Voltage Direct Current Transmission Lines Research Articles

Economic viability assessments of high voltage direct current for wind energy systems

This research shows an economic assessment for decision-makers of high voltage direct current utilization in wind energy systems applied to a case study in Turkey. The increasing energy demand in Turkey can be supplied effectively by this transmission in long distances and leading the use of renewable energy sources. Thereby, wind energy systems are being one of the main developed renewable sources, but the economic feasibility of its feature has been demonstrated only in some cases. The transmission of wind energy is possible both inside a country and between the countries, depending on the deployments about the utilization of high voltage direct current technology, operating with renewable energy systems. Thus, life-cycle cost scenarios are proposed by recommending a 1,000 km length high voltage direct current overhead transmission line in optimum economic conditions between Canakkale and Samsun-Bafra to transport energy from wind farms. The economic feasibility of these systems can be proven by showing the comparison between investment cost and profit from the 25 years life-time of the project. A novel cumulative cash flow analysis is applied for this comparison employing the net present value. A voltage source converter and a current commuted converter are considered in the scenarios. The findings show that voltage source converter can be chosen for both overhead and cable transmission for wind energy systems with the need of government subsidies in the investment. Moreover, the possibility of the investment is discussed through economic terms, i.e., the positive externality, the opportunity cost and the economies of scale. Therefore, this study can be taken as a pre-model for both the other regions of Turkey and for the developing countries.

Artificial Neural Network-based Fault Location in Terminal-hybrid High Voltage Direct Current Transmission Line

In this article, a fault location technique based on artificial neural networks (ANN) for Terminal-Hybrid LCC-VSC-HVDC has been assessed and scrutinized. As is known, in conventional HVDC systems (LCC-based and VSC-based HVDCs), the same type of filter is used on both sides due to the use of similar converters in both sender and receiver terminals. In this article, it is concluded that due to the use of two different types of converters at the both ends of the utilized Terminal-hybrid LCC-VSC-HVDC system, and the use of different DC filters on both sides, fault location using positive and negative pole currents of the rectifier side has much better results than the rest of input signals. Therefore, it will be finalized that by increasing and designing suitable DC filters on the transmission line of HVDC systems, fault localization matter will be remarkably and surprisingly facilitated. Nowadays, the fault location of HVDC transmission lines with a value of more than 1% is generally discussed in most articles. In this research, the fault location with a value of 0.0045%, i.e., a distance of 22.5 meters from the fault point in the most satisfactory case is obtained, which shows the absolute feasibility of the ANN along with the wavelet transform. To validate the proposed method, a ±100 KV, Terminal-hybrid LCC-VSC-HVDC system is simulated via MATLAB. The outcomes verify that the proposed technique works perfectly under various fault locations, resistances, and fault types.

Optimal Configuration Method for the Installed Capacity of the Solar-Thermal Power Stations

Because of the randomness of wind power and photovoltaic (PV) output of new energy bases, the problem of peak regulation capability and voltage stability of ultra-high voltage direct current (UHVDC) transmission lines, we proposed an optimum allocation method of installed capacity of the solar-thermal power station based on chance constrained programming in this work. Firstly, we established the uncertainty model of wind power and PV based on the chance constrained planning theory. Then we used the K-medoids clustering method to cluster the scenarios considering the actual operation scenarios throughout the year. Secondly, we established the optimal configuration model based on the objective function of the strongest transient voltage stability and the lowest overall cost of operation. Finally, by quantitative analysis of actual wind power and photovoltaic new energy base, this work verified the feasibility of the proposed method. As a result of the simulations, we found that using the optimal configuration method of solar-thermal power stations could ensure an accurate allocation of installed capacity. When the installed capacity of the solar-thermal power station is 1 × 106 kW, the transient voltage recovery index (TVRI) is 0.359, which has a strong voltage support capacity for the system. Based on the results of this work, the optimal configuration of the installed capacity of the solar-thermal power plant can improve peak shaving performance, transient voltage support capability, and new energy consumption while satisfying the Direct Current (DC) outgoing transmission premise.

Numerical Investigation on the Effects of Wind and Shielding Conductor on the Ion Flow Fields of HVDC Transmission Lines

Ion flow field is an important aspect of high voltage direct current (HVDC) transmission lines. In this paper, we apply the upwind finite volume method for solving the ion flow field of three HVDC configurations to clarify the effect of the wind and the role of shielding conductors. For the monopolar configuration installation, the ground current distribution with underbuilt shield wires was studied numerically and experimentally. For the ±250 kV bipolar configuration, the calculated peak electric field and current density are verified with the values in a reference. The ±500 kV bipolar configuration is used to investigate the change in electric field and ion current within the same corridors of the existing HVAC lines. We analyze the ion flow field with and without the dedicated metallic return conductor (DMRC). In the absence of wind, the maximum of the electric field is lower than that of the HVAC lines and the current density is very low on the ground. In the presence of wind, the electric field and the current distribution become unsymmetrical on the ground level. The peak current density increases significantly on the downwind side. The HVDC line without DMRC has the electric field peak higher than that of the HVAC lines. With the higher wind shear coefficient, the peak of the electric field and the current density increases on the downwind side. Overall investigations summarize that DMRC can effectively reduce the peak of the electric field to be lower than that of the existing 500 kV HVAC lines under all wind conditions.

