Long-distance Power Research Articles

Cause Analysis of Distance on Rural Power Network Voltage Based on Power Flow Model

In order to analyze the influence of long-distance power transmission on the terminal voltage of agricultural network, this paper establishes the low voltage model of agricultural network based on the basic power flow model, and obtains the semi-quantitative relationship between the terminal voltage deviation and various factors by formula derivation. By introducing reference data for calculation, the influence of distance factor on the voltage reduction of the rural power grid is obtained. Under the same active and reactive power transmission conditions, the farm network voltage gradually decreases with the increase of the length of the agricultural network feeder. On the other hand, for the same feeder length, as the active power increases, the farm network voltage gradually decreases. As the reactive power increases, the voltage of the rural network gradually decreases. The trend of the rural power grid voltage with the reduction of the active power is greater than the reactive power, that is, the same percentage of the active power and the reactive power change. The active power has a more significant effect on the voltage reduction of the rural power grid. Therefore, the active, reactive and feeder lengths will have an impact on the terminal voltage of the rural network. By reducing the radiation range of the feeder, the terminal voltage of the rural network can be effectively improved.

Решение задачи комплексного энергоснабжения автономного потребителя с целью уменьшения экономических затрат

The paper dwells upon reliable power supply to off-grid consumers and presents a solution that minimizes the costs of electricity generation over the lifetime of a generator set. Emphasis is made on integrated systems comprising a variety of sources, including renewable energy, which in most cases is more cost-effective than fuel-fired generators alone or constructing long-distance power grids. The paper presents the structural diagram of an integrated system comprising energy storage, photovoltaic converters, wind farms, a small high-pressure hydroelectric power plant, free-flow SHPs, inverters, fuel-fired generators, and a grid. It further describes a mathematical model for optimizing the layout and structural makeup of primary and secondary renewable energy equipment, which helps tailor the technical and economic performance of generator sets to the actual climate of the selected region. The paper also briefly presents VizProRES application.

Study on AC Resistance of Layering Enamelled Stranded Conductor

In recent years, with the rapid development of large-length ultra-high-pressure voltage extrusion insulated submarine cable technology, the cable system in the medium-length offshore power grid interconnection project has been gradually replaced by XLPE insulation by traditional oil-paper insulation. There are many large cross-section conductors used in long-distance power transmission cables, and according to the IEC 60287-1-1, it is recommended to use Milliken conductors to reduce the AC resistance of conductors, at the same time, in submarine cables, there is a high requirement on the water-blocking performance of conductors and the water resistance of Milliken conductors is poor, so it is not used in submarine cable conductors. This paper puts forward a layering enamelled stranded conductor and a calculation method of AC / DC resistance ratio for it. The validity of the calculation method is verified by experimental tests. At the same time, the calculation shows that the AC / DC resistance of the conductor at 1800 mm2 nominal cross section can be reduced by 16% compared with the conventional round compacted conductor in the prior art. The effectiveness of this conductor in reducing AC resistance is verified by finite element simulation.

Анализ перспективных технологий передачи электрической энергии на дальние расстояния

The article analyzes the influence of global and regional challenges on the prospective technologies of electric power transmission over long distances. The analysis is carried out proceeding from the data of the National Technical Initiative set forth by the Agency for Strategic Initiatives, the international financial organization (The World Bank), and the Concept of Long-Term Social and Economic Development of the Russian Federation. To identify the most significant challenges and analyze their influence on the social and economic sphere, the strategic analysis method (SWOT analysis) was used, which has shown that global and regional challenges are closely linked with each other. Active development of renewable energy sources (RES), which entails the development of distributed generation, is the main factor able to compromise the technology of power transmission over long distances. On the other hand, the emergence of new large remote generation centers based on RES opens prospects for developing the technology of power transmission over long distances. Active development Arctic regions, formation of global energy rings, and energy security concerns give a strong impetus for further development of electric power transmission over long distances. In the context of global challenges in terms of their effect on the social sphere, the technology of power transmission over long distances is seen as an important tool for providing all regions around the world with accessible electric energy under the conditions of globally changing power industry. Electric power should be accessible to regions for personal use by the population in the region, and for setting up favorable conditions for functioning of existing and creation of new energy-intensive city-forming enterprises. In connection with the importance of solving this problem, a need for development of various long-distance power transmission technologies with the maximum technical and economic efficiency should emerge around the world. The need for gradually restructuring the electric power supply arrangements in different regions around the world will have the strongest influence on the economy in the context of global challenges. Active efforts taken by developed countries to diversify the structure of their power industries through expanding the use of non-hydrocarbon renewable energy sources and to make them less dependent on countries exporting conventional energy carriers will entail a gradual shift of the world centers of generation. In contrast, the factors that prompt India and China to become the main locomotives of economic growth around the world and the emergence of the world’s new economic development centers in Asia and Latin America will entail the shift of the world’s centers of electricity consumption by the population and industry toward new parts of the globe. The above-mentioned tendencies will generate the need to dynamically change the existing structure of electricity production, and a need will arise to use entirely new modern adaptive electric networks with long transit lines over the territory of Eurasian Asian part and South America. If a significant progress is achieved in the efficiency of solar power generation technologies, power bridges may emerge between Africa and Eurasian European and Asian parts.

