental setup is obtained from the cascaded-multiplying of the partial matrices. The proposed modeling proved to be accurate and provides a faster way to obtain the S-parameters from distinct faulty rods if compared to the traditional methodologies using electromagnetic tools.

Sensing Method Using Multiple Quantities for Diagnostic of Insulators in Different Ambient Conditions

Insulators are one of the many components responsible for the reliability of electricity supply as part of transmission and distribution lines. Failure of the insulator can cause considerable economic problems that are much greater than the insulator cost. When the failure occurs on the transmission line, a large area can be without electricity supply or other transmission lines will be overloaded. Because of the consequences of the insulator’s failure, diagnostics of the insulator plays a significant role in the reliability of the power supply. Basic diagnostic methods require experienced personnel, and inspection requires moving in the field. New diagnostic methods require online measurement if it is possible. Diagnostic by measuring the leakage current flowing on the surface of the insulator is well known. However, many other quantities can be used as a good tool for diagnostics of insulators. We present in this article results obtained on the investigated porcelain insulators that are one of the most used insulation materials for housing the insulator’s core. Leakage current, dielectric loss factor, capacity, and electric charge are used as diagnostic quantities to investigate porcelain insulators in different pollution conditions and different ambient relative humidity. Pollution and humidity are the main factors that decrease the insulator´s electric strength and reliability.

Mode-Selective Transmission Line—Part II: Excitation Scheme and Experimental Verification

In Part I of this two-part work, we have presented the theoretical foundation and physical mechanism of the mode-selective transmission line (MSTL). This part is devoted to its excitation scheme, practical transition design, and experimental verification. The MSTL excitation is first explained by comparison with a conductor-backed coplanar waveguide (CBCPW). To produce the specific mode excitation, an ultrabroadband transition between CBCPW and MSTL is proposed. It has a tapered structure operating as a tapered-mode coupler, which supports smooth evolution from the fixed CPW mode of CBCPW to the frequency-dependent dominant mode of MSTL. This modal evolution along the transition is analytically treated based on a local normal mode theory. Couplings between the local normal modes are negligible as a result of gradual tapering, thereby effectively suppressing higher order modes in MSTL and sustaining a mode purity over an ultrabroad frequency range. For experimental demonstration purposes, back-to-back CBCPW-to-MSTL transition circuits are physically realized. The measured results are in agreement with the prediction, showing a return loss of 15 dB from 3 to 109 GHz; the single transition introduces a relatively low insertion loss of 1.84 dB at 100 GHz. The propagation characteristics of MSTL are also extracted from the measured S-parameters, which provides an excellent validation of the proposed structure.

Mode-Selective Transmission Line—Part I: Theoretical Foundation and Physical Mechanism

Mode-selective transmission line (MSTL) has been studied and realized in support of ultrabroadband and ultrafast electromagnetic signal guidance. Its operation is based on the fact that its dominant mode behaves as a quasi-TEM microstrip mode at low frequencies and is gradually converted into a quasi-TE10 waveguide mode at higher frequencies notwithstanding its longitudinal uniformity. In the first part of this work (Part I), the physical mechanism of the frequency-dependent modal behavior is presented. From the viewpoint of mode coupling, MSTL is heuristically considered as a coupled system consisting of one microstrip line and two half-mode substrate-integrated waveguides (HM-SIWs). Coupled-mode theory and normal-mode analysis are combined to sequentially analyze HM-MSTL, a relatively simple case, and MSTL. The coupled-mode theory provides an approximate representation for the normal modes of each coupled system, thus gaining in-depth physical insight into the MSTL mode-guidance behavior. A comparison between approximate fields derived from the theoretical analysis and exact fields extracted from the rigorous numerical simulation is made to support the modal analysis. A parametric study is then carried out to examine the effect of geometrical parameters on the MSTL characteristics and performance, thereby providing meaningful guidance in the MSTL design and optimization. A further discussion of mode selectivity is given at the end of this article.

Detection of Insulator Defects With Improved ResNeSt and Region Proposal Network

Insulator is an important part of transmission line. Defective insulators will cause potential safety hazard to transmission lines. Image detection technology can improve the efficiency of insulator defect detection and greatly reduce the maintenance cost. However, the existing insulator defect detection technology has the disadvantages of low accuracy and long detection time. An insulator defect detection method based on improved ResNeSt and Region Proposal Network (RPN) was proposed. First, this method builds a new network based on ResNeSt. Secondly, we added the improved RPN to the improved ResNeSt for feature extraction, to better detect minor defects on insulators. Finally, we enhanced the data processing and labeled the open insulator data set. On this data set, the proposed model is tested and a large number of controlled experiments are done. The results show that the proposed network is more accurate and faster than the control group. Moreover, the proposed network has an accuracy rate of 98.38% for insulator defect detection, which can detect 12.8 pictures per second. The proposed method has good efficiency and practicability in aerial photo insulator defect detection.

