Direct current circuit breaker with adjustable current injection

For high voltage multi-terminal direct current (MTDC) system using overhead lines for power transmission, such as Zhangbei demonstration project, mechanical direct current circuit breakers (DCCB) with current commutation drive circuit (CCDC) are used to deal with short-circuit DC faults. Considering most of the short-circuit faults occurring to overhead lines are temporary, mechanical DCCB should be capable of auto-reclosing, and this paper is aimed to realize its auto-reclosing function without overcurrent and overvoltage. In this paper, the topology and working principle of mechanical DCCB with CCDC is presented first. Then, the auto-reclosing strategy for mechanical DCCB with CCDC is proposed. By using this auto-reclosing strategy, the permanent fault and the temporary fault could be easily distinguished, and no overcurrent and overvoltage, which might cause damage to vulnerable devices in converters, are produced. In the end, simulation model in PSCAD is established to verify this auto-reclosing strategy.

Vacuum arc commutation is an important process in natural-commutate hybrid direct current (DC) circuit breaker (NHCB) interruption, as the duration of vacuum arc commutation will directly affect the arcing time and interrupting time of NHCB. In this paper, the vacuum arc commutation model of NHCB was established by simplifying solid-state switch (SS) and vacuum arc voltage. Through theoretical analysis and experiments, the vacuum arc commutation characteristics of NHCB were studied. The mathematical formula of the effect of main parameters on the duration of vacuum arc commutation is obtained, and the changing law of the influence of the main parameters on the duration of the vacuum arc commutation is explored. The concept of vacuum arc commutation coefficient is proposed, and it is a key parameter that influences the vacuum arc commutation characteristics. The research on the characteristics of vacuum arc commutation can provide theoretical foundation for the structure and parameter optimization of NHCB and other equipment that uses vacuum arc commutation.

For stability in the direct current (DC) power grid, it is very important to limit the current of the fault section and to protect the system in the fault condition. That is the core technology of the DC power grid. This paper suggests characteristics and a limited range of the fault current for the new model as the significant protecting technology in the DC power grid. Such new model is the arc-induction-type DC circuit breaker (CB) combined with a magnet. The magnetic arc-induction-type direct-current circuit breaker (DCCB) consists of a neodymium magnet, an induction needle, and electrical contacts. During fault operation, the arc occurring between the contacts is induced to the induction needle. To increase the induction effect, Lorentz force is applied to blow the arc. A magnet was applied to reduce the initial fault current and to induce magnetic flux. The simulation data were analyzed using the Maxwell 3D software program. The electric field included the electric force and the electric charge. Therefore, it could analyze the arc as the electric field. The simulation was performed based on the preceding study on induction needle. As a result of the simulation, it was confirmed that the electric field value of the induction needle increased when the DCCB was combined with a magnet.

With the development of a distributed generation, direct current (DC) load and energy‐storage equipment, voltage‐source‐converter‐based medium‐voltage DC systems (VSC‐MVDC) have attracted more attention due to its low power consumption, high reliability, independent power control and so on. However, VSC‐MVDC has the problem of DC fault isolation, which requires the fast‐acting DC circuit‐breakers to isolate faulty lines and ensure low cost. This problem can be solved by coordinating resistive type superconducting‐fault‐current‐limiter (R‐SFCL) and integrated‐gate‐commutated‐thyristor (IGCT) based hybrid circuit breaker. Based on this, IGCT based superconducting DC circuit breaker (SDCCB) is proposed and analysed. Combining R‐SFCL with IGCT could realise large current limiting and interruption and ensure low cost. In addition, the IGCT based hybrid DC circuit breaker (IGCT‐HDCCB) is compared with the traditional insulated gate bipolar transistor (IGBT) based hybrid DC circuit breaker (IGBT‐HDCCB) to evaluate which circuit breaker is more suitable for VSC‐MVDC. The results show that, coordination based on R‐SFCL and SDCCB, the fault current is successfully limited from 17.6 to 2.1 kA, and then interrupted within 3.8 ms. In addition, IGCT‐HDCCB overcomes the disadvantage that IGCT has less interrupting capacity than IGBT, retains the advantage of low cost of IGCT and is more suitable for MVDC system.

