Overhead Lines Research Articles

Modelling dynamic pantograph loads with combined numerical analysis

Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains. Changing heights of overhead lines to accommodate level crossings, overbridges, and tunnels pose significant challenges in maintaining consistent current collection performance as the pantograph aerodynamic profile, and thus aerodynamic load changes significantly with operational height. This research aims to analyse the global flow characteristics and aerodynamic forces acting on individual components of an HSX pantograph operating in different configurations and orientations, such that the results can be combined with multibody simulations to obtain accurate dynamic insight into contact forces. Specifically, computational fluid dynamics simulations are used to investigate the pantograph component loads in a representative setting, such as that of the recessed cavity on a Class 800 train. From an aerodynamic perspective, this study indicates that the total drag force acting on non-fixed components of the pantograph is larger for the knuckle-leading orientation rather than the knuckle-trailing, although the difference between the two is found to reduce with increasing pantograph extension. Combining the aerodynamic loads acting on individual components with multibody tools allows for realistic dynamic insight into the pantograph behaviour. The results obtained show how considering aerodynamic forces enhance the realism of the models, leading to behaviour of the pantograph–catenary contact forces closely matching that seen in experimental tests.

Modeling of electromagnetic influences of multi-wire traction networks for pipelines

In this work, digital models for determining the electromagnetic influences of multi-wire traction networks on pipelines are developed. When developing models, an approach based on multiphase behaviour simulation of electric power systems was used. This approach adequately addresses all the influencing factors, which include modules and phases of currents flowing through the overhead contact wire suspension, 6–10–25 kV power transmission lines laid on the supports of the overhead line, and lines of rails. In addition, it is possible to take into account similar parameters for stresses at the nodal points of a multi-wire system. Among the key factors are the railway clearance when laying pipes parallel to the railway track, railway clearance trajectory in the presence of non-parallel sections, and the electrical characteristics of the soil along the clearance route. The research results demonstrated that a 25 kV electromagnetically unbalanced traction network exerts significant influence on a pipeline running in parallel. It was shown that the maximum induced voltages at specific points along the pipe fall within the range of 300–700 V, which significantly exceeds the permissible level of 60 V. It was revealed that currents exceeding 20 A flowing through the pipe can have an adverse effect on anticorrosive protection devices. To mitigate electromagnetic impacts on the pipeline, the following measures are recommended: reducing the length of pipeline and railway clearance sections, increasing the gap between the traction network and the pipe, and installing an additional grounding source. The pipe can be connected to the supplementary grounding source through filters tuned to a frequency of 50 Hz, which involve capacitor units to prevent malfunctions during the operation of pipeline protection devices. Thus, the developed digital models allow the induced voltages generated by multi-wire traction networks and the currents flowing through the pipes to be adequately determined. These models offer an informed choice of measures that ensure the safety of pipeline maintenance.

Line electrical transmission damage identification tool in distributors electrical networks

In the paper showing that one of the main way for Ukraine electric power industry evolution is electric power networks and systems improvement and construction considering Smart Grid concept. The main idea of Smart grid is the reliable, energy-efficient and high-quality energy supply system. To implement the idea, it is necessary to create a high-performance information and computing infrastructure. The main components of Smart Grid is emergency mode diagnostics and damage monitoring. Providing fault diagnostics and fault monitoring can improve the power supply reliability and quality to consumers. So, the task of quickly and accurately determining the place of damage is important. In the article showing that emergency detection tools in sections of both cable and overhead electrical networks it’s a way to improve efficiency of the networks. The diagram of the placement of damage indicators on the section of the electrical distribution network is presented, which allows determining the direction of the search for the location of the damage. A comparative analysis of measuring current transformers of optical and electromagnetic type was carried out. It is shown that a significant number of advantages of optical measuring current transformers, which can be used in damage indicators, can be provided by measuring current transformers of the electromagnetic type. Creating fault indicator based on the Smart Grid concept lets do to reduce searching time for the cause and location of an emergency situation to a minimum. In this concept application fault indicator in energy grid ensure it connection to operating overhead and cable lines without removing voltage by connecting the output of the secondary winding of the measuring current transformer of the detachable design to the measuring converters directly placed near the current measuring transformers with the help of a mechanical spring fastener. A block diagram of a specialized information-measuring system with a damage indicator was created, taking into account the requirements of the Smart Grid concept, which allows to reduce the time of searching for the cause to a minimum.