Aspects of ultra-high voltage half-wavelength power transmission technology

The necessity of large-scale and long-distance power transmission in future energy development is analyzed and some application scenarios of ultra-high voltage (UHV) half-wavelength transmission (HWLT) system are presented in the paper. Steady state and transient characteristics of half-wavelength transmission lines are reviewed in detail. The characteristics of UHV HWLT are very different from those of conventional UHV transmission mode, especially the overvoltage problem. To analyze the particularity and key techniques of UHV HWLT, current research results are summarized from simulation method, steady-state voltage control, relay protection, tuning network, secondary arc and overvoltage suppression, economic evaluation and engineering design. Some future research directions are also briefly addressed.

Asian international grid connection and potentiality of DC superconducting power transmission

In 2011, a large scale earthquake and tsunami hit the northeastern coast of Japan, and nuclear plants were damaged to a large extent. Before the Tsunami, 54 nuclear plants were operated, however presently, only three nuclear plants are in operation. Therefore, Japan is suffering from high price of electricity and low supply reliability. In generation mix, nuclear plants generate only one percent and 87 percent of electricity is generated by fossil energy. This is not preferable for Japan from the viewpoints of energy security and stable electricity supply. Therefore, it is mandatory to increase sustainable energy and to decrease consumption of fossil fuel. International grid connection and the Global Energy Interconnection will be one of countermeasures against these problems existing in Japan. In this paper, international grid connection initiatives proposed in Asia are described and features and issues of electric power grids in Japan are discussed to implement the international grid connection. As the key technology for implementing the international grid connection, the present status of DC superconducting power transmission lines and power converters for long-distance power transmission lines are presented. In conclusion, conditions and legal frameworks for realizing the international grid connection are described.

Performance of Cross-Linked Polyethylene Insulated Cable Based on Detection of High Voltage Electric Field

High voltage direct current transmission has been widely used in long-distance power transmission because of its advantages such as low loss and large throughput. The safety of cable is very important in the long-distance transmission process. Cross-linked polyethylene insulated cable has the advantages of simple manufacture, good heat resistance and easy installation; therefore it has been widely used in long-distance power transmission. In this study, conductance, dielectric and voltage withstanding performance of the insulating layers of cross-linked polyethylene cables with working voltage of 220 kV which was never used and has been used for 2, 4, 6 and 8 years were tested by various evaluation methods. The conductivity of the insulating layers was affected by temperature only under high and low electric field intensities and was affected by temperature and electric field strength under middle electric field intensity. Dielectric loss factor could reflect dielectric properties of materials; the larger the dielectric loss factor, the poorer the performance. The dielectric loss factor decreased with the increase of applied electric field frequency and increased with the increase of service years. Breakdown electric field strength could reflect voltage resistance of materials; the larger the breakdown electric field strength, the better the performance. The breakdown electric field strength was inversely proportional to the service years of the insulating layer, and the decrease amplitude increased significantly when the service time exceeded 2 years. In summary, cross-linked polyethylene insulated material satisfies the safety requirement of high voltage direct current transmission and can be used for manufacturing long-distance transmission cables.

