HVDC Transmission Lines Research Articles

A Stable and Efficient Hybrid Method by Imposing Kapzov Assumption Explicitly for the Space Charge Problem of the HVDC Transmission Lines

To overcome the problem of the inefficiency and oscillation when applying the secant methods to impose the boundary conditions, this study presents a hybrid method for the space charge problem of the HVDC transmission lines. The proposed method imposes the boundary conditions by solving the dimension-reducing problems defined on the field lines, which has taken the nonlinear relations between the space charge and the electric field into consideration. Numerical experiments show that the proposed method only takes two steps to obtain the solutions within the error tolerance and the whole procedure is much stable than the secant based methods. The proposed hybrid method can significantly reduce the computation time of the space charge problem.

Analysis of Relay Protection in Power System Based on High Voltage

In recent years, China’s economic development level has continuously improved, great achievements have been made in the construction of electric power, the size of the power grid has also been continuously expanded, and higher requirements have been placed on the safety and stability of power systems. Power system protection occupies an important position. The essential. In the context of today’s high-voltage direct current transmission, line construction has gradually increased, and with it came defects in relay protection technology, which have seriously affected the further development of the power system. This article will specifically analyze the strengthening of relay protection technology in HVDC transmission lines, and improve the power system safety level by improving the performance of relay protection devices.

Innovative compensation methods for voltage drop effects in long HVDC transmission systems

This paper discusses the impacts of large voltage drops on very long HVDC transmission lines, especially when operating in a monopolar mode. The effect of using dedicated metallic return (DMR) conductors is discussed. The main focus is on the potential rise at the neutral point of the converters and the need for an increased range for the converter transformer tap changers. Two grounding schemes for multiterminals transnational HVDC systems are presented: single point low impedance grounding and high impedance multi-point grounding. The advantages of the high impedance scheme are discussed. An innovative compensation method for voltage drop effects using a series HVDC converter is presented along with simulation results. The novel series converter can address both issues of neutral voltage rise and the impractical tap changer range. To put the ideas into the perspective, a realistic example of a transnational HVDC connecting China, central Asia, Russia and West Europe is presented.

A Backup Protection Algorithm for Bipolar Line-Commutated Converter HVDC Lines

This article proposes a new backup protection algorithm for bipolar high voltage alternative current (HVdc) lines using two-end synchronized sampled currents. Unlike traditional differential protection, the proposed algorithm can be applied to detect and recognize the faulted poles directly without the requirements for long time delay. The currents at both line ends are sampled at 1 kHz and the noise in the current signals is removed utilizing the stationary wavelet transform. To activate the proposed backup protection algorithm, initialization unit is proposed. In addition, the internal faults can be discriminated from external faults and the faulted poles can be recognized using adaptive signed correlation indices. Comprehensive studies are simulated on PSCAD/EMTDC software considering several cases for external and internal faults. In addition, the frequency dependent phase model is employed to simulate the HVdc transmission line. The simulation results assure the satisfactory performance of the proposed backup protection algorithm for several fault locations, all fault types, and several fault resistances up to 1000 Ω.

A novel pilot protection scheme for HVDC lines based on waveform matching

The traditional current differential protections for HVDC transmission lines are easily affected by distributed capacitive current. Although some improved differential principles have been presented in literatures, they still risk maloperation caused by synchronization error, noise or parameter errors. To overcome the problems above, this paper proposes a novel pilot protection scheme based on waveform matching. After the electrical quantities on both sides are low-pass filtered, the HVDC line is simplified to two PI models from the midpoint, which can eliminate the effect of distributed capacitive current and has simple computation as well as satisfying precision. The midpoint currents, which can be calculated based on the simplified DC line model with the information of either side, will be matched under external faults while have opposite trend under internal faults. The improved Pearson correlation coefficient (IPCC) is proposed to measure the similarity between the waveforms of the calculated midpoint currents and establish the protection criterion. A ± 800 kV HVDC test system is modeled in PSCAD/EMTDC. Extensive simulations of various fault situations indicate that the new protection has absolute selectivity, great reliability and strong fault resistance withstand ability. Sensitivity analysis and comparisons with other pilot protections further demonstrate that the proposed protection stands out for high accuracy and strong robustness to many non-ideal factors.