Engineering fault intelligent monitoring system based on Internet of Things and GIS

Abstract The power grid (referred to as PG for convenience) structure is becoming increasingly complex. Aiming at the problem that it is difficult for traditional PG monitoring methods to accurately detect PG faults, an intelligent PG fault monitoring system is constructed using Internet of Things (IoT) and geographic information system (GIS) to improve the effectiveness of fault monitoring. The sensor equipment is used to collect the current information in the circuit, and the change of induced current is used to judge the cause of the fault, and the fault information is transmitted to the monitoring center through communication technology. The staff can directly locate the geographical location of the fault in the visual interface. One hundred overhead lines of Xianyang Power Supply Company are selected for analysis, and the performance of the traditional PG monitoring method and intelligent PG fault monitoring system is compared. The average fault detection accuracy of the traditional PG monitoring method and the system proposed in this article is 72.0 and 94.8%, respectively. The average fault location accuracy of the traditional PG monitoring method and this system is 80.8 and 96.5%, respectively. The intelligent monitoring system of PG fault based on IoT and GIS has high accuracy in PG fault detection and fault location, which can improve the effectiveness of fault monitoring.

Identification of Free Components during Non-Simultaneous Complex Faults in Overhead Lines: A Review

This study concerns the identification and interpretation of current and voltage signals during complex non-simultaneous disturbances in high-voltage overhead lines. It includes topics related to both the search for the optimal model of the system during complex disturbances as well as the analysis of the obtained results. The available EMT-like tools for the analysis of these phenomena are discussed. Models of high voltage overhead transmission lines are presented along with a discussion of their suitability for the study of electromagnetic transients during the analysis of complex non-simultaneous faults. Examples of transient waveforms of currents and voltages during non-simultaneous faults are presented, and the conditions for the occurrence of delayed current zero during short circuits in the system are discussed. The maximum values of the overvoltage factors and the conditions of their occurrence are described. Faults in transmission lines with various voltage levels suspended on the same supporting structures are discussed, together with an indication of the dangerous consequences of unusual intersystem faults. In the final part of the paper, the summary and recommendations for non-simultaneous fault studies are presented.

Research on Non-Contact Voltage Measurement Method Based on Near-End Electric Field Inversion

Aiming at the problems of complex equations, low accuracy, and the strict measurement point layout requirements of the existing electric field integration method, a non-contact measurement method based on the inversion voltage of the near electric field is proposed. Firstly, the field source relationship is clarified, the connection between the spatial electric field and the voltage is derived, and a near-end electric field inversion method is proposed. Secondly, a three-dimensional simulation model of an overhead line is established using COMSOL finite element software, the three-dimensional spatial potential distribution of the overhead line is obtained, and the voltage is inverted and calculated. Finally, an overhead line simulation test platform was built, and MEMS electric field sensors were used for testing and verification. The results show that the maximum error of the three-phase voltage inversion of the proximal electric field measurement is 6.8%, and the error between the voltage obtained by the experimental inversion measurement and the reference voltage is less than 7.2%. The simulation and experimental results also verify the accuracy and feasibility of the inversion voltage of the proximal electric field. The results of this paper can lay a foundation for the practical application of small and miniaturized electric field sensors, and help in the construction and development of smart grids.

The problem of the actual insulation coordination for 500 kV with overvoltage in substations and the needed for more surge arresters in high voltage grid

The new extra high voltage overhead lines and substations have increased the overvoltage phenomenon in the electrical interconnected system, especially in high voltage circuit breakers operate in a failure condition. This research develops a new methodology for transitory analysis, due to limits in the insulation coordination, available in the international standards IEC 60071, however it is not enough, more surge arresters should be required with the new overhead lines caused by overvoltage. The influence by lightning, circuit breaker failure (50BF), grounding system, towers and insulation chains are affected, in three-phase reclosing, maneuvers and transformer energization, finally a new assessment of the performance develops an accurate calculation of the overvoltage. Our findings are in the three-phase reclosing, the maneuvers have introduced overvoltage through the transmission line, higher values ​than 2.3625p.u. However, the insulation coordination is less than 2.32p.u.; compared with the limit of 2.28p.u. Finally, the overvoltage has increased from 160% to 258% according to the distance in the overhead line in 500 kV, with the needed of surge arresters, with the new equipment the overvoltage has decreased from 258% to 100%.