Polymeric insulation for high-voltage dc extruded cables: challenges and development directions

High-voltage DC (HVDC) power transmission plays a key role in the global power grid today and will continue to play a key role in the future, particularly for high-voltage, largecapacity, long-distance power transmission and regional power grid interconnection [1]. HVDC was first developed in the 1930s as a reliable technology that can effectively convert AC electricity produced at the point of generation to DC electricity for transmission. In 1954 the world’s first commercial HVDC project connected the Swedish mainland and the Island of Gotland with a ±100 kV mass-impregnated cable with a power rating of 20 MW [2], [3]. Since the 1960s the number of HVDC systems has grown rapidly with the maturation of thyristor and transistor technologies. Two main technologies were developed in the past half century:

A new hybrid DC circuit breaker topology

Being advantageous for long-distance power transmission and new energy connection, DC system has wide range of applications in many scenarios. As the capacity of DC power grids increases, the fault current is more difficult to interrupt. And the DC circuit breaker which is very important for protecting DC grid attracts more and more attention of researchers. In this paper, a new hybrid DC circuit breaker topology based on the technique of thyristor forced current zero is proposed. The breaker is able to interrupt the fault current in several milliseconds, and the mechanical switch can be cut off at zero current. In addition, no extra power supply and control devices are needed, the pre-charging capacitor can obtain energy from DC grid directly. Therefore, the control process is simpler and the reliability is greatly improved. The operating principle of the proposed circuit breaker is analyzed in detail, and then the simulation is carried out in PSCAD/EMTDC which verifies the correctness of the theoretical analysis and the feasibility of the breaker.

컴솔 멀티피직스를 이용한 양극형 1회선 HVDC의 전계 해석

Recently, there has been an increasing interest in HVDC(High Voltage Direct Current) transmission as a core technology required for a Super grid. Compared with HVAC(High Voltage Alternating Current) transmission, HVDC transmission has no loss due to skin effect and reactance components, so long-distance power transmission is possible, and asynchronous power system can be interconnected. Also, in case of a DC electric field, there is no induction phenomenon. However, the human body may cause irritation such as electrostatic discharge and discomfort, therefore electric field analysis through simulation is absolutely necessary. In this paper, electric field simulation was performed using COMSOL Multiphysics, a multi-physics analysis program, for a Bipolar single line DC ±400kV, DC ±500kV, DC ±800kV model. In order to verify the validity of the simulation, comparative analysis with the related literature was conducted.

Multi-Terminal High Voltage Direct Current Transmission System with DC Resonant Semiconductor Breakers

AbstractIn consideration of the natural environment and depletion of energy resources, the widespread use of electric power system is expected in which the power is generated from sources of renewables such as wind and solar. When these plants are introduced in large scale, the use of broad land is required. Due to low transmission losses and small stability problems, multi-terminal high voltage direct current (MTDC) transmission becomes advantageous as long-distance power transmission system. Since DC current does not incorporate a zero cross point, therefore it’s blocking is difficult. This paper proposes a DC resonant semiconductor breaker which enables rapid fault clearance for self-excited HVDC transmission. This circuit breaker is connected as a semiconductor switch, in parallel with a group of capacitors, and resistors in the DC transmission line. The capacitor is charged to a higher voltage from the DC transmission line. For generating reverse current to allow the zero cross point in the transmission line, the semiconductor switch turns on to open the circuit breaker. After blocking, the inductance of the line is demagnetized by the resistor and fault clearing is achieved. The system except fault point can continue its normal operation.

Suitable Cable Structure of HTS Triaxial Cable Cooled by Counter Flow Cooling Method for Long-Distance Power Transmission

A high temperature superconducting (HTS) triaxial cable fits long-distance power transmission compared to the three-in-one superconducting (SC) cable, since the HTS triaxial cable has lower ac loss and larger cooling channel, and the HTS tape length used for the HTS triaxial cable is much shorter than that of the three-in-one SC cable. We investigated a suitable cable structure of the HTS triaxial cable, which has the limitation of the outer diameter (150 mm), cooled by counter-flow cooling for long-distance power transmission using the numerical analysis that considered the heat transfer from the cable outside and the heat generation caused by the electrical loss and the frictional loss of a coolant inside the cable. Our results show that it is very important to expand an outside channel and increase the flow rate in order to operate the HTS triaxial cable for a long-distance. The suitable flow rate for increasing the cable length that each cooling station can cool the HTS cable at 77 K or lower is about 50 L/min. The maximum cable length is 1.7 km at the conductor diameter of 88 mm. This cable length of 1.7 km is larger than that of the three-in-one cable; the maximum cable length of the three-in-one cable is less than 1 km. Therefore, the number of cooling stations can be reduced by adopting HTS triaxial cable.

