Voltage Direct Current Transmission Lines Research Articles

Analysis of heating defects in extension rods of extra-high voltage direct current overhead transmission lines

This paper studies the overheating defect of an extension rod in a ± 800 kV extra-high voltage direct current overhead transmission line, and proposes various factors that affect the overheating of the extension rod. Establish an equivalent model of an extra high voltage DC transmission line based on equipotential point and line parameter analysis, and calculate the model parameters. The proposed model can also be applied to ultra-high voltage DC overhead transmission lines such as ± 500 kV, and has strong universality. Simulation experiments show that if the equivalent resistance value of the split wire side is reduced by 0.01Ω, the power loss on the extension tie rod can be increased to 380.951 W; if the equivalent resistance value of the jumper side is increased by 0.01Ω, the power loss on the extension tie rod can be increased to 273.41 W. Combined with theoretical analysis and simulation verification, it is concluded that the main factor affecting the overheating of the extension rod is the change in the resistance value on the jumper side caused by the increase in contact resistance. A systematic troubleshooting plan for related defect problems is proposed, which has important reference and guidance significance for such line fault problems.

A method for calculating space charge distribution in ultra-high voltage direct current transmission lines based on the transport of diluted species theory

The occurrence of corona discharge in ultra-high-voltage direct current transmission lines results in the generation of space charge, which significantly affects the nearby electromagnetic environment. To investigate the micro-physical mechanisms of discharge and provide better guidance for the calculation of the ground ion current density and total electric field, a method based on the theory of the transport of diluted species is proposed. This method enables the visualization and analysis of the movement process of space charge in air medium, as well as the calculation of the total electric field below the transmission lines. To validate the effectiveness of this algorithm, experimental tests of the total electric field are conducted on actual transmission lines. The experimental results demonstrate that the algorithm not only highlights the evident differences in the transient microscopic processes between positive and negative corona discharges but also accurately calculates the total electric field below the transmission lines. In addition, considering the weather conditions in the Chongqing region, relevant recommendations are provided under the influence of wind speed, aiming to offer protection guidelines for individuals engaged in activities near transmission lines.

Experimental and theoretical study on the influence of bundle number on corona loss characteristics of ultra high voltage corona cage positive/negative DC conductors at high altitude

The corona loss generated by the conductor is one of the important factors in the design of ultra-high voltage (UHV) direct current transmission lines. This article is based on the high-altitude (2200 m) ultra-high voltage corona cage experimental platform built in Xining City, Qinghai Province. For the LGJ400-35 conductor used in the typical ± 800 kV DC transmission lines from Qinghai to Henan Province, positive and negative polarity corona experiments were conducted on LGJ400-35 conductors with 4, 6, 8, and 10 bundle under surface field strength conditions of 14–22 kV/cm. For the first time, corona loss data of bundle conductors in positive/negative polarity ultra-high voltage DC transmission lines were obtained, Fit the prediction formula for corona loss of transmission lines under different bundle numbers and surface electric field strengths of wires. And build a model in COMSOL Multiphysics software for simulation analysis, fitting the correction factor for the impact of wind speed on wire corona loss. The research results in the article can provide data reference and support for the construction of ultra-high voltage direct current transmission lines in high-altitude areas.

Failure analysis of strain clamps on a ± 800 kV transmission line

During X-ray testing of a ± 800 kV ultra-high voltage direct current transmission line tension clamp, it was found that the internal steel core had broken. To investigate the cause of the steel core fracture, the failed clamp was dissected and analyzed, including chemical material testing, mechanical performance testing, fracture morphology inspection, and analysis of the compression process of the tension clamp. A preliminary judgment was proposed on the cause of the internal steel core fracture of the tension clamp, And verification experiments and simulation analysis were conducted to preliminarily determine the cause of the steel core fracture, and it was ultimately concluded that the main reason for the steel core fracture was the incorrect compression sequence of the large cross-section wire tension clamp.

