HVDC Transmission Lines Research Articles

A novel primary and backup relaying scheme considering internal and external faults in HVDC transmission lines

Discrimination of different DC faults near a converter end of a DC section consisting of a filter, a smoothing reactor, and a transmission line is not an easy task. The faults occurring in the AC section can be easily distinguished, but the internal and near-side external faults in the DC section are very similar, and the relay may cause false tripping. This work proposes a method to distinguish external and internal faults occurring in the DC section. The inputs are the voltage signals at the start of the transmission line and the end of the converter filter. The difference in voltage signals is calculated and given to an intelligent controller to detect and discriminate the faults. The intelligent controller is designed using machine learning (ML) and deep learning (DL) techniques for fault detection. The long short-term memory (LSTM-) based relay gives better results than other ML methods. The proposed method can distinguish internal from external faults with 100% accuracy. Another advantage is that a primary relay is suggested that detects faults quickly within a fraction of milliseconds. Nevertheless, another advantage is that a backup relay has been designed in case the primary relay cannot operate. Results show that the LSTM-based protection scheme provides higher sensitivity and reliability under different operation modes than the conventional traveling wave-based relay.

A pilot directional protection based on low frequency voltage variable quantity for LCC-HVDC transmission lines

In this paper, a pilot directional protection based on low frequency voltage variable quantities for LCC-HVDC transmission lines is proposed. Based on the regularities of low frequency voltage distribution along the HVDC transmission line, the low frequency voltage variable quantities of the positive pole and negative pole are defined. Then, the theory of low frequency voltage variable quantities based directional protection is presented. The low frequency voltage variable quantity variation characteristics of the relay device location point and calculation point under different fault conditions are analyzed. If a forward fault occurs, the low frequency voltage variable quantity of the calculation point would be larger than that of relay device location point. If a reverse fault occurs, the low frequency voltage variable quantity of the calculation point will be less than that of relay device location point. Next, the criteria of the low frequency voltage variable quantity based pilot directional protection is proposed. Finally, an LCC-HVDC transmission system is modelled for simulation. Simulation results reveal that the presented pilot directional protection has obvious physical significance with simple calculation and is adaptive to lower sampling frequency. Besides, the presented algorithm is independent on the HVDC transmission line boundary and invulnerable to strong noise and high fault resistance.

Novel wavefront detection and fault location method based on Hilbert-Huang transform for long HVDC transmission lines

For the newly constructed ± 1 100 kV HVDC system with 3 324 km transmission lines in China, fast and accurate fault location is vitally important for its stable operation. This paper proposes a novel method based on Hilbert-Huang Transform (HHT) for detecting wavefronts and locating faults occurring on the HVDC transmission lines. False instantaneous frequency maximum points may reduce the accuracy and reliability of wavefront detection. The novel criterion, named the product of amplitude and frequency (PAF), has significant advantages and robustness in characterizing the singularity of the signal and precisely capturing the arrival time of wavefronts. A realistic model of the Changji-Guquan ± 1 100 kV transmission system is constructed using PSCAD/EMTDC to verify the effectiveness of the proposed method. The simulation results give the maximum location error of 0.843 km in given cases of different fault distance, fault impedance, sampling frequency, and other parameters. Noise conditions and the dynamic arc model are also considered in this paper. The comparison against other methods demonstrates the superior performance of the proposed method in terms of accuracy and robustness. The proposed method has broad application prospects and guiding significance for practical projects.

Direct current compensation – field experience under service conditions

Modern grain oriented core steel used in power transformers has a very high magnetic conductivity. This advanced material makes the transformer susceptible even for small direct current (DC) in the power grid. Already minor DC increases the no-load noise and no-load losses of the transformer considerably. This effect is known as half-cycle saturation. In order to overcome these parasitic DC an active compensation method called “DC compensation” (DCC) was recently developed by Siemens [1]. The question about the origin of the DC is not fully answered yet. However the following sources have been already identified: power electronics, renewable power generation (wind, solar), HVDC transmission lines and DC operated railroad or subway systems. The parasitic direct currents can flow over the power lines to ground or asymmetrically in the power line phases only. In this paper field data, a four-month DC load profile, of single-phase core type transformers, equipped with active DC compensation, are shown. The discussed unit, a bank of three single-phase autotransformers, is in service mainly exposed to DC flowing from the overhead lines through the windings to the common neutral. DC magnitude varies from 0.05 A to about 0.2 A DC per phase throughout the day. From factory tests we know that only 0.2 A DC causes a noise increase of 5.6 dB(A) compared to the noise level without any DC compensation. This might cause troubles at the substation when noise has to be below a guaranteed level. Data analysis of the field data shows that the DC throughout the day follows a clear profile with its highest level during midnight and lunch time. This might indicate a correlation to the load and / or switching operations in the grid to adjust to the actual needed load. However, the DC compensation equipment fully eliminates the direct flux in the core and thus the DC caused increase in noise.

