Direct Current Transmission Lines Research Articles

MMC-HVDC line fault identification scheme based on single-ended transient voltage information entropy

High resistance faults are the main cause of protection refusal action in high voltage direct current transmission line protection based on modular multilevel converters (MMC-HVDC). Furthermore, noise can affect the protection method. It is imperative to mitigate the High resistance faults and the influence of noise on the protection method. This paper analyzes the reasons for the difference in the initial voltage slopes of the internal and external faults under the traveling wave level. Subsequently, it analyzes the reasons for the difference in the complexity of the internal and external fault waveforms. Based on these analyses, a complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) information entropy method for line fault identification in the presence of white noise is proposed in this paper. The fault identification criteria are subsequently used to identify the internal and external faults. The transmission model of 77 level bipolar MMC-HVDC system grounded via a grounding electrode lead is simulated in the RTDS. The results show that the proposed method can enhance the anti-interference ability of the signal, identify the high resistance fault effectively and reliably, and avoid the error problem caused by a synchronous clock.

Model parameter identification for scaled-down analogous HVDC transmission lines using broad spectral response analysis

Traditional analogous π-shape transmission line models are mainly designed based on the amplitude and phase response characteristics of the distributed-parameter transmission lines at the power frequency. It cannot be directly used to build analogous high-voltage direct current (HVDC) transmission line models because the signals in a wide frequency band from 0 Hz to 10 kHz are used to protect HVDC transmission lines instead of power frequency components. In this paper, a novel model parameter identification method for scaled-down analogous HVDC transmission lines is proposed based on broad spectral response analysis. The broad spectral responses of distributed parameter-based and π-shape lumped parameter-based models are analyzed and compared with each other first. And then frequency-dependent per-unit parameters of HVDC transmission lines are obtained and used to form a modified π-shape HVDC transmission line model with the same zero- and positive-sequence​ impedance as those of distributed parameter lines. The element parameters of the π-shape circuit model are identified optimally based on the weighted sum of the results at selected several frequencies in the broadband from 0 hertz to thousands of hertz. The simulation results show that the amplitude and polarity of the dc voltage and current in our scaled-down analogous lines are close to distributed parameter-based HVDC transmission lines once a fault occurred on the lines.

Locating Natural Frequency Faults in HVDC Transmission Systems Based on the Rotation-Invariant Technology Signal Parameter Estimation Algorithm and the Total Least Squares Method

After a fault occurs in a high-voltage direct current transmission (HVDC) line, the natural frequency of the fault wave contains a wealth of transient information. The mathematical relationship between the main component of the natural frequency and the fault point can be determined and used for rapid and high-precision fault locations. To accurately extract the natural frequency of a fault and improve the positioning accuracy, a single-ended ranging scheme for extracting the natural frequency of an HVDC transient traveling wave based on the rotation-invariant technology signal parameter estimation algorithm (TLS-ESPRIT) and the total least square method is proposed for the first time. The simulation platform is used to build a dual-ended unipolar and bipolar DC transmission system model, and the scheme is simulated and verified for metallic grounding at different locations and with different transition resistances at the same location. The verification experiment was carried out on the recorded wave data of the “3.21” grounding fault of the Tianguang (Tianshengqiao-Guangdong) DC line. The results showed that the algorithm can rapidly locate the ground fault in the HVDC line and provide high ranging accuracy and good practicality.

Locating Faults in Thyristor-Based LCC-HVDC Transmission Lines Using Single End Measurements and Boosting Ensemble

Most of the fault location methods in high voltage direct current (HVDC) transmission lines usemethods which require signals from both ends. It will be difficult to estimate fault location if the signal recorded is not correct due to communication problems.Hence a robust method is required which can locate fault with minimum error. In this work, faults are located using boosting ensembles in HVDC transmission lines based on single terminal direct current (DC) signals. The signals are processed to obtain input features that vary with the fault distance. These input features are obtained by taking maximum of half cycle current signals after fault and minimum of half cycle voltage signals after fault from the root mean square of DC signals. The input features are input to a boosting ensemble for estimating the location of fault. Boosting ensemble method attempts to correct the errors from the previous models and find outputs by combining all models. The boosting ensemble method has been also compared with the decision tree method and thebagging-based ensemble method. Fault locations are estimated using three methods and compared to obtain an optimal method. The boosting ensemble method has better performance than all the other methods in locating the faults. It also validated varying fault resistance, smoothing reactors, boundary faults, pole to ground faults and pole to pole faults. The advantage of the method is that no communication link is needed. Another advantage is that it allowsreach setting up to 99.9% and does not exhibitthe problem of over-fitting. Another advantage is that the percentage error in locating faults is within 1% and has a low realization cost. The proposed method can be implemented in HVDC transmission lines effectively as an alternative to overcome the drawbacks of traveling wave methods.