Evaluating Power Sharing Performance of Distributed Generators in Microgrids With Hybrid Sources and Mixed Tie-Lines

Proportional output power sharing amongst distributed sources in islanded microgrids is necessary to maintain a good voltage profile, avoid tripping of sources and avoid circulating current flows. Underground (UG) cables are popular in densely populated areas and military applications. However, researchers typically consider microgrid networks with overhead lines (OHL) in their studies. This paper examines the power sharing performance among droop controlled inverters and virtual synchronous generators in a system with mixed tie-line configurations i.e., network sections with both OHL and UG cable tie-lines. Furthermore, two proposed control strategies to vary the virtual impedance linearly as a function of the DG output currents are examined for their effectiveness to improve the proportional power sharing. The studies are performed considering a system with four inverter based sources operated with the popularly used <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$RL$</tex-math></inline-formula> droop controllers through detailed simulations in MATLAB/Simulink. The enhancement of power sharing is verified for both uniform and non-uniform inverter controls, different R/X ratios of the OHL and UG cables, and in a meshed network configuration with different loading conditions. Controller hardware in the loop (CHIL) based experiment validation is carried out in Typhoon HIL with linear, non-linear and induction motor load, showing that proposed control strategy results in enhanced power sharing in addition to damping oscillations due to dynamic loads.

Assessing the impact of long-term operation, pollution and housing damage on the medium voltage surge arresters using non-destructive diagnostic techniques

Surge arresters installed in substations and overhead lines play a fundamental role in limiting atmospheric and switching overvoltages. In principle, surge arresters help to protect devices against fatal damage by choosing the specified protection level below the equipment withstand voltage. The reliability of surge arresters is still an important topic in many studies. Pollution and damage affect the performance of surge arresters and significantly impact their lifespan. It is necessary to analyze pollution problems and the effect of internal or external damage of surge arresters to find out the possibility of failure. The paper focused on an extensive study of medium voltage surge arresters from different manufacturers in various operation time, surface contamination, and damage types. In this study, we investigated new, used, damaged, and polluted metal-oxide medium voltage surge arresters to determine how these problems affect the performance of the surge arrester and whether the selected parameters exceed the standardized values defined in the standards. Research deals with the volt–ampere characteristic, Fourier analysis, reference voltage, and active losses to analyze the surge arrester’s performance.

MOBILIZE – Aufrechterhaltung der Betriebssicherheit und Absicherung großer Eisenbahnsysteme

AbstractIn this paper we describe the concept and ongoing work of the research project MOBILIZE, which addresses the operational safety and security of large railway systems to prevent sabotage and vandalism. Examples of such acts are manipulation of system components, intentional placement of objects on the tracks, theft of copper cables or damage to property such as graffiti on parked trains. The prevention of personal injuries resulting from crossing tracks or climbing on parked wagons and thereby getting too close to or even touching the overhead lines is also an important aspect. A permanent installation of video surveillance systems for the entire railway infrastructure is not feasible and, what is more, state-of-the-art video surveillance alone is currently not up to the challenges of monitoring very large areas completely. Therefore, MOBILIZE focuses on the development of a reliable portable system with multi-sensor modalities. In case of increased incidents in a specific region, the system can be deployed quickly and easily. The development of such a system raises questions that represent the main scientific challenges to be explored within MOBILIZE: which combination of sensor technologies is the most suitable to reduce false alarm rates to a minimum in practical operation, legal issues such as the changing regulations regarding the usage of drones, usability for the operator, integration into the operational procedures of the railway operators as well as future economic exploitation of the MOBILIZE project. The current paper focuses on the work done on ground-based visual sensors as well as their fusion with other sensors employed within MOBILIZE, and an assessment of their social impact.

Admittance-based modelling of cables and overhead lines by idempotent decomposition

This paper presents a new modelling approach based on idempotent decomposition of the nodal admittance matrix for representation of cables and overhead lines (OHL). By subjecting the idempotent matrices rather than the nodal admittance matrix to rational fitting, the poor observability of the smallest eigenvalues in the lower frequency range is overcome. Unlike the well-known method of characteristics (MoC), this alternative representation yields a so general fully-coupled admittance matrix suitable to tackle scenarios encompassing short and long lengths. Besides retaining the frequency dependence of parameters, the proposed phase-domain model showed to be accurate and suitable to circumvent the requirement of small time-steps.

A Comprehensive Analysis on the Influence of the Adopted Cumulative Peak Current Distribution in the Assessment of Overhead Lines Lightning Performance

Backflashover rate (BFR) is strongly dependent on the cumulative peak current distribution (CCD) adopted in the calculations. An original aspect of the present work is that such dependence is simultaneously assessed in estimating the probability of the critical current being exceeded as well as in the annual number of flashes to the line. An IEEE brochure recommends that the distribution values that characterize the atmospheric characteristic of the region under study as accurately as possible be used. The objective of this article is to evaluate the impact of the use of different CCDs, related to several measurements carried out around the world, in the estimation of the lightning performance of transmission lines (TLs). Structures of 138, 230 and 500 kV were analyzed. In the simulations, representative curves of lightning associated with measurements taken at Monte San Salvatore (MSS), Morro do Cachimbo (MCS) and TLs in Japan (TLJ) were considered. The distributions recommended by the IEEE and by the CIGRE and the distributions of Berger obtained from MSS, MCS and TLJ were considered. The presented results indicate differences of up to 100% between the considered work distributions and the IEEE one for certain values of tower footing impedance.