Multi-level PWM Inverter for PV Systems Improving the THD

In the last few years, the use of semiconductors in the electronic market has increased a lot, due to which its utilization in power electronic devices has also increased greatly, including UPS, AC drives, HVDC transmission line rectifiers, inverters and many more. We categorize the inverter in many ways like diode line capacitor cascade h-bridge diode climb like this but we do voltage source inverter in two ways if we look like multi-level inverter then two-level inverter multi-level letter Maybe and we are using multi-level inverter here. In this paper, we are discussing the performance of second level inverter using space vector PWM and further using for mains performance using disposition multicarrier moderation. In this paper we are using fuzzy logic to control WM, the factors we are working out are the total harmonics distortion switching frequency switching losses and the number of switching devices. Here the complete simulation is using MATLAB/Simulink software.

Mal-operation analysis of LCC-HVDC protection schemes in simulation studies due to inaccurate transmission line modelling

ABSTRACT Protection in HVDC transmission lines, considering the significant amount of energy being transferred, has an undeniable importance on integrity of power systems. Due to unavailability of real HVDC transient data for protection studies, accurate modelling of HVDC systems through simulation software is the most practical alternative. One crucial part of a detailed transient simulation study is accurate line modelling, which, if not performed properly, can invalidate the results and conclusions. Therefore, in this study, three of the most accepted line models, namely the frequency-dependent, Bergeron and -section line models, will be discussed, and their impact on the performance of some of the most accepted HVDC protection methods will be investigated. In comparison to the frequency-dependent line model, which produces the most accurate response, other line models are such inaccurate that their responses in simulation studies are not usable for designing a reliable protection scheme. The simulation study shows that some of the distance or boundary protection methods, designed based on integrating a Bergeron or -section line model into their studies, can be completely unreliable. The validity of these claims is assessed based on the modified bipolar version of the CIGRE HVDC test system, simulated in the PSCAD/EMTDC software.

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

The influence of charge characteristics of suspension droplets on the ion flow field in different temperatures and humidity

In order to clarify the charging characteristics of suspension droplets in ion flow field under different temperatures and humidity, the effective charging factor used to characterize the charging characteristics of suspension droplets is introduced in this paper, and a calculation method of charging factor is proposed based on the upstream finite element method (FEM). Then, the charging factor under different temperatures and humidity is calculated, and the analytic expression of the charging factor considering the influence of temperature and humidity is obtained by fitting the calculation results. The influence of suspension droplets on the ion flow field is analyzed. The results show that the charging factor is small and increases little with the relative humidity when the relative humidity is less than 60%, and the charging factor is large and increases rapidly with the relative humidity when the relative humidity is more than 60%. At the same relative humidity, the charging factor increases linearly with the temperature. The influence of charged suspension droplets on the ion flow field can be ignored when the relative humidity is less than 60% and must be considered under high temperature and humidity. The calculation method and analytic expression of the charging factor proposed in this paper can be used to model of ion flow field considering the influence of temperature and humidity and provide technical support for the construction of HVDC transmission lines across high temperature and humidity.

Research on electromagnetic environment of HVDC transmission line under sand and dust conditions

To study the impact of dust weather on the electromagnetic environment of the HVDC transmission line, this paper first analyzes the changes of transmission line corona field intensity under different dust conditions, and puts forward the prediction formula of transmission line corona field intensity under dust conditions. According to the Deutsch hypothesis and Kaptzov hypothesis, the calculation formula of ground synthetic electric field under sand and dust conditions is deduced, and the ±500 kV HVDC transmission line is analyzed and calculated. The results show that with the increase of dust particle size and dust concentration, the ground synthetic electric field shows a similar attenuation trend to the Halo electric field, which shows that the dust conditions mainly affect the ground synthetic electric field by affecting the space charge electric field. In the study of dust conditions on the line electromagnetic environment, coarse sand shows a greater impact, and the worse the dust weather intensity, the more obvious the decline of the ground synthetic electric field intensity.