Calculation of ion flow environment of DC transmission lines in the presence of charged aerosol particulates based on upwind-FEM

Atmospheric environment has a significant influence on ion current, space charge and ground-level electric field profiles of HVDC transmission lines, which attracts a huge amount of interest already. This work presents that the upwind finite element method is applied to calculate the ion flow model in the presence of aerosol particulates. The ion-aerosol attachment coefficient, electrical mobility and diffusion coefficient of charged aerosol are calculated by Fuchs theory and Stokes–Einstein relation. Application of the proposed approach to calculate monopolar and bipolar DC line provides an insight into the physical mechanism of effect of aerosol. Making some appropriate assumptions, computational results present a reasonable agreement with the long-term measured data within a certain aerosol density. It is found that aerosol has a significant influence on the spatial distributions of charge density. In the downwind direction, the ground-level electric field increases significantly because of the dominant of charged aerosol particles.

Dynamic behavior analysis of backup protection for HVDC transmission line

The backup protection of HVDC transmission line consists of differential undervoltage protection and differential protection. In this paper, based on the actual parameters, the simulation model of differential undervoltage protection and differential protection for DC line is built. The response regularity of each criterion of the two protections under different fault conditions is studied. The basic functions of each criterion are defined, which provides an important basis for the setting calculation of DC line backup protection.

A novel single-ended fault location method for long-distance HVDC transmission lines based on cross-correlation analysis

The transmission line, as the faultiest device in power system, cross many complex areas which will cause worse work condition. This is, both the rate of faulty and the difficulty of the manual fault location are raised. While accurate fault location method could reduce the workload and outage cost, increase the speed of repairing and improve both the reliability and economics of power system. Therefore, it is essential for HVDC systems which have much longer transmission lines. The existing fault location device of HVDC transmission lines are based on the principle of transient travelling-wave. However, due to the interference caused by on-off of power electronic devices and signal resonances, the single-ended travelling-wave method can not be applied in HVDC. The characteristics of clutter interferences of HVDC system and the coupling between double pole lines are analyzed in paper. A novel single-ended travelling-wave fault location method for HVDC transmission lines based on the correlation between two pole lines is proposed. The signal of the non-fault pole line is applied as reference signal; the method suppresses interference through the cross-correlation calculation between the fault and the no-fault pole line. So the reflected wave is enhanced and the identification reliability of the reflected wave is improved. The validity of the method is verified by simulation and on-site data analysis.

Adaptive Refinement Method for Solving Ion-Flow Field of HVDC Transmission Line

To improve the accuracy for solving the ion-flow field problem, an adaptive refinement method based on the streamline upwind Petrov–Galerkin (SUPG) formula is proposed. The error transport equation has been decomposed to a series of local boundary value problems and solved by the method of local characteristic. An equidistributional strategy is applied to steer the refinement. Numerical examples show that the results using the grid generated by the proposed method are more accurate and efficient than the ones with the regular refinement strategy. An example of application shows that this method is suitable for simulating the ion-flow problem with a complex geometry.

Coupling characteristic analysis and a fault Pole detection Scheme for single-circuit and double-circuit HVDC transmission lines

The mis-operation and protection issues associated with non-fault poles caused by electromagnetic coupling effects threaten the security and stability of HVDC power systems. Based on the distributed parameter model, the coupling characteristics of single-circuit HVDC transmission lines and double-circuit HVDC transmission lines are studied in this paper. The decoupling method of double-circuit HVDC transmission lines that are structurally unbalanced is discussed. Based on waveform and frequency characteristic analyses of electrical quantities considering coupling effects, a fault pole detection scheme is proposed. A rapid fault pole detection criterion is formulated based on the backward travelling wave, and an adaptive threshold selection method is proposed. A reliable fault pole detection criterion is formulated using the low-frequency component voltage, and a short-window fast-filtering method is proposed. The travelling wave-based fault pole detection method can be rapidly applied using only the electrical quantities of the protected line, and the sensitivity and reliability of the method are enhanced by using adaptive thresholds. Based on the frequency characteristics of the coupling effects, the fault pole detection method can be reliably applied using only the electrical quantities of the protected pole. Simulations demonstrate the feasibility and validity of the fault pole detection scheme.

