Voltage Direct Current Transmission Lines Research Articles

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.

A new combined adaptive cumulative sum‐based fault detector for multi‐terminals high voltage direct current transmission lines

A new combined adaptive cumulative sum‐based fault detector for <scp>multi‐terminals high</scp> voltage direct current transmission lines

Optimal Location of High Voltage Direct Current (HVDC) Transmission Line using Genetic Algorithm

The aim of this research is to study the effect of HVDC transmission systems on reducing power losses and improving voltage profile. This paper presents a solution to the problems of an overloaded transmission line through selecting the optimal location for the HVDC system. For this purpose, a Genetic Algorithm (GA) uses to optimize the voltage profile, reduce power losses and handle power flow in overloaded transmission lines. MATLAB utilizes to engage both the GA and Newton Raphson method to solve the load flow problem. The proposed approach examined and tested on the IEEE Large Scale 57-bus test system. Power System Simulator for Engineering (PSS/E) package Version 32.0 is used as practical part to solve the functions of power system performance. The results demonstrated the ability of the proposed method to determine the optimum location of the HVDC line which reduces power loss and improves the “voltage profile” of the bus.

A Novel Relaying Scheme Using Long Short Term Memory for Bipolar High Voltage Direct Current Transmission Lines

In this paper, a novel relaying scheme is proposed for bipolar line commutated converter (LCC) high voltage direct current (HVDC) transmission lines that detects the fault, identifies the pole of fault and estimates the location of the fault. The scheme uses features extracted from rectifier end DC current and voltage signals. Long short term memory (LSTM), a deep learning method has been designed as classifier as well as predictor for carrying out different relaying tasks. Three modules have been designed namely LSTM-FD (LSTM module for fault detection (FD)), LSTM-FI (LSTM module for fault pole identification (FI)) and LSTM-FL (LSTM module for fault location estimation (FL)). The voltage and current signals are obtained from measuring units. Then with a moving window of one cycle, the RMS of signals is calculated. The current and voltage features are obtained in the time domain. The voltage and current features obtained are used as input to fault detection and fault pole identification module. For fault location estimation, half cycle samples of RMS current and voltage after the fault have been taken. From half cycle sample, maximum value of current and minimum value of voltage has been obtained. This single value of current and voltage are used as input feature to the fault location module. All the relaying modules have been tested varying fault types, locations, resistances, smoothing reactors, noisy signals, etc. Sensitivity and reliability of the proposed relaying scheme is 100% with all the tested fault cases. Error in location estimation is within 1% for all the tested fault cases. Advantage of the method is that it does not require communication link. Another advantage of the proposed method is that it can work with low sampling frequency. Additionally, reliability and sensitivity of proposed method is very high, hence can be used as an alternative to travelling wave based relaying schemes.

Improved Flux Tracing Method Based on Parametric Curve for Calculating Ion Flow Field of HVDC Transmission Lines

An improved method for tracing electric flux lines in the vicinity of the overhead high voltage direct current (HVDC) transmission lines is developed by using parametric curves. Based on the geometric relation between the electric field vector and the derivative of the parametric curve function, the electric flux lines can be successfully traced without accumulation of the numerical error caused by the differentiation for calculating the electric potential. Considering the structural characteristics of the transmission line, the control points at both ends of the parametric curve can be easily located, and the remaining control points are modified to minimize an error function defined by the electric field vectors at nodes along the curve. Once the electric flux lines are traced, a series of flux tubes is created by bundling adjacent flux lines, and the nodal electric field vectors and space charge densities are iteratively updated. In order to consider the ionized space charge effect, new flux lines of modified electric field are traced, which in turn affects the existing space charge distribution. The process is repeated until the effect of the space charge is fully considered. The performance of the proposed algorithm is verified by comparing the resulting ground profiles of the ion flow field distribution with the result of the analytical model and the long-term measurement of the full-scale transmission line.