A Novel Single DC Source Three-Phase Wye Packed U-Cell (Y-PUC) Converter

A new configuration of three-phase Wye Packed U-cells (Y-PUC) with a single DC source is proposed in this paper. In fact, this configuration represents a single DC source modular three-phase PUC converter. The DC source on PUC topology is replaced by a flying capacitor to obtain a suitable submodule. Moreover, the modularity of the Y-PUC configuration makes it an appropriate alternative for MMC applications. Furthermore, the proposed structure is an advantageous configuration for high voltage applications such as high voltage direct current (HVDC) transmission lines with the capability of DC fault handling. All PUC topologies such as PUC5, PUC7, PUC9, PUC15 can be replaced in the modules of this proposed single-phase and three-phase configuration to multiply the load voltage levels for improving the output waveform. Active voltage balancing technique through carrier-based modulation is applied. System modeling and operating sequences are developed. Simulation and experimental results are presented and discussed to validate the performance of the proposed structure.

Location of Sequential Shunt Faults in HVDC Lines

This work deals with the problem of the diagnosis of two shunt faults in a high-voltage direct current (HVDC) transmission line modeled by a set of linear partial differential equations. Because the fault scenario of a transmission line subject to two simultaneous shunts is indistinguishable from measurements at the boundaries in steady state, a sequential fault scenario is assumed in this work. This consideration allows estimating on-line the magnitude of the shunt current and the position for a weighted average fault by using the magnitude position fault estimator (MPFE), and also isolating the faults by recording the data history of the line. To identify the sequence of faults from the error of the MPFE, a new weighted average position relation (WAPR) is derived, which is part of the main contribution. Thus, the solution consists of a combination of detection and isolation stages; the first one determines the presence of weighted average shunt faults through an MPFE. Furthermore, the second one uses historical data to calculate the physical fault parameters. Simulations for HVDC transmission line data by ATPDraw show the performance of the approach.

A Sensor for Three-Dimensional Component Measurement of Synthetic Electric Field Vector in HVDC Transmission Lines Using Unidirectional Motion

High voltage direct current (HVDC) transmission lines have been widely used in China, and the electromagnetic effects of the synthetic electric field generated by them on the surrounding environment have attracted more and more attention. Especially when there are residential buildings around the transmission lines, the distortion of the electric field makes the research and development of synthetic electric field sensors with three-dimensional (3D) measurement capability an urgent technical demand. Based on the basic principle of the field mill electric field sensor, this paper presents a three-dimensional field mill structure to obtain the three-dimensional component of the electric field vector by using unidirectional motion. With the signal processing circuit, we realize the reading of three-dimensional electric field data. The feasibility of the proposed structure is verified by theoretical deduction analysis, numerical simulation, and prototype tests. The proposed structure provides a new scheme to solve the problems of three-dimensional synthetic electric field measurement and can enrich the existing methods.

The hybrid simulation system of hydropower generation units in islanding AC grid and its applications

It is a trend for the large hydropower bases to transport the electricity to consuming center with High Voltage Direct Current (HVDC) transmission lines. The fault of HVDC has great significance impact on hydropower units in islanding sending AC grid. In this paper, a hybrid simulation system is established to analyze the dynamic characteristic of hydropower units in islanding system. The simulation system is based on Real Time Digital Simulator (RTDS) and Digital Signal Processor (DSP). The simulation of electromagnetic transient process in the generator, the load, the network and HVDC is completed by RTDS. The Hydroturbine Real Time Simulator (HRTS) based on DSP completes the simulation of hydraulic-mechanical-electrical transient process in hydroturbine, division system and governing system. The real time data communication between RTDS, HRTS and external equipment ensures the real time calculation of simulation. The simulation results show high coincidence with field data. The hybrid simulation system is an effective approach for the research of islanding system at sending terminal with HVDC.

