Ultra High Voltage Transmission Research Articles

Competitiveness analysis of coal industry in China: A diamond model study

Under the effects of environmental pollution, macro-economical conditions, markets downturn, and squeeze of clean energy, the operation condition of China's whole coal industry attracts more attentions in recent years. This study aims to investigate the comprehensive competitiveness of coal industry in Chinese policy and economy environment. Then, this paper adopts diamond model to analyze internal and external factors that have significant influences on the competitiveness of China's coal industry, namely resource condition, demand condition, industry structure and enterprise strategy, related and support industries, the government, technology and chance. The research indicates that Chinese coal industry suffers from excessive capacity, low coal price and substitute of clean energy, etc. The current performance of Chinese coal industry is not optimistic. Fortunately, Chinese government unceasingly issues policies to support and regulate coal industry, and coal enterprises actively participate in industrial structure adjustments to deal with pressure of downturn. Furthermore, some national strategies, such as Ultra High Voltage transmission and ‘One Belt And One Road’, will greatly promote the recovery of domestic coal industry. In order to survive the downturn and sustain its fundamental position, coal industry should attach importance to these key factors in diamond model for each of them has crucial influences on the comprehensive competitiveness of Chinese coal industry.

Operational adaptability evaluation index system of pumped storage in UHV receiving-end grids

Pumped storage is an effective solution to deal with the emergency reserve shortage, renewable energy accommodating and peak-shaving problems in ultra-high voltage (UHV) transmission receiving-end grids. However, governments and public opinion in China tend to evaluate the operational effectiveness of pumped storage using annual utilization hour, which may result in unreasonable and unnecessary dispatch of pumped storage. This paper built an operational adaptability evaluation index system for pumped storage in UHV-receiving end grids from three aspects: security insurance, peak-shaving and renewable energy accommodating, which can provide a comprehensive and objective way to evaluate the operational performance of a pumped storage station.

Study for the Pile Foundation on Steep Slope Applied in UHV Transmission projects

When designing a pile on the steep slope, the calculation is based on a hypothesis of horizontal ground. Obviously, it is difficult to estimate the difference between the calculation result and the actual loading behaviour of the pile foundation. For a UHV (Ultra High Voltage) power transmission project in China, results are compared by two kinds of methods. One is traditional theory; the other is numerical simulation method. It shows that quite different deformation of ground foundation occurs near two sides of the pile cap. The traditional calculating method for the pile foundation can consider the effect by increasing the part of the pile above the ground surface. Reasonability of the increased value can be assessed by the numerical method. The result of numerical simulation shows that the maximum deformation appears in the middle of the pile, but it occurs in the top of the pile by the traditional method. And deformation is evidently larger by the traditional method. Deformation curve is different between the traditional method and the numerical method which can consider frictional resistance around the pile. Quite different are vertical stress values of the pile obtained by two methods.

Energy management of WSN-based charge measurement system of ultra high-voltage direct-current transmission line

With the construction of ultra-high-voltage direct current (UHVDC) transmission lines, the complex electromagnetic environment around the lines has been a widespread concern. The ZigBee-based field measurement system is widely used in ground space charge density measurements of HVDC transmission projects. In actual use, the power consumption of the space charge density measurement system is a key limitation of the device performance.Research on low-power and energy-management strategies of this measurement system can improve the device lifetimes. This capability is very important for improving monitoring efficiency of the surrounding electromagnetic environment of HVDC transmission projects.

In-situ investigation of the hydrogen release mechanism in bulk Mg2NiH4

Abstract Hydrogen storage is an important aspect to enable the so-called hydrogen economy. Mg-Ni alloys are among the most promising candidates for solid-state hydrogen storage systems yet many questions remain unanswered regarding the hydriding/dehydriding mechanism of the alloys. Mg2NiH4 particularly has received much attention both for its potential as a hydrogen storage medium and also exhibits interesting properties relating to its different polymorphs. Here, the dehydriding mechanism in bulk Mg2NiH4 is investigated using in-situ ultra-high voltage transmission electron microscopy (TEM) combined with Synchrotron powder X-ray diffraction (XRPD) and differential scanning calorimetry (DSC). We find that the hydrogen release is based on a mechanism of nucleation and growth of Mg2NiHx (x∼0–0.3) solid solution grains and is greatly enhanced in the presence of crystal defects occurring as a result of the polymorphic phase transformation. Also importantly, with atomic resolution TEM imaging a high density of stacking faults is identified in the dehydrided Mg2NiHx (x∼0–0.3) lattices.