Modeling and experimental validation of a proposed distance protection system for MVDC transmission lines

Protecting direct current transmission lines (DC-TLs) against faults is challenging and crucial, especially when locating faults. This research aims to develop a novel distance protection approach for Medium voltage direct current transmission lines (MVDC-TLs). Various faults in the computerized experiments and practical models have been applied to the proposed system in the AC network and DC transmission lines to evaluate the performance of the proposed method. The proposed protection system employs the wavelet transforms (WT) and ANFIS as detailed coefficients ‘feature extracting’ tools and classifiers, respectively. The mechanism operation of the proposed method is composed of three stages. Firstly, it extracts the features of the faults by WT. Hence, the ANFIS training process uses such features to identify and classify the faults. The third stage utilizes the ratio value between the fault current and the healthy operation current as an input of another ANFIS model to locate faults on the DC TL. The performance of the proposed protection method has been tested and evaluated for MVDC and MVAC networks. Also, the research executes both practical and simulation experiments utilizing different faults. It examines various fault locations on the entire MVDC line. The mechanism measures the current signals on both sides of the DC-TL. The paper built the MVDC-TLs model and the different cases using the software PSCAD/EMTDC and the proposed method via MATLAB. The study tested faults along the TL in the presence of the AWGN noise. The research utilizes practical experiments to verify the accuracy of the proposer. The accuracy of the proposed fault location is 99.923 %. Based on the results of this research paper and comparison with the recent related research works, the proposed method is more effective and efficient than the previous methods in detecting, classifying, and locating system faults.

A Two-Terminal Directional Protection Method for HVDC Transmission Lines of Current Fault Component Based on Improved VMD-Hilbert Transform

The traveling wave protection of high voltage direct current (HVDC) transmission lines is susceptible to the influence of transition resistance. As a backup protection, current differential protection has absolute selectivity, but usually requires an increase in delay to avoid misoperation caused by distributed capacitance on the line, resulting in a longer action time. Based on this, a two-terminal directional protection method for HVDC transmission lines is proposed based on Sparrow Search Algorithm (SSA)-Variational Mode Decomposition (VMD) and Hilbert phase difference. On the basis of analyzing the directional characteristics of the current fault component at both ends of the rectifier and inverter sides under different faults, SSA is first used to optimize the parameters of VMD. The residual components representing the direction of the current fault component at both ends are extracted through VMD, and then the Hilbert phase difference of the residual components at both ends is calculated to identify faults inside and outside the line area. In addition, fault pole selection can be achieved based on the ratio of the sum of multi-band Hilbert energy of single-terminal voltage fault components at the positive and negative poles. Simulation experiments have shown that the proposed protection scheme can quickly and effectively identify fault and has good tolerance to transition resistance and noise interference.

Adaptive fault ride through control of VSM Grid-forming converters

Recently, many high voltage direct current (HVdc) transmission lines are being constructed with the intention of becoming “backbones” of future power grids. Grid-forming (GFM) controlled Voltage Source Converters (VSCs) are anticipated to provide significant stability advantages compared with Grid-following (GFL) VSCs in HVdc converters connected to weak ac grids or to grids with high penetration of renewable inverter-based resources (IBRs). This paper proposes an adaptive fault ride through controller for Virtual Synchronous Machine (VSM) GFM control, which has significantly improved fault ride through capability over the more conventional GFM control with cascaded or switchable current limiting. The performance of the proposed adaptive control is investigated using Electromagnetic Transient (EMT) simulation. The results show that the proposed adaptive control has superior post disturbance recovery from ac faults as well as phase angle shifts, and overcomes the instability reported in GFM converters connected to strong ac networks.

Finite Element Method Assisted Audible Noise Detection for Overhead Line Conductors Using the Cage Experiment

Audible noise (AN) has been the main concern in recent years when considering electromagnetic environmental impact in designing overhead lines (OHLs). Driven by the increased demand of high voltage direct current (HVDC) transmission lines, a novel corona cage experiment is built in association with an acoustic simulation using the finite element method (FEM). The characteristics of the acoustic wave propagation within the testing hall are analyzed using FEM, and the optimized locations for AN detection are determined. On the basis of complying with measurement standards, the location of the measurement is selected to be closer to the sound source and further away from the reflecting surface, to generate more accurate measurement results. In the designated test hall for this paper, the influence of refraction and reflection of sound waves is not obvious. The attenuation of sound waves below 4 kHz is negligible, while for higher frequencies such as 4 kHz and 8 kHz it is significant. Finally, FEM simulation is used to optimize the location for measurement microphones, and further experiments are carried out to verify its accuracy.

