Ultra-high Voltage Power Transmission Research Articles

Simulation of breakdown voltage associated with phase-to-phase air gap for ultra high voltage transmission lines under switching impulse voltage

Abstract Knowledge of the breakdown voltage of air gaps when subjected to positive switching impulse voltage is fundamental to the design of insulation coordination for power transmission systems. However, the length of phase-to-phase air gaps in ultra-high voltage power transmission lines has reached more than 30 m. It is very difficult, costly, and impossible to conduct full-scale test experiments to obtain the breakdown voltage of these gaps. Here, the numerical simulation method based on the self-consistent leader inception and propagation model was first used to simulate the air gap discharge process at four different scales and to obtain the gap breakdown voltage. The simulated data was compared with the measured data to verify the validity of the model. Then, the numerical simulation method was used to simulate the discharge process of phase-to-phase air gap for ultra-high voltage transmission lines with 30.3 m in length. The current and the development trajectory of the leader tip were obtained for the discharge process. More importantly, the breakdown voltage, which could not be obtained by full-scale testing, was obtained by simulation.

Discharge characterization and altitude correction of shielding sphere-plate gap at an altitude of 3400 m

Southeast Tibet in China is rich in clean energy such as water energy, light energy, and wind energy. As the key means of large-scale clean energy transmission in southeast Tibet, the ultra-high voltage (UHV) power transmission projects will be constructed at an altitude of nearly 4000 m. To accurately acquire the external insulation strength of electrical equipment operating at different altitudes, the standard positive switching impulse voltages were applied to a rod electrode and a 1.1 m diameter shielding sphere at the altitude of 3400, 2100, and 80 m. The switching impulse discharge characterization and altitude correction factors of the 1.1 m diameter shielding sphere-plate gap under different clearances at different altitudes were obtained. The discharge voltage of the rod-plate gap at the altitude of 80 m was corrected to the altitude of 3400 m using altitude correction methods recommended by GB 311.1, GB/T 16927.1, and DL/T 2305. Further comparison was made between the calculation results using the three altitude correction methods mentioned above and the test results at an altitude of 3400 m. The discharge characterization and the minimum clearance of the end fittings of the electrical equipment in the valve hall at the altitude of 3800 and 4500 m were obtained by fitting and extrapolating the test data. The research results provide important reference significance for the external insulation configuration of UHV converter stations constructed in areas with an altitude of 3000 m and above.

A CASE STUDY OF ELECTROMAGNETIC EXPOSURE FOR HIGH TENSION POWER LINES AND TRANSFORMER WITH AND WITHOUT BASE STATION ANTENNA

With the fast growth of electric activity and the spreading out of town scale, our lives are approached by extremely high voltage power transmission lines. And with the expansion of ultra-high voltage power transmission line, the ultra-high voltage transformer substation will come out in the place with intense inhabitants and the electromagnetic exposure of this transmission and transformer apparatus and its contamination to the inhabitants stimulate the immense anxiety from the civilization. This paper deals with electromagnetic radiation of extremely high voltage power transmission line. Here we have observed the electric and magnetic field beneath the transmission line by the process of equivalent charges and put forward the anticipation rule to the electromagnetic radiation in the engineering of extremely high voltage power dissemination and remodeling. Recognition the safe distance from the EMF produced from the high-tension overhead power lines in the locality of the precise region is the detailed goal of this study. The high-tension transmission lines generated EMF that bounded the projected site has to be underneath 0.2 µT. The safety approval distance has been allotted as 200 m from the active 300-KV high-tension power line.

Experimental Evaluation of 3D Tortuosity of Long Laboratory Spark Trajectory for Sphere-Sphere and Sphere-Plane Discharges under Lightning and Switching Impulse Voltages

Evaluation of attractive areas of high- and ultra-high voltage power transmission lines to direct lightning strokes is based on modeling of propagating progress of the lightning leader approaching the transmission line. The aim of the modeling is to determine the effectiveness of lightning protection for a given line design. The statistical models are currently being developed to extend the conventional deterministic models by embracing the randomness of the discharge channel in space and hence to reproduce the statistical distribution of the striking points. These models require experimental data for understanding of the lightning leader development process and to validate the model across the measurement data. This paper reports on the measured trajectories of discharge channels of long laboratory sparks in various high voltage laboratory arrangements. The sparks were initiated by switching and lightning impulses with peak values ranging from 1200 kV to 3364 kV of positive and negative polarity for two types of high-voltage electrode systems (sphere-sphere and sphere-plane), arranged at distances of 3.3 m and 5.5 m from each other. Statistical distributions of angles describing trajectory of discharge channels in space are reported for a total number of 540 recorded discharges. The results can serve as reference measurement data to develop and evaluate the accuracy of simulation models incorporating statistical nature of the lightning leader development process.

