High Voltage AC Transmission Line Research Articles

Analysis of gap distance of ultra high voltage AC transmission lines in areas with altitude above 2000m

Abstract Research on long-wave front discharge characteristics of lines and long gaps of substation equipment in high-altitude areas needs to be conducted in a systematic manner immediately in order to guarantee the safety and economy of high-altitude UHV lines with respect to external insulation. However, at present, the gap discharge test of transmission lines is mainly carried out in areas below 2000m above sea level. The actual test is challenging to conduct in the high altitude region, and the test data is incomplete. To further confirm the validity of extrapolation of existing altitude test data to high altitude areas, this paper conducts theoretical analysis based on the real test data under standard meteorological conditions provided by GB/T 24842 standard. The altitude correction methods in IEC 60071-2: 2018 and IEC 60060-1: 2010, the m-coefficient method and g-parameter method, are used to correct the lightning impulse, power frequency, and standard switching impulse of AC transmission line gaps. The discharge voltage in areas below 5000m above 2000m is obtained, and several significant discharge characteristic parameters are obtained. Based on the 50% discharge voltage requirements of various voltage types of 1000kV transmission lines, combined with the discharge voltage curves at multiple altitudes, the minimum air gap distance of transmission lines at the altitude of 2000m-5000m is obtained. The comparative analysis of the correction results of the two methods provides a way of thinking for the next step to carry out the true test of UHV AC transmission line gap discharge in higher elevation regions.

Research on Induced Electrical Characteristics of Agricultural Machinery Operating under Ultra High Voltage AC Transmission Lines in Agricultural Area

Research on Induced Electrical Characteristics of Agricultural Machinery Operating under Ultra High Voltage AC Transmission Lines in Agricultural Area

New Cascaded 1+PII2D/FOPID Load Frequency Controller for Modern Power Grids including Superconducting Magnetic Energy Storage and Renewable Energy

Having continuous decrease in inertia and being sensitive to load/generation variation are considered crucial challenging problems for modern power grids. The main cause of these problems is the increased penetration capacities of renewables. An unbalanced load with generation power largely affects grids’ frequency and voltage profiles. Load frequency control (LFC) mechanisms are extensively presented to solve these problems. In the literature, LFC methods are still lacking in dealing with system uncertainty, parameter variation, structure changes, and/or disturbance rejection. Therefore, this paper proposes an improved LFC methodology using the hybrid one plus proportional integral double-integral derivative (1+PII2D) cascaded with fractional order proportional-integral-derivative (FOPID), namely, the proposed 1+PII2D/FOPID controller. The contribution of superconducting magnetic energy storage devices (SMES) is considered in the proposed design, also considering hybrid high-voltage DC and AC transmission lines (hybrid HVDC/HVAC). An optimized design of proposed 1+PII2D/FOPID controller is proposed using a new application of the recently presented powerful artificial rabbits optimizers (ARO) algorithm. Various performance comparisons, system changes, parameter uncertainties, and load/generation profiles and changes are considered in the proposed case study. The results proved superior regulation of frequency using proposed 1+PII2D/FOPID control and the ARO optimum parameters.

Calculation and test analysis for power frequency electromagnetic field of transmission line crossing agricultural greenhouse area

To assess the electromagnetic environment (EME) of high-voltage AC transmission lines (TLs) across agricultural greenhouses (AGs), a program that can calculate the power frequency electromagnetic field (PFEMF) under various AC TLs is compiled based on the principle of the simulated charge method and the simulated current method, and the power frequency electric field (PFEF) and magnetic field (MF) strength of AGs are calculated and compared with the field measurement results. The results show that the field measurement values of PFEF intensity and magnetic induction intensity in AGs do not exceed the standard requirements of 10kV/m and 0.1mT. The existence of AGs has a certain influence on the electric field (EF) distribution, but has little influence on the power frequency magnetic field (PFMF). For the PFEF and PFMF in AGs, the numerical calculation results are basically consistent with the field measurement results. The above results provide a reference for the EME assessment of high-voltage AC TLs across AGs.