Non-unit Protection for Asymmetrical DC Line Faults in Bipolar LCC-HVDC Transmission Systems

The faults in high voltage direct current (HVDC) transmission lines cause a sudden rise in DC, resulting in over-stressing of converter valves and transformer windings. DC line faults of longer duration, or permanent nature, will lead to a severe disturbance in the associated AC network as well. Thus, the HVDC line faults must be detected immediately to interrupt the fault current by initiating proper actions of control and protection. This paper implements a new method to detect the asymmetrical (pole-to-ground) faults in the conventional bipolar LCC-HVDC transmission system. The proposed method defines a Fault Indicating Parameter (FIP) based on the transient voltage and current elements of each pole. The transient elements are obtained based on single-end measurements. Single-end or non-unit measurements lead to the development of simple, cost-effective and fast protection criteria. Also, the method is applicable to faults close to the line boundary and of high resistivity. A two-terminal bipolar LCC-HVDC transmission system, based on ±500 kV, 1000 MW and 900 km length, is used to evaluate the performance of the proposed technique in offline mode, using MATLAB/Simulink software. Also, the results are validated using an OPAL-RT real-time simulator under divergent fault conditions. The simulation results prove the robustness, selectiveness and accuracy of the proposed scheme.

An Improved Method of Traveling Wave Protection for DC Lines Based on the Compensation of Line-Mode Fault Voltage

The protection of high voltage direct current (HVDC) transmission line is the key to development of the HVDC transmission technology. To deal with the problem that the traditional traveling wave protection (TWP) has low sensitivity under high resistance faults, an improved TWP scheme based on the compensation of the line-mode component of fault voltage (LMCFV) is proposed. The expressions of the LMCFV of HVDC system at different fault locations are derived. Conclusions can be drawn that the LMCFV and fault resistance are linear when the DC line fault occurs, whereas the linear state will be broken for the external fault. Based on this, the LMCFV for the metal fault occurring at the DC line midpoint is used as the reference value to compensate for the faults in other cases of the HVDC systems. The protection scheme constructed based on the compensatory LMCFV and compensation coefficient can accurately identify fault of the DC line. Finally, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\pm }$</tex-math></inline-formula> 800 kV model of HVDC systems is built in PSCAD to verify the protection performance. The effect of fault resistance can be eliminated by compensatory LMCFV, and the DC line fault can be quickly and reliably identified by the simulation results.

Short-term operation of cascade hydropower system sharing flexibility via high voltage direct current lines for multiple grids peak shaving

The escalating pressure for peak shaving presents a significant challenge for the power grid's operation, particularly with the rapid growth of renewable energies. Huge cascade hydropower stations (CHS) send power to the local power grid and multiple power grids via long-distance high voltage direct current (HVDC) transmission lines, how to share hydropower flexibility for multiple power grids in peak shaving while considering constraints of hydropower and HVDC lines challenges power dispatching management. This study proposed a multiple power grids peak shaving model of cascade hydropower stations with HVDC sharing flexibility for receiving power grids. Firstly, the objective of minimizing the peak-valley difference of multiple power grids is adopted. The model then takes into account the operation constraints of CHSs and HVDC tie-lines to share hydropower flexibility. Finally, the model is transformed into a Mixed-Integer Linear Programming problem through piecewise linearization. The case studies of practical examples in southwest China show that the proposed model reduces peak-valley differences by 23.3%, 46.9%, 99.1% and 19.6%, 34.3%, 99.5% for three receiving power grids in two typical days by sharing hydropower flexibility. Moreover, adjusting the HVDC daily power regulation times and electricity deviation tolerance helps coordinate power grids to improve their peak shaving performance.

