Ultra High Voltage AC Research Articles

Transmission Technologies and Implementations: Building a Stronger, Smarter Power Grid in China

The state grid corporation of china has been deploying ultrahigh-voltage (UHV) ac technology on a large scale since launching its Strong and Smart Grid plan in 2009. China has 80% of its hydropower generation in the southwest and 76% of its coal generation in the northwest. However, more than 75% of the country's energy demand is distributed in the eastern and southern coastal areas. This geographical mismatch between supply and demand made it necessary to build UHV transmission networks: transmission technologies at voltage levels of 1,000 kV for ac and p1,000 kV for dc. In this article, the development of UHV transmission-system technologies and projects is detailed, with a focus on the UHV ac transmission system.

Technical committees

When the electric field strength around an electrode is high enough, complex ionization processes take place in the air nearby, leading to the discharge phenomena known as corona [1]. The occurrence of discharge, as shown in Figure 1, can cause audible noise (AN), radio frequency interference (RFI), and corona loss (CL) which should be minimized for economic reasons [2–3]. Due to its adverse effects, it becomes an important consideration in the design and operation of ultra-high voltage (UHV) AC and DC transmission lines and other electrical devices [4]. On the other hand, when the discharge occurs, an ionic wind can be formed as air ions are accelerated by the electric field and exchange momentum with neutral air molecules. As there is no noise and in fact no moving parts at all, it offers an attractive method to cool down electronic devices such as the iPad [5–6]. The latest application of air discharge was achieved by MIT engineers who built and flew the first ever plane which was propelled only by the ionic wind instead of fossil fuels [7]. The study of discharge in air can date back to the middle of the 20th century by Meek, Raether, and Loeb [8–9]. However, because of the complexity of this problem, investigation of the discharge mechanism has continued up to the present day [10–12]. As a good understanding of the basic processes involved is essential to utilize or prevent the discharge, especially for the UHV projects which are being built in China, India, and many other countries, it is still of great importance to further investigate the discharge phenomena in air.

Optimal Design of 1200 kV UHV AC Transmission Lines in India using Newly Developed Standalone MATLAB GUI

Owing to tremendous growth in requirement of electrical power in the country, technological advancement in transmission systems is essential for transmission of bulk amount of power over long distances. Deciding value of corridor width for transmission lines are greatly influenced by magnitudes of electric and magnetic fields along its length. The precise evaluation of the electromagnetic fields and effects of corona like Radio Interference and Audible Noise generated by overhead transmission lines are thus of greater interest. This paper presents implementation of a novel GUI based technique to compute the fields generated by power transmission lines using three dimensional techniques. Actual case of Ultra High Voltage AC (UHVAC) line is considered for study. Transmission lines are analyzed by using newly developed software that facilitates computation and plotting of electromagnetic fields and corona effects in 3D coordinates. MATLAB is used as platform for development of GUI based software to analyze the fields along the entire length of transmission lines under study. It uses concept of charge simulation method (CSM) along with most fundamental Maxwell’s potential coefficient theory and 3D integration techniques.

Calculation of Power Frequency Electric Field Around Ultra-High Voltage AC Transmission Lines

Under the increasingly stringent situation of environmental protection management, it is necessary to research the distribution law of power frequency electric field around Ultra-High Voltage (UHV) AC transmission lines to provide technical basis for the design of transmission lines and the environmental impact assessment. Firstly the basic principle of equivalent charge method and its mathematical model are introduced in this paper. Then it is researched how to use equivalent charge method to analyze the electric field near the transmission lines. Based on the three-phase double-circuit overhead transmission line model, the influences of several factors on the power frequency electric field have been analyzed. These factors include the conductor-to-ground height, the phase sequence arrangement, the number of split conductors and the split spacing. Finally the frequency electric field of parallel UHV AC transmission lines is discussed. The results can provide reference for engineering design of UHV AC transmission lines.

Discharge voltage prediction of UHV AC transmission line–tower air gaps by a machine learning model

Full-scale discharge tests of transmission line–tower air gaps are costly and time-consuming, and they cannot exhaustively simulate all the gap configurations in practical engineering. In this paper, a machine learning model established by support vector machine is introduced to predict the switching impulse discharge voltages of the ultra-high-voltage (UHV) AC transmission line–tower air gaps. The three-dimensional finite element models of a UHV cup-type tower and a UHV compact transmission line were established for electric field calculation, and some features were extracted from the hypothetic discharge channel and the shortest path between the bundled conductor and the tower. These features under a given voltage were normalised and input to the SVM model, while the output is two binary values, respectively, representing gap withstanding or breakdown. Trained by experimental data of one type of the UHV transmission line–tower gaps, the SVM model is able to predict the discharge voltages of another gap type. The mean absolute percentage errors of the two engineering gap types, under different gap distances, are 8.31 and 4.86%, respectively, which are acceptable for engineering applications. The results provide a possible way to obtain the discharge voltages of complicated engineering gaps by mathematical calculations.