Transient Surface Charge Characteristics of DC-GIL Insulator Under Thermal-Electric Coupled Fields

The insulator in direct current gas-insulated transmission lines (DC-GIL) would suffer discharge risk due to surface charge accumulation under thermal-electric coupled fields. In this paper, the transient surface charge accumulation characteristics of a basin-type DC-GIL insulator is investigated via finite element method based on a three-dimension horizontally installed GIL model. The stationary temperature distribution of the model is obtained and then applied to the transient simulation of charge. Weak form partial differential equation is employed to deal with the ion transportation equation. Equations and parameters in the simulation are optimized to reduce the computing memory and time. Results indicate that the charge accumulation is accelerated due to the promotion of conduction through the insulator under thermal gradient. Higher charge density is obtained under thermal gradient. And the surface charge density of the convex surface is higher due to the promoted conduction. The highest field strength increases and the corresponding location moves along the convex surface during the transient process. This could attribute to the influence of transient charge behavior under thermal gradient on the electric field distribution. This study indicates that the thermal gradient and transient charge accumulation should be considered when dealing with the insulation characteristics of DC-GIL with insulators.

Significance of fault-current-limiters and parameters optimization in HVDC circuit breakers for increased capacity of VSC-HVDC transmission networks application

The voltage and current ratings of the voltage source converter (VSC) based high voltage direct current (HVDC) transmission line projects have increased over the years. It testifies the increasing popularity of VSC-HVDC technology. Since the long-distance, VSC-HVDC transmission lines are more exposed to commonly appearing short circuit faults; thus, protection equipment with increased fault-current handling capability is required. The DC circuit breakers (DCCBs), with or without fault current limiters (FCLs), can effectively handle the fault-current. The variations in VSC-HVDC projects’ ratings and their impact for DCCB with FCL and without FCL are thoroughly analysed in this paper. The paper further includes an in-depth discussion on DCCBs with FCL and without FCL. An equivalent circuit modelling approach is used for simulation analysis of three case studies under the influence of these breakers to analyse current behaviour; the case studies include the Zhoushan HVDC Project, Xiamen HVDC Project, and Zhangbei-I HVDC Project. All these projects have different capacities in terms of their power, voltage, and current ratings. For DCCBs, this paper includes a detailed analytical model to understand the fluctuations in the size of fault-current limiting components (in DCCBs) for increased fault-current handling requirements. The simulation results using PSCAD/EMTDC and MATLAB are presented to verify different aspects of this study. A small scale laboratory prototype is also developed to validate the performance of DCCB with and without FCL. Based on theoretical, simulation, and experimental validations, it is substantiated that for increased VSC-HVDC projects’ ratings, DCCB with FCL can perform better compared to conventional DCCB without FCL.

Multifunctional scheme for frequency/voltage/stability control in HVDC line under concurrent cyber‐attacks and faults

This paper presents a control mechanism on high voltage direct current (HVDC) transmission line for frequency/voltage regulation, fault ride through (FRT) capability, and cyber-attack/fault detection. The network under study consists of two areas with different frequencies that are connected through one 300 km HVDC line. The proposed control system regulates the frequency in both areas by managing power through HVDC line. The converters on both sides of HVDC line are controlled to handle faults on the DC and AC sections as well as improving fault ride through capability. The control strategies are implemented and operated depending on fault/cyber-attack type and behaviour. In this respect, the control mechanism may change the firing angle of converters, switch their operating mode from rectifier to converter and vice-versa or even block the converters. The proposed paradigm successfully distinguishes between the cyber-attacks and faults. The simulations in MATLAB software validate that the proposed mechanism realizes all the objectives and the cyber-attacks are completely identified and separated from the faults.

Power Transfer Control Strategy Based on True Bipolar MMC-MTDC System

The true bipolar modular multilevel converter-based multi-terminal direct current (MMC-MTDC) DC transmission line is prone to single-pole grounding fault, which may cause overload and overcurrent of the non-fault DC line with fault poles, resulting in system protection misoperation and system collapse. Therefore, the power transfer control strategy should be adopted to improve system stability. In addition, considering that the commutator stations of true bipolar MMC-MTDC system may have unipolar faults, it is necessary to adopt the control strategy of inter-pole power transfer or inter-station power transfer to improve the transmission capacity of the system under fault conditions. In this paper, a power transfer control strategy is proposed, which is widely applicable to MMC-MTDC system. In the case of line fault, the power transfer takes into account the line power margin and the power margin of converter station. The inter-pole power transfer is better than the inter-station power transfer under the converter station fault condition, and the inter-station power transfer takes into account the priority of the power margin of the converter station. At the same time, based on the Zhangbei four-terminal flexible direct current transmission project, the Zhangbei four-terminal flexible direct current transmission system is built by using PSCAD/EMTDC, and the flexibility and effectiveness of the proposed strategy are verified by simulation.

