High-voltage Direct Current Cable Systems Research Articles

An Intelligent Method for Fault Location Estimation in HVDC Cable Systems Connected to Offshore Wind Farms

Large and remote offshore wind farms (OWFs) usually use voltage source converter (VSC) systems to transmit electrical power to the main network. Submarine high-voltage direct current (HVDC) cables are commonly used as transmission links. As they are liable to insulation breakdown, fault location in the HVDC cables is a major issue in these systems. Exact fault location can significantly reduce the high cost of submarine HVDC cable repair in multi-terminal networks. In this paper, a novel method is presented to find the exact location of the DC faults. The fault location is calculated using extraction of new features from voltage signals of cables’ sheaths and a trained artificial neural network (ANN). The results obtained from a simulation of a three-terminal HVDC system in power systems computer-aided design (PSCAD) environment show that the maximum percentage error of the proposed method is less than 1%.

Advanced insulating materials contributing to “carbon neutrality”: Opportunities, issues and challenges

Advanced insulating materials contributing to “carbon neutrality”: Opportunities, issues and challenges

High voltage direct current transmission cables to help decarbonisation in Europe: Recent achievements and issues

High Voltage Direct Current (HVDC) underground and submarine cables constitute an essential technology for the long-distance transmission of renewable electrical power with low losses, thereby fostering decarbonisation. In the past 2 decades, all this yielded a quasi-exponential rise of HVDC cable systems installed worldwide, but has also made the working conditions of HVDC cables harsher. In this paper, the contribution of HVDC cables to decarbonisation is tackled, with particular reference to the situation in Europe, and a few simple calculations showing in general terms the quantitative contribution provided by HVDC cable systems to decarbonisation are given. Then, the major issues towards long-lasting and reliable HVDC cable systems are summarised briefly, focussing—for the sake of brevity—on the influence of the main HVDC cable technologies, of cable laying environment and of duty service. Some hints are also provided at the chances given by multiterminal HVDC systems.

Bulletin Board: Activities of the DEIS Technical Committee on “HVDC Cable Systems (Cables, Joints and Terminations)” for the development of IEEE Std. 2862TM-2020

High voltage direct current (HVDC) cable systems with extruded insulation are becoming increasingly attractive versus the traditional mass impregnated non-draining (MIND) HVDC cable systems [1]. Voltage and power ratings of HVDC extruded cable systems commercially available-after being qualified according to CIGRE Technical Brochure (TB) 496 [2]-are exceeding 500 to 600 kV and 1 GW, respectively [3]-[6]. Of course, HVDC extruded cable systems still have issues.

Towards Electrothermal Optimization of a HVDC Cable Joint Based on Field Simulation

Extruded high-voltage direct current cable systems transmit electric power over long distances. Numerical field simulation can provide access to the internal electrothermal behavior of cable joints, which interconnect cable sections. However, coupled nonlinear electrothermal field simulations are still a challenge. In this work, a robust numerical solution approach is implemented and validated. This approach allows for efficient parameter studies of resistively graded high-voltage direct current cable joint designs. It is assessed how the dielectric stress distribution between the conductor connection and the grounded cable sheath is influenced by nonlinear field and temperature dependent electric conductivity of the field grading material. Optimal field grading material parameters, which fulfill the field grading and power loss requirements, are suggested based on the simulation studies.

A Review about the Modeling and Simulation of Electro-Quasistatic Fields in HVDC Cable Systems

In comparison to high-voltage alternating current (HVAC) cable systems, high-voltage direct current (HVDC) systems have several advantages, e.g., the transmitted power or long-distance transmission. The insulating materials feature a non-linear dependency on the electric field and the temperature. Applying a constant voltage, space charges accumulate in the insulation and yield a slowly time-varying electric field. As a complement to measurements, numerical simulations are used to obtain the electric field distribution inside the insulation. The simulation results can be used to design HVDC cable components such that possible failure can be avoided. This work is a review about the simulation of the time-varying electric field in HVDC cable components, using conductivity-based cable models. The effective mechanisms and descriptions of charge movement result in different conductivity models. The corresponding simulation results of the models are compared against measurements and analytic approximations. Different numerical techniques show variations of the accuracy and the computation time that are compared. Coupled electro-thermal field simulations are applied to consider the environment and its effect on the resulting electric field distribution. A special case of an electro-quasistatic field describes the drying process of soil, resulting from the temperature and electric field. The effect of electro-osmosis at HVDC ground electrodes is considered within this model.

Overvoltage characteristics in symmetrical monopolar HB MMC-HVDC configuration comprising long cable systems

This contribution focuses on high voltage direct current (HVDC) transmission systems comprising modular multilevel converters (MMC) equipped with half-bridge (HB) submodules and analyses cable voltage stresses during various station internal as well as dc side faults. In order to examine relevant overvoltage characteristics affecting HVDC cable systems, a systematic approach to evaluate overvoltage stresses is presented and an extensive set of time-domain simulations is analysed for schemes operating in symmetrical monopolar configuration. Obtained results are relevant for considerations on insulation co-ordination of HVDC cable systems and for a comprehensive definition of high voltage testing requirements.