Research on Electromagnetic Field, Eddy Current Loss and Heat Transfer in the End Region of Synchronous Condenser with Different End Structures and Material Properties

Aiming at the problem of end structure heating caused by the excessive eddy current loss of large synchronous condensers used in ultra-high voltage (UHV) power transmission, combined with the actual operation characteristics of the synchronous condenser, a three-dimensional transient electromagnetic field physical model is established, and three schemes for adjusting the end structure of the condenser under rated condition are researched. The original structure has a copper shield and a steel clamping plate. Scheme 1 has no copper shield but has a steel clamping plate. Scheme 2 has no copper shield but has an aluminum clamping plate. By constructing a three-dimensional fluid–solid coupling heat transfer model in the end of the synchronous condenser, and giving the basic assumptions and boundary conditions, the eddy current loss of the structure calculated by the three schemes is applied to the end region of the synchronous condenser as the heat source, and the velocity distribution of the cooling medium and the temperature distribution of each structure under the three different schemes are obtained. In order to verify the rationality of the numerical analysis model and the effectiveness of the calculation method, the temperature of the inner edge of the copper shield in the end of the synchronous condenser is measured, and the temperature calculation results are consistent with the temperature measurement results, which provides a theoretical basis for the electromagnetic design, structural optimization, ventilation and cooling of the synchronous condenser.

What is driving the remarkable decline of wind and solar power curtailment in China? Evidence from China and four typical provinces

The world’s key renewable power markets are generally challenged by wind and solar power curtailment. Research on the influencing factors of curtailment improvement can provide a reference for the further penetration of renewable energy (RE) into the power system. Based on the logarithmic mean Divisia index (LMDI) method, this paper analyzes the factors influencing the wind and solar power consumption rate in China from 2015 to 2018, and four typical provinces are discussed in detail. By decomposing the consumption rate into six factors (transmission structure, generation proportion, power self-sufficiency, resource development, resource utilization, and power consumption), and focusing on the transmission structure factors, this paper further clarifies the contributions of local use, ultra-high-voltage (UHV) transmission, and conventional transmission to the improvement of curtailment. The results reveal the following. (1) At the national level, the power mixing effect and the resource development effect have played major roles in the change of the consumption rate, but the influences of these two effects have been decreasing. (2) The UHV power lines provide a robust resource for the inter-provincial deployment of renewable power (such as the RE power transfer in Inner Mongolia and Gansu), but the role of UHV transmission has not yet been fully utilized. (3) The impact of the electricity consumption effect on renewable power consumption is increasing year by year, but the local consumption capacity remains insufficient (both at the national level and in the four typical provinces analyzed), so it is necessary to further increase the share of renewable electricity in UHV power transmission and the local consumption capacity. (4) The expanding development of wind and solar power may be the reason for the curtailment in Shaanxi, and a reasonable renewable power development plan must be further formulated.

Analysis on Electromagnetic Environment from 750 kV Transformer Substation in Gansu Power Network

In order to understand the influence of 750 kV power transmission and transformation project on electromagnetic radiation of surrounding environment, the data of electric field intensity, magnetic field intensity and noise from 750 kV substation equipment transmission and transformation system in some areas of Gansu Province were monitored and analyzed. The results showed that the areas near circuit breaker, switch and reactance in the power transmission system were the main areas producing high electric field intensity. The electric field intensity near the circuit breaker is the highest in substation equipment, with the average value of 12.40 ± 1.25 kV/m, while the main noise producing area is near the reactor. The study could provide scientific basis for environmental assessment and prevention of ultrahigh voltage power transmission projects.

Research status of the external insulation pollution flashover of high voltage transmission line

In recent years, China’s electric power industry has made great progress, especially the achievements of ultra high voltage and ultra high voltage power transmission and transformation technology have attracted worldwide attention. At present, China has put into operation power transmission projects such as ±660kV yin-East DC extra-high voltage, ±800kV upward, Yunnan-Guangzhou DC extra-high voltage and 1000kV Dongnan Jindong-Jingmen AC extra-high voltage. These long-distance and large-capacity power transmission projects provide strong technical support for the realization of the national strategic goal of “west power transmission to the east and North power transmission to the south”.With the rapid industrialization and environmental deterioration, various industrial and natural pollutions deposited on the insulators of high-voltage transmission lines are becoming increasingly serious. In severe weather, such as fog, dew, drizzle and snowmelt, the external insulation strength will be greatly reduced. Therefore, it is very important and necessary to thoroughly study the pollution flasking of uHV and UHV insulators and comprehensively consider the influence of China’s complex geographical environment on their external insulation characteristics, which is one of the key issues related to the safe and stable operation of power grid.