Investigation of high voltage ACSR transmission line dead end connector fault

Transmission line plays important roles in delivering electric energy from generation site closer to the customer. Failure of a transmission line can cause significant economic loss due to undelivered energy and may lead to catastrophic system black out. One critical part of transmission line is dead end connector, thus ensuring good condition of transmission line dead end connector is critical to avoid extensive losses. This paper investigates the cause of failure of dead end connectors that were installed in 150 kV ACSR lines. The failed connectors were examined and tested to find out the cause of the breakdown. Several samples of suspected bad connectors are also tested for comparison. Simulations using finite element software were conducted to provide broader insight on failure propagation. The investigation found that the dead end connectors were failed due to high current flowing through the steel part of the conductor which is caused by high contact resistance between the aluminium part of the conductor and the connector. Further study is needed to mitigate similar condition to occur in the dead end connector installation.

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.

Novel HVDC Spacers by Adaptively Controlling Surface Charges – Part I: Charge Transport and Control Strategy

A spacer is a challenging part of high voltage direct current (HVDC) gas-insulated substations and gas-insulated transmission lines. This paper proposes a novel design of HVDC spacers by self-adaptively controlling the surface charge. The paper briefly reviews dielectric modification methods that aim to limit surface charge accumulation. A novel design of HVDC spacer is introduced that is based on the concept of adaptively controlling surface charges using nonlinear materials, and its surface charge control and regulation abilities are investigated. The surface charge accumulation and decay properties of the novel spacer are compared to a downsized spacer. The results show that the proposed model spacer can restrict surface charge accumulation in the charge adaptive control region of the spacer. Doping the nonlinear material can facilitate surface charge decay in the charge adaptive control region when the electric field exceeds a threshold. These positive results represent a new idea of designing a suitable spacer to avoid surface flashover in HVDC SF 6 apparatus.

Opportunities for High-Voltage AC Superconducting Cables as Part of New Long-Distance Transmission Lines

The purpose of this study is to compare possible superconducting 380-kV cables with existing overhead lines and underground cables. The study compares the required corridors and energy losses of different versions of a 1.7-km transmission system with a power of 6.6 GVA. Comparison covers the following setups: 4 × 380 kV high-voltage overhead lines, 8 × 380 kV conventional cables, 2 × 380 kV and 4 × 380kV superconducting cables with warm and cold dielectrics. The paper will present the description of the different setups as well as the calculation of energy losses. The required widths of the underground cable corridors are also considered in this study. Finally, the temperature profile and pressure drop of the superconducting cables are investigated. The main results can be summarized as follows. 1) For the assumed voltage level and power, overhead lines require a corridor width of 70 m, whereas a corridor of less than 7.7 m in width is necessary for superconducting 380 kV cables. 2) The 380-kV superconducting cable reduces the energy loss by approximately 8100 MWh per year in comparison to the conventional overhead lines. This yields a feasible energy loss reduction of up to 75%.

Altitude Correction of Radio Interference of HVdc Transmission Lines Part II: Measured Data Analysis and Altitude Correction

The prediction and control methods of radio interference (RI) for HVdc transmission lines passing through high-altitude region are main key factors in design of the HVdc transmission lines. In order to obtain the altitude effect and correction of RI for HVdc transmission lines, four HVdc reduced-scale test lines with the same parameters were built up at 50, 1700, 3400, and 4300 m elevation, respectively. Simultaneously, two HVdc full-scale test lines with the same conductor type of 4 × JL/G1A-500/45 had been set up at altitude 50 and 4300 m as well, respectively. Using these test facilities, a lot of RI measured data were accumulated in a long time span, from Jan. 2010 to Jul. 2014. By analyzing the RI measurement data at different altitude regions, it is indicated that the altitude correction of RI has a nonlinear relation to the altitude. Meanwhile, the RI altitude correction formula for HVdc transmission lines has been proposed in this paper. Using the proposed RI altitude correction formula, the RI levels at high altitude are lower than that predicted by using the RI correction formula of ac transmission lines, which means that it could save a lot of investments at high altitudes.