Peak Shaving Model for Coordinated Hydro-Wind-Solar System Serving Local and Multiple Receiving Power Grids via HVDC Transmission Lines

To meet the rapid growth of electricity demand and reduce carbon intensity, China is developing renewable energies rapidly including hydropower, wind and solar power. Due to the geographical mismatch of energy sources and demands in China, many long-distance and large-scale UHVDC and HVDC transmission projects have been built to transmit electric power from the western renewable bases to eastern coastal load centers. Some provincial power sources serve both local demands and deliver power to multiple regional power grids via HVDC transmission lines. As large capacity HVDC power transmission projects have great impacts on receiving-end power grids. Thus, the local exporting power grid should consider both local demands and energy importing area demands. A mixed-integer linear programming day-ahead peak shaving model to minimize the peak-valley difference in residual load after renewable generation of multiple power grids is developed. The model uses chance constraints to compensate for forecast errors of wind and solar power with hydropower, and introduces maximum daily power regulation times and stair-like power curve constraints of HVDC tie lines to avoid frequent HVDC power change and ensure power grid safety. The case studies in Yunnan province, which has large scale hydro, wind and solar power sources and delivers power to multiple regional power grids via HVDC transmission lines, shows the proposed model can shave peaks from multiple power grids effectively, hydropower can compensate for wind and solar forecast error and obtain satisfying results for multiple power grids, and that HVDC constraints can avoid their frequent power change and ensure the power grid safety.

Longitudinal Protection of LCC-VSC Bipolar HVDC Transmission Line Based on Model Identification and Current Polarity

For hybrid bipolar DC transmission systems, combined with model identification and current polarity, a new principle of longitudinal protection of transmission lines is proposed. This paper analyzes the fault network and finds: when the front end of the inverter side fails, the fault model is equivalent to the C model, and when the back side of the inverter side fails, the fault model is equivalent to the RL model; when the front end of the rectification side fails, the rectification side fault current has a positive polarity, and when the rectification side back side fails, the rectification side fault current has a negative polarity. In conclusion, DC line area failure, namely the inverter side front and rectifier side front fault at the same time, the fault model matching C model, there was a positive polarity fault current at the same time; Failure occurs outside the DC line area, namely the inverter side front and rectifier side front no fault at the same time, inverter side failure model does not match the C model, or rectifier side fault current with a negative polarity. This new principle compensates for primary protection and can be used as an improvement to backup protection.

Frequency Control of Power System with Renewable Power Sources by HVDC Interconnection Line and Battery Considering Energy Balancing

Recently, introduction of renewable energy sources like wind power generation and photovoltaic power generation has been increasing from the viewpoint of environmental problems. However, renewable energy power supplies have unstable output due to the influence of weather conditions such as wind speed variations, which may cause fluctuations of voltage and frequency in the power system. This paper proposes fuzzy PD based virtual inertia control system to decrease frequency fluctuations in power system caused by fluctuating output of renewable energy sources. The proposed new method is based on the coordinated control of HVDC interconnection line and battery, and energy balancing control is also incorporated in it. Finally, it is concluded that the proposed system is very effective for suppressing the frequency fluctuations of the power system due to the large-scale wind power generation and solar power generation and also for keeping the energy balancing in the HVDC transmission line.

Ann based Shortcoming Area in HVDC Transmission Line

This paper is to ponder the use of Neural systems for shortcoming discovery and area in HVDC framework. The proposed Neural system learns examples and relationship on transient information. The Back-propagation algorithm has the ability to match map complex and nonlinear input - output behavior. A MATLAB model was created for the 500kv,1000MW,12 pulse-based converter-based distribution system and various fault events were simulated. The limitations of AC over long transmission lines has led to the use of DC for bulk transmission over long distances. Fault condition like rectifier fault, inverter faults and transmission line faults are discussed in this paper.

Harmonics and THD in Five Phase Inverters

Now-a-days most of the appliances and machine works on AC power. If AC power is unavailable for a short period of time, then during that period we need to supply AC power by converting the stored DC power. This can be possible using an Inverter. Inverters can be of multi-phase i.e. 3phase, 5phase, 6phase and so on. Since inverters have wide application in industries and HVDC transmission lines, the improvement in the output voltage and the reduction in harmonics are of utmost importance. In this paper a detailed analysis of harmonics and THD in a five phase inverter with different conduction angle along with the derived mathematical equations has been presented. A comparative study between three phase and five phase inverters at different conduction angle has been presented.