B2O3- and Y2O3-doped ZnO varistor ceramics: Enhanced voltage gradient and nonlinear properties for UHV

In this paper, the effects of boron and yttrium co-doping on the electrical properties of ZnO varistors were determined. The presence of both B3+ and Y3+ co-dopant improved the electrical performance of varistor ceramics. The nonlinearity coefficient α and potential barrier ϕb were increased noticeably. The nonlinearity coefficient α was 73 and ϕb was 2.75 eV, at the same time, a voltage gradient of 425 V/mm and leakage current of 0.9 μA/cm2 were obtained. This work provided a way to enhance the protective effects of ZnO varistor arresters for ultra-high voltage power transmission systems.

Can ultra-high voltage power transmission bring environmental and health benefits? An assessment in China

Long-distance power transmission is a very important way of energy utilization, which can achieve regional environmental benefits through the transfer of air pollutants. But, how to evaluate such benefits has not been well presented. This study uses a generalized approach to assess the environmental and health benefits of power transmission based on the GAINS model. The impact pathway approach is adopted to evaluate the health losses in the electric power industry. The epidemiological relative risk is calculated by integrated exposure-response function. An inter-regional health loss impact matrix is constructed to reflect indirect effects due to the regional diffusion of air pollution. Using the case of China, this study evaluates whether the current ultra-high voltage (UHV) power transmission lines can bring environmental and health benefits, and discusses in which provinces the establishment of electricity interconnection can bring more benefits. The results highlight the importance of considering air quality, pollutant diffusion, and health losses in environmental benefit assessment, which is significantly different from the results obtained by using air pollutant emissions alone. Most UHV direct current lines can bring high environmental and health benefits, but the performances of UHV alternating current lines are relatively poor. The power transmission from Northwest China, Southwest China, and Inner Mongolia to Central China can bring relatively large environmental and health benefits, which may become a direction for future long-distance power transmission planning.

System operational dispatching and scheduling strategy for hybrid cascaded multi-terminal HVDC

A hybrid cascaded Multi-terminal HVDC (MTDC) system involving both series and parallel-connected converters, which combines the advantages of line commutated converter based (LCC) and voltage source converter based (VSC) HVDC for ultra-high voltage, large-capacity and flexible power transmission, is proposed and is to be implemented in a real project in China. Due to complexity of operational control and difficulty of operational scheduling brought by the hybrid cascaded MTDC system and the lack of prior related research works, this paper establishes the mathematical model of the hybrid cascaded MTDC system and then proposes a system operational dispatching and scheduling strategy, which includes: 1) feasible coordinated operational control strategies investigation; 2) security operating range of the whole hybrid cascaded MTDC system analysis; 3) operating points of the hybrid cascaded MTDC system calculation. Simulations results based on PSCAD/EMTDC are used to validate the proposed system operational dispatching and scheduling strategy.

The Role of Electric Power Sector in China’s Global Economic Expansion

The article discusses some of the major characteristics and trends of China’s economic expansion in the global power industry. It argues that by investing in electricity infrastructure China creates prerequisites for long-term dominance in one of the key sectors in a number of countries and regions. Deals in the power sector are mainly implemented by state-owned companies and facilitated by state-owned financial institutions. In terms of structure and geography, foreign investment in the electricity sector is dominated by traditional types of generation in developing countries. However, China has been diversifying into renewables, nuclear power and grids and entering markets of the developed countries. The creation of a special international organization (GEIDCO) should facilitate its expansion in the electricity sector abroad. It is worth noting that foreign economic expansion plays an important role in supporting China’s slowing economy amid the transformation of its growth model. It allows China to adopt advanced technologies and best management practices in developed countries while forming alternative value chains, as well as promoting its own equipment and standards (especially in ultra-high voltage power transmission) in the developing countries. However, given the impact of the trade war, increasing securitization of the Chinese foreign investments, Chinese authorities’ control over capital outflows and the rising environmental concerns in developing countries, further expansion of the Chinese capital in the global electricity industry is likely to be held back, while competition from non-Chinese electricity companies is likely to grow.