Altitude Correction of Radio Interference of HVDC Transmission Lines Part I: Converting Method of Measured Data

It is a serious problem in the development of power transmission technology in China that the high-voltage direct-current (HVDC) transmission lines have to pass through the high-altitude areas. To satisfy the demands of environmental protection, it is important to predict radio interference (RI) performance of the HVDC transmission lines in the high-altitude areas. The existing method to evaluate the altitude effect on RI of the HVDC transmission lines refers to the conclusion of the alternating-current (AC) transmission lines, because of lack of supporting HVDC test data. It was found by the measurement data on Qinghai-Tibet ±500 kV DC transmission line built in China that the ac altitude correction conclusion of RI is inappropriate for the HVDC transmission lines in the high-altitude regions of China. In this paper, RI experiments were carried out on two full-scale HVDC test lines and four reduced-scale dc test lines at different altitudes in China from 2010 to 2014. The method to convert the data on the test lines with different lengths and terminations into that of the infinite-long lines is proposed and verified; then the measurement data of the full-scale and reduced-scale test lines were converted by this method to derive the RI altitude correction of the HVDC transmission lines. It is proved that the proposed method may provide a feasible way to obtain RI altitude correction of the HVDC transmission lines.

Power and polarization monitor development for high power millimeter-wave.

A new type monitor of power and polarization states of millimeter-waves has been developed to be installed at a miter-bend, which is a part of transmission lines of millimeter-waves, for electron cyclotron resonance heating on the Large Helical Device. The monitor measures amplitudes and phase difference of the electric field of the two orthogonal polarizations which are needed for calculation of the power and polarization states of waves. The power and phase differences of two orthogonal polarizations were successfully detected simultaneously.

Pollution performance of HVDC SiR insulators at extra heavy pollution conditions

As an integral part of transmission lines, insulators play a major role in the reliability of power systems and their failure exposes the performance of the whole system into risk. Compared to AC systems, DC static field and corresponding arc without zero crossing makes DC flashover performance more problematic. Although the utilization of composite insulators in HVDC transmission lines continues to grow, there is still a lack of investigation on DC pollution flashover performance of SiR insulators especially at extra heavy pollution conditions. This paper presents the measurement and analytical results for DC flashover of SiR insulators in terms of different polarities of voltage, hydrophobicity levels and geometrical characteristics of SiR insulator at extra heavy pollution conditions. According to the results flashover strength in positive voltage is 4% higher than that in negative voltage. In addition, different profiles of SiR insulators did not show the same pollution flashover sensitivity on hydrophobicity. The empirical modeling of pollution flashover performance of insulators in terms of specific leakage distance, average diameter, form factor and the ratio of shed spacing to shed depth, revealed that specific leakage has the highest impact on pollution-flashover voltage gradient. This is of importance especially for designing and dimensioning of SiR insulators to be used under HVDC voltage.

The Loadability of Overhead Transmission Lines—Part II: Analysis of Double-Circuits and Overall Comparison

This is the second part of an investigation aimed at providing a thorough technical comparison between traditional and alternative overhead power transmission lines based on the loadability characteristics. The previous Part I outlined and applied the fundamentals of the loadability analysis to three comparable single-circuit lines. In Part II, the analysis is broadened to three comparable double-circuit lines: traditional three-phase ac double-circuit lines (assumed as the reference system for the comparison) and bipolar HVDC lines and nonconventional combined ac-dc lines. As in Part I, the loadability analysis takes into account thermal limits, voltage drop, power losses, and - when feasible - steady state and transient stability. Part II also performs an overall comparison among the different systems in single-circuit and double-circuit configuration to draw final conclusions.

Effects of Segmented Shield Wires on Signal Attenuation of Power-Line Carrier Channels on Overhead Transmission Lines—Part II: Signal Attenuation Results Analysis

A previous paper has been written on the generalized modeling method of overhead transmission lines for use in power-line carrier (PLC) systems. Knowledge of the effects of shield wires on PLC signal attenuation for various coupling methods would be useful to relay engineers. In addition to the effect of the coupling method on PLC signal attenuation, other problems, such as resonance conditions resulting in high signal attenuation may also occur depending on the PLC signal frequency and the length of the shield wire segments. Therefore, the purpose of this paper is to provide awareness to relay engineers of problems that may arise when applying PLC systems on transmission lines with segmented shield wires.