Causal theory on acceleration of seed germination in the vicinity of high voltage direct current transmission line

Seed germination is the primary stage of growth in a seed. A wealth of experiments exist in literature to support the existence of correlation between seed germination to the electric and magnetic fields. This becomes more important as researchers have suggested to develop technologies to build ecologically clean and environment-friendly solutions to agricultural practices. Although the literature supports the existence of seed germination acceleration, the lack of a definite causal theory has been observed by numerous researchers over decades. After considering all the existing experimental data, we have formulated a causal theory to explain the factors influencing seed germination around high voltage DC transmission lines. This work opens new avenues of research in this field.

AN ECONOMIC AND TECHNICAL REVIEW FOR THE UTILIZATION OF HVDC IN TURKEY AND IN THE WORLD

In recent years, it is seen that High Voltage Direct Current (HVDC) transmission line systems have come to the fore in the field of energy efficiency in the world. Therefore, it is predicted that analyzing the technological and economic advantages of HVDC transmission line systems will make an important contribution to energy efficiency policies. In this regard, this study aims to examine the technological and economic advantages of HVDC transmission systems through the historical development with applications in Turkey and in the world. In addition to this, it is expected that the evaluation of the effects of energy efficiency on the economy will bring a different perspective to the energy and economic literature. Therefore, it is thought that energy and economic policies for the spread of HVDC transmission line systems worldwide will be essential. The asymmetric distribution of natural energy sources in the world causes energy supply security problems in the countries such as Turkey in terms of high foreign dependence on energy. For this reason, it is necessary to meet the increasing energy demand and increase the existing capacity day by day. Besides, it is important to develop policies for efficient use of energy. HVDC technology is extremely important for a developing country like Turkey. Moreover, it is known that this energy transmission technology has become widespread in developed countries. Thereby, a technical comparison is done for investment costs of the transmission system in Germany. As a result, other than bringing economic benefits with the energy transmission of Turkey through HVDC, it has important potential for making energy transmission possible with her neighbors and European Union countries.

Metal particle induced spacer surface charging phenomena in direct current gas-insulated transmission lines

The interpretation of the surface charge pattern of spacers in gas-insulated transmission lines (GIL) is a research topic with great importance, which requires a comprehensive understanding of charge behaviors at physical interfaces. Here, we report a surface charging phenomenon of spacers in the presence of metal particles inside the direct current (DC) GIL. The charging of spherical metal particles on the spacer surface appears as dotted discontinuously distributed charge spots, which are due to the charge injection from the induced charge of the metal particle and gas ionization over the metal particle surface. Concentrically distributed bipolar charge patterns are seen to build up, which are due to the surface trapping of charges from gas ionization at the end tip of the acicular metal particle. The lateral type of ionization obeys the law of dielectric barrier discharge of the needle-plate electrode in an intense DC electric field, which may bring significant influence on the safety of the spacer. The study in this letter provides direct evidence demonstrating the surface charge patterns of spacers in the presence of metal particles, which serves as an important basis for the design of DC GIL.

Testosterone synthesis in testicular Leydig cells after long-term exposure to a static electric field (SEF)

China’s clean energy and resources are mainly located in the west and north while electric load center is concentrated in the middle and east. Thus, these resources and energy need to be converted into electrical energy in situ and transported to electric load center through ultra-high voltage direct current (UHVDC) transmissions. China has built 25,000 km UHVDC transmission lines of 800 kV and 1100 kV, near which the impact of electric field on health has attracted public attention. Previous studies showed that time-varying electromagnetic field exposure could disturb testosterone secretion. To study the effect of non-time-varying electric field caused by direct current transmission lines on testosterone synthesis, male ICR mice were continually (24 h/d) exposed to static electric field of 56.3 ± 1.4 kV/m. Results showed that on the 3rd day of exposure and on the 7th day after ceasing the exposure of 28 d, serum testosterone level and testicular oxidative stress indicators didn’t change significantly. On the 28th day of exposure, serum testosterone levels, testicular glutathione peroxidase (GSH-Px) activity, the mRNA and protein levels of testicular StAR, PBR, CYP11A1 decreased significantly, and testicular malondialdehyde (MDA) content increased significantly. Meanwhile, electron-dense edges and vacuolation appeared in lipid droplets of Leydig cells. The gap between inner mitochondrial membrane (IMM) and outer mitochondrial membrane (OMM) enlarged, which would cause the swelling of mitochondria, the rupture and deficiency of mitochondrial membranes. Analysis showed that testicular oxidative stress could induce the damage of mitochondrial structure in Leydig cells, which would decrease the rate of cholesterol transport from cytoplasm to mitochondria. Since cholesterol is the necessary precursor of testosterone synthesis, testosterone synthesis was inhibited. The decrease of the mRNA and protein expression levels of StAR and PBR in testes could diminish the cholesterol transported from OMM to IMM. The decrease of the mRNA and protein expression levels of CYP11A1 could reduce the pregnenolone required in testosterone synthesis and inhibit testosterone synthesis consequently.