Asynchronous fault location scheme for half‐wavelength transmission lines based on propagation characteristics of voltage travelling waves

Due to prominent attenuation of travelling waves, double-end fault location method produces considerable errors when applied to ultra-high voltage AC half-wavelength transmission (UAHT) lines. In order to address this problem, this study presents a novel fault location scheme based on the attenuation, refraction and reflection principles of aerial-mode voltage travelling waves (AVTWs). In the scheme, the faulted section of an UAHT line is first determined according to the accumulated amplitude ratio of the pre-determined frequency components of AVTWs asynchronously sampled at both terminals of the line. Then, the Teager energy of the first two wavefronts of the AVTW - measured at the terminal in the faulted section - is used to define two factors for selecting the appropriate accurate fault location method. Finally, the single-end travelling wave method is adopted for locating the faults near the line terminal. The presented double-end method utilises the amplitude ratio of AVTWs to locate the faults far from the line terminal. A 1000 kV UAHT line model is considered with various fault conditions in PSCAD/EMTDC simulations. The simulation results and analysis demonstrate that the proposed fault location scheme is accurate and immune to fault distances, fault types, fault impedances and fault inception angles.

Research on application of active current differential protection method on AC transmission lines in UHV AC–DC interconnected system

The rapid development of ultra-high voltage (UHV) AC–DC interconnected system has brought with it some new features, such as characteristics of distributed parameters becoming more distinct, internal parameters changing faster, and harmonic becoming more unstable, which pose new challenges for the correct operation of relay protection and automation devices. The aim here is to study the application of active current differential protection method in UHV AC–DC interconnected system. Firstly, the negative influence of UHVDC connection on the effectiveness of traditional current protection method is analysed. Next, the principle of active current differential protection method is introduced, which shows that this method is less susceptible to the variation of system parameters and unstable harmonics. On this basis, simulations have been conducted on PSCAD platform to explore the application of this method on AC transmission lines in case of various fault types. The simulation results show that the active current differential protection can increase the sensitivity of protection of UHV AC–DC interconnected system.

Research on overvoltage and minimum air clearance on 1000 kV AC side of converter transformer in ±1100 kV Guquan converter station

In the hierarchically connected ultra-high voltage (UHV) DC projects, the minimum air clearance on the 1000 kV AC side of converter transformer directly affects the layout and area of the valve hall. The minimum air clearance is determined by the overvoltage and the flashover characteristics of different electrodes. Since the UHV DC projects are hierarchically connected to the AC power grid, the overvoltage and the electrode flashover characteristics are different from that of general UHV AC projects, necessitating the relevant overvoltage calculation and test studies. The electromagnetic transients software PSCAD is used for modelling of the ±1100 kV Wannan convertor station and the related AC system. The power frequency overvoltage, switching overvoltage, time-to-crest value, and coefficient α of phase-to-phase overvoltage on the AC side of the 1000 kV converter transformer are calculated. Tests are carried out on air clearances between bundle conductors, tubular buses, and equipment grading rings under switching impulse with 1000 μs long wave-front. The minimum phase-to-earth and phase-to-phase air clearances on the 1000 kV AC side of the converter transformer are given.

Wear Mechanism and Mass Loss Characteristic of Arcing Contacts in SF6 Circuit Breaker in Making Process

Large-capacity capacitor banks have been used to control the reactive power of ultra high voltage ac grid in China. The high switching inrush current of SF6 circuit breakers used for large-capacity capacitor banks has caused great mechanical wear after arc ablation, which leads to the serious erosion of the arcing contacts of the circuit breakers, thus shortening the electrical life. To improve the electrical life of circuit breakers, the wear mechanism and mass loss characteristic of arcing contacts in the making process were studied in this paper. Through erosion experiments in the making process and arc ablation experiments in the circuit breaker test device, the wear mechanism and the mass loss characteristics were analyzed via the detection of worn contacts and wear theory. At normal temperature, the wear mechanism is mainly abrasive wear. At high temperature, the wear mechanisms in three stages mainly include adhesive and abrasive wears. When the closing inrush current amplitudes are 10, 20, and 30 kA, the mass loss of mechanical wear is greater than that of arcing ablation. The total mass loss and mass loss rate per unit charge increase with the interference radius between two contacts and with test current. However, with current amplitude higher than 20 kA, the total mass loss rate decreases. Suggestions to reduce wear are proposed to improve the electrical life of circuit breakers.

