Fault Location Methods in HVDC Transmission System—A Review

The transfer of bulk electrical power over long distances can be done by high voltage alternating current (HV AC) transmission systems. These HV AC power transmission systems have their perfections and imperfections. To enhance the existing power transmission systems, high voltage direct current (HVDC) power transmission systems are a sustainable solution. The emergence of advanced HVDC systems is so rapid that they are replacing their counterpart HV AC systems in many parts of the world. In this paper, the prominence of modern HVDC power transmission systems is highlighted. The topologies, converter assortments, contrasts, and modeling methods are discussed. The renewable energy sources (RES) including solar photovoltaic (PV) parks and mainland/ onshore/ offshore wind farms can be assimilated into the existing AC grids via advanced HVDC converters. The perceptions of multi-terminal HVDC systems and DC grids are presented, whereas, the challenges concomitant with the future DC grids are also emphasized.

Direct Current (DC) transmission system is an important part of the interregional grid. However, the frequency impact of power grid caused by DC blocking is more serious with the continuous increase of scale of single DC transmission. The frequency coordination control system is applied to the receiving-end power grid in High Voltage Direct Current (HVDC) transmission system. In the cases of single-infeed HVDC blocking, multi-infeed HVDC blocking or fast power drop, the frequency coordination control system can reduce the frequency fluctuation of power grid by instantly promoting the transmission power of the rest normal DC systems and reducing power loss. The frequency coordinated control substation is an executive device of the system at the converter station. It keeps communicating with the coordinated control master station for real-time monitoring the operation of converter station, reports the fault and executes the remote power boost instructions. Taking the frequency coordinated control substation of 500 kV conventional DC systems as a research background, the load of converter station in a regional power grid is analyzed. The working mechanism of frequency coordination control system in the cases of current converter station fault or other station faults is analyzed. The actual effect of a frequency coordination control system on a converter station in East China power grid is investigated by testing the actual power, voltage and current variation of a conventional DC transmission system.

As Europe integrates more renewable energy resources, notably offshore wind power, into its super meshed grid, the demand for reliable long-distance High Voltage Direct Current (HVDC) transmission systems has surged. This paper addresses the intricacies of HVDC systems built upon Modular Multi-Level Converters (MMCs), especially concerning the rapid rise of DC fault currents. We propose a novel fault identification and classification for DC transmission lines only by employing Long Short-Term Memory (LSTM) networks integrated with Discrete Wavelet Transform (DWT) for feature extraction. Our LSTM-based algorithm operates effectively under challenging environmental conditions, ensuring high fault resistance detection. A unique three-level relay system with multiple time windows (1 ms, 1.5 ms, and 2 ms) ensures accurate fault detection over large distances. Bayesian Optimization is employed for hyperparameter tuning, streamlining the model’s training process. The study shows that our proposed framework exhibits 100% resilience against external faults and disturbances, achieving an average recognition accuracy rate of 99.04% in diverse testing scenarios. Unlike traditional schemes that rely on multiple manual thresholds, our approach utilizes a single intelligently tuned model to detect faults up to 480 ohms, enhancing the efficiency and robustness of DC grid protection.

Recent developments in power semiconductor devices have made High Voltage Direct Current (HVDC) transmission systems the most crucial technology for future power systems. Today several HVDC projects have been commissioned around the world. The primary concern for such an advanced HVDC grid is to follow standard grid codes to maintain the safety and stability of the electrical equipment during transient and dynamic circumstances. Although the HVDC system has been recognized as the most prominent technology to transmit electric power, some issues must be addressed, such as selective and quick detection of faults. For selective fault detection, it is essential to look into the several fault detection strategies that fortify the HVDC system with time-frequency signal processing techniques. This research uses a time frequency-based method to identify the different HVDC transmission line faults. The most suitable mother wavelet for various transient states is selected by analyzing fault voltage and current signals based on variance, standard deviation, and range parameters. An experimental setup of a thyristor-based HVDC transmission system has been developed in the MATLAB/Simulink environment, and multiple fault scenarios have been analyzed. The simulation outcomes reveal that the most effective mother wavelet for detecting DC line, symmetrical and unsymmetrical faults occurs at the 6th level of fault signal decomposition. By examining current and voltage signals, our work has determined the best mother wavelet for various faults. Using more than one mother wavelet to detect faults is more reliable than using a single mother wavelet to detect all faults. Additionally, it has been noted that each fault's voltage and current signals have two distinct mother wavelets.