Direct current volt-ampere characteristics of long arc on ice surface

With the continuous construction of ultra-high voltage transmission lines, the problem of long insulator string ice flashover in the icing area is becoming more and more prominent. At present, only the volt-ampere characteristics of short arc on the ice-surface have been studied in the previous research. However, the volt-ampere characteristics of the long arc on ice-surface are significantly different from the short arc, so the flashover characteristics obtained from the short insulator string aren’t suitable for the long string under icing conditions. Therefore, in this paper, the volt-ampere characteristics of direct current long arc on the ice-surface are measured by using ice column in a multi-functional artificial climate chamber. The results show that the arc length has an effect on the volt-ampere characteristic constant A, exponent n and expression. In addition, the dynamic volt-ampere characteristics and the static volt-ampere characteristics are redefined and studied, which lays a foundation for the flashover voltage prediction of long iced insulator string. The research of this paper has important theoretical guiding significance for the external insulation design of ultra-high voltage direct current transmission lines in icing areas.

Stability Behavior and Optimization of Tension Plates in Transmission Lines in Heavy Ice Zones

Finite element model of a typical ultra-high voltage direct current transmission line section, in which buckling collapse of the tension plate took place during operation, is established. In the finite element model, the tension plate and the connected hardware fittings are discretized with 3D solid elements and the sub-conductors, spacers, clamps and insulator strings with spatial beam elements. Dynamic responses of the line after ice shedding are numerically simulated and the maximum loads on the tension plate in the cases with different ice thicknesses and ice-shedding are obtained. Buckling behaviors of the tension plate are analyzed and the conditions leading to buckling collapse are discussed. Finally, the topology optimization of the tension plate is performed and two optimized schemes of the tension plate are proposed based on the optimization result and manufacture cost. Efficiency analysis demonstrates that the buckling loads of the optimized tension plates increase more than 20% nearly without increasing weight.

Faults identification in high voltage direct current transmission lines using adaptive neuro-fuzzy inference system

ABSTRACT This paper presents an innovative approach in line commutated converter-based high-voltage direct-current (LCC-HVDC) transmission line for recognizing the section of the faults. In this work, three adaptive neuro-fuzzy inference system (ANFIS) modules have been suggested to investigate the safety responsibilities in the LCC-HVDC line. The ANFIS-1 aims to ascertain the faults in both sections; ANFIS-2 is to distinguish the section of the fault; and ANFIS-3 is to recognize the characteristics of the fault. To ascertain the effectiveness of the ANFIS approach, it has been compared with the differential protection (DP), wavelet transform (WT), fuzzy and artificial neural network (ANN). Furthermore, the proposed methods have been tested by varying the fault resistance (up to 500 Ω), power angle (from 5 to 15 degrees), near and end faults, and changing the transmission line parameters (±15 %). The simulation outcomes are disclosed that the proposed ANFIS technique yields better performance than other studied methods in terms of percentage of accuracy, time of fault section recognition, and reach setting.

GADF-VGG16 based fault diagnosis method for HVDC transmission lines.

Transmission lines are most prone to faults in the transmission system, so high-precision fault diagnosis is very important for quick troubleshooting. There are some problems in current intelligent fault diagnosis research methods, such as difficulty in extracting fault features accurately, low fault recognition accuracy and poor fault tolerance. In order to solve these problems, this paper proposes an intelligent fault diagnosis method for high voltage direct current transmission lines (HVDC) based on Gramian angular difference field (GADF) domain and improved convolutional neural network (VGG16). This method first performs variational modal decomposition (VMD) on the original fault voltage signal, and then uses the correlation coefficient method to select the appropriate intrinsic mode function (IMF) component, and converts it into a two-dimensional image using the Gramian Angular Difference Field(GADF). Finally, the improved VGG16 network is used to extract and classify fault features adaptively to realize fault diagnosis. In order to improve the performance of the VGG16 fault diagnosis model, batch normalization, dense connection and global average pooling techniques are introduced. The comparative experimental results show that the model proposed in this paper can further identify fault features and has a high fault diagnosis accuracy. In addition, the method is not affected by fault type, transitional resistance and fault distance, has good anti-interference ability, strong fault tolerance, and has great potential in practical applications.

A waveform-similarity-based protection scheme for the VSC-HVDC transmission lines

The protection for the voltage source converter based high voltage direct current (VSC-HVDC) transmission lines must detect the faulty DC lines and faulty poles within a few milliseconds, because the fault current rises quickly. The traditional protections are easily influenced by fault resistance and signal noise. What is worse, the double-pole-to-ground (DPG) fault with its positive-pole fault resistance unequal to negative-pole fault resistance cannot be detected accurately. To solve the problems, a non-unit protection scheme based on the waveform similarity and wavelet transform modulus maximum (WTMM) theories for the VSC-HVDC lines is proposed in this paper. A four-terminal VSC-HVDC power network is modeled in PSCAD to verify the protection. Extensive simulations of various fault situations prove that the protection scheme can detect high-fault-resistance, DPG, and remote faults. Moreover, it is insensitive to the sampling frequency, signal noise, smoothing reactor, and start delay. Furthermore, it can meet the rapidity requirement. Therefore, the proposed protection can identify the DC faults accurately, which minimizes the disturbance to power grids and improves system security and stability.