Influence factors analysis of ionized field characteristics of Zhangbei ±500kV flexible direct current transmission lines

The ionized field should be controlled in order to insure the environmental friendliness of high voltage direct current (HVDC) transmission lines. Different with traditional HVDC transmission lines, the metal return lines is first employed in Zhangbei ±500kV flexible HVDC lines. In this paper, the characteristics of ionized field with and without metal return lines are calculated on the basis of numerical method with Deutsch’s assumption. The influence factors, i.e. roughness coefficient, distance between metal return line and height of the metal return line, are analysed in detail. The results show that the metal return lines will have a shield effect on the ionized field on the ground. The distribution of ionized field is nearly independent on the height of metal return line. The shielding effect of the metal return line mainly contributes to the projection position of the metal return line. The presented results can give instructions for the design and control of the ionized field level of flexible HVDC lines with metal return lines.

Novel pilot protection scheme for line‐commutated converter high voltage direct current transmission lines based on behaviour of characteristic harmonic impedances

Novel pilot protection scheme for line‐commutated converter high voltage direct current transmission lines based on behaviour of characteristic harmonic impedances

A Review on Real-Size Epoxy Cast Resin Insulators for Compact High Voltage Direct Current Gas Insulated Switchgears (GIS) and Gas Insulated Transmission Lines (GIL)—Current Achievements and Envisaged Research and Development

Due to the ever-increasing demand for electricity in the one hand and the environmental constraints to use clean energy on the other hand, the global production of energy from remote renewable sources, particularly from large hydropower plants and offshore wind farms and their connection to the grid are expected to grow significantly in the future. Consequently, the demand to carry this electric power by high voltage direct current (HVDC) technology will increase too. The most suitable HVDC power transmission technology to deliver large amounts of power, exceeding a capacity of 5 GW per bipolar system over long distances with lower losses is by using compact HVDC gas insulated transmission lines (DC GIL) and gas insulated switchgears (DC GIS) with rated voltage (maximum continuous operating voltage) of ±550 kV and 5000 A which are presently under development worldwide. Among the critical challenges for the development of these HVDC gas insulated systems, there are the epoxy cast resin insulators that are used to separate gas compartments also called spacers. Indeed, thorough research studies have been and still being carried out to well understand and clarify the electrical insulation characteristics of HVDC spacers using mainly cylindrical samples and small insulator models, where useful results have been obtained and proposed for implementation in real compact gas insulated systems. However, few practical investigations have been undertaken on real size spacers (product scale) to verify such research outcomes and validate the reliability of the spacers to collect experiences or for commercial use. This paper reviews the current achievements of real size HVDC spacers development. It describes the basic electric field calculation and spacers design, the verification of the insulation performance and validation testing. It gives today’s commercially available compact HVDC GIS/GIL and finally it presents the envisaged future research and development.

Progress in Gas/Solid Interface Charging Phenomena

Surface charge accumulation in the spacer modifies local electric fields, which restricts the industrialization of high voltage direct current (HVDC) gas-insulated transmission lines (GILs). In this paper, the state of art in gas/solid interface charging physics and models, covering areas of charge measurement techniques, charge transport mechanisms, charge related DC surface flashover models, and charge control methods, is reviewed and discussed. Key issues that should be considered in future studies are summarized and proposed. The purpose of this work is to provide a brief update on the most important and latest progress in this research area, and to educate readers as to the current state of the gas-solid interface charging phenomenon, which has seen great progress in the past few years.

A traveling-wave-based protection scheme for the bipolar voltage source converter based high voltage direct current (VSC-HVDC) transmission lines in renewable energy integration

The voltage source converter based high voltage direct current (VSC-HVDC) technology is a feasible solution to realize wide-area complementarity and flexible consumption of the renewable clean energy resources but DC line faults are crucial problems. The traditional traveling wave protection for HVDC transmission lines are easily affected by the fault resistance and signal noise. Besides, it cannot detect the double-pole-to-ground fault. To overcome these problems, a single-ended protection scheme based on the phase-mode transformation and wavelet transform modulus maximum (WTMM) theories for DC lines in the VSC-HVDC transmission system is proposed in this paper. The protection scheme includes the protection startup unit, the internal fault identification unit, and the faulty pole detection unit. Extensive simulation tests carried out in PSCAD/EMTDC verify that the protection scheme has high selectivity in the high fault resistance faults, remote faults, and close-by faults with different fault types. And it does not rely too much on data synchronization. Furthermore, sensitivity analysis and comparisons with other methods indicate that the protection is insensitive to signal noise and suitable for different operational modes. And the effectiveness of the protection is independent of the high sampling frequency. Moreover, it can identify the double-pole-to-ground fault correctly.

