Insulator Strings Research Articles

Numerical Simulation of Wind-induced Swing Angle of 1000kV Transmission Line Suspension Insulator Strings Considering Dynamic Response

The wind-induced swing angle of insulator strings directly affects the electrical insulation performance and the construction cost of the UHV transmission project. However, due to not considering the fluctuating wind pressure, the calculation results of wind-induced swing tend to be conservative when adopting the recommended guidelines of standard especially in the face of severe weather. This paper simulates the transient wind field of strong winds based on time-space correlation characteristics and constructs the fluctuating wind load distribution model exerting on the UHV transmission line. Then a refined finite element model of the multi-span transmission line including the entire tensile section is established. And the swing angle of the insulator strings calculation formula is fitted based on the calculation results of the wind-induced swing response. The calculation result shows the swing angle decreases with the increase of ice thickness, and the magnified coefficient of the wind-induced swing angle at the target tower under the basic wind speed of 15m/s is 1.03.

Dynamic Windage Yaw Angle and Dynamic Wind Load Factor of a Suspension Insulator String

A simplified calculation method is proposed for determining the peak dynamic windage yaw angle φ ^ of electricity transmission line (TL) tower suspension insulator strings (SISs). According to the rigid-body rule, the geometric stiffness matrix in the calculation of the windage yaw angle φ of SISs is dominated by the average wind loads, while the fluctuating wind loads are the dominant factor in the elastic stiffness. With the average wind state of conductors as the initial calculation condition, the load-response-correlation (LRC) method can be used to determine the fluctuating windage yaw angle φ d and the corresponding equivalent static wind loads (ESWLs). Then, the improved rigid straight rod model, which uses the actual length of conductors rather than the projected length, was used to determine the average windage yaw angle φ ¯ . Through the linear superposition of the horizontal increments of φ ¯ and φ ^ d (the peak value of φ d ), the formulae to calculate the φ ^ of SISs were derived. Additionally, the formulae for the dynamic wind load factor, β c , which is a key factor in designing wind loads for φ , were derived according to the principle of ESWLs, rather than being empirically determined by the Chinese code. Thus, the calculation model regarding the loads and response for the φ of SISs was established, and an actual TL was used to verify the established calculation model. Afterward, the influence of the different engineering design parameters on φ and its β c were analyzed. The parameter analyses show that the wind speed, span, and ground roughness influence the magnitudes of φ ^ and β c , however, the height difference between the two suspension points of the conductors, the nominal height, and the sag-to-span ratio may be neglected in the approximate calculation. Our method offers a new solution to TL design when there are large deformations and small strains.

Polymeric Insulator Conditions Estimation by Using Leakage Current Characteristics Based on Simulation and Experimental Investigation.

The current work contributes an estimate of the time-frequency characteristics of a leakage current in assessing the health condition of a polluted polymeric insulator. A 33 kV polymer insulator string was subjected to a series of laboratory tests under a range of environmental conditions, including pollution, wetting rate (WR), non-soluble deposit density (NSDD), and non-uniform distribution pollution (FT/B). The temporal and frequency features of the leakage current were then extracted and used as assessment indicators for insulator conditions based on laboratory test findings. Two indices were generated from the leakage current waveform in the time domain: the curve slope index (F1), which is determined by measuring the inclination of the curve between two successive time peaks of the leakage current, and the crest factor indicator (F2). The frequency domain of the leakage current signal was used to calculate the other two indices. These are the odd harmonic indicators derived from the odd frequency harmonics of the leakage current up to the 9th component (F3) and the 5th to 3rd harmonics ratio (F4). The findings showed that the suggested indicators were capable of evaluating insulator conditions. Finally, the confusion matrix for the experimental and prediction results obtained with the proposed indices was used to assess which indicator performed the best. Therefore, the analysis suggests an alternative and effective method for estimating the health condition of a polluted insulator through leakage current characteristics obtained in the time and frequency domains.

The Technology of Space Electric Field Detection of Deteriorated Insulator Strings Based on Multi Rotor UAV

Porcelain insulator with good insulation performance is the key to the stable operation of power system. In order to characterize its insulation performance safely and accurately, a 1:1 three-dimensional electric field simulation model of 220 kV porcelain tension insulator string is established by using COMSOL finite element software, and a UAV live detection platform for degraded insulator string is built according to the optical electric field sensor. The results show that when the insulator deteriorates, the distribution electric field curve will appear obvious distortion; comparing the simulation results with the live measurement results, it is found that the electric field waveform curve obtained by the live detection platform of degraded insulators based on UAV can be accurate and can effectively judge the insulators with deterioration.