A life-cycle cost analysis of High Voltage Direct Current utilization for solar energy systems: The case study in Turkey

With technological advancements in High Voltage Direct Current, solar energy transmission over long distances and between countries is now possible. As a result, this paper conducts a thorough Life-cycle cost analysis in Turkey. To that end, a 1000 km long High Voltage Direct Current Overhead Transmission Line between Mersin, Balikesir, and Istanbul is being built, which will transport energy generated by solar power plants from potentially high solar regions to the most energy-deficient regions. The motivation is testing the hypothesis that any investment should be contingent on the investment cost, being it amortized and generating profits for the interest rate of any country. This hypothesis is tested in this paper with a comparative cumulative cash flow for High Voltage Direct Current converters using the net present value. Data is gathered from various studies as well as the Central Bank of the Republic of Turkey. The 27-year Life-cycle cost projection has shown that the Voltage Source Converter-High Voltage Direct Current-Overhead Transmission Line outperformed the best with a 448,61 M€ net present value, and a break-even 9 years after the beginning of the project pertained to a 1500 MW power rating option. This investment satisfies Turkey's condition in terms of opportunity cost and positive externality. The innovation of this paper is the proposal of an efficient operation of increasing solar energy systems with increasing High Voltage Direct Current transmission systems as an alternative energy solution to meet energy demands in the context of a growing economy. Meanwhile, this research can serve as a model for developing countries, not only for economic reasons, but also for environmental concerns.

Research on audible noise of ultra-high voltage direct current (UHV DC) transmission lines with a digital twin

Much attention has been paid to audible noise in the design of ultra-high voltage (UHV) direct current (DC) transmission lines because of its negative impact on residents' lives. In order to analyze audible noise, shorten the research period, and reduce experimental costs, firstly, a digital twin model for audible noise of UHV DC transmission lines is proposed. Then, the model’s structure and related principles are explained in detail. Finally, an application, as a research paradigm, uses digital twin to study the source distribution on transmission lines and influencing factors of audible noise. The A-weighted sound level of audible noise on the ground is calculated and compared with the data obtained by the BPA empirical formula. The results show that the position of the sound source tends to have uniform distribution and the intensity tends to have Gaussian distribution, while temperature and relative humidity exert obvious effects on audible noise, illustrating the great value of digital twin technology in the study of audible noise. This paper not only provides a new method for audible noise research, but also provides a reference for the design of UHV DC transmission lines.

Fault Detection Using Backward Propagating Traveling Waves for Bipolar LCC-HVDC Lines

The line commutated converter (LCC)-high voltage direct current (HVDC) transmission lines may have various complementary protection algorithms based on derivatives of line parameters or differential line currents. The DC line fault detection based on distance relaying, traveling wave (TW), artificial neural network, fuzzy logic, and wavelet are a few of the popular schemes. However, the TW-based technique has been reported as one of the fastest techniques to detect and locate faults. The conventional TW techniques face limitations in detecting high resistance DC line faults. Therefore, this paper introduces an improved fault detection, classification, and location algorithm based on backward propagating TWs and fault classifier indices. The proposed algorithm is tested to detect, classify, and locate the faults under different system conditions such as pole-to-ground, pole-to-pole, and rectifier and inverter sides’ external faults. A bipolar LCC-HVDC transmission system of 900 km length is utilized to simulate the various fault conditions. The simulation results indicate fast, accurate, and reliable detection of faults. This scheme uses only single-end data measurement. The simulation study was performed for various fault locations (0–900 km) and transition resistances (0–150 Ω).

Fault detection and diagnosis of monopolar configured VSC based high voltage direct current transmission line

The development of HVDC transmission technology using an MMC has been promoted, by overcoming the drawbacks of traditional VSC technology. The extension of flexible transmission to overhead lines, especially the use of HVDC transmission based on an MMC, raises the issue of DC fault. So identification of fault, clearing the dc fault, and design of fast-acting protection system operating against fault becomes significant. This article provides insights on the monopolar structured MMC and operational characteristics, fault analysis, and a fault protection scheme. DC line faults on HVDC lines using MMC-VSC are major issues; isolation of complete system is not a viable option. It is observed that Pole to ground fault is the most common fault, which leads to generous overcurrent in the AC grid and results in converter valves getting damaged. This article analyzes the response of MMC-HVDC under different DC and AC faults conditions for five-level MMC HVDC systems, to better understand systems under fault. Faults also have an impact on the converter stations' performance. The voltages fluctuate in faulty situations. In comparison to the inverter station, the rectifier station has the most impact. Simulation is performed out in PSCAD software. The correctness and effectiveness of DC and AC fault analysis helps to check the capability of locating fault occurring on HVDC transmission lines quickly and accurately

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.

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.

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.

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.