Analysis of the Behavior of a HV AC Line during an Atmospheric Discharge and Evaluation of the Spatio-Temporal Distribution of the Lightning Current Wave

In high voltage networks for the transport of electrical energy, lightning, a phenomenon as dangerous as it is impressive, with an easily recognizable form, can affect a power line by striking either a phase conductor, a tower or a guard cable, thus causing more dangerous and constraining stresses on the lines for its proper operation. Thus, this article aims to analyze the behavior of a HV line during an atmospheric discharge and assess the spatial and temporal distribution of the lightning current wave. For this purpose, the generalities on the transmissible power in case of link without resistance and the modeling of the atmospheric surge propagation established on the basis of the theory of the lines with distributed constants implementing the wave equation known as the Alembert equation have been developed. Through this research, we are interested in the study of the space-time distribution of the lightning current wave in order to model the radiated electromagnetic field and to examine the influence of the atmospheric discharge induced overvoltage on the transportable power of a High Voltage AC Transmission line, for a good selective protection in order to illuminate the parasites. The 2D simulation based on engineering and “Transmission Line” models have been developed as well as the verification of the coherence of the different models, by comparing the fractal dimensions of the program results with those of the experimentally obtained figures.

Start-Up and Saturation Optimization of High-Power Energy Harvester With Compound Topologies Overhead AC Transmission Line

With the continuous development of power automation and smart grids, online monitoring equipment has been utilized more widely for inspection of the state of high-voltage ac transmission lines. To ensure the stable and effective work of the monitoring device, the problem of power supply needs to be solved urgently. Although the inductive energy harvester penetrated through line has been extensively researched, the practical process has been greatly hindered caused by the core materials, which cannot simultaneously combine two advantages of both high permeability and high saturation. Based on the inherent contradiction of the inductive energy harvester, the structure of compound cores with different intrinsic properties is adopted. In addition, three optimization topologies for the structure are proposed. Theoretical analysis and experimental results show that the proposed structures and topologies have certain advantages over the conventional structure in terms of effective start-up sensitivity, saturation performance, and gained power. The proposed energy harvesters also broaden the effective working range by enduring the primary current fluctuation. The simulation and experimental results verify the correctness of the theoretical analysis and the validity of the topologies.

Study on Calculation and Mitigation Measurements of Power Frequency Electric Field Strength of Residential Buildings Near High Voltage AC Transmission Lines

In this paper, based on the charge simulation method, the distorted electric field of a 500kV transmission line adjacent to the residential building is simulated and compared with the field test results. The calculated value is close to the measured value, which indicates that the distorted power frequency electric field calculation based on the charge simulation method has engineering application accuracy. Furthermore, the requirements of the height of the 500kV transmission line and the minimum horizontal distance of the adjacent residential buildings are determined by the charge simulation method. Two feasible power frequency electric field mitigation measures are proposed for the design of the transmission line.

A New Magnetic-Linked Converter for Grid Integration of Offshore Wind Turbines Through MVDC Transmission

A medium-voltage ac network is commonly used to interconnect wind turbines to the offshore substation, which can create significant power losses, as the distance between wind turbine and offshore substation can vary from 5 to 9 km. The copper-conductor-based high-voltage dc (HVDC) or high-voltage ac (HVAC) transmission lines are generally used to transmit the electrical power from the offshore substations to the onshore grids. With the recent advancement of the high-temperature superconducting (HTS) cables, it is now possible to replace the traditional HVAC/HVDC transmission lines with a medium-voltage dc (MVDC) cables. A new MVDC converter is proposed in this paper to convert the generator low ac output voltage to MVDC directly. The proposed new technology not only eliminates the requirement of low-frequency heavy and large step-up transformers and line filters, but can also eliminate the voltage conversion stages to allow the entire power transmission networks to use MVDC HTS cables. A compact, lightweight, and efficient high-frequency common magnetic link is used in the proposed converter. The magnetic link can inherently solve the isolation problem. In this paper, a scale-down prototype converter is developed in the laboratory to validate the feasibility of the proposed MVDC converter.