Nonlinear Buckling Analysis and Optimization Design of the Y‐Type Composite Insulator String

Under the action of extreme wind load, the overhead transmission line will lead to the fracture of the traditional V‐type insulator string, which greatly affects the safety of the power system. Compared with the V‐type insulator string, the Y‐type insulator string has better stability under the wind load. Therefore, the overhead lines in the mountainous areas of Anhui Province are taken as the research object, considering the combined effect of wind load and conductor dead weight, and through theoretical derivation, the calculation formula of insulator string wind deflection angle is obtained. Using numerical simulation software, the nonlinear mechanical analysis of Y‐type insulator strings is conducted, and under the action of different wind speeds, the windage yaw angle and unloading angle of the Y‐type insulator string are obtained. Compared with the calculation results of the V‐type insulator string, the stability of the Y‐type insulator string in the structure is better than that of the V‐type insulator string, and the Y‐type insulator string can make full use of the distance between layers and the gap margin of the tower head, reduce the length of the cross arm, and reduce the weight of the tower, which has obvious advantages. Combined with the results of theoretical analysis and numerical simulation, the optimal design method of the Y‐type insulator string is given. Under the condition of ensuring the safety and stability of insulators, the distance of the cross arm is shortened as much as possible and the weight of the transmission line tower is reduced. The research results will provide a theoretical reference for engineering design and improvement.

A New Current Transducer for On-Line Monitoring of Leakage Current on HV Insulator Strings

This paper presents the design, implementation and testing of a transducer to measure and monitor in real time leakage currents on high-voltage insulators. The new proposed transducer has the particularity of not affecting the insulation capacity of the insulator strings and can be installed without the need to de-energize the power system. The transducer is made up of a toroidal current transformer with a high permeability magnetic core, and an amplifier circuit, the output voltage of which is acquired, processed and transmitted by a dedicated device installed in the lower part of the HV tower. The leakage current is reconstructed from the transducer output voltage by applying the FFT technique and its own inverse transfer function. The transducer makes it possible to obtain the leakage current with its characteristic harmonics and the technique presented here reduces the electromagnetic noise present in the power systems. The proposed transducer was tested on an insulator inside an artificial fog chamber, built according to the IEC 60507 standard. Finally, the transducer was tested on an insulator string in a 220 kV substation. The results obtained show that the designed transducer correctly measures the leakage current on HV insulator strings and can be used for the on-line monitoring of pollution levels of insulator strings.

Calculation Method for Dynamic Stiffness of Multispan Overhead Transmission Lines

The dynamic motion of a span is coupled to the other spans in transmission lines. From the continuity conditions, force equilibrium conditions, and dynamical equations of every span conductor and insulator string, a close-form expression for the dynamic stiffness of a coupled two spans in harmonic motion is presented. Unlike some existing theories of single span conductor, the effect between the conductors and insulator strings is considered here. By means of example calculations, the validity of the dynamic stiffness of two-span is demonstrated by the consistency of the results determined by the ABAQUS. Meanwhile, the dynamic stiffness and natural frequency are discussed under variation of the span lengths ratio, Irvine parameter, and insulator string length. Moreover, the modal shape function corresponding natural frequency is derived, and the contribution of localization mode is studied. The results show that the contribution is either sensitive to or independent of transmission line parameters in certain parameter ranges. Finally, generalizing the work of two-span, the dynamic stiffness of arbitrary span number is obtained.