Evaluation of ceramic insulators for UHVDC transmission

Currently there is a significant requirement for the electrical energy across the globe. Many countries including India are adopting ultra high voltage (UHV) AC and DC transmission. HVDC transmission is increasingly being adopted for long distance transmission for evacuating huge power transfer in comparison to UHVAC. The design of overhead transmission insulators for UHVDC particularly during contaminated conditions is an important issue faced by the utilities. In the present investigation exhaustive simulation studies are conducted under different environmental conditions on three types of newly developed HVDC insulators used for ± 500 kV and ± 800 kVDC transmission. It is also known in case of faulty discs in a string, redistribution of field and potential occurs, hence estimation of surface potential, electric field is conducted by using a code developed based on surface charge simulation method (SCSM). Some experiments are conducted using the developed HVDC experimental facility. It is believed the results obtained from the study will be useful to the utility and design engineers.

Design and Application Research of an Power Grid Safety Supervision and Management Business Integrated Platform Based On SoTower3.0

Power grid is a kind of important public infrastructure which plays an essential role in guaranteeing the normal operation of economy and society. With several decades of technological development application, State Grid Corporation of China (SGCC) has made remarkable achievements such as the Ultrahigh voltage(UHV) AC and DC hybrid power system, the widespread use of new technology and equipments and the continuing large quantities of projects construction. New problems occur due to the abovementioned new situation, especially in the power grid information technology aspect. The integrated platform for safety supervision and management of power grid enterprises can improve the informatization level of the power grid safety supervision and management and provide a solid guarantee for the reliable operation of the power grid. This paper introduces SoTower3.0 power grid safety supervision and management integrated platform software, which has8 types of functions, including safety accident analysis, potential safety hazard management, comprehensive business management, safety supervision management, safety evaluation, safety training examination, basic security construction and system management, providing informatization support for the efficiency improvement of the power grid safety supervision and management. In addition, the paper analyzes the advantages of the developed SoTower platform application, introduces the system framework design and the specific contents of the above-mentioned 8 functions. Nowadays, the platform has already been applied in power grid enterprises in China, so the network structure and the effectiveness of the applied platform have also been given in this paper.

Influence of Hybrid Reactive Power Compensation on the Secondary Arc of Ultra-High-Voltage Transmission Lines (May 2018)

Hybrid reactive power compensation (HRPC) which consists of series compensation and a stepped-controlled shunt reactor will see use in China's future ultra-high-voltage (UHV) transmission system. As a result, some new characteristics of the secondary arc during a single-phase-to-ground fault on UHV transmission lines with HRPC may be raised. In this paper, the secondary arc characteristics during the single-phase auto-reclosure (SPAR) operation have been simulated with regard to the UHV AC system installed with HRPC. Based on the UHV system model with HRPC and its secondary arc model, the influence mechanism of HRPC on secondary arc current is theoretically derived with the simulated waveforms and the Fourier analysis. Besides, the relationship among the secondary arc current, the arcing time with different HRPC compensation degrees, neutral reactance, as well as the grounding fault locations have been investigated in detail. Finally, an improved time sequential control strategy of bypass breaker and SPAR has been put forward. The research presented in this paper will provide necessary theoretical basis and technical support for the future application of HRPC in UHV transmission lines.

Audible Noise Performance of Conductor Bundles Based on Cage Test Results and Comparison with Long Term Data

A reasonable acoustic power formula is vital to precisely evaluate the audible noise (AN) level of ultra-high-voltage (UHV) AC power lines. This study derived a formula by taking several AN measurements under heavy rain conditions, using multiple conductor bundles in a UHV corona cage, and then subjecting these measured values to least squares fitting. The validity of the proposed formula was subsequently verified with statistical data obtained from two long-term stations at Henan and Hubei Province, which are located under the Jindongnan-Nanyang-Jingmen UHV AC transmission lines operating at 1000 kV. The deviation between the prediction and the long-term (L50) value was 0.76 dB for the Henan station and 0.17 dB for the Hubei station. It shows that the acoustic power formula derived in this paper is more accurate than the widely used Bonneville Power Administration formula, in which the corresponding deviations are much larger (3.07 and 2.53 dB).