Research on 3‐D total electric field of crossing high voltage direct current transmission lines based on upstream finite element method

Research on 3‐D total electric field of crossing high voltage direct current transmission lines based on upstream finite element method

Robust optimisation framework for SCED problem in mixed AC‐HVDC power systems with wind uncertainty

Wind power uncertainties have made the large integration of wind power generating units in the power system highly challenging. One promising solution to overcome the challenges associated with the intermittency of the renewable energy resources (RESs) is to connect areas with diverse renewable energy portfolios via high voltage direct current (HVDC) transmission lines with controllable power transfer capability. The installation of HVDC transmission lines in the power system has resulted in the evolution of conventional alternating current (AC) networks to mixed AC-HVDC power systems. In this study, to address wind power uncertainties in mixed AC-HVDC multi-area power systems, a modified robust optimisation (RO) model for the security-constrained economic dispatch (SCED) problem is proposed. The proposed RO model is used to minimise the generation cost and wind power curtailment under the worst-case scenario of actual wind power. Unlike the existing RO models, the proposed RO model considers a modified uncertainty set based on the wind power admissibility and addresses the budget of uncertainty more accurately to adjust the solution's level of conservatism. Extensive numerical studies demonstrate the economic and operational advantages of the proposed RO model for solving the SCED problem in mixed AC-HVDC power systems with high penetration of RESs.

Modular High-Power DC–DC Converter for MVDC Renewable Energy Collection Systems

Medium-voltage (MV) dc collection system is a promising solution for future integration of large-scale renewables at remote places. This requires a high-power dc–dc converter to step up the voltage and connect with the high voltage direct current transmission line. In this article, a novel modular high-power dc–dc converter is proposed, with the combination of half-bridge and full-bridge submodules (SMs), as well as thyristors and diodes. It alternatively configures the SMs into parallel connection with the MV side to effectively share high current stress while series connection with the high voltage side to share the high voltage stress. It presents attractive features such as high device utilization rate, low cost, high step-up ratio, high efficiency, and small footprint. The circuit structure, operation principle, and the control schemes are discussed. Simulation results demonstrate the effectiveness, and the experimental results from a scaled down prototype further prove the proposed concept.

Design and Implementation of Subsynchronous Damping Controller for HVDC

The interaction between High Voltage Direct Current (HVDC) transmission lines and turbogenerator units will cause the damage of the generator shafting and the electrical system by exchanging energy at one or more lower synchronous frequencies, resulting in the damage or even breakage of the generator shafting, seriously affecting the safe operation of the power system. To solve this problem, the Supplementary Subsynchronous Damping Controller (SSDC) is an effective method to suppress the secondary synchronous oscillation of turbogenerator units connected to rectifier side caused by HVDC. This paper combines the first standard model parameters of IEEE subsynchronous oscillation with CIGRE HVDC transmission system, and builds a HVDC transmission test system for Subsynchronous Oscillations(SSO) research in PSCAD. Based on signal test method, a narrow band SSDC is designed, and the damping in each synchronization frequency band is greatly increased. When the proportional coefficient is appropriate, the electrical damping is positive. The effectiveness of the designed SSDC is also verified by time domain simulation.

A novel intelligent fault identification method based on random forests for HVDC transmission lines.