Many kinds of high temperature superconducting (HTS) devices are being developed due to its several advantages. In particular, the advantages of HTS devices are maximized under the DC condition. A line commutated converter (LCC) type high voltage direct current (HVDC) transmission system requires large capacity of DC reactors to protect the converters from faults. However, conventional DC reactor made of copper causes a lot of electrical losses. Thus, it is being attempted to apply the HTS DC reactor to an HVDC transmission system. The authors have developed a 8 mH class HTS DC reactor and a model-sized LCC type HVDC system. The HTS DC reactor was operated to analyze its operational characteristics in connection with the HVDC system. The voltage at both ends of the HTS DC reactor was measured to investigate the stability of the reactor. The voltages and currents at the AC and DC side of the system were measured to confirm the influence of the HTS DC reactor on the system. Two 5 mH copper DC reactors were connected to the HVDC system and investigated to compare the operational characteristics. In this paper, the operational characteristics of the HVDC system with the HTS DC reactor according to firing angle are described. The voltage and current characteristics of the system according to the types of DC reactors and harmonic characteristics are analyzed. Through the results, the applicability of an HTS DC reactor in an HVDC system is confirmed.

Soft computing likes ANFIS now penetrating the control system, especially for power semi-conductor and power system controls. Control of trigger angle is one of an important method to deliver power through high-voltage direct current (HVDC) transmission system effectively. Higher transient of current is one problem of HVDC on start-period, for up-ramp at 20 pu/s or higher. To cove this problem, the ANFIS control scheme is proposed to suppress the transient current in this research. The ANFIS control is built by using data train that these data are obtained from the simulation of HVDC system equipped by PI control under various loads and up-ramp rates. Training of ANFIS controller is done by input–output in 5000 data points. After training stage, the ANFIS controller is embedded into HVDC converter through fuzzy logic controller tool. Simulation results show that the proposed control is more effective to reduce the transient current in all scenarios compared to conventional PI control. Where the peak overshoot of transient current is achieved at the value of 1.11 pu for the proposed control. While the peak overshoot of transient current for conventional PI control is obtained at the value of 1.148 pu.

The strategic intent of the African Union is to develop a “Smart Integrated African Electric Power Super Grid” driven by modern tools and advances in high-voltage direct current (HVDC) engineering and flexible alternating current technology systems (FACTS), which is central in supporting Africa’s sustained economic growth and development. The southern African region, including South Africa, is beset by the critical challenges of perennial load-shedding, which impedes economic growth and aggravates unemployment. This has led to the insecurity of electricity supplies and degraded the quality of life. The parallel operation of high-voltage direct current (HVDC) and flexible AC technology systems (FACTS) controllers is gaining traction as system conditions become more complex, such as weak power networks which requires increased stability requirements, resulting in load-shedding and power outages. These adversely affect business productivity and adversely affect GDP and economic growth. Thus, the application of innovative technologies such as HVDC links can stabilize weak power systems. It is established that HVDC delivery systems reduce losses in long transmission lines transporting bulk power compared with high-voltage alternating current (HVAC) transmission lines for power wheeling. This paper evaluates the parallel operation of the Cahora Bassa 1414 km bipolar HVDC link and a weak parallel 400/330 kV alternating current (AC) link. It demonstrates the use of FACTS controllers to enhance the technical performance of an existing network, such as voltage control, and technical loss reduction. It combines an HVDC line commutated converter (LCC) and HVAC transmission lines, in hybrid notation to increase the voltage stability of the system by controlling the reactive power with a Static Var Compensator (SVC). These modern tools can increase the transmission power controllability and stability of the power network. In this study, HVDC–LCC was used with a setpoint of 1000 MW in conjunction with the 850 MVAr SVC. The results show that the technical losses were reduced by 0.24% from 84.32 MW to 60.32 MW as Apollo 275 kV SVC was utilized for voltage control. The network analysis was performed using DIgSILENT PowerFactory software that is manufactured by DIgSILENT GmbH at Gomaringen, Germany