Multi-regional power generation expansion planning with air pollutants emission constraints

Air pollution has become a severe problem in the world. The power sector accounts for a large percentage of air pollutants emissions and has large emission reduction potential due to its centralized emissions. In order to find a cost-effective development pathway for the power sector to realize emission reduction, a multi-regional power generation expansion planning model is proposed in this paper and China is used for a case study. The model integrates air pollutants emission constraints, multi-regional interconnected power system and hourly power scheduling. Detailed regional characteristics and Ultra-High-Voltage (UHV) power transmission lines among regions in China are included whilst the power scheduling process is incorporated on an hourly basis. The scenario analysis shows that existing actions including the planned long-distance UHV power transmission lines and the corresponding coal plants groups in resource-rich regions would significantly help to reduce emissions in load-centered regions and realize the national emission reduction target. However, building coal plants groups in resource-rich regions for power exports turns out to be pollution transfer and cause their emissions to exceed local environmental carrying capacity. Regional power generation expansion planning incorporating regional environmental carrying capacity constraints presents a solution to this problem of unbalanced regional emission reduction. The result shows that substituting 68.4 GW of planned coal plants with renewable energy power plants in resource-rich regions for power exports could control the emissions in all regions to lower than local environmental carrying capacity.

Research and application of electroscope identification for UHV transmission and transformation equipment based on electrochromic materials

At present, due to the relatively large insulation gap of UHV(Ultra High Voltage) equipment, the traditional hand-held capacitive electroscope is difficult to operate; the non-contact electroscope is mainly based on the principle of electromagnetic induction, and the reliability is poor in complex areas such as substations and other electromagnetic environments. The power verification problem of AC/DC UHV transmission and transformation equipment has not been effectively solved. In order to optimize and solve the above problems, this research conducts performance testing and reliability analysis for new inorganic electrochromic materials, and uses the color change of inorganic materials to indicate the electrification state of power transmission and transformation equipment, thereby realizing the electricity inspection function. In this project,ZnS Electro-luminescent materials and GaN luminescent materials were prepared, which were packaged into electroscope identification, and the application scheme of electroscope identification on UHV power transmission and transformation equipment was determined. The field practice shows that the electroscope identification prepared by this project can realize spontaneous luminescence discoloration in the electric field, and can effectively indicate the charging state of the equipment, and the effect is very obvious. Thereby effectively solving the problem of power inspection of UHV power transmission and transformation equipment.The economic and social benefits are huge and the application prospects are wide.

Measurement and analysis of sound radiation from coherently vibrating shunt reactors

In parallel with the rapid development of ultra-high voltage (UHV) power transmission systems, noise contamination radiated from UHV shunt reactors is becoming an urgent concern. This investigation explored the distributed structural vibration of reactors and their near-field and far-field sound radiation characteristics based on a thorough on-site measurement and a combined numerical method. The proposed method could realize sound field reconstruction of on-site shunt reactors by directly measuring their surface vibration, thus avoiding complex modelling with fluid-structure interactions and multi-physics problems. Furthermore, the combined method was utilized to investigate the effect of acoustical environments upon reactors’ sound radiation. The results show that reflection boundaries composed of firewalls among reactor units could introduce a higher noise level in the parallel radiation region due to their influence on the sound source directivity. Finally, the sound power levels of the on-site reactors were derived from the constructed sound field, which could avoid on-site background noise concerns in the current executive standards.

Lightning Attachment to UHV Power Transmission Lines: Effect of the Phase Voltage

The self-consistent leader inception and propagation model is used to analyze the influence of the phase voltage on the attachment of lightning to ultra-high voltage power transmission lines (UHV-TLs). An UHV-ac line with shielding failures reported in the literature is used as a case study. It is shown that the length of upward leaders initiated from conductors and their striking distances are longer under positive voltages than when energized with the opposite polarity. Therefore, the fraction of shielding failures of each conductor changes significantly with the phase angle in ac lines. However, it is found that the overall effect of voltage on lightning attachment can also be limited by the electrostatic screening produced by shield wires and their leaders. This proximity effect mainly reduces the velocity of upward leaders launched from energized conductors. Therefore, the effect of voltage on the lightning attachment process cannot be generalized since it is strongly coupled to the proximity of shield wires and their associated leaders. Thus, the lightning shielding performance should consider case-to-case variations in the upward leader velocity in different UHV-TLs designs, given not only by the line voltage but also coupled to the proximity of other wires and their launched leaders.