Experimental Study on Sound Characteristics Produced by DC Corona and Pulsed Discharges

The audible noise (AN) production mechanism caused by corona discharge in ultrahigh voltage transmission lines is less understood. The study on sound pressure characteristic is necessary to obtain the inherent relation between AN and corona discharge. In this paper, the experimental research on single-point direct current (dc) corona discharge was evolved and the time-domain sound pressure waveform was obtained using capacitor microphone. The experiment results show that the dc corona discharge comprises multiple subsequent discharge pulses. The discharge voltage and the electrode polarity have a direct effect on the rising time and pulsed width of the single current pulse. The waveform of sound pressure produced by single discharge is a bipolar microsecond pulse, which lags behind the current pulse in time domain. The time delay is propagation time of sound signal from the discharge spot to the measurement spot. Based on the corona discharge characteristic in dc voltage, the experiment platform for nanosecond pulsed discharge was built to obtain the relation between discharge parameter and sound parameter. The characteristics of sound pressure in different discharge conditions were analyzed. The study results indicate that the sound pressure produced by pulsed discharge is similar with that produced by corona discharge. The experiment platform for pulsed discharge can be used to research the AN production mechanism by dc corona discharge.

Experiment on the Hillside Effects of Lightning Shielding of Ultrahigh Voltage Common Tower Double-Circuit Transmission Lines

To study the lighting shielding of ultrahigh voltage (UHV) transmission lines across mountains and the hillside effects on discharge process, experiments have been carried out with a reduced scale tower model. As the spatial electric field is changed by the slope, the space of shielding failure is enlarged. When the high-voltage electrode is 5 m to the transmission line, the vertical length of shielding failure is 8 m for the 30° slope, which is larger than 5.17 m for the flat ground. The maximum probabilities of striking the lines are 95% for the slope and 75% for the flat ground. When the vertical distance from the high-voltage electrode to the hillside is less than that to the transmission lines, the probabilities of discharge striking the flat ground are 85% for the 5-m gap and 94% for the slope for the same gap. When the vertical distance from the high-voltage electrode to the hillside is equal to that to the flat area, the hillside does not affect the average discharge voltage apparently but discharge time and discharge dispersity. The results of this paper are valuable for lighting protection of UHV transmission lines in mountainous areas.

In Situ TEM Observations of Cu6Sn5 Polymorphic Transformations in Reaction Layers Between Sn-0.7Cu Solders and Cu Substrates

Direct evidence of the relationship between the polymorphic phase transformation from monoclinic Cu6Sn5 to hexagonal Cu6Sn5 and stress accumulation/release in Cu6Sn5, formed at the interface between Sn-0.7Cu lead-free solder and their Cu substrates, has been obtained. To explore this challenging phenomenon, we developed an in situ heating/isothermal observation technique in ultrahigh-voltage transmission electron microscopy that enables the observation of thick samples (around 0.5 μm) for solder joints, including Cu/Cu3Sn/Cu6Sn5/Sn-0.7Cu solder interfaces prepared by a focused ion beam milling technique. The results show evidence of stress creation and release events by imaging bend contours that may arise due to the polymorphic transformations of the Cu6Sn5 phase and the associated volumetric change.

Influence of Bundle Conductors in UHV Transmission Lines

This paper aims to study the surface gradient potential (SGP) of overhead line conductors in ultra-high voltage (UHV) transmission lines. The SGP is crucial for the performance due to the corona effect. The purpose is to assess the calculation of the gradient of bundle conductors and the main factors that influence this calculation. It is accomplished a critical analysis of the main analytical and numerical existing methods. In addition to that, it is presented a study of special conductors concerning the application of both new materials and innovative wire stranding. The successive images numerical method is applied to the study and verified the accuracy for transmission lines with multiple bundle conductors. The methodology is evaluated by considering numerical simulations on a 1000 kV AC transmission line. The partial results indicate that gradient distribution is sensitive to bundle spacing and different bundle arrangements. The latter being the most influential. In view of these results, it is recommended to use numerical methods based on finite elements to better evaluate the surface gradient. This adequate method enables simulations of multiphysics problems regarding different geometries.

Laboratory investigation of AC corona loss and corona onset voltage on a conductor under icing conditions

Corona losses generated from energized conductors, especially in foul weather conditions, is one of the most important economic factors influencing the design of extra-high voltage (EHV) and ultra-high voltage (UHV) transmission lines. In the present paper, results of laboratory experiments under icing conditions are presented. Two types of ice are considered: rime and glaze. The conditions of ice formation on the test conductor are presented. During the ice accretion, an electric field was applied to the conductor to investigate corona loss and corona onset voltage. The presence of glaze results in a higher corona loss and a lower corona onset voltage compared with rime. The influence of wind velocity and freezing water conductivity were also studied. The test results can help to estimate corona losses of transmission lines in cold climate regions and to improve the design of transmission lines.