The present PhD thesis deals with transformer inrush current in offshore grids including offshore wind farms and High Voltage Direct Current (HVDC) transmission systems. The inrush phenomenon during transformers energization or recovery after the fault clearance is one of important concerns in offshore systems which can threaten the security and reliability of the HVDC grid operation as well as the wind farms function. Hence, the behaviour of wind turbines,Voltage Source Converters (VSC) and transformer under the normal operation and the inrush transient mode is analyzed. For inrush current reduction in the procedure of the offshore wind farms start-up and integration into the onshore AC grid, a technique based on Voltage Ramping Strategy (VRS) is proposed and its performance is compared with the operation of system without consideration of this approach. The new methodology which is simple, cost-effective ensures minimization of transformer inrush current in the offshore systems and the enhancement of power quality and the reliability of grid under the transformer energizing condition. The mentioned method can develop much lower inrush currents according to the slower voltage ramp slopes. Concerning the recovery inrush current, the operation of the offshore grid especially transformers is analyzed under the fault and the system restoration modes.The recovery inrush transient of transformers can cause tripping the HVDC and wind farms converters as well as disturbing the HVDC power transmission. A voltage control design based on VRS is proposed in HVDC converter to recover ali the transformers in offshore grid with lower inrush currents.The control system proposed can assure the correct performance of the converters in HVDC system and in wind farm and also the robust stability of the offshore grid. Esta tesis doctoral estudia las corrientes de energización de transformadores de parques eólicos marinos con aerogeneradores con convertidores en fuente de tensión (VSC) de plena potencia conectados a través de una conexión de Alta Tensión en Corriente Continua (HVDC). Las corrientes de energización pueden disminuir la fiabilidad de la transmisión eléctrica debido a disparos intempestivos de las protecciones durante la puesta en marcha o recuperación de una falta. Para la mitigación de las corrientes de energización durante la puesta en marcha del parque esta tesis propone una nueva estrategia basada en incrementar la tensión aplicada por el convertidor del parque eólico en forma de rampa (VRS). Este método persigue energizar el parque eólico con el menor coste y máxima fiabilidad. La tesis analiza diferentes escenarios y diferentes rampas. Otro momento en que las corrientes de energización pueden dar lugar a un disparo intempestivo de las protecciones es durante la recuperación de una falta en la red de alterna del parque eólico marino. Esta tesis extiende la estrategia VRS, utilizada durante la puesta en marcha del convertidor del parque, para los escenarios de recuperación de una falta.

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 multi-terminal 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 paper, 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.

This paper presents a model of double-ring type grounding pole unequal depth embedding for high-voltage direct current (HVDC) transmission system; and introduces calculation formula of DC ground potential distribution when double-ring type grounding pole is unequal buried. Furthermore the ground potential distribution and stride voltage level around the grounding pole and influence of grounding depth and soil parameters on the current field are discussed in this paper. The electric field zoning model of the ring current source is established by using the power system grounding pole analysis software CDEGS to verify the feasibility of this method. As the model is able to make the grounding current overflow density and potential distribution as uniform as possible, there is no serious local current concentration.

High voltage direct current (HVDC) technology has been widely used for its advantages of interconnection of non-synchronous networks and off-shore wind farm to the main power system. In Peru, the perspective of the energy trade between Peru and Chile by a traditional line-commutated converter HVDC (LCC-HVDC) link is being evaluated by Comite de Operacion del Sistema Interconectado Nacional (COES) recently. Meanwhile voltage-source converter HVDC (VSC-HVDC) technology is considered to be a preferable solution to transport off-shore wind energy reserved abundantly along Peruvian coastline through DC cable. This paper firstly reviewed the impact of the strength of AC system at the busbar where LCC-HVDC is connected on LCC-HVDC transmission capacity by SCR index. Then, a hybrid HVDC system topology is studied to evaluate the improvement of it by connecting VSC-HVDC at the same busbar. The PSCAD/EMTDC model of the hybrid HVDC system has been built for the study. The advantages of connecting a VSC-HVDC link are discussed by LCC-HVDC Maximum Power Curves (MPC) and Maximum Available Power (MAP).

The evacuation of bulk electrical power over long distances can be done mainly by high voltage alternating current (HVAC) transmission systems. However, where there are large water bodies and long distance between the generation source and demand centres like most islands in European countries, high voltage direct current (HVDC) power transmission is gaining more traction and is proving to be a sustainable solution. Regarding the distance between HVDC and HVAC, the break-even threshold in terms of cost is approximately 600 - 800 km for overhead line systems (OHLs) and 40 - 70 km for systems with cables. The global thirsty to harness the renewable energy sources is diverting the attention towards efficiency and flexibility of power transmission. Traditional HVAC systems are being quickly replaced with HVDC systems in various parts of the world. This report highlights the significance of modern HVDC power transmission networks, topologies, converter varieties, contrasts, and main equipment associated with HVDC systems. Through the use of HVDC converters, renewable energy sources (RES), such as offshore, onshore, coastal wind farms and photovoltaic power plant can be linked to the current existing AC grids. Although the difficulties associated with the upcoming DC grids are also highlighted, the views on multi-terminal HVDC systems and DC grids are also outlined.