Non‐unit protection scheme for HVDC transmission lines based on energy of voltage difference

This paper presents a non-unit protection scheme for LCC-HVDC transmission lines based on the energy of voltage difference. The change in the line average voltage is used to detect the fault, whilst faulted pole selection criterion is calculated by using the ratio of the average voltage change at positive and negative poles. The protection criterion calculated as the energy of second-order difference of the DC line voltage determines whether the fault is internal or external. Numerous simulation and field data test are performed to validate effectiveness of the proposed scheme under a vast variety of fault conditions. The tests include different types of internal and external faults, sensitivity to transferred power variation, sampling frequency, length of data window, change of smoothing reactor, effect of lightning interference, change of the line length, change of the operation mode, and effect of noise. The scheme is a single-end protection method and does not require sophisticated computations.

Estimation of stored energy for TWIN source HVDC transmission line

TWIN source is a two driver based negative ion source currently operational at IPR. The two driver RF negative ion source test bed to extract and accelerate H- ion beams up to 50 keV. For Negative Neutral Beam Injectors (NNBI) utilizing RF negative ion source, grid breakdown is a routine phenomenon during system conditioning and operation phases. During the grid breakdown event, there are chances that electrostatic energy stored in the transmission line is dumped in the grids, which may possibly damage them. In case of NNBI system with long high voltage transmission line, contribution for the stored energy emanates from their inter-conductor capacitance. The inter-conductor capacitance and thus stored energy could be reduced by proper designing of the HVDC Transmission line. However, it is equally difficult and challenging to estimate the inter-conductor capacitance of the transmission line with non-generic cross sections. This paper discusses estimation of inter-conductor capacitance, an experimental set up to realize a grid breakdown and thus estimate the stored energy of a HVDC transmission line prototype (1m length). The HVDC transmission line prototype (1m length) has vertical placement of conductors. Inter-conductor capacitance is estimated for vertical topology. The stored energy values from estimated inter-conductor capacitance value is compared with experimental results for HVDC transmission line prototype (1m length). Also, modeling of HVDC transmission line is done to simulate a grid breakdown and thus compute the stored energy for entire transmission line length (120m).

Technical Comparison of Modern HVAC and HVDC Transmission System Along with Cost Analysis

This research aims to provide comprehensive information on current state-of-the-art technology in the field of high voltage transmission lines. Also, this study compares the performance of present high voltage AC/DC power systems and classifies potential future opportunities. It presents a contextually updated cost analysis for researchers’ working on modern HVAC and HVDC transmission systems. Besides this paper explained the most important aspects of the modern features of transmission systems. It also describes the modern technology, conductors, and accessories equipment for the transmission system, which greatly reduces the loss of power transmission. This paper further describes the cost breakdown of HVAC and HVDC overhead and underground transmission lines, cost estimation, explanation of comparative HVAC and HVDC transmission costs, and price variation. As the variation between the HVAC and HVDC transmission lines increases, a certain amount of voltage drops and losses occurs which is explained in detail.

Travelling wave fault location for LCC–MMC–MTDC transmission lines based on frequency-dependent characteristic

The paper studies the fault location principles of multi-terminal direct-current (MTDC) hybrid transmission systems based on line-commutated converter (LCC) and modular multi-level converter (MMC). Two issues should be addressed: i) the travelling wave (TW) fault location principle adaptable for the hybrid multi-terminal transmission system; and ii) the algorithm of obtaining frequency-dependent characteristic of the TW signal. In the paper, a novel TW fault location principle adaptable for the LCC–MMC–MTDC hybrid transmission lines is developed based on the frequency-dependent characteristic of TW signal. Firstly, the frequency-dependent characteristic of HVDC transmission line is studied. Secondly, a novel TW fault location principle is proposed, comprised of TW arrival time detection, TW propagation velocity calculation, fault section identification and fault location method. A typical ±400kV LCC–MMC–MTDC hybrid system is constructed using PSCAD/EMTDC for case study to validate the accuracy of the proposed principle. Its robustness against fault location, fault resistance and fault type is well demonstrated.

