HVDC Transmission Research Articles

Rio Madeira HVDC System: Commissioning of the Ground Electrode for Bipole 2 at Porto Velho

The original ground electrode of the Madeira River HVDC transmission system, bipole 2, was discarded due to the risk of saturation of the transformers in the Converter Substation of Porto Velho, located 15 km away, during the monopolar operation with ground return. After an extensive geophysical survey, a new site was selected, 40 km from the converter substation. For the confirmation of the new site, it was built in the central area of the site, a single-well 47 m deep test electrode, interconnected to the original 15 km electrode line by an additional 40 km long temporary line. A new electrode was then designed. This paper summarizes the test electrode procedure and the activities developed for the new electrode commissioning after its construction, which can be divided into two phases–pre-commissioning and commissioning. The electrode pre-commissioning was performed before its energization for the evaluation of the integrity of its components. The commissioning tests started with electrode energization, employing the electrode line, and an unbalanced bipole operation, which allowed the evaluation of its electrical performance. However, the main objective of the paper is the evaluation of the electrode resistance, which is an essential HVDC electrode parameter.

Accurate Modeling Simulation and Experimental Study of Hybrid Multi-Terminal UHVDC Transmission System

This study researches on the Wudongde hybrid multi-terminal Ultra High-Voltage Direct Current Transmission (UHVDC) project (referred to as Wudongde transmission project in short) from the electromagnetic transient model and simulation and establishes an accurate simulation model of the hybrid multi-terminal UHVDC transmission system with the Power Systems Computer-Aided Design (PSCAD). The hybrid multi-terminal UHVDC transmission system consists of the primary system and the control system. The simulation model of the primary system adopts the parameters of the Wudongde transmission project, and the simulation model of the control system refers to the control system benchmark model of HVDC transmission and 9-terminal DC grid in the International Council on Large Electric Systems (CIGRE). According to the characteristics of the hybrid multi-terminal UHVDC control system, the benchmark model of HVDC transmission and 9-terminal DC grid control system in the CIGRE is modified accordingly, and a simulation model of the control system applicable to the hybrid multi-terminal UHVDC transmission system is established. The accuracy and credibility of the model are verified through the comparison of the recording waveform and the simulating waveform of the steady-state and transient operation. The simulating and field recording waveforms show that the model can accurately simulate the Wudongde transmission project and be used as an effective tool for further studying the electromagnetic transient characteristics of the hybrid multi-terminal UHVDC transmission system.

HVDC Transmission and its Potential Application in Remote Communities: Current Practice and Future Trend

High voltage direct current (HVdc) transmission systems play an essential role in our modern power grids, not only providing bulk power transmission and asynchronous ac connection, but also enabling renewable energy integration into power grids. Renewable energy integration through HVdc transmission systems leads to the creation of multiterminal HVdc (MT-HVdc) grids. Recently, the idea of electrifying remote communities by HVdc transmission systems has emerged, and multi-terminal small-scale HVdc grids have been investigated in such applications. Despite numerous applications and significant potential of HVdc transmission systems, various technical and economic challenges in utilizing these systems still persist. In this article, an extensive literature review is conducted on HVdc transmission systems, particularly focusing on their role in renewable energy integration, and their potential application in remote communities. Future research directions are also recommended.

Resilient DC Voltage Control for Islanded Wind Farms Integration Using Cascaded Hybrid HVDC System

To integrate large-scale islanded onshore wind power with different sizes, this paper proposes an integration system based on the cascaded hybrid HVDC transmission system, which consists of LCC and several MMCs in series connection at the DC side of the rectifier. A large-scale wind farm is connected with one LCC and one MMC while several small-scale wind farms are connected with MMCs directly. Owing to the hierarchical integration arrangement, the operating flexibility can be improved with reduced capacity and the number of step-up interfacing transformers. A resilient DC voltage control is proposed for the integration system to adaptively redistribute power among the converters during wind power fluctuations. Firstly, the topology and operating characteristics of the wind power integration system are introduced. Then, a resilient DC voltage control is proposed to ensure stable operation during wind power curtailments. Finally, a simulation model of the hybrid cascaded HVDC transmission system is built in PSCAD/EMTDC to verify the effectiveness. The research results show that the system provides a new option for long-distance transmission of large-scale islanded wind power.

Corrosion Behavior of Aluminum in Dilute Acetic Acid Solution Simulating Cooling Water in HVDC Transmission

Corrosion Behavior of Aluminum in Dilute Acetic Acid Solution Simulating Cooling Water in HVDC Transmission

Continuous commutation failure suppression strategy in hybrid multi-infeed HVDC transmission system

Continuous commutation failure suppression strategy in hybrid multi-infeed HVDC transmission system

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.