Electrical Property Test and Research of Insulated Operating Rods with Metal Joint for Live Working

Sectional structure with metal joint is commonly found in an insulated operating rod for live working in an extra- or ultra-high voltage power transmission line but the metal joint is inclined to discharge because uneven distribution of electric fields around the metal joint. In this paper, power frequency discharge tests are made on operating rods with metal joint and insulated joint, including even boost and discharge test and 300s power frequency voltage withstand test and test results are analyzed and studied. Results show: operating rods with two types of joints in the even boost test have basically the same discharge voltage values; the operating rod with insulated joint has significantly higher discharge voltage value than that with metal joint in the 300s voltage withstand test; the metal joint causes local electric field concentration and internode capacitance effect, leading to uneven electric field point position distribution of the insulated operating rod and reduced electrical property. However, the electrical property of the operating rod may be enhanced by mounting a grading ring at the end of the operating rod or coating functional coating outside the operating rod.

Protecting Distance between Radar Stations and UHV Power Transmission Lines

With the construction of UHV (Ultra-High Voltage) transmission lines and radar stations, the interference of UHV transmission lines to air intelligence radar stations has become increasingly prominent. Aiming at the problem that it is difficult to solve the loss of radar detection range caused by UHV transmission lines, the idea of using RCS (Radar Cross Section) of UHV transmission towers as an intermediate parameter to solve the radar detection range loss is proposed. In order to solve the problem of accuracy when using Physical Optics (PO) to solve such electromagnetic scattering problems of complex structures, the traditional PO method needs to be improved when used in the calculation of the large-size’s scattering field like the UHV tower. It is proposed to use Incremental Length Diffraction Coefficient (ILDC) to revise the diffraction of the edge of the tower, and to study the coupling conditions with the PO method, so as to solve the scattering field of the complex structure of the tower. Based on this, 5 UHV transmission towers’ model is established to simulate the UHV transmission lines, and the regular variation of radar detection loss with the distance between the two systems is studied. These results show that when the distance between the UHV transmission lines and the radar station is more than 2200 m, the loss can reach within 0.9 dB of the standard, which is in line with the standard for the construction around the air intelligence radar station.

Research and application of UHV power transmission in China

The power demand increases rapidly in China; however, the areas of huge power demands are of long distance from most areas of abundant energy resource in the country. Therefore, China put in great effort to develop ultrahigh voltage (UHV) power transmission systems to optimise its energy allocation. This includes (i) systematically developing key technologies such as overvoltage suppression, external insulation design, and electromagnetic environment control, and (ii) developing key equipment such as UHV alternative current (UHVAC) transformers, circuit breakers, and series compensated equipment, and UHV direct current (UHVDC) converter transformers, smoothing reactors, converter valves, and DC transmission control and protection systems. Eight AC UHV projects and 11 DC UHV projects have been built in China, which play an important role in the optimal allocation of energy. Plus there are one more UHVAC and three more UHVDC transmission projects in construction, while UHVAC gas-insulated lines will be applied in the UHVAC line crossover the Yangtze River and the ±1100 kV UHVDC power transmission technology is in development. Here, the development and application of UHV power transmission technologies in China are described, some main challenges the UHV projects encountered are discussed, and experiences obtained from the operation of UHV systems are introduced. It is concluded that China obtained mature experience in developing, constructing, and operating UHV systems and successfully realised long-distance, large-capacity power transmission, and the UHV power transmission technology has become an important measure for energy allocation in large areas.

Review of Research Progress on the Electrical Properties and Modification of Mineral Insulating Oils Used in Power Transformers

In November 2017, the first ±1100 kV high-voltage direct-current power transformer in the world, which was made by Siemens in Nurnberg, passed its type test. Meanwhile, in early 2017, a ±1000 kV ultra-high voltage (UHV) substation was officially put into operation in Tianjin, China. These examples illustrate that the era of UHV power transmission is coming. With the rapid increase in power transmission voltage, the performance requirements for the insulation of power transformers are getting higher and higher. The traditional mineral oils used inside power transformers as insulating and cooling agents are thus facing a serious challenge to meet these requirements. In this review, the basic properties of traditional mineral insulating oil are first introduced. Then, the variation of electrical properties such as breakdown strength, permittivity, and conductivity during transformer operation and aging is summarized. Next, the modification of mineral insulating oil is investigated with a focus on the influence of nanoparticles on the electrical properties of nano-modified insulating oil. Recent studies on the performance of mineral oil at molecular and atomic levels by molecular dynamics simulations are then described. Finally, future research hotspots and notable research topics are discussed.