Discussion on Sensitivity of Circuit Breaker Protection of Longdistance Power Distribution Line in Tunnel

Discussion on Sensitivity of Circuit Breaker Protection of Longdistance Power Distribution Line in Tunnel

Cloud-based parallel power flow calculation using resilient distributed datasets and directed acyclic graph

With the integration of distributed generation and the construction of cross-regional long-distance power grids, power systems become larger and more complex. They require faster computing speed and better scalability for power flow calculations to support unit dispatch. Based on the analysis of a variety of parallelization methods, this paper deploys the large-scale power flow calculation task on a cloud computing platform using resilient distributed datasets (RDDs). It optimizes a directed acyclic graph that is stored in the RDDs to solve the low performance problem of the MapReduce model. This paper constructs and simulates a power flow calculation on a large-scale power system based on standard IEEE test data. Experiments are conducted on Spark cluster which is deployed as a cloud computing platform. They show that the advantages of this method are not obvious at small scale, but the performance is superior to the stand-alone model and the MapReduce model for large-scale calculations. In addition, running time will be reduced when adding cluster nodes. Although not tested under practical conditions, this paper provides a new way of thinking about parallel power flow calculations in large-scale power systems.

All-Electric Subsea Well Brings Benefits vs. Traditional Hydraulic Technology

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27701, “World-First All-Electric Subsea Well,” by Thomas Schwerdtfeger, Total E&P Netherlands; Bruce Scott, Halliburton; and Jan van den Akker, SPE, OneSubsea, a Schlumberger Company, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. Currently, the state of the art for subsea well control is based on hydraulic technology. Hydraulic fluid is supplied from a host facility to the subsea wells through dedicated tubes within an umbilical and is distributed to the wells. Shifting that trend, K5F3, the world’s first all-electric well in the subsea industry, opened to production on 4 August 2016. This paper presents the benefits of electric subsea control compared with current state-of-the-art hydraulic methods. Rationale for Electric Production System Expenditure Savings. When looking at the introduction of a new technology such as an electric system, successful introduction is a direct consequence of a perceived reduction in capital expenditure (CAPEX) and factors such as operating expenditure (OPEX); health, safety, and environment (HSE); and future readiness also need to be addressed. To perform preliminary system engineering for the implementation of the electric system and provide a comparison with a conventional electrohydraulic multiplex system, a case with five oil-production wells, one gas-injection well, and three water-injection wells was used as a base case for cost. The study concludes that the electric system is likely to show a range of benefits over the equivalent electrohydraulic multiplex system. Improved System Efficiency. Electric subsea production brings advantages in most scenarios, particularly in an ultradeepwater field or with long-distance step outs. Electric motors maintain their high level of efficiency and full torque capability regardless of water depth, unlike hydraulic pressure, which must over-come seawater hydrostatic pressure. Use of high-voltage direct current for long-distance power transmission is far more efficient than use of either alternating current or hydraulic pressure. Removing hydraulic tubing from the umbilical and reducing the number of conductors bring several advantages. The electric umbilical has a smaller cross section, allowing longer continuous lengths to be manufactured and spooled. Overall weight is reduced, facilitating the use of a smaller installation vessel. And, on very long stepouts, splices in the umbilical can be either reduced or eliminated altogether. HSE Improvement. An all-electric system eliminates the discharge of hydraulic fluid to the environment and hydraulic-pressure safety issues. Future Potential and Readiness. Having much higher levels of electric power available at the subsea end of the system (compared with the electrohydraulic system) offers a greater scope for powering additional tools and sensors such as multiphase flowmeters. It also facilitates the addition of intelligent wells, new sensors, and digital flow-control valves.