Electrical tree degradation in high‐voltage cable insulation: progress and challenges

High-voltage direct current (HVDC) and high-voltage alternating current (HVAC) cables are the most important equipment for high-voltage, large-capacity and long-distance power transmission. Electrical tree is a pre-breakdown phenomenon leading to failure of insulation materials, and it is the major issue that threatens the safe and stable operation of HVDC and HVAC cable systems. This study summarises and analyses the achievements in the research of electrical tree for HVDC and HVAC cables. The initiation mechanisms of the electrical tree, including Maxwell electro-mechanical stress, charge injection–extraction, charge trapping and electroluminescence theories, are elaborated for fully understanding the electrical degradation process in insulation materials. Then, the influences of the high electric field, high temperature and mechanical stress on electrical tree behaviours are discussed, and the relationship between charge transport and the electrical tree is analysed and illustrated. The suppression methods of the electrical tree are put forward by introducing inorganic and organic additives into insulation materials, and the suppression mechanisms are presented from the viewpoints of the structure-property and microscale–macroscale relationships. Recently, the electrical tree research studies are focused on the high-precision of initiation models, high-dependence of multi-physical fields and high-efficiency of suppression methods. The achievements provide theoretical support for improving the electrical performance of insulation materials, while it is a practical problem to explore their application feasibility in HVDC and HVAC cable.

Analysis of Extruded HVDC Cable Systems Exposed to Lightning Strokes

In high-voltage direct current (HVDC) transmission systems comprising overhead line (OHL) sections as well as cable sections, the dc cable system is exposed indirectly to lightning strokes. In case of HVDC cable systems with extruded insulation the present test recommendations do not specify lightning impulse test levels related to rated system voltage. Instead, preliminary electromagnetic transient studies are required to determine the absolute maximum lightning impulse voltage the cable might experience. Within this paper, the general lightning behavior of OHL-cable mixed systems subsequent to the occurrence of a backflashover as well as a shielding failure is investigated for a 525 kV HVDC transmission scheme. This paper presents a modeling method to calculate occurring lightning overvoltages along a dc cable embedded between OHL sections. Based on a detailed parametric study using time-domain simulation, maximum lightning impulse voltages along the cable system are determined, and evaluated with regard to impulse level and polarity. The impact of project related parameter such as cable length, tower design, and tower grounding conditions on lightning overvoltage affecting the cable is demonstrated.

HVDC grid protection algorithm design in phase and modal domains

To meet the required operation speed for protection of meshed voltage source converter (VSC) high-voltage direct current (HVDC) grids, travelling wave-based algorithms operating in the submillisecond time-frame can be used. The domain in which these algorithms operate, i.e. modal or phase, determines their performance in fault discrimination, fault type classification, and faulted pole selection. In the recent literature, high-speed algorithms have been proposed for various VSC HVDC grid configurations and transmission line types; yet, the choice of domain has received insufficient attention. This study offers recommendations for the choice of domain for protection algorithm design of HVDC overhead line or cable systems in symmetric monopolar and bipolar configurations. The theoretical analysis of this study, which is based on fundamental wave propagation theory, indicates that the preferred domain for protection algorithms for cable and overhead line systems are the phase and modal, respectively. Furthermore, the study provides comprehensive guidelines to construct detection functions for both configurations and discusses the errors introduced by approximations. Finally, study results from a bipolar overhead line test system demonstrate the advantages of modal over phase domain for fast fault discrimination and classification and illustrate practical problems associated with non-ideal detection functions.

Review on HVDC cable terminations

With modern power utilities going green by utilising renewable energy technologies and the development of the smart power grid, high-voltage direct current (HVDC) technologies become more and more important in the energy transmission. In particular, HVDC cable systems play a prominent role in undersea power transmission and offshore renewable energy integration. As an essential part of a complete HVDC cable system, the cable termination is one of the most critical components. The mathematical and physical background of HVDC cable systems is discussed and the development of various types of HVDC cable terminations is reviewed. Regarding the non-uniform field distribution, the influence of temperature on the non-linear conductivity is briefly discussed. Furthermore, faults of terminations caused by inappropriate installation and testing of cable systems are discussed.

Next generation polymeric high voltage direct current cables—A quantum leap needed?

The attention given to high voltage direct current (HVDC) cables appears to be at an all-time high. In the July/August 2017 issue of IEEE Electrical Insulation Magazine, the focus was on different aspects of the design and testing of HVDC cable systems. There are several reasons for this, one of the most important probably being the worldwide attention on harvesting renewable energy at a scale never seen before. The prices of building large offshore windfarms in Europe as reflected in a recent normalized cost of electricity have unexpectedly dropped in the last year, as illustrated in Figure 1, which will further accelerate the development of HVDC cables to link offshore and onshore substations. The winning bid in 2016 for the Borssele II, 700-MW windfarm in the Netherlands was as low as 54.5€ ($61)/MWh [1].