A New Press Pack IGBT for High Reliable Applications With Short Circuit Failure Mode

The modular multilevel converter (MMC or M2C) technology becomes the mainstream solution in today's voltage source converter-high voltage direct current (VSC-HVDC) transmission lines because of its unique performance. Recently press pack IGBT (PPI) has come into focus as a preferred realization for high power rating VSC-HVDC stations, it could offer the highest current rating IGBTs and advanced features in reliability. A new PPI is introduced in this paper, which is designed for several innovative improvements based on the application demands from VSC-HVDC systems. The chip is optimized for low on-state voltage with advanced trench technology, and well protected in a chip-stack by double side sinter process. The disc package is designed with hermetic sealed ceramic housing to avoid environmental erosion and could provide a robust feature of short circuit failure mode (SCFM), which is fully qualified under the worst-case scenario. In addition to the PPI device, system solutions had also been developed and investigated to support field developments, including electrical and mechanical design. An example of a power stack is analyzed in commutation loop, pressure distribution, and power losses.

Particle simulation of streamer discharges on surface of DC transmission line in presence of raindrops

The streamer discharge occurring on the surface of a conductor in rain is one of the critical problems associated with the design of high voltage direct current (HVDC) transmission lines. In this paper, the streamer discharges on the conductor surface in the presence of raindrops at atmospheric pressure are studied by use of two-dimensional particle-in-cell simulations with Monte Carlo collisions included. The influences of the drop angles, volumes, and spatial distributions of raindrops on the development of streamer discharges have been demonstrated. The formation of streamer discharges and the involved electric fields, plasma densities, propagation velocities, and discharge currents are presented. It is found that the discharge intensity decreases significantly with an increasing of the drop angle. The dividing point at the 95° angle is suggested. With an increase of the raindrop volume and the distance of raindrops, strong discharges with the advanced discharge time, faster propagation velocity, larger electric field, and higher plasma density are initiated. Moreover, the electron energy probability functions of different discharges have been studied, which are nonequilibrium and reveal kinetic behavior of the discharges. The simulation results, which are qualitatively in agreement with the previous experimental observations, bring new insight into the discharge dynamics and provide useful references for the protection of HVDC transmission lines in rainy days.

Impacts of moisture absorption on electrical properties of rigid polyurethane foam for composite post insulator of UHVDC transmission line

Polyurethane-based porous material is a promising candidate for internal insulating medium of composite post insulators of ultra-high voltage direct current transmission line because it avoids the gas leakage of SF6 or N2 post insulator and is superior to the epoxy resin post insulator in weight. In this paper, firstly, a series of rigid polyurethane foams with various diphenylmethane diisocyanate contents are synthesized and cell morphology is investigated. Thereafter, the effects of temperature and exposure time on hygroscopicity of polyurethane foams at various humidity levels (non-immersion in water) are explored. With the ultimate goal of polyurethane foams for use in internal insulation of composite insulator, the impacts of moisture absorption on electrical properties of polyurethane foams are studied systematically. The moisture absorption results of polyurethane foams of various ratios demonstrate that they increase with the relative humidity and temperature and they exhibited a saturation state. The volume resistivity and breakdown strength of polyurethane foam with various diphenylmethane diisocyanate contents all decrease significantly with the increase of relative humidity. The great differences of breakdown field are found at different Weibull slope of intrinsic breakdown. Simultaneously, the permittivity and loss of foam specimens all increase significantly after the moisture absorption, especially foams of 1:0.9 and 1:1.3. It is found that the appropriate ratio of raw material could result in a significant improvement of the dielectric losses.

Renewable energy transport via hydrogen pipelines and HVDC transmission lines

The majority penetration of Variable Renewable Energy (VRE) will challenge the stability of electrical transmission grids due to unpredictable peaks and troughs of VRE generation. With renewable generation located further from high demand urban cores, there will be a need to develop new transmission pathways to deliver the power. This paper compares the transport and storage of VRE through a hydrogen pipeline to the transport of VRE through a High Voltage Direct Current (HVDC) transmission line. The analysis found a hydrogen pipeline can offer a cost-competitive method for VRE transmission compared to a HVDC transmission line on a life-cycle cost basis normalized by energy flows for distances at 1000 miles with 2030 technology. This finding has implications for policy makers, project developers, and system operators for the future development of transmission infrastructure projects given the additionality which hydrogen pipelines can provide in terms of energy storage.