Fault Location Study of Overhead Line–Cable Lines with Branches

A new fault location method based on the three-terminal travelling wave method is proposed for the fault location problem of multi-branch overhead line–cable transmission lines. Firstly, the process of fault travelling wave propagation in overhead transmission lines and the phenomenon of refraction are analysed, and an improved phase-mode transformation is introduced to decouple the electromagnetic coupling and perform fault phase selection. Secondly, the Pearson correlation coefficient is introduced to compare the similarity of the current travelling waveforms at different measurement points in order to implement fault segmentation. To solve the problems of the complexity of the fault travelling wave propagation process and the difficulty of identifying the travelling wavehead, the Hilbert–Huang transform is used to extract the fault signal characteristics, and the travelling wave arrival moment is accurately calculated by the sampling error correction method to determine the fault location. Finally, the accuracy and stability of the method are verified via a simulation test on the MATLAB/Simulink platform. The results show that the proposed positioning method combining the three-terminal travelling wave method with HHT and sampling error correction can locate the fault location more accurately, and it has good potential for application in the engineering field. It provides a new technical means for fault location in overhead transmission lines, which is expected to become one of the most important technologies in the future power system.

Review of Technological Advances in High Temperature Overhead Line Composite Conductors

ACSR (Aluminium Conductor Steel Reinforced) conductors consisting of pure aluminum wires helically stranded around a core of high strength galvanized steel core wires are widely used in overhead transmission line applications. While the steel wires provides the required strength, the outer aluminium serves as electricity conducting member. The thermal rating or ampacity of conductors is the maximum current that a circuit can carry within the temperature limits as dictated by the allowable conductor sag or by the annealing onset temperature of the conductor, whichever is lower. On a continuous basis, ACSR may be operated at temperatures up to 100°C without any significant change in the conductor’s physical properties. Above 100°C, aluminum wires loses tensile strength over time and becomes "fully annealed" giving rise to increased thermal expansion of the conductor; this causes excessive sagging reducing the clearance between the ground and the energized conductors.&#x0D; While, the electric utilities are posed with increased challenges of production of additional capacities and building new transmission circuits to meet the ever growing demand and the high cost and environmental restrictions of constructing new lines, methods are being explored to increase their capacity with minimum changes in the existing towers. Replacement of the existing conductor with a advanced high temperature composite (HTC) conductors operating upto temperatures of 200°C with reduced sagging characteristics have been attempted and an increase in capacity of 30-80%, can be achieved through application of these composite conductors.&#x0D; The advanced HTC conductors with varied combinations of core material and outer conducting wires are being tried so as to achieve wide ranging properties. In general, HTC conductors features the combinations of either soft aluminum wires with ultra high strength steel or temperature resistant aluminium with or fiber reinforced metal/polymer matrix composites as the core. Both the alumina fiber reinforced temperature resistant aluminium metal matrix composite and the carbon fiber reinforced high temperature polymer resin composite wires as the core material appears to have favorable applications. The comparative performance of the HTC depends on the degree to which both outer aluminum strand and reinforcing core’s physical properties are stable at high temperature and on the elastic, plastic, and thermal elongation of the combined HTC.&#x0D; The summary of various developments realized in the area of composite conductors and their relative merits and demerits have been discussed in detail.

Study of the basic criteria of the pantograph and overhead line interaction in operating conditions

In this work, the basic criteria of the process of the pantograph and overhead line interaction of railway rolling stock are considered. An analysis of the causes and consequences of impaired current collection was also performed. The analysis of existing systems and technical means for determining the qualitative and quantitative indicators of the pantograph and overhead line interaction was carried out and their classification was carried out according to the location, the principle of obtaining information and controlled parameters. Based on the results of research, the main quantitative and qualitative indicators of the interaction of current collectors with the overhead line in the conditions of operation on the railways of Ukraine, which should be subject to control, have been established. Field tests were also conducted to determine such indicators in real operating conditions of railway rolling stock. According to the results of the research, an experimental complex was developed to determine the indicators of the interaction of current receivers of various types of rolling stock with the contact network in operating conditions.