A novel HVDC circuit breaker for HVDC application

Flexible direct current (DC) grid can realize large-scale renewable energy, wide-area coordinated complementation, and reliable power transmission. It is an important development that can be used to support high-voltage and large-capacity flexible DC transmission in the future. The short-circuit current of the DC line is one of the important bases for the selection of key main equipment parameters such as converter valves, DC circuit breakers, and reactors in the flexible DC grid. In this paper, a flexible DC grid equivalent circuit network model with alternating current (AC) feed-in is established. Aiming at the monopolar ground fault of the flexible DC grid grounded through the metal loop, an optimized traditional matrix calculation method is proposed to obtain the accurate line fault current value. On this basis, with an actual engineering background, the equivalent circuit model of the four-terminal bipolar flexible DC power grid is established, and the influence of grounding position, grounding parameters, and current-limiting reactor on the fault current of the DC line is analyzed. Finally, simulation using the PSCAD software verifies the effectiveness and accuracy of the proposed method. The method proposed in this paper can provide the necessary bases and references for the selection of flexible DC grid equipment.

High-voltage direct current (HVDC) system is difficult to proliferate due to the absence of a useful brake for the HVDC circuit breaker. To overcome this problem, this study proposes a useful brake, termed as an Eddy current brake (EB). A time-consuming time step analysis using the finite element method (FEM) is required to analyse the EB. To address this problem, a rapid and accurate analysis method is proposed using the equivalent circuit model, equation of motion, and the Runge–Kutta method. This technique is termed as the EER method in this research. The characteristic of the EB is analysed by using the proposed EER method and the results are compared with those of the 2D FEM analysis. The usefulness of the proposed EER method with regard to accuracy and rapidness is confirmed via 2D FEM analysis.

Fast detection and isolation of direct current (DC) faults are key issues for DC grids. Therefore, it is very necessary to study the fault protection principle for DC grids. This paper firstly presents the main difficulties in DC fault protection. Then, a local protection and local action strategy for isolating the DC faults is proposed. To illustrate the performance of the proposed protection strategy, a four-terminal DC grid with the hybrid high voltage direct current (HVDC) circuit breakers (HVDC CBs) is constructed in the time-domain simulation software PSCAD/EMTDC as the test system. The systematical comparison between the ordinary protection strategy and the proposed strategy is carried out. The protection selectivity of the proposed local detection and local action strategy is thoroughly studied through complete DC line fault scanning of the test system. The simulation results show that the proposed strategy is of high protection selectivity and speed. In addition, the current rating and the voltage of HVDC CB could be greatly reduced with the proposed strategy, which proves the economic benefits of the proposed strategy.

A Direct Current (DC) circuit breaker (CB) needs to interrupt fault current very quickly to avoid catastrophic system damage. A significant barrier of DC power transmission and distribution is the lack of adequate breakers for fault protection. In this paper, a Gallium Nitride (GaN) switch based Resonance Current Source (RCS) is modeled, designed and tested. The RCS is used for creating an artificial zero current crossing in an vacuum interrupter of a medium voltage Ultra-fast Resonance Direct Current Breaker (UFRDCB). The performance of the RCS has been tested separately and in a hybrid dc breaker system. The high speed operation of the GaN significantly reduced the size and cost of the inductor and capacitor of the RCS circuit. In this application, the voltage rating of the GaN switches required are a fraction of the line voltage and cooling is not necessary for the semiconductors resulting in significantly reduced volume and cost of the breaker. Finally, the performance of the RCS is verified by experiment and test results are presented.