Analysis of faults on high voltage direct current HVDC transmissions system

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

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.

Short-term generation capacity expansion planning considering multi-terminal VSC[sbnd]HVDC links using a linear programming framework improved by shift factors

This paper describes the modelling of short-term generation capacity expansion planning (GCEP) for multi-terminal VSC-based HVDC transmission systems. The GCEP formulation is based on a mixed-integer linear programming (MILP) framework where transmission losses are considered by piecewise linearisation. As opposed to existing methods, the present GCEP formulation is based on shift factors which enable the representation of the hybrid AC/DC grids including VSC stations. This way new power generation investments can be efficiently determined at any of the VSC-connected AC systems. This new method lies in sharp contrast with the so-called classic GCEP method where the system nodal power balances are formulated using the voltage phase angles as decision variables thus increasing the model complexity. Indeed, to determine the GCEP investments, the present model aimed to multi-terminal HVDC links only uses AC/DC transmission line losses, power generations and projected generating power plants as decision variables. The new GCEP formulation is compared to the classic method using two compelling multi-terminal VSCHVDC test systems for validity and applicability purposes. Results show that the proposed formulation reduces the simulation running time by more than 80%, compared to the standard model, accompanied by acceptable accuracy of results since errors inferior to 5% are obtained.

Measurement and Safety Criteria of Step Voltage of High Voltage Direct Current Grounding Electrode

Grounding electrode is an indispensable part in HVDC transmission projects. During its design and safety evaluation, step voltage is a crucial aspect. By reviewing and sorting out the present standards involving step voltage measurement and its safety limit, this paper illustrates the contradiction between the measurement methods and the safety evaluation. Reasons for the contradiction are explained by analyzing the principal of step voltage measurement and safety evaluation. The Open-circuit step voltage measurement method and the measurement method with a human body equivalent resistance paralleled are compared to find out their advantages and disadvantages. Suitable circumstances and corresponding safety criteria of these two methods are put forward. Method proposed in this paper can be applied to step voltage measurement and safety evaluation of HVDC grounding electrode, providing reference when revising the related standards.

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).

A detection method for HVDC commutation failure based on the variation rate of commutation inductance energy

Concerning the insufficient accuracy of the criterion for identifying commutation failure in HVDC transmission systems, a new detection method for commutation failure based on the variation rate of commutation inductance energy is proposed. First, the conducting states of the converter valves in both normal commutation and commutation failure conditions are analysed, and the correlation between the differential of valve-side line current and the conducting state of the converter in different commutation scenarios is established. On this basis, combining the topologies of D/Y-bridge converters, a model to calculate the variation rate of commutation inductance energy is built. Then, considering the fault characteristics of DC current, DC voltage and valve currents, it is found that the calculated value of the variation rate of commutation inductance energy is consistent with the actual value under normal commutation conditions but inconsistent under commutation failure conditions. This allows for the construction of a criterion for identifying the commutation failure. Finally, the simulation results obtained with the RT-LAB platform verify that, the proposed method can detect the occurrence of commutation failure quickly without measuring the valve currents, and it remains accurate when dealing with commutation failure near the threshold.

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.

Intelligent Fault Diagnosis Framework for Modular Multilevel Converters in HVDC Transmission.

Open circuit failure mode in insulated-gate bipolar transistors (IGBT) is one of the most common faults in modular multilevel converters (MMCs). Several techniques for MMC fault diagnosis based on threshold parameters have been proposed, but very few studies have considered artificial intelligence (AI) techniques. Using thresholds has the difficulty of selecting suitable threshold values for different operating conditions. In addition, very little attention has been paid to the importance of developing fast and accurate techniques for the real-life application of open-circuit failures of IGBT fault diagnosis. To achieve high classification accuracy and reduced computation time, a fault diagnosis framework with a combination of the AC-side three-phase current, and the upper and lower bridges’ currents of the MMCs to automatically classify health conditions of MMCs is proposed. In this framework, the principal component analysis (PCA) is used for feature extraction. Then, two classification algorithms—multiclass support vector machine (SVM) based on error-correcting output codes (ECOC) and multinomial logistic regression (MLR)—are used for classification. The effectiveness of the proposed framework is validated by a two-terminal simulation model of the MMC-high-voltage direct current (HVDC) transmission power system using PSCAD/EMTDC software. The simulation results demonstrate that the proposed framework is highly effective in diagnosing the health conditions of MMCs compared to recently published results.