Adaptive Strategies in the Leader Propagation Model for Lightning Shielding Failure Evaluation: Implementation and Applications

Lightning shielding failure accounts for the highest proportion of lightning accidents for transmission systems above 500 kV. The leader propagation model (LPM) was found to be effective in the analysis of lightning shielding failure of high-voltage transmission lines, especially for the ultrahigh voltage (UHV) transmission systems. However, it was generally inefficient to calculate the shielding failure rate by LPM, since the progress of lightning development must be simulated repeatedly, which is time-consuming, and no adaptive implementation of LPM has been reported. In this paper, adaptive strategies to accelerate the computation of shielding failure analysis by LPM were proposed, which include the adaptive time step control according to the electric field at the conductor surface, non-uniform lightning current sampling based on the lightning current amplitude probability distribution, and the adaptive lightning location sampling based on recursive adaptive Simpson’s method. The analysis results were validated by the field data of the UHV transmission line in Japan, and the efficiency of the adaptive strategies was shown by the shielding failure analysis of a typical 500 kV ac transmission line.

Experimental Study on Branch and Diffuse Type of Streamers in Leader Restrike of Long Air Gap Discharge**supported by the Fund of the National Priority Basic Research of China (2011CB209403) and National Natural Science Foundation of China (Nos. 51325703, 51377094, 51577098)

One of the main problems in the Ultra High Voltage (UHV) transmission project is to choose the external insulation distance, which requires a deep understanding of the long air gap discharge mechanism. The leader-streamer propagation is one of most important stages in long air gap discharge. In the conductor-tower lattice configuration, we have measured the voltage, the current on the high voltage side and the electric field in the gap. While the streamer in the leader-streamer system presented a conical or hyperboloid diffuse shape, the clear branch structure streamer in front of the leader was firstly observed by a high speed camera in the experiment. Besides, it is found that the leader velocity, width and injected charge for the branch type streamer are greater than those of a diffuse type. We propose that the phenomenon results from the high humidity, which was 15.5-16.5 g/m3 in our experiment.

National Strategy and Industrial Governance Shift: Transformation of the Power Transmission and Distribution Industry in China

During the past decades, there has been a shift in the governance structure of the power transmission and distribution (PTD) industry from a market-oriented scheme to vertical integration. Such a shift in industrial governance was driven by the change in national strategy from “market in exchange for technology” to “independent innovation”. Under this new policy paradigm, the ultra-high voltage (UHV) transmission technology was perceived as strategically important for the country. The State Grid Corporation of China (SGCC), whose control over the industry was initially reduced in the reform, leveraged the paradigm shift in the state policy and strengthened its position in the industry by redefining the main and auxiliary services. The State Grid successfully brought back all UHV industry-related services, such as power design, equipment manufacturing, power grid construction and capital operation, into its main business category, which could be exempted from market competition according to state regulation. Eventually, the State Grid was able to establish strong vertical integration in the whole sector.

Implementation and Application of Practical Traveling-Wave-Based Directional Protection in UHV Transmission Lines

Traveling-wave-based protection is becoming attractive in ultra-high-voltage (UHV) transmission systems due to the requirement for high-speed protection. However, the poor transfer characteristics of coupling capacitor voltage transformers (CCVTs) for high-frequency voltage have strictly limited its application. A novel traveling-wave-based protection scheme considering the characteristics of CCVTs and current transformers is proposed in this paper. The dyadic wavelet transform is used to extract the polarities of voltage and current traveling waves for fault direction identification. A prototype is further developed for practical applications. Extensive laboratory tests are performed to assess the performance of the developed scheme. The prototype has been applied to the 750-kV substations in China and an external fault was recorded during the operation period, validating the effectiveness and reliability of the proposed protection principle.

Failure analysis of CuW/CuCrZr contact materials in capacitor bank switch

The type test of CuW/CuCrZr arc contact used for ultra-high voltage system capacitor bank switch was conducted. Through the comparative analysis of morphologies, compositions, properties and microstructures of the contact materials before and after failure, it can be found that the abnormal open of moving arc contact and the arc erosion and mechanical wear of static arc contact are the major reasons affecting the arc contact failure. The failure mechanism and main affecting factors were investigated in detail. The results showed that arc erosion and mechanical wear are the two main factors that affect the service lifetime of arc contacts used for ultra-high voltage transmission lines and cannot be ignored. Therefore, improving the arc erosion resistance and mechanical wear resistance simultaneously is the key to prepare the arc contact materials with longer lifetime.