Improving the efficiency of medium voltage (MV) distribution lines using risk matrix for optimized maintenance

Medium Voltage overhead lines within North-West power utility companies in South Africa are confronted by higher volumes of deficiencies leading to frequent power failures. An essential quality of service factor considered in power distribution is the electricity supply to customers free of interruptions. Due to the higher number of electrical power line faults associated with the power system life span, achieving the desired level of reliability becomes an enormous task. The paper shares the findings of a study on performance improvement of MV distribution overhead lines using a risk matrix for deficiency analysis and clearing of such defects. A pilot study was conducted, and the risk matrix strategy developed in the study improved the reliability and key performance indicators by trimming down the overhead power line deficiencies. Defect clearing lowered outage frequency, durations, and power losses. The System Average Interruption Duration Index (SAIDI) was enhanced by lowering the outage duration by 108.64 h annually. The System Average Interruption Frequency Index (SAIFI) improved by reducing the outage frequency by 45.45 sustained occurrences annually and Reticulation Supply Loss Index (RSLI) by 8.31 MVA monthly.

A protocol for selecting viable transmission line arrester for optimal lightning protection

Direct lightning strikes on overhead lines and towers causes power system outages. Optimal surge arrester placement is a practical and economical protection technique. From research trends, three types of transmission line arresters are in practice: Non-Gapped Line Arrester (NGLA), Externally Gapped Line Arrester (EGLA) and Multi Chamber Insulator Arrester (MCIA). This study proposed a simplified guide for selecting the most suitable line arrester considering the placement configurations, double circuit outage prevention and energy capabilities. Electromagnetic Transient Program was implemented to analyze back flashover performance of a typical 275 kV double circuit transmission line in Malaysia. Critical flashover parameters considered are lightning current magnitude, tower footing resistance, and power frequency angle. Analyzed results from the three arresters found that installing four arresters, two per circuit, at the lower and upper phases respectively, is the most optimal and universal double outage mitigation technique. Energy comparison reveals that MCIA discharges 54% and 44% less energy than NGLA and EGLA respectively. Also, from 132 kV system results, MCIA discharges 74% and 22% lesser energy respectively. From further validation of the simulation model, NGLA discharged 23.8% more energy than EGLA from experimental results. The proposed guide is applicable to double circuit lines below 275 kV.

A multiport hybrid DC circuit breaker with high economic efficiency and adaptive reclosing capability

In a high voltage direct current (HVDC) grid, hybrid DC circuit breakers (HCBs) are one of the effective solutions to interrupt fault currents. The conventional two-port HCB features high economic costs since the expensive insulated gate bipolar transistors (IGBTs) are needed. Each line in the multiterminal HVDC grid must be equipped with the HCB, which is extremely costly to implement. In addition, the likelihood of temporary faults is considerably raised by the fact that the HVDC grid transfers power across overhead lines (OHLs). By reclosing operations after temporary faults, the HVDC grid can resume normal operation. However, it is vital to discern between temporary faults and permanent faults before reclosing operation to prevent secondary shocks to the HVDC grid caused by blindly reclosing on permanent faults. For the problems of high cost and blind reclosing of HCBs, this article proposes a multiport HCB (MHCB) with high economy and adaptive reclosing capability. All ports of the MHCB share a single main breaker (MB) for fault isolation. The MHCB utilizes the capacitor voltage to lower the operating voltage of the metal oxide varistor (MOV), which reduces the number of IGBTs connected together at both ends of the MOV. With the above design, the expense of the MHCB is significantly decreased. Additionally, the MHCB achieves adaptive reclosing by using the difference of current amplitudes in the capacitor branch under permanent and temporary faults.

Fault location for overhead and cable hybrid DC line based on the energy transmission characteristics

Fault location for overhead and cable hybrid DC line based on the energy transmission characteristics

Fault Section Identification of Hybrid Transmission Lines by the Transients in Modal Domain Free From the Refractions and Reflections at Cross-Bonded Nodes

Compared with the homogeneous transmission lines, the hybrid ones are composed of the overhead, underground and submarine cable lines, resulting in three different sets of parameters over the transmission path and posing great challenge to fault location. This paper proposes a fault section identification method for two types of the hybrid lines based on modal-domain analysis which eliminates the effects of the refractions and reflections at the cross-bonded nodes. First, a method for decoupling the transients in the high-voltage cable is proposed to obtain the unified model of two types of the hybrid lines in modal domain. Then, the concept of the energy of the decoupled transient is defined, the reflection and refraction features of the energy of the transient signal are analyzed, and a novel fault section identification method is developed based on the transient energy ratio. Finally, the model of a 110kV hybrid transmission line is established in PSCAD/EMTDC. Various fault experiments are conducted. The results show the effectiveness of the proposed method.