A Study of the Cleansing Effect of Precipitation and Wind on Polluted Outdoor High Voltage Glass Cap and Pin Insulator

In this work, the extent of natural cleansing effect of rainfall, wind and fog or a combination of these on an insulator string were investigated. Results showed that pollution losses progress with time, with a considerable fraction of losses occurring within 15 minutes of testing. While wind alone played little or no role in surface cleansing, it increases the extent of cleansing by rainfall. The topsides of insulators were found to be more affected by natural cleansing compared to the underside. Equivalent Salt Deposit Density (ESDD) and Non-Soluble Deposit Density (NSDD) measurements were carried out. ESDD was found to be higher in the lower disc irrespective of the weather condition the insulator string has been subjected to. NSDD measurements established no pattern on how natural cleansing was impacted by disc position on a string, demonstrating the random nature of pollution-cleansing cycle of outdoor insulators. Insulator performance was assessed by high voltage AC tests and monitoring of partial discharge events using Radio Frequency antennas and a High Frequency Current Transformer (HFCT). Measured output by the HFCT showed that leakage current decreases uniformly with time, and the speed at which this occurs is an indication of the intensity of natural cleansing activity.

Dynamic Characteristic of Conductor After Ice-Shedding and Simulation Analysis of the Tension Insulator String

Electric power fittings are the link between conductors and transmission towers, and it is essential to improve their ability to withstand damage. In order to obtain the actual load of electric power fittings and study the stress of each electric power fitting under the actual load, a transmission line model of catenary-shaped and an integral model of tension insulator string are established in this paper. Then, conductors with uniform thickness of ice coating and ice shedding process are simulated by changing density method. The results show that the maximum dynamic tension of the conductor of isolated span transmission line is greater than the static tension of conductor icing only when the length of ice-shedding section is small. Under any ice-shedding condition, the maximum dynamic tension of the conductor of multi-span transmission line will be close to or greater than the static tension after conductor icing. When the form conductor tension is loaded on the tension insulator string, it can be found that the most dangerous and secondary dangerous fittings in the tension insulator string are found, and the stress analysis is carried out on the key connecting fittings, which provides a reference for the design and optimization of electric power fitting.

Wind tunnel experiments on the pollution characteristics of suspension insulators in an ion flow field

Contamination particles in the air are charged by the ion flow field around a DC corona discharge wire. The electric force acting on the charged particle is associated with the ion flow field and affects the particle deposition on insulators. In this study, the pollution characteristics of the porcelain insulators in an ion flow field were investigated by pollution experiments in a wind tunnel. The conductor wire was applied a higher DC voltage than the corona onset voltage and connected to a test insulator string. As the test parameters, the DC voltage was variable, the contamination particle diameter was set at 20 μm, and the wind speed was 2 m/s. The nonsoluble deposit density (NSDD) and its distribution on test insulators were measured, compared, and analyzed. The relationship was discussed between insulator pollution characteristics, the electric force on dust particles, and the ion flow field. The pollution characteristics revealed that the pollution on the upper part of the string increased with the test voltage and corona current. The non-uniformity of pollution along the string and on the upper/lower insulator surfaces also increased. However, the non-uniformity of pollution on the windward/leeward of the insulators decreased. The discussions indicated that the spatial ion flow field around the conductor affected dust motion when the dust was away from the insulator. The direction and magnitude of the electric force on the charged particles impacted the pollution distribution. The pollution level of the strings in the unenergized test was considerably lower than that in energized tests. The pollution level could be reduced by increasing the conductor corona under a specific corona current range.

Parameters Optimization of UAV for Insulator Inspection on Power Transmission Line

In recent years, Unmanned Aerial Vehicle (UAV) technology has been widely used in power transmission line inspection. UAV operating parameters determine the quality of the acquired insulator image, which directly affects the efficiency of transmission line inspection. Regarding the inspection of ceramic insulators, this work establishes a three-dimensional (3D) model of ceramic insulators, and simulates the changes in shooting distance, angle, and height of the UAV through three geometric transformations: rotation, translation, and scaling. The influence of those three UAV operating parameters (the shooting distance, angle, and height) on the integrity of the ce-ramic insulator steel cap is studied. In the infrared zero value detection of 110kV ceramic insulators, It is found that the best setting for obtaining the maximum steel cap area is: shooting distance of 3 - 7 meters, shooting height of 1 meter below the center of the insulator string, and a shooting depression angle of 0°. The UAV operating parameters setting method proposed in this paper will provide theoretical and practical basis for the in-depth intelligent inspection of transmission line insulators.

