This is the accepted version of a paper published in IEEE Transactions on Power Delivery. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.

This paper deals with the modelling of high-voltage direct current (HVDC) breakers in PSCAD. The models are aimed at HVDC grid simulation and are kept as simple as possible. An overview is given over recently proposed HVDC breaker concepts. Assumptions and simplifications are explained as well. The main result is that even these simplified models are too detailed for grid simulations. The reason for this is that from a grid perpective the only thing that matters is when the metaloxide varistor is inserted. The models can be used to estimate interruption times.

In future high-voltage direct current (HVDC) systems, a large number of HVDC breakers will be required. In this paper, the influence of HVDC breakers on the transient performance of point-to-point HVDC links in both asymmetrical and symmetrical monopolar configuration with half-bridge modular multilevel converters is studied with simulations in PSCAD. As HVDC breakers, the active resonant breaker and ABB's hybrid breaker are considered. The analyzed scenarios include DC line faults, DC bus faults, and AC faults between the converter and the transformer. The highest DC breaking capability is required during DC line faults in the asymmetric and symmetric monopole. The converter stress is highest for DC bus faults and unbalanced converter AC faults in the asymmetric monopole and for DC bus pole-to-pole faults in the symmetric monopole. During DC pole-to-ground faults in the symmetric monopole, the HVDC breaker combined with DC side arrestors yields the lowest overvoltage stress on the cable of the healthy pole. The fault current shapes depend strongly on the interaction of the converter and the travelling waves on the lines, and differ from the fault current shapes in typical HVDC breaker test circuits. Furthermore, the active resonant breaker and the ABB hybrid breaker perform similarly in the used benchmarks due to the very fast DC line fault detection.

One of the major challenges of DC circuit breakers is the required fast mechanical actuator. In this paper, a Thomson coil actuator system for a vacuum interrupter is designed. Active damping is used to decelerate the moving contacts. Challenges are discussed, especially concerning the power supply needed for the Thomson coil actuator. The design philosophy is explained and FEM simulation results are presented. The results indicate that a wide range of combinations of drive circuit capacitance and voltage fulfill the requirements for armature acceleration. However, active damping requires a very careful selection of drive circuit voltage and timing of applied damping.

Enhanced active resonant (EAR) DC circuit breakers (DCCBs) are a promising set of recently proposed DCCB concepts. As other DCCBs, EAR DCCBs still require a fast mechanical switch. The requirements on the actuator of the mechanical switch depend on the DCCB concept and the DC grid and are derived here for an EAR DCCB. Thomson-coil actuators can open and close mechanical switches sufficiently fast to satisfy the requirements. This work studies experimentally a Thomson-coil actuator system with active damping for an off-the-shelf industrial vacuum interrupter used as mechanical switch in an EAR DCCB. The prototype is explained in detail and extensive measurement results are presented showing that active damping must be perfectly timed to be effective. A novel Thomson-coil driver is proposed and studied experimentally, which operates the Thomson-coil actuator more efficiently by recycling energy during the actuation. Moreover, the novel Thomson-coil driver reduces the capacitive storage by 50 % and allows for faster recharging with lower charging current. Finally, the auto-reclosing and proactive commutation operation of the Thomson-coil actuator system and the interruption capability of the prototype EAR DCCB are demonstrated experimentally.