VSC-HVDC Bipolar Grid Based On Novel Distance Protection Scheme

Mostly distance protection is widely used in HVAC system no practical implementation is done for HVDC system. It is essential to measure accurately difference in internal fault from external correctly in distance protection at the zone boundary. The smoothing reactor in HVDC system is present at two ends and it can be considered as the operating boundary of distance protection. Considering these feature this paper introduce distance protection method for HVDC transmission line. Current and voltage at end-point are planned accurately using those at the relay point, based on distributed parameter model. The line between the fault point and end point is simplified as RL model lumped parameter and differential equations obtain fault distance. In this way, accuracy of calculation at the zone boundary is attained, that contributes to the improvement in operation of protection. Simulation results show that proposed method is used as primary protection for HVDC transmission and is capable of protecting the whole line with high rapidity.

A Pilot Protection for HVDC Transmission Lines Based on Transient Energy Ratio of DC Filter Link

To overcome shortages in the traditional current differential protection for HVDC transmission lines, a pilot protection based on transient energy ratio is proposed. The fault identification criterion is put forward based on the impedance-frequency characteristic of the line boundary, and the fault analysis which shows that under internal faults, with regard to either terminal of the dc line, the transient energy within a specific frequency band on the line side of the boundary is much greater than that on the valve side of the boundary, whereas after rectifier-terminal (inverter-terminal) external faults, the transient energy on the line side of the rectifier-terminal (inverter-terminal) boundary is much less than that on the valve side of the boundary. Moreover, the lightning disturbance identification criterion is implemented based on the magnitude ratio of fault components of high- and low-frequency band currents. Fault-pole selection is constructed by using the fault components of pole voltages. Simulation results demonstrate that the proposed scheme, with low computational complexity, can distinguish internal faults from external ones and protect the entire line reliably. It can also identify high-impedance faults and select the faulted pole correctly. Besides, it is not subject to lightning interferences and the dc line distributed capacitor.

A novel approach to estimate fault location in current source converter–based HVDC transmission line by Gaussian process regression

A novel approach to estimate fault location in current source converter–based HVDC transmission line by Gaussian process regression

Estimation of HVDC transmission lines shielding failure using LPM method and an adapted SLIM model

In this study, the shielding system of HVDC transmission lines against direct lightning strokes is analysed and the shielding failure rate is investigated. The lightning downward leader is modelled using 3D leader progression model (LPM) and the striking point is distinguished employing the self-consistent upward leader inception and propagation model (SLIM). For determination of striking point more accurately, the required parameters of SLIM model are extracted from the recent experimental results. Different effective objects in the space of study including cloud, lightning channel, towers, wires, and ground are modelled using fictitious charges. Moreover, the charge simulation method is used for electric field calculation. Using the foregoing model, the shielding failure rate of an HVDC transmission line is calculated. Also, the percentages of lightning strokes to each part of the structure are obtained in order to investigate the differences between the positive and negative poles in attracting the lightning. In addition, the effect of height and shielding angles of positive and negative poles are studied. All the results are compared with those of electrogeometric model models.

Pearson correlation coefficient of current derivatives based pilot protection scheme for long-distance LCC-HVDC transmission lines

This paper proposes a pilot protection scheme for long-distance LCC-HVDC transmission lines based on Pearson correlation coefficient of current derivatives. According to the impedance frequency characteristics of converter and DC filter, and the superposition principle, the correlation characteristics between line current derivative (LCD) and DC filter current derivative (DFCD) are analysed for internal and external faults. For internal fault, there is completely negative correlation between line current derivative and corresponding DC filter current derivative at both rectifier side and inverter side; for external fault, the correlation of current derivatives (CDs) at the faulty side is positive, yet completely contrary at the other side. The Pearson correlation coefficient (PCC) is utilized to detect the correlation characteristics of current derivatives. And based on these characteristics, a novel protection scheme for long-distance HVDC transmission lines can be constructed to detect internal and external faults. Comprehensive simulation results show that the proposed protection scheme can quickly identify internal and external faults with high reliability. Furthermore, it is insensitive to fault resistance, fault location and measurement noise, and does not require data synchronization.