L A T E X IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. XX, NO. XX, NOVEMBER 2020 1 HVDC Circuit Breakers: A Comprehensive Review Fazel Mohammadi, Senior Member, IEEE, Kumars Rouzbehi, Senior Member, IEEE, Masood Hajian, Senior Member, IEEE, Kaveh Niayesh, Senior Member, IEEE, Gevork B. Gharehpetian, Senior Member, IEEE, Hani Saad, Member, IEEE, Mohd. Hasan Ali, Senior Member, IEEE, and Vijay K. Sood, Life Fellow, IEEE Abstract—High Voltage Direct Current (HVDC) systems are now well-integrated into AC systems in many jurisdictions. The integration of Renewable Energy Sources (RESs) is a major focus and the role of HVDC systems is expanding. However, the protection of HVDC systems against DC faults is a chal- lenging issue that can have negative impacts on the reliable and safe operation of power systems. Practical solutions to protect HVDC grids against DC faults without a widespread power outage include (1) using DC Circuit Breakers (CBs) to isolate the faulty DC-link, (2) using a proper converter topology to interrupt the DC fault current, and/or (3) using high power DC transformers and DC hubs at strategic points within DC grids. The application of HVDC CBs is identified as the best approach that satisfies both DC grids and connected AC grids’ requirements. This paper reports a comprehensive review of HVDC CBs technologies, including recent significant attempts in the development of modern HVDC CBs. The functional analysis of each technology is presented. Additionally, different technologies based on information obtained from literature are compared. Finally, recommendations for the improvement of CBs are presented. Index Terms—DC Circuit Breakers (CBs), DC Faults, High Voltage Direct Current (HVDC) Systems, Multi-Terminal HVDC (MT-HVDC) Systems, Voltage Sourced Converter (VSC)-HVDC Systems. I. I NTRODUCTION T HE fast development of power electronics technology and the urgent need for integration of large amounts of Re- newable Energy Sources (RESs) have led to further developing and expanding High Voltage Direct Current (HVDC) systems. The fundamental advantages of HVDC systems are: (1) the Fazel Mohammadi (corresponding author) is with the Department of Electrical and Computer Engineering, University of Windsor, Windsor, ON N9B 1K3, Canada (e-mail: fazel@uwindsor.ca, fazel.mohammadi@ieee.org). Kumars Rouzbehi is with the University of Seville, Seville 41092, Spain (e-mail: krouzbehi@us.es). Masood Hajian is with the Department of Electrical and Computer Engi- neering, Isfahan University of Technology, Isfahan 84156-83111, Iran (e-mail: m.hajian@iut.ac.ir). Kaveh Niayesh is with the Department of Electric Power Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway (e-mail: kaveh.niayesh@ntnu.no). Gevork B. Gharehpetian is with the Electrical Engineering Depart- ment, Amirkabir University of Technology (Tehran Polytechnic), Tehran 1591634311, Iran (e-mail: grptian@aut.ac.ir). Hani Saad is with the R´ eseau de Transport d’Electricit´ e, Paris 92932, France (e-mail: hani.saad@rte-france.com). Mohd. Hasan Ali is with the Department of Electrical and Computer Engineering, University of Memphis, Memphis, TN 38152, U.S.A. (email: mhali@memphis.edu). Vijay K. Sood is with is with the Department of Electrical and Computer Engineering, Ontario Tech University, Oshawa, ON L1H 7K4 Canada (e-mail: vijay.sood@uoit.ca). Manuscript received November 04, 2020; Revised February 17, 2021. ability to connect long-distance underground/underwater ca- bles, (2) fewer transmission lines required to transfer the same power compared to High Voltage Alternative Current (HVAC) systems, (3) the ability to connect asynchronous networks, (4) improve power flow controllability and stability, (5) preventing propagation of faults and disturbances between networks, (6) interconnection of multiple power generation units and/or loads at different DC voltage levels using high power DC transformers and multi-port DC hubs, and (7) reactive power support to interconnected AC grids during AC faults. Such advantages have led to an emerging need for the development of Multi-Terminal HVDC (MT-HVDC) systems [1]. MT-HVDC systems development is mainly possible using Voltage Sourced Converter (VSC) technology, in which power flow reversal on each terminal is achieved using DC-link current direction change [1]–[3]. Since VSCs are particularly vulnerable to DC faults, using fast detection and isolation mechanism is vital. Although fast DC Circuit Breakers (CBs) are now feasible, they are still in their infancy and are not yet commercially viable, and the only possible solution for isolating DC faults in HVDC links is to open CBs on the AC side [4]–[7]. However, this practice is not amenable for MT- HVDC systems because it can bring down the entire power flow of grids following a DC fault on a single DC cable or overhead link [8]. It is also noted that not only very large fault levels are expected following a DC fault because of low total line impedances of DC transmission links, but also a very fast Rate of Rise (RoR) of fault current is envisaged compared to counterpart AC systems. Furthermore, the stability of the interconnected AC systems may be adversely impacted by DC faults in MT-HVDC systems [9],[10]. This is of particular importance for connections to weak AC systems where long power disruptions due to DC faults can highly impact their stability. This issue implies that the application of fault-tolerant hybrid or full-bridge Modular Multilevel Converter (MMC) stations with conventional mechanical DC CBs cannot fully resolve the protection of such grids. While uncontrolled VSC operations discharging AC grids into a DC fault is avoided, AC power systems may not tolerate long power flow interruptions associated with the slow response of mechanical CBs. This further highlights the urgent need for a fast HVDC CB for such MT-HVDC systems deployment. Typically, the DC fault current has to be interrupted in less than 20 ms in total to limit them within their acceptable fault levels [11]. It should be noticed that the location of the DC fault within MT-HVDC grids is challenging [12],[13]. Another challenging issue in