This paper investigates the problem of the insensitivity of synchronous generators out of step protection when they are operating close to a High-Voltage Direct Current (HVDC) transmission system. Commercial out of step protection devices are based on the measurement of the impedance seen at the terminals of the generators and on the fact that this will be reversed when a loss of stability occurs. However, when these generators operate near an HVDC system, the out of step protection is desensitized, because the HVDC controls are able to maintain constant power when a loss of synchronism condition starts. As a consequence, the generators are exposed to serious damage. Our investigations also showed that the academy’s recent proposals to detect the out of step conditions were ineffective to solve the problem. Therefore, investigating the causes of this phenomenon and under what conditions it occurs is fundamental to develop efficient methods to solve it.

High voltage direct current (HVDC) transmission offers several operation advantages over high voltage alternating current (HVAC) transmission systems. HVDC transmission lines have no frequency and hence minimal problems of harmonics, oscillations or transients; they actually damp out transients with effective controllers. Precise and fast power control in either direction is easier to achieve in HVDC than HVAC systems as dc power is minimally affected by reactance. This curtails system instability, cascading effect or voltage collapse. The ease of power flow control in HVDC lines makes it easy to achieve the maximum power and thermal capacity of transmission lines. It is also simple to control active power transfer at a predetermined level or even to modulate this to improve system damping. For weak AC grids, voltage source converter (VSC) based HVDC systems offer better controllability and grid flexibility for integrating intermittent renewable energy sources such as wind and solar-power. HVDC systems offer technical advantages: all angular stability problems disappear and even connection of systems at different frequency is feasible. The problems of cable charging current are eliminated. Thus cables can readily be used for underwater crossings. HVDC is the established technology of choice for long distance transmission and subsea electrical power transmission systems. In this paper, an investigation of voltage stability margin on Eskom high voltage eastern grid is carried out. Using the Newton Raphson iterative method, the impact of HVDC link controller and transformer tap changers on voltage stability were evaluated on Athene substation of Eskom eastern grid, an area of rapid load growth. Results obtained show that by introducing HVDC line, transmission capacity is enhanced, with lower line losses and improved voltage profile. Simulations were carried out using DigSILENT PowerFactory.

High Voltage Direct Current (HVDC) technology has recently emerged as a significant option in current power networks to address power transmission challenges. Therefore, this research project examines the potential impact of HVDC technology on the Nigerian transmission system. Based on the information provided by the Nigerian Electricity System Operator (NESO), a model of the 330 kV transmission network in Nigeria was created using DIgSILENT PowerFactory. Summer and winter load flow scenarios were examined to enhance the model's precision and consistency. The system performance was evaluated through stability and reliability studies, which helped identify suitable locations for HVDC links. The load point indices (LPIs) and system indices were used for the reliability evaluation, while the PV and QV analyses were used for the stability evaluation. An HVDC model was created and connected to the transmission network at two locations identified by the studies, Gombe and Yola buses. A comparison was conducted using two separate HVDC connections (Case 1: Azura-Gombe and Case 2: Azura-Yola) to identify the critical impact of HVDC on the system reliability and stability. The reliability and stability simulation showed that HVDC technology significantly boosts the reliability and stability of the transmission network and reduces energy losses. However, adding an HVDC link between Azura and Yola, Case 2, significantly improved overall performance, as evidenced by improving the system and load point indices and a better voltage profile and reactive power margin. The system indices, SAIDI improved by 0.07 h/yr, SAIFI by 0.19 interruption/yr, and ASAI enhanced by 0.11%, while the LPIs improved effectively by zeroing the Load Point Interruption Frequency (LPIF) and Load Point Interruption Time (LPIT). During the stability analysis, the loadability increased by 119% while the critical point improved by 0.061 pu/ -394 MVAR. Economically, the cost incurred in Case 1 is 79.17% lower than the base case even though new equipment (HVDC) is installed; this also applies to Case 2, which is 85% lower than the base case. Integrating HVDC technology could improve financial gain, considering improved energy supply, increased production, and general economic growth. This research has contributed significantly to revealed improvements in system and load indices, increased loadability, increased stability, and boosted financial gain with the HVDC connected.