Effect of temperature and water penetration on the interfacial bond between epoxy resin and glass fiber: A molecular dynamics study

According to the hydrothermal working environment, accidents related to composite insulator string rupture are frequently encountered in transmission line, which cause serious hazard to the stability of power system. The interface between epoxy resin matrix and glass fiber fillers is one of the microscopic interfaces in the insulator core rod. The adhesion strength of that interface has important implications for the overall mechanical properties of the core rod. This study aims to analyze the influence of temperature and water intrusion on the interfacial adhesions. By molecular dynamics (MD) simulation, a molecular modelling of epoxy resin / glass fiber interface under water molecular environment was established. The mechanism of deterioration is indicated through the interfacial binding energy, ester number, radial distribution function (RDF) and H-bonds number of the interface model. It was found that when the temperature increased to a certain level, the water molecules were easy to migrate to the interface through the holes in the epoxy resin. When the temperature reaches 373 K, the epoxy resin occurs hydrolysis reaction, which will promote the cracking of epoxy resin. Meanwhile, water molecules migrated to the interface can hinder the formation of hydrogen bonds between epoxy resin and glass fiber. Under the synergistic effect of the above factors, water gradually causes the degradation of epoxy resin / glass fiber interface.

Electric field characteristics of UHV DC tension string during insulator replacement by two workers

The UHV DC tension insulator strings are often large-tonnage suspension porcelain or glass insulators with high mechanical strength. The single insulator is heavy, so two workers working at the same time are required to make a replacement on insulator strings in live working conditions. One of the key problems that must be solved in live working conditions is to select an appropriate way to reach the working position and realize the potential transfer between two workers. In this paper, the electric field calculation model of live working of ±800 kV tension strings was established. The process that two workers enter and leave the working position along the tension string and different conditions that two workers replace insulators were simulated and analyzed, and distribution characteristics of the electric field of insulator strings and live workers were obtained. According to the calculation results, when the two workers replace the tension insulators in different tension strings, it is easy to realize the potential transfer, so as to reach the same potential for work. The study results of this paper provide a basis for the selection of replacement method of large-tonnage single insulator by two workers, and a theoretical basis for UHV DC live working.

Finite element simulation of wire’s sag considering tension insulator string

A finite element simulation process based on methods of mutual calling between MATLAB and ANSYS software packages are proposed, which has the ability to consider the influence of tension insulator string weight on the sag of a span in a tension section. The convergence criterion of the process can be controlled artificially and is defines to converge when the maximum sag of two calculation steps is very small. A simplified theoretical analysis method is also developed for comparison and verification. These proposed methods are then applied to a tension section and a three-span actual line. Results show that when using a finite element simulation to obtain the curve of a wire, if the number of elements in the span is 10, the mid-span sag in the span is consistent with the theoretical result. And if the number of elements in the span is greater than 50, the sag curve of the conductor is almost unchanged. The two methods and the difference between them are very small, indicating the efficiency of the proposed process.

Simulation Research on Electric Field Distribution of Insulator String in ULTRA High Voltage Transmission Line

Insulators are one of the important components of overhead transmission lines. Because of their excellent characteristics, insulators have obvious advantages in the selection of external insulation in UHV AC transmission projects. The potential distribution of insulator string is not even due to the shape characteristics of insulator string, the structure of metal tool, the low conductivity of silicon rubber material and the stray capacitance between insulator string and wire, iron tower and metal tool. When the surface field intensity of insulators and fittings exceeds the initial field intensity, corona discharge will occur, which will affect the electromagnetic environment and the operation characteristics of insulating materials. Therefore, it is of great significance to determine the potential distribution of insulator strings of UHV transmission lines for detecting low and zero value insulators, implementing voltage equalization measures effectively, and ensuring the safe and stable operation of transmission lines. Based on Ansys software of 500kv transmission line insulator string, this paper establishes a three-dimensional model, the method of using finite element numerical simulation respectively with no equalizing ring and equalizing ring in both cases the umbrella skirt on simulation, the distribution of electric field along the roots, and further studies the equalizing ring the effect of different parameters on the electric field distribution. Finally, an optimal solution is established.

Improved U-Net based insulator image segmentation method based on attention mechanism

To realize the accurate identification and segmentation of the insulator string in the complex background image with diverse appearance and obscuration, this paper proposes an insulator segmentation method based on improved U-Net. The algorithm embeds the attention mechanism ECA-Net (Efficient Channel Attention Neural Networks) in the coding stage of U-Net to improve the model’s ability to extract semantic features, thereby improving the accuracy of insulator detection. Experimental results show that the average overlap IOU of the proposed method is 96.8%, which can more accurately segment different types of insulators in complex backgrounds.