Single terminal coordination-protection scheme for hybrid three-terminal DC line based on station terminal current characteristics

Grounding electrode is an essential component in hybrid multi-terminal HVDC transmission system, By connecting converter station to the bus bar as a main station, this work analyzes the fault current component characteristics of grounding electrode line under various fault conditions for a hybrid three terminal DC transmission system. It is concluded that under single pole line grounding fault, current at the measuring ends of grounding, fault and sound electrodes satisfies the Kirchhoff current theorem, while considering converter station as a node. However, for reverse fault of line protection, current at above mentioned electrodes doesn’t follow the Kirchhoff law. Under various DC line faults, fault line is selected according to the mutation direction of current at the back-side of bus bar. Essentially, the current obtained by grounding electrode’s measuring point is a zero mode current, hence, it can sense the fault current precisely and has directivity. A comprehensive single terminal coordination-protection scheme for DC lines in hybrid multi-terminal transmission system is constructed by using currents’ characteristics of station terminal. The proposed method does not rely on boundary elements, and has an ability to quickly identify internal and external faults, select the fault pole, and withstand high resistance. The developed algorithm for protection scheme is simple, requires low sampling rate, and ensures high reliability for protection scheme.

Frequency Domain Characteristic Analysis of Fault Electrical Quantities in HVDC Transmission System

The transient frequency domain characteristics of different fault electrical quantities in HVDC transmission system are studied in this paper firstly using analytical calculation. Firstly, the equivalent model of LCC converter suitable for DC system fault characteristic analysis and the equivalent model of DC line considering parameter frequency variation effect are established. On this basis, the DC system fault equivalent circuit is constructed. The frequency domain expressions of relevant electrical quantities under different DC line fault conditions are obtained according to the solution of equivalent circuit. On the basis of the frequency domain expression of fault electrical quantity, the frequency component diagram of fault electrical quantity is obtained. Finally, the frequency spectrum of fault voltage under different fault conditions is analyzed and compared.

Low Impedance Fault Identification and Classification Based on Boltzmann Machine Learning for HVDC Transmission Systems

Identification and classification of DC faults are considered as fundamentals of DC grid protection. A sudden rise of DC fault current must be identified and classified to immediately operate the corresponding interrupting mechanism. In this paper, the Boltzmann machine learning (BML) approach is proposed for identification and classification of DC faults using travelling waves generated at fault point in voltage source converter based high-voltage direct current (VSC-HVDC) transmission system. An unsupervised way of feature extraction is performed on the frequency spectrum of the travelling waves. Binomial class logistic regression (BCLR) classifies the HVDC transmission system into faulty and healthy states. The proposed technique reduces the time for fault identification and classification because of reduced tagged data with few characteristics. Therefore, the faults near or at converter stations are readily identified and classified. The performance of the proposed technique is assessed via simulations developed in MATLAB/Simulink and tested for pre-fault and post-fault data both at VSC1 and VSC2, respectively. Moreover, the proposed technique is supported by analyzing the root mean square error to show practicality and realization with reduced computations.

An Adaptive Protection Scheme for Power Systems Considering the Effects of HVDC Interfaced Distributed Generations

Distributed Generations are usually connected to the ac grid through HVDC transmission systems. However, due to the current injected by the grid-side voltage source converter (GVSC), the voltage drop after a short-circuit fault will be partly compensated. For this reason, the viewed impedance of distance relays will be affected, which is a challenge for the distance protection scheme. For this issue, this paper proposed an adaptive distance protection scheme for the system containing distributed generations. Firstly, the proposed scheme controls the current of the GSVC to be proportional to the current of the AC transmission line. Secondly, an adaptive distance protection criterion is proposed, which can obtain the impedance from the relay to the fault-point accurately. The effectiveness of the proposed approach was validated through simulation using MATLAB/Simulink.

4-Pole Hybrid HVDC Circuit Breaker for Pole-to-Pole (PTP) Fault Protection

Numerous problems have emerged with the development of HVDC transmission technology. One of them is the fault current that occurs when there is an issue in the line. In particular, in the case of a PTP (pole-to-pole) fault, a DCCB design suitable for the direction is required because the fault current flows through the positive and negative poles. In the case of PTP fault, a fault current of the same value occurs in the opposite direction, and in the case of DCCB, the breaking efficiency may be reduced or even impossible to break due to a mistake in the emission direction or a wrong design. In particular, when designing using several unidirectional DCCBs, it is cheaper and consumes less area than typical DCCBs, so it is economical, but this problem may be more prominent. To solve this problem, this paper proposes a 4- pole Hybrid HVDC circuit breaker to solve this problem. This circuit optimizes the DCCB internal components through quantitative analysis of the fault current to reduce the influence of the residual fault current as well as the previously most important parameter, Zero-Cross Time (ZCT). We also verified the circuit’s energy dissipation process to increase reliability. The circuit in this paper is simulated based on the VSC-based HVDC transmission link. Physically analyze the derived results and described the circuit mechanism.