Minimization of Electric Fields Underneath High Voltage Direct Current Transmission Lines Based on Shielding Technique

Minimization of Electric Fields Underneath High Voltage Direct Current Transmission Lines Based on Shielding Technique

Dynamic interactive characteristics between icicle growth and corona discharge on HVDC outdoor insulators during icing accretion

AbstractIn order to improve the stability and reliability of high voltage direct current (HVDC) transmission lines in cold regions, this article investigated the corona discharges and the icicle growth characteristics on outdoor insulators under DC voltages. The experiments were conducted at CIGELE laboratory at University of Quebec. The simulation model of corona discharges and the theoretical model of icicle growth were established. The dynamic process and interactive characteristics between the icicle growth and corona discharges under different HVDC voltages were obtained. The results showed that the discharge activity was strong and the cooling effect of ionic air was weak under negative DC voltage, resulting in a large number of bubbles inside the icicle. More negative ions were produced under negative DC voltage, which enhanced the polarisation of water droplets, leading to a greater density of ice beads outside the icicles. In addition, the longest icicles of each insulator under high humidity could bridge the shed gap. The accumulated charge and leakage current were higher under negative DC voltage, as well as the corona discharge at the top of the icicles lasted longer. Therefore, the negative DC corona discharge more significantly inhibited the growth of the icicle, resulting in a slower growth rate of the icicles.

Static electric field inhibits the proliferation and secretion functions of splenic lymphocytes in mice

ABSTRACT In recent years, the effects of static electric field (SEF) generated by ultra-high voltage (UHV) direct current (DC) transmission lines on health has drawn public attention. To study the effects of SEF on the spleen, mice were exposed to 56.3 ± 1.4 kV/m SEF. Results showed that on the 28th day of SEF exposure, the contents of IL-10 and IFN-γ in the supernatant of homogenate, the proliferation levels of lymphocytes and the content of intracellular ROS decreased significantly, while the activity of SOD increased significantly. Meanwhile, the rupture of cellular membrane, the deficiency of mitochondrial cristae and the vacuolization of mitochondria appeared in lymphocytes. Analysis showed that the rupture of the cellular membrane caused the death of T lymphocytes, which would lead to the reduction of IL-10 and IFN-γ secretions. The damage of mitochondria could reduce the production of ATP and the content of ROS, which could inhibit the proliferation of splenic lymphocytes.

An Improved Calculation Method Based on Newton–Raphson Method for Ion Flow Field of UHVDC Transmission Lines at High Altitude

The fast and accurate solution of the total electric field and ion current density is crucial for the electromagnetic environment of ultra high voltage direct current (UHVDC) transmission lines. In this article, an improved method based on Newton–Raphson method (NRM) and upstream finite element method (UFEM) is proposed to calculate the ion flow field under complex conditions. According to the gas motion theory, the corona-onset electric field, ion mobility, and recombination coefficient are obtained at high altitude and put into the ion flow field model in this article. Subsequently, the charge density is used to solve Poisson’s equation, and the current continuity equations are calculated by UFEM. After that, the charge density of the conductor surface is updated based on NRM. These three parts are iterated repeatedly until the convergence conditions are met. According to the test results of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 800-kV UHVDC transmission line at high altitude, the validity and rationality of the proposed method are verified. The result demonstrates that due to the reduction of atmospheric pressure at the high altitude, the corona-onset electric field decreases, and the ion mobility and recombination coefficient increase, which makes the total electric field and ion current density at ground level increase. Compared with the traditional methods, the improved method is insensitive to the initial value of the surface charge density. Moreover, this proposed method can effectively improve the convergence ability and achieve the stable and fast calculation of the ion flow field at high altitude.

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.

Research on Total Electric Field Prediction Method of Ultra-High Voltage Direct Current Transmission Line Based on Stacking Algorithm

Research on Total Electric Field Prediction Method of Ultra-High Voltage Direct Current Transmission Line Based on Stacking Algorithm

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.