Analysis on the Development of the Optimal Design for the UHV Transmission Tower

At present, the Ultra High Voltage (UHV) transmission has become the focus of grid. The development of the UHV transmission lines not only can guide the power construction but also make our resources more reasonable. Because of the inexperience, the steel consumption of the transmission towers in China increases about 30% comparing with the foreign similar ones. At first, it analyzes the main problems that UHV transmission towers are facing and simply introduces the optimal method based on failure mode in this article. Then it introduces the application of modern optimal algorithms, such as: genetic algorithm, particle swarm optimal algorithm, artificial neural networks optimal algorithm and so on.

Research on Wind-Induced Reliability of Double Column Suspended Guyed Tower in Strong Wind Area

The ultra-high voltage transmission line is long, which needs to pass through the various complex terrains. In order to ensure the safe structural system, understanding and grasping the wind-induced response and reliability of double column suspended guyed tower (DCSGT) in strong wind area of Gobi Desert are basic requirements. Through combining the conditional probability density of wind speed and frequency function of wind direction, the successive-type joint distribution model of wind speed and direction is obtained by multiplication theorem. In accordance with the principle of equivalent extreme value event, through utilizing the statistical moment point estimation method, the first four-order statistical moment information of equivalent extreme value variables is solved. The probability density function (PDF) of DCSGT response is calculated in accordance with these statistical moments. The dynamic reliability index and failure probability of DCSGT are solved by the moment method.

Radio interference excitation function of conductor bundles based on cage test results and comparison with long‐term data

A reasonable excitation function is vital to make a precise evaluation about the radio interference (RI) level of ultra-high-voltage (UHV) AC power lines. To obtain this function, a large number of RI measurements in heavy rain condition were done using different conductor bundles in a corona cage. Then, the excitation function in heavy rain condition was obtained by least-square fitting these measured values. After that, the validity of this function was verified with the statistical data measured from the Hubei long-term station, which is located under the operating 1000 kV Jindongnan–Nanyang–Jingmen UHV AC transmission lines. It turns out that the deviation between the prediction and the long-term average value is 1.1 dB in heavy rain condition, and 1.3 dB in fair weather condition. In addition, the long-term data measured in Hubei Station show that the conversion laws of RI at different weather conditions in International Special Committee on Radio Interference (CISPR)18 are also applicable to 1000 kV UHV transmission lines.

Secondary Arc Current Analysis of an Untransposed EHV/UHV Transmission Line With Controllable Unbalanced Shunt Reactor

A conventional four-legged shunt reactor serving untransposed extra-high voltage or ultra-high voltage transmission lines may cause the secondary arc difficult to extinguish and result in single-phase autoreclosing (SPAR) failure. This paper proposed an unbalanced shunt reactor (USR) scheme and focuses on the secondary current analysis with respect to untransposed extra high-voltage/ultra-high voltage transmission lines. The fundamental theory of secondary arc calculation for the untransposed transmission line with USR was provided first, followed by the formulation of USR controlling principles and strategy. To validate the effectiveness of secondary arc current suppression, untransposed 1000-kV single-circuit and double-circuit UTL with USR were simulated using the Electromagnetic Transients Program. The results show that USR is effective in suppressing secondary arc current and recovery voltage for single-circuit and double-circuit UTL, which helps increase the SPAR success probability. Furthermore, the secondary arc current and recovery voltage are not sensitive to the variation of USR neutral reactance; hence, the value of neutral reactance can be decided in a wide range. Finally, USR’s role and effect in reducing the inductive electrostatic voltage in double-circuit UTL was discussed when one line is transferred to maintenance.

Research on Helicopter Live-Line Work by Platform Method on 1000 kV UHV AC Transmission Lines

This paper focuses on the security condition of line worker during the implementation of helicopter live-line work by platform method on 1000 kV ultrahigh voltage (UHV) transmission lines. First, a model of helicopter live-line work is presented, and the electric field distribution of line worker when performing live-line work on 1000 kV UHV transmission lines is analyzed. Then, the capacitances between helicopter live-line work platform, transmission lines, and ground are obtained by energy method, and an equivalent circuit model is presented to analyze the current characteristic of bonding procedure. At the end of this paper, an experiment of helicopter live-line work is performed, the electric field distributions of line worker and the discharge current are measured and compared with simulation results, which will be used to judge the security condition of line worker and the feasibility of helicopter live-line work by platform method on 1000 kV UHV transmission lines.