Design and Control of a Wearable Hand Rehabilitation Robot

This paper proposes a wearable hand rehabilitation robot for assisting patients to do rehabilitation training such as the flexion and extension of fingers. This robot prototype has a modularized structure with nine degrees of freedom for the independent control of the patient’s fingers. To alleviate the weight applied on the patient’s hand and arm, the entire control system is placed in the patient’s backpack and the cable-driven approach is employed to achieve the long-distance power transmission. Because of the repetitive training manner and the existence of external disturbances, a controller combining the iterative learning control (ILC) and the active disturbance rejection control (ADRC) has been proposed for the control of the finger’s joints. The contributions of this paper lie in the robot’s modularized structure design and the proposed “ILC + ADRC” controller. Experimental results have verified the function of the proposed robot and demonstrated the satisfactory control performance achieved by the proposed controller.

Advances in inductively coupled power transfer technology for rail transit

Traditional power supply method for moving electric railway vehicles is based on contact type power collection technology. This sometimes cannot meet the requirements of modern rail transportation. A new wireless power transfer (WPT) technology can offer significant benefits in modern rail transportation particularly in some stringent environments. This paper reviews the status and the development of rail transit power supply technology, and introduces a new challenging technology--inductive power transfer (IPT) technology for rail transit. Tesla established the underpinning of IPT technology and creatively and significantly demonstrated power transfer by using highly resonant tuned coils long time ago. However, only in recent years the IPT technology has been significantly improved including the transfer air-gap length, transfer efficiency, coupling factor, power transfer capability and so on. This is mainly due to innovative semiconductor switches, higher control frequency, better coil designs and high performance material, new track and vehicle construction techniques. Recent advances in IPT for rail transit and major milestones of the developments are summarized in this paper. Some important technical issues such as coupling coil structures, power supply schemes, segmentation switching techniques for long-distance power supply, and bidirectional IPT systems for braking energy feedback are discussed.

Long-distance WPT unconventional arrays synthesis

Two innovative array concepts are introduced for the design of long-distance Wireless Power Transfer (WPT) radiating systems. The achievable tradeoffs between complexity/cost mitigation and power focusing capabilities of unconventional WPT architectures with respect to state-of-the-art optimal WPT solutions are investigated. To this end, clustered or sparse WPT arrangements are introduced by formulating their syntheses either as excitation or as pattern matching problems then solved by ad-hoc versions of the Contiguous Partition Method and Compressive Sensing algorithms. Selected numerical examples are presented to assess the features and the potentialities of unconventional WPT designs also in comparison with traditional state-of-the-art optimal methods.

Deformation processed Al/Ca nano-filamentary composite conductors for HVDC applications

Efficient long-distance power transmission is necessary as the world continues to implement renewable energy sources, often sited in remote areas. Light, strong, high-conductivity materials are desirable for this application to reduce both construction and operational costs. In this study an Al/Ca (11.5% vol.) composite with nano-filamentary reinforcement was produced by powder metallurgy then extruded, swaged, and wire drawn to a maximum true strain of 12.7. The tensile strength increased exponentially as the filament size was reduced to the sub-micron level. In an effort to improve the conductor’s ability to operate at elevated temperatures, the deformation-processed wires were heat-treated at 260°C to transform the Ca-reinforcing filaments to Al2Ca. Such a transformation raised the tensile strength by as much as 28%, and caused little change in ductility, while the electrical conductivity was reduced by only 1% to 3%. Al/Al2Ca composites are compared to existing conductor materials to show how implementation could affect installation and performance.

A Case Study of Wind-PV-Thermal-Bundled AC/DC Power Transmission from a Weak AC Network

Wind power generation and photovoltaic (PV) power generation bundled with the support by conventional thermal generation enables the generation controllable and more suitable for being sent over to remote load centre which are beneficial for the stability of weak sending end systems. Meanwhile, HVDC for long-distance power transmission is of many significant technique advantages. Hence the effects of wind-PV-thermal-bundled power transmission by AC/DC on power system have become an actively pursued research subject recently. Firstly, this paper introduces the technical merits and difficulties of wind-photovoltaic-thermal bundled power transmission by AC/DC systems in terms of meeting the requirement of large-scale renewable power transmission. Secondly, a system model which contains a weak wind-PV-thermal-bundled sending end system and a receiving end system in together with a parallel AC/DC interconnection transmission system is established. Finally, the significant impacts of several factors which includes the power transmission ratio between the DC and AC line, the distance between the sending end system and receiving end system, the penetration rate of wind power and the sending end system structure on system stability are studied.