Simulation study on transient electric shock characteristics of human body under high voltage ac transmission lines

Human body under high-voltage AC transmission lines will produce a certain induced voltage due to the electrostatic induction. When the human body contacts with some grounded objects, the charges transfer from the body to the ground and produce contact current which may cause transient electric shock. Using CDEGS and ATP/EMTP, the paper proposes a method for quantitatively calculating the transient electric shock characteristics. It calculates the human body voltage, discharge current and discharge energy under certain 500kV compact-type transmission lines and predicts the corresponding human feelings. The results show that the average root value of discharge current is less than 10mA when the human body is under the 500kV compact-type transmission lines and the human body is overall safe if the transmission lines satisfy the relevant design specifications. It concludes that the electric field strength above the ground should be limited to 4kV/m through the residential area for the purpose of reducing the electromagnetic impact.

Research on Safety Protection for Live Working on 1000kV AC Transmission Line with AC and DC Multi-circuit Transmission Lines

In recent years, in order to save line corridors and reduce the scope of demolition, some new transmission modes for high voltage AC and DC power transmission line are proposed. According to the characteristics of the parallel transmission line, this paper studies the distribution characteristics of the electric field intensity of multi circuit parallel transmission lines and the single circuit transmission line. Comparing and analysing the simulation results of the electric field strength, the safety measures for live working of 1000kV AC transmission line with multi circuit parallel transmission lines is put forward. That is the electric field protective equipment and measures used in the live line work of the 1000kV UHV AC single circuit line can meet the requirements of the live operation of the 1000kV UHV AC double circuit line.

Research on safety protection for live working on ±800kV DC transmission line with AC and DC multi-circuit transmission lines

In recent years, in order to save line corridors and reduce the scope of demolition, some new transmission modes for high voltage AC and DC power transmission line are proposed. According to the characteristics of the parallel transmission line, this paper studies the distribution characteristics of the electric field intensity of multi circuit parallel transmission lines and the single circuit transmission line. Comparing and analysing the simulation results of the electric field strength, the safety measures for live working of ±800kV DC transmission line with multi circuit parallel transmission lines is put forward. That is the electric field protective equipment and measures used in the live line work of the ±800kV UHDC single circuit line can meet the requirements of the live operation of the ±800kV UHDC multi-circuit transmission line.

Application Analysis of Expanded Conductor in 1000kV UHV Double-Circuit Line

This paper discusses the feasibility and effectiveness of the application of expanded conduct in 1000kVultra high voltage AC (UHVAC) transmission line. Through the comparison and analysis between expanded conduct and conventional conduct in transmission capacity, mechanical properties, project investment, annual cost and other aspects, it shows that the initial investment of expanded conduct is 4% lower than that of conventional conduct; and the annual cost of expended conductor is superior to that of conventional conduct when transmission capacity, power price and use hours are low.

Simplification Study of FE Model for 1000kV AC Transmission Line Insulator String Voltage and Grading Ring Surface Electric Field Distribution Calculation

The finite element model of the 1000kV Ultra High Voltage (UHV) AC transmission line porcelain insulator string voltage distribution and grading ring surface electric field distribution calculation has the characteristics of large size, complicated structure and various mediums. To insure the accuracy, related influencing factors should be considered to simplify the model reasonably for improving computational efficiency. A whole model and a simplified 3D finite element model of UHV AC transmission line porcelain insulator string were built. The influencing factors including tower, phase conductors, hardware fittings, yoke plate and phase interaction were considered in the analysis. And finally, the rationality of the simplified model was validated. The results comparison show that building a simplified model of three-phase bundled conductors within a certain length, simplifying the tower reasonably, omitting the hardware fittings and yoke plate and containing only single-phase insulator string model is feasible. The simplified model could replace the whole model to analyze the voltage distribution along the porcelain insulator string and the electric field distribution on the grading ring surface, and it can reduce the calculation scale, improve optimization efficiency of insulators string and grading ring parameters. DOI : http://dx.doi.org/10.11591/telkomnika.v12i2.3833