A Novel Single-Ended Protection Scheme for Hvdc Transmission Lines Based on the Time Domain Convolution Power Ratio

A Novel Single-Ended Protection Scheme for Hvdc Transmission Lines Based on the Time Domain Convolution Power Ratio

Study on Blocking Mechanism of Hvdc Transmission Lines Under Cloud-to-Ground Lightning with Long-Continuous Current

Study on Blocking Mechanism of Hvdc Transmission Lines Under Cloud-to-Ground Lightning with Long-Continuous Current

초고압 AC/DC 송전선로 병행에 따른 상호 유도현상 연구

In general, large-scale power generation such as nuclear power and thermal power have low social acceptability, so they are mainly located on the coast far from densely populated urban areas. Due to this discrepancy between production and consumption regions, construction of a new transmission line is essential, but in Korea, it is very difficult to secure a place for transmission lines due to the narrow land area and negative perception of transmission towers. In this regard, the construction of an additional transmission line is currently under consideration to provide a stable supply of new power generation along the east coast to the metropolitan area, and in this case, it is highly likely that the existing transmission line will be very close to the new HVDC transmission line. Therefore, in this paper, we assumed the construction of a new 500kV HVDC transmission line to transmit an additional power source from the east coast to the metropolitan area, and analyzed the mutual induction phenomenon that occurs when operating close to the existing AC 765kV transmission line. When ultra-high voltage AC/DC transmission lines are operated in close proximity and parallel, electrostatic induction and electromagnetic induction occurs. We analyzed how much influence each other in the normal condition and the fault condition, and considered it from the point of view of protection cooperation. For the analysis, it was modeled assuming the existing Shintaebaek-Singapyeong 765kV transmission line and the newly built Shinhanul-Singapyeong 500kV HVDC transmission line, and reviewed through PSCAD/EMTDC.

A pilot protection scheme for flexible HVDC transmission lines based on modulus power

Existing protection methods for Flexible HVDC transmission lines easily fail to detect the fault location fast and reliably. Concerning this problem, a modulus power based pilot protection scheme is proposed. By analyzing the dynamic switching process of sub-modules in flexible DC converter station, the expression of converter station DC voltage taking into account the influence of AC system is derived. On this basis, the modulus voltage and modulus current are calculated by phase-modulus transformation, and the modulus power calculation model containing DC components alone is built. Then, the expressions of modulus power in different fault cases are derived, and a protection criterion based on the polarity difference characteristics of modulus power is established. Finally, the RT-LAB is used to build the model of a flexible DC system for simulation verification. The results of simulation tests verify that, the proposed protection scheme can detect the fault line and fault pole fast and accurately, with easy threshold setting and low demand on communication synchronization. Besides, it is unaffected by the fault resistance and the specific boundary conditions of current-limiting reactor, etc.

Research on the Influence of Haze Weather on Audible Noise of HVDC Transmission Line

In order to study the influence of haze weather on audible noise of HVDC transmission line, a calculation model of ion flow field of HVDC transmission line considering the influence of haze is established, and then the relationship between different haze levels, different haze particle concentrations and audible noise is analyzed by taking the maximum potential gradient on the conductor surface as the intermediary. Then a ± 800kV DC transmission line is simulated and the results show that the audible noise will be more prominent with the increase of haze concentration, and the increment is more obvious at higher haze concentration; The charging of haze particles is the principal origin for the increase of audible noise, and the effect of PM2.5 is the most significant.

A distance protection scheme for HVDC transmission lines based on the Steady-state parameter model

To improve the performance of the protection scheme for HVDC lines, a novel distance backup protection scheme is proposed in this paper. First, it is proved that the DC line model can be equivalent to lumped parameter model during the steady-state. Based on the equivalent model, the fault distance can be calculated, and the criterion of the distance relay is implemented. Secondly, a directional relay based on the transient currents is added to solve the dead zone problem of distance protection. Finally, a ± 800 kV HVDC system is built in PSCAD/EMTDC simulation environment to test the performance of the protection. Comprehensive test studies show that the proposed protection scheme can correctly distinguish internal faults from external faults. Besides, the proposed protection has a clear setting principle, low requirements of the calculation amount and sampling rate.

Transient Overvoltage on HVDC Overhead Transmission Lines With Background DC Space Charges and Impulse Corona

The space charges around a HVDC transmission line may not only lead to electromagnetic environmental problems but also affect the occurrence of impulse corona and then the transient overvoltage propagation. This paper derives the equations governing the transient overvoltage propagation along a HVDC transmission line when there is either space charges surrounding the line or impulse corona. In contrast to conventional transmission line equations, the proposed equations adopted the dynamic capacitance C ′ and conductance G to characterize the corona discharge in all cases, which can be obtained by a time-domain finite element method. A finite-difference time-domain method is introduced to solve the nonlinear transmission line equations. The validity of the proposed approach is verified by comparison with the lightning overvoltage waveforms measured in a literature. The transient overvoltage propagation along a long UHVDC transmission line surrounded by space charges is analyzed.