No‐load performance study of 1200 kV Indian UHVAC transmission system

Major load centres of India are located at northern part and western–southern part of country, whereas most of the generating units are concentrated at eastern and North-eastern parts. Economic transmission of bulk power over a long distance is a basic requirement for which ultra-high voltage AC (UHVAC) transmission system is identified as a feasible solution resulting in reduced transmission loss and reduced corridor width (right of way), protection of precious flora and fauna. For this, Powergrid Corporation of India along with Central Power Research Institute had made a call for indigenous development of UHVAC technology. As a result, 1200 kV UHVAC National Test Station is developed in India at Bina. One 400/1200 kV bay is successfully charged, along with one 1200 kV single circuit and one 1200 kV double-circuit test transmission line. This study deals with the study of on-site acceptance test such as sweep frequency response analysis, frequency-domain spectroscopy (FDS), along with inrush current measurement, voltage withstand test, corona measurement, thermo-vision scanning conducted on-site at no load, to ensure the performance of transmission system. A brief review of technical studies related to UHVAC technology developed throughout the World is also presented. The power transmission at 1200 kV is a feasible and viable option but further research is required in this area to make UHV transmission a global success.

Research on the electric unbalance degree of multiple transmission lines non-parallelly erected entirely in one common corridor

When multiple transmission lines are not entirely parallel erected in one common corridor, the electric unbalance degree of double-circuit ultra-high voltage (UHV) AC transmission line can be affected by several factors, such as severe electromagnetic coupling between lines in parallel section, various phase sequence arrangements and transposing modes of the lines, active power of the lines changing constantly. This paper presents a detailed analysis on the electric unbalance degree of double-circuit UHV AC line in common corridor, with particular attention to the effects of the parallel section’s length, number and the active power of the lines. The causes and factors of unbalanced currents of double-circuit UHV AC line were taken into account by phase-sequence conversion of current and voltage, and the above effects were proved by an actual example. The main factors were studied by simulating in PSCAD/EMTDC. The results show that the parallel section’s length, number and the active power of lines have considerable influences on the electric unbalance degree of double-circuit UHV AC line in common corridor. Finally, some suggestions have been proposed to provide as a construction reference to confine the level of electric unbalance degree of double-circuit UHV AC line which is not entirely parallel erected with other lines in common corridor.

An UHV Grid Security and Stability Defense System: Considering the Risk of Power System Communication

An ultra high voltage (UHV) ac and dc interconnection will become the foundation of China’s future smart grid. Due to the wide spread of interconnected regions, the distance between control stations will increase dramatically. Therefore, the communication system’s reliability and real-time performance will become increasingly crucial. However, failures of the communication system, such as interruptions, latency, and bit error, are inevitable. This paper uses the UHV grid security and stability defense system (SSDS) as an example to analyze its requirements for communication and the impact of communication failure on the system’s performance. The effect of communication latency on the power system’s stability is analyzed quantitatively and qualitatively. Based on this analysis, a framework of an UHV grid SSDS considering the risk of the communication system is proposed. A preliminary power system and communication system co-simulation tool is developed to perform a case study. The case study demonstrates that communication latency in the UHV grid changes the control strategy’s effectiveness due to a delay in executing the control strategy. Furthermore, communication latency will negatively affect the power grid’s stability.

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.

Debates on ultra‐high‐voltage synchronous power grid: the future super grid in China?

This study presents the analysis of debates on the future super grid in China. The rapid increase of power demands and the uneven distribution of energy bases and load demands in China require bulk-capacity long-distance power transmission. Two candidate solutions are thus proposed, that is, the ultra-high-voltage ac (UHVAC) synchronous power grid and the extra high-voltage ac (EHVAC) asynchronous super power grid. The debates on the above two power grids are first reviewed. The two candidate power grids are then compared in detail in terms of security, economic and environmental aspects. Finally, this study provides a suggestion for the construction of UHV synchronous power grid in China as well as the future research direction. The research, discussion and conclusion related to UHVAC and EHVAC transmissions in China are expected to provide useful references for power system planning in other countries and to promote the development of the global power industry.

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.

Investigations on Requirements for UHV/EHV AC Switchgear by CIGRE Study Committee A3

On request of IEC Technical Subcommittee 17A, CIGRE Study Committee A3 “High Voltage Equipment” investigated the requirements for ultra-high voltage ac switchgear, especially for parameters which cannot be extrapolated linearly from the corresponding equipment characteristics with lower-rated voltage, namely 800 kV. For circuit breakers, such aspects are the first pole-to-clear factor, the amplitude factor, the time to peak to define the transient recovery voltage envelope, the surge impedance of overhead lines, the damping and refraction of traveling waves, long-line faults, transformer-limited faults, initial transient recovery voltage, and the influence of shunt and series compensation. Disconnectors utilized for interrupting the bus transfer currents, bus charging currents and very fast transients, ground switches used for interrupting induced line currents, and high-speed ground or earthing switches have been studied as well. Based on these system and substation studies and simulations, recommendations have been provided to IEC SC 17A.