Analysis of Different 500kV HVAC Transmission Lines Lightning Shielding

The lightning shielding of different 500 kV HVAC-TL high voltage AC transmission lines was analyzed. The studied transmission lines were horizontal flat single circuit and double circuit transmission lines. The lightning attractive areas were drawn around power conductors and shielding wires. To draw the attractive areas of the high voltage transmission lines, transmission line power conductors, shielding wires and lightning leader were modeled. Different parameters were considered such as lightningslope, ground slope and wind on lightning attractive areas. From the calculated results, the power conductors voltages affected on attractive areas around power conductors and shielding wires. For negative lightning leader, the attractive area around the transmission line power conductor increased around power conductors stressed by positives voltage and decreased around power conductors stressed by negative voltage. In spite of this, the attractivearea of the transmission line shielding wire increasedaround the shielding wire above the power conductor stressed by the positive voltage and decreased around the shielding wire above the power conductor stressed by negative voltage. The attractive areas around power conductors and shielding wires were affected by the surrounding conditions, such as lightning leader slope, ground slope. The AC voltage of the transmission lines made the shielding areas changing with time.

Operation and Control of a DC-Grid Offshore Wind Farm Under DC Transmission System Faults

So far, all existing offshore wind farms have an ac collection system, and the collected power in the offshore wind farm is sent to an onshore ac grid through high-voltage ac (HVAC) or DC (HVDC) transmission lines. However, future offshore wind farms may use dc also for power collection. Consequently, the protection and control strategies of dc systems need to be established. This paper studies a dc-grid offshore wind farm, where the wind power collection system and power transmission system adopt dc technology. In this paper, the redundancy of the HVDC transmission system under faults is studied, and a fault ridethrough strategy for the dc-grid offshore wind farm is proposed. The proposed strategy can effectively minimize the impacts of the power transmission system disturbance on the offshore wind farm, and on the ac grid. A dc-grid offshore wind farm example is simulated with PSCAD/EMTDC, and the results validate the feasibility of the presented redundancy configuration and operation approach, and the fault ridethrough control strategy.

High-voltage DC-feeder solution for electric railways

For AC railway power supply systems with a different frequency than the public grid, high-voltage AC transmission lines are common, connected to the catenary by transformers. This study suggests an alternative design based on an high-voltage DC (HVDC)-feeder, which is connected to the catenary by converters. Such an HVDC line would also be appropriate for DC-fed railways and AC-fed railways working at a public-grid frequency. The converter stations between the public grid and the HVDC-feeder can be sparsely distributed, not denser than on 100 km distances, whereas the converters connecting the HVDC-feeder to the catenary are distributed denser. Their ratings can be lower than present-day substation transformers or converters, since the power flows can be fully controlled. Despite a relatively low-power rating, the proposed converters can be highly efficient because of the use of medium frequency technology. The proposed feeding system results in lower material usage, lower losses and higher controllability compared with the present solutions. Simulations of the proposed solution show clear advantages regarding transmission losses and voltages compared with conventional systems, especially for cases with weak feeding, and when there are substantial amounts of regeneration from the trains.

An Investigation into Magnetic Field Management under Power Transmission Lines using Delta Configurations