In order to remedy the current problem of having been buffeted by competing requirements for both protection sensitivity and quick reaction of High Voltage Direct Current (HVDC) transmission lines simultaneously, a new intelligent fault identification method based on Random Forests (RF) for HVDC transmission lines is proposed. S transform is implemented to extract fault current traveling wave of 8 frequencies and calculate the fluctuation index and energy sum ratio, in which the wave index is used to identify internal and external faults, and energy sum ratio is used to identify the positive and negative pole faults occurred on the transmission line. The intelligent fault identification model of RF is established, and the fault characteristic sample set of HVDC transmission lines is constructed by using multi-scale S transform fluctuation index and multi-scale S-transform energy sum ratio. Training and testing have been carried out to identify HVDC transmission line faults. According to theoretical researches and a large number of results of simulation experiments, the proposed intelligent fault identification method based on RF for HVDC transmission lines can effectively solve the problem of protection failure caused by inaccurate identification of traditional traveling wave wavefront or wavefront data loss. It can accurately and quickly realize the identification of internal and external faults and the selection of fault poles under different fault distances and transitional resistances, and has a strong ability to withstand transitional resistance and a strong ability to resist interference.

Optimization Design of AC Filters for HVDC Systems Based on Improved Particle Swarm Optimization Algorithm

In order to reduce the adverse effect of harmonic currents on AC systems and ensure the effective transmission of power in high voltage direct current (HVDC) transmission lines, AC filters (ACF) must be installed on AC buses. Aiming at the limitations of current design methods for AC filters in HVDC systems, this paper proposes a new optimization design method using improved particle swarm optimization (PSO), which aims at the cost of filter investment and constrains the total harmonic distortion rate of AC bus voltage and the telephone harmonic form factor. The optimization mathematical model of AC filters is established, then an improved PSO algorithm is proposed to achieve the optimal design of AC filters. This algorithm introduces a mutation operator and the constraint processing mechanism to improve the exploration ability of this algorithm. Lastly, the simulation model of the ±500 kV HVDC system is established, and the simulation results show that the AC filters optimized by improved PSO have the lowest investment cost while satisfying the harmonic restriction standard.

Single Pole-to-Ground Fault Analysis of MMC-HVDC Transmission Lines Based on Capacitive Fuzzy Identification Algorithm

The probability of a single pole-to-ground fault in high voltage direct current (HVDC) transmission lines is relatively high. For the modular multilevel converter HVDC (MMC-HVDC) systems, when a single pole-to-ground fault occurs, the fault current is small, and it is difficult to identify the fault quickly. Through a detailed analysis of the characteristics of the single pole-to-ground fault of the MMC-HVDC transmission line, it is found that the single pole-to-ground fault has obvious capacitance-related characteristics, and the transient process after the single pole-to-ground fault is the discharge process of the distributed capacitance of the line. However, other faults do not have such obvious capacitance-related characteristics. Based on such feature, this paper proposes a novel capacitive fuzzy identification method to identify the single pole-to-ground fault. This algorithm can effectively identify both the fault of single pole-to-ground and the fault pole, which can contribute to the large database of the future smart grid.

Machine Learning Assisted Prediction Algorithm of Atmospheric Ion Mobility

Atmosphere ion mobility is an important electrical parameter related to the filamentary ion flow field of high voltage direct current (HVDC) transmission lines and other characteristics of the glow and streamer corona discharge. Many machine learning (ML)-based algorithms have already been widely used in the prediction of air discharge. This article proposes a genetic algorithm (GA)-support vector regression (SVR) combined with kernel principal components analysis (PCA) to predict the ion mobility, involving dimensionality reduction, feature selection, parameter optimization of SVR. Kernel PCA could reduce the dimension of data and GA with adaptive probability parameters is employed to optimize the parameters of SVR model. An improved parallel-plates ion generator is employed to produce corona discharge and then measure the saturation ion current density and then obtain the training data and testing data of ion mobility. The prediction results show that the proposed algorithm outperforms the other methods in terms of mean relative error and mean squared error criteria. In addition, the parameters of model and data features have a major influence on the performance of the prediction algorithm. Based on the measured data and reference data, the prediction result obtained on ion mobility under different humidity shows a satisfactory generalization and effectiveness of proposed model for the prediction.