Cooperating with secondary protection system, DC circuit breakers are used to deal with direct current (DC) faults in low voltage DC distribution system. To realize ultra-fast operating of DC breakers, optimization based on simulation of coil-coil type electromagnetic repulsion actuator (EMRA) is discussed in this paper. Considering exiting simulation based on finite element method (FEM) is quite time-consuming, an equivalent circuit method (ECM) for the Coil-Coil type EMRA is established. In the equivalent circuit equation, lumped equivalent inductance which contributes to the induced electromotive force (EMF) is used to reflect the coupling effect of distribute electromagnetic field on electric circuit, the gradient of equivalent inductance which contributes to the motional EMF reflecting the coupling effect of mechanical motion on electric circuit and the equivalent resistance that varies with temperature reflecting the coupling effect of temperature field on electric circuit. The lumped equivalent inductance and its gradient are extracted by solving static magnetic field based on FEM. By solving the state equations, the transient electrical and operating characteristic of EMRA are obtained. In the end, the results of the model based on ECM are compared with FEM, and as expected, they are in good consistence.

This work was supported by the European Union’s Horizon 2020 research and innovation programme under grant No. 691714

Solid-state high-voltage direct current (HVDC) circuit breaker safeguards the power system of more-electric aircraft against fault transients, within which power components are soldered in print circuit boards (PCB) for operation at low air pressure and limited space. The electric field near the components can be influenced by the insulation polarization, and flashover could be induced at ramp voltage. It is of great significance to study the flashover characteristics of PCBs at ramp and DC voltage. In this paper, PCB layouts with different polygon shapes and insulation distances were prepared and their flashover voltage subjected to different ramping rates were measured at different pressures. The relation between the flashover voltage, gas pressure, surface insulation distance, and ploygon shape was studied. The content of this paper is of great significance for the development of PCB layouts and busbars for use in future aerospace hybrid propulsions.

The cathode sheath (CS) formation of the direct current air circuit breaker is simulated by a fluid model, and the influence of metal vapor concentration between the contacts after liquid metal bridge rupture is considered. The CS conductivity increases with the increasing concentration of copper vapor. The copper vapor concentration increases from 5% to 95%, and the thickness of the positive space charge layer and ionization layer increases from 22.3 and 49.1 μm to 51.8 and 81.7 μm, respectively. Increasing the CS conductivity is beneficial for the motion of arc roots in a certain range.

This paper proposes two novel active snubbers for direct current (dc) solid-state circuit breakers (SSCBs): metal-oxide-varistor with resistor-capacitor-switch (MOV-RCS) and active-MOV with resistor-capacitor-diode (AMOV-RCD). In the snubber branch, either half- or full-controlled switch can be applicable, leading to four novel topologies. There are two main contributions: 1) MOV is disconnected from the power line during SSCB OFF-state, which enhances reliability as neither voltage nor power appears on MOV; 2) voltage utilization rate η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>v</i></sub> of the main switch is remarkably increased, which improves efficiency and power density, and reduces design cost. Experiments of five prototypes are conducted including four proposed snubbers and a comparison with conventional MOV-RCD snubber. Results show that, for 1.2 kV MOSFETs as the main switch, new snubbers can enhance η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>v</i></sub> from 37.5% to 60%, achieving 183 A dc current interruption under 720 V dc bus voltage within 2.4 μs. Meanwhile, the voltage peak is limited to 1.112 kV.

This paper presents two-stage high-power mechanical-thyristor switches developed as 40-kA direct current (dc) circuit breakers for the superconducting coil energy dump system of Korea superconducting Tokamak advanced research (KSTAR). An advanced switching system used in the quench protection should allow multishot mode of operation without maintenance and long lifetime with arcless dc current commutation. The system is designed to combine the advantages of the both mechanical and solid-state power switches. The mechanical stage is to conduct dc current for normal superconducting coil operation and the thyristor stage is to provide fast arcless dc current interruption for quench protection (QP). Compared with the all solid-state switches and vacuum interrupters of equal capabilities the proposed switch is much cheaper than the dc breakers and has lower power dissipation in current conducting state "Kuchinski in Proc. Power Ele., 899-903, 1995;" "Benfatto IEEE Power Del., Vol. 3, No. 4, pp. 1372-1376, Oct. 1998." Also, it is much faster than the vacuum interrupters. The system is designed to break 40-kA dc current within 200 ms. Also, KSTAR device, a configuration of the energy dump system and coil power supplies are presented