The increase of power demand has increased the need for transmitting huge amount of power over long dis- tances. Large transmission lines configurations with high voltage and current levels generate large values of electric and magnetic fields stresses which affect the humanbeing and the nearby objects located at ground surfaces. This has in turn prompted increased activity in the documentation of calculation techniques to accurately predict field strengths in isolated conducting bodies coupled to lines of all voltages and design configurations. Overhead transmission systems required strips of land to be designed as right-of-ways (R.O.W.). These strips of land are usually evaluated according to some aspects; the most important one is the operating effects of the energized line includ- ing magnetic and electric field effects. Therefore determination of the maximum value of the magnetic and electric field stress at ground surface is very necessary and important. It is always required to minimize the amount of land set for high voltage (or current) transmission facilities. This can be achieved by the reduction of the field stress at ground level which is also considered as the most object of efforts to minimize the field effects of such high voltage AC transmission lines. This paper investigates the effects of the transmission line towers configurations, on the mitigation of the induced mag- netic fields, around and near the transmission lines, of the 500 kV systems. The magnetic fields of the conventional 500 kV normal horizontal (flat) power transmission line configuration are compared with that of the normal delta, inverted delta, compact normal delta and compact inverted delta configurations, and in turn its effects on the right of way (R.O.W) distance around the transmission line. The obtained results show that, for compact normal delta, and full compact inverted delta configurations, the resultant magnetic fields produced are lower than that produced from the conventional flat line configuration.

Superconducting fault current limiter with fast vacuum commutation modulus

A new approach to a problem of creation of a resistive version of superconducting fault current limiters (FCL) on the basis of HTS materials has been considered. According to this approach, a scheme of FCL is added by a commutation modulus which contains a fast vacuum interrupter. This interrupter allows one to switch off the transport current as soon as 5 ms after transition of the HTS element to the normal state. The proposed scheme allows one to restrict more than an order in value a necessary operation time of FCL in a regime of a current limitation. As a result, a time of recovering the superconducting state can be significantly reduced that allows FCL to operate in automatic iterative regime. The considering device can operate not only in high voltage ac transmission lines but also in dc electrical networks. A numerical simulation of transit processes in a proposed scheme of FCL has been performed for different regimes and its features are analyzed with respect to other schemes of FCL. An experimental study of test mock-up commutation elements of FCL has been performed. This study demonstrates an efficiency of the proposed scheme. A test of a FCL model with the limiting current up to 15 kA has been realized.

Flashover Performance of Pre-contaminated and Ice-covered Composite Insulators to be Used in 1000 kV UHV AC Transmission Lines

A method is introduced for testing insulators under icing conditions. The method is based on and developed from those described in the standard of IEC60-1, IEC 60507 and IEEE Task Force on Insulator Icing Test Methods, which give instructions to test insulators under pollution. Then, the paper explores the effects of various factors, including ice thickness, pollution severity on the surface of insulators before ice accretion, atmospheric pressure, and shed profiles, on the flashover performance of short samples of two different types of silicone rubber (SIR) composite long rod insulators intended for ultra high voltage (UHV) ac transmission lines. The experiments were carried out in the multi-function artificial climate chamber in the High Voltage and Insulation Technological Laboratory of Chongqing University, China. The experimental results reveal the regularity of the effects of ice thickness, pollution severity and atmospheric pressure on the average flashover voltage of two types of composite insulators. Those can provide reference for the outdoor insulation design for UHV ac transmission lines.

A New Environmentally Friendly Design Program, TLCALC 2001 for High Voltage AC Transmission Lines

Various noises produced by corona discharges from high voltage transmission lines are the important considerations in line design. HVAC transmission lines must be designed to satisfy national environmental regulations too. Therefore, it is necessary for line designers to pre-evaluate environmental problems using prediction tools. In this paper, an environmental design software, TLCALC 2001 for AC transmission lines as a comprehensive window program is introduced. It has 6 modules including audible noise, radio noise, television noise, magnetic field, electric field and conductor surface gradient module. TLCALC 2001 has solved some of the problems of the existing foreign tools and has several advantages over those. 1) It is a common tool that has solved calculating limitations of foreign formulas. 2) It has a wide application range and enhanced prediction accuracy. 3) It can be applied to almost all transmission line configurations in Korea. 4) Experienced designers can get calculation results within about 15 minutes. As the use of TLCALC 2001 is easy and practical, it will be applied to the environmentally friendly design and construction of transmission lines. It is expected that public complaints and social environmental costs will be considerably reduced by the use of TLCALC 2001 in the future.