Research on Scale Model of Typical Tension String of UHVDC Transmission Lines under Ice-Shedding Loads

Tension insulator string is one of the important components of transmission lines and it needs to have enough mechanical strength to transfer the load between conductors and towers. However, due to the large size of the tension insulator strings, it is usually impossible to carry out the true type experiments. In this paper, the dimensional analysis was adopted to establish the mapping scale models of typical tension strings, namely 8N42-50100-55P at first. Then, the load scaling ratios of three typical tension insulator strings were obtained based on the results of the ice shedding calculation on an actual UHVDC transmission lines. Finally, the dynamic experiments of the scale tension insulator strings were carried out to access the feasible of technical route and to provide a technical support for the following research.

Study on Adaptive Excitation System of Transmission Line Galloping Based on Electromagnetic Repulsive Mechanism

Due to the uncontrollable weather conditions, it is difficult to carry out the controllable prototype test to study fatigue damage of transmission tower and armour clamp and the effect evaluation of antigalloping device under actual transmission line galloping. Considering the geometric nonlinearity of the transmission line system, this study proposed an adaptive excitation method to establish the controllable transmission line galloping test system based on the Den Hartog vertical oscillation mechanism. It can skip the complicated process of nonlinear aerodynamic force simulation. An electromagnetic repulsion mechanism based on the eddy current principle was designed to provide periodic excitation for the conductor system according to the adaptive excitation method. The finite element model, including conductor, insulator string, and electromagnetic mechanism, was established. Newmark method and fourth-order Runge-Kutta algorithm were used to complete the integrated simulation calculation. By comparing with the measured data record of the actual transmission line galloping test, the results show that the proposed adaptive galloping excitation system can effectively reconstruct the key characteristics of the actual transmission line galloping, such as amplitude, frequency, galloping mode, and dynamic tension, and make the galloping state controllable. Thus, a series of research about transmission line galloping with practical engineering significance can be carried out.

Pollution Flashover Characteristics of Coated Insulators under Different Profiles of Coating Damage

Based on experiments and numerical analysis techniques, this paper aims to investigate the influence of the four different coating damage profiles on the performance of coated 33 kV porcelain insulator strings under polluted and clean surface conditions. The performance of the insulators coated with room temperature vulcanizing (RTV) under partial coating damage and undamaged coating was evaluated. The influence of humidity on pollution flashover was taken into consideration. The ring-shaped, fan-shaped, and random-shaped coating was applied following coating damage. The results showed that the flashover characteristic of the RTV-coated insulators had a significant difference as compared to the normal insulators. Electrical characteristics such as the flashover voltage, critical current, and surface resistance were significantly affected by coating damage distribution and humidity level on the insulators’ surface. The electric field and potential difference were analyzed as well using the finite element method (FEM). The initiation of the arc was observed to appear at the area of insulators where the electric field was the highest. It was also observed that different coating distributions of pollution and humidity levels resulted in a change in the surface pollution layer resistance and an uneven distribution of the electric field. This indicates that the coated insulators’ parameters are directly related to the coating damage distribution on the insulator surface, particularly in the presence of humidity.

Prediction models for dynamic response parameters of transmission lines after ice-shedding based on machine learning method

The maximum vertical jump height, horizontal swing of conductor line and unbalanced tension of suspension insulator string, known as the dynamic response parameters, of transmission lines after ice-shedding are key parameters determining the electric insulation clearance and strength of the tower-line system in the ice zone. Numerical studies on the dynamic responses of lines with various structural, ice and wind parameters are carried out, and from the dynamic responses the maximum jump height, horizontal swing and unbalanced tension are extracted to create a dataset. Based on the dataset and the back-propagation neural network and the extra-trees algorithm, two prediction models for the three parameters, i.e. the jump height, horizontal swing and unbalanced tension, are constructed. With eight input variables, the three dynamic response parameters can be predicted quickly and effectively by the two models. These prediction models are suitable for transmission lines with a wide range of structural parameters such as long span and large elevation difference, and provide an efficient means for electric insulation clearance and strength design of transmission lines in ice zone.