Limited by the turn- off ability of single power module, parallel connection of insulated-gate bipolar transistors (IGBTs) is essential to enable breaking ability of current in the order of tens of kA. To realize high utilization rate of parallel power modules with turn- off inconsistency in dc circuit breaker, breaking current balance enhancement method is proposed in this article. There are two main contributions. First, by addressing transient switching behavior of parallel IGBT modules with centralized- and decentralized-snubber circuit (C-SC, D-SC) which consists of RC and metal oxide varistor (mov), It is revealed D-SC exhibits superior switching performance than C-SC for the first time, especially in terms of breaking current balance and voltage overshoot suppression. Second, as breaking current imbalance is generated by the turn -off inconsistency of parallel IGBTs with D-SC, the imbalance current can be calculated by turn- off time difference, parasitic inductance and residual voltage of mov, and increasing parasitic inductance is a practical way to suppress this imbalance current. Theoretical analysis based on the circuit modeling and current commutation process elaborates the findings, which are then confirmed by simulation and experimental results.

As one of the most important component in mechanical and hybrid dc breaker (MCB and HCB), operating time of ultrafast vacuum switch (VS) determines the breaking speed of MCB and HCB. However, limited by the high capacitive storage energy requirement of Thomason-coil actuator (TCA), the low-efficiency and large-volume of operating mechanism are main restrictions for wide application of ultrafast VS. This article proposes a high-efficient and miniaturized operating method for ultrafast VS by recycling the residual energy in capacitor banks for sequential open- and close-operations (O-C). Mathematical model of ultrafast VS during the sequential O-C operation process is established, and the prototype with rated parameters of 3.6 kV/2.5 kA/1ms is developed for experimental verification. The research shows that by using the proposed method, the total required capacitive storage capacity for sequential O-C operation is decreased by 50%, from 2038 to 1019 J, resulting in the doubled operating efficiency. In addition, the cost and volume of the operating mechanism for ultrafast VS are decreased significantly.

Overvoltage may occur in low-voltage direct current (LVDC) distribution system during fault recovery, and cause permanent damages to the vulnerable power electronics devices. To suppress the overvoltage, the parameter matching principle of the inductance type superconducting fault current limiter (SFCL) is proposed. First, by deriving the equivalent circuit of LVDC system during fault recovery, mechanism and related factors of the overvoltage were studied. It is found the inconsistent drop rate of voltages of converters during the fault is the main reason for fault recovery overvoltage. Then, the method was proposed by designing the inductance in accordance with the capacitance of each converter with keeping voltage drop rate of the converter is the same and the fault current is within the breaking ability of DC circuit breaker. Finally, the method is validated by simulation in PSCAD/EMTDC, resulting in the overvoltage is reduced by 50%.

Multiport dc breaker (MP-CB) contains multiple fast vacuum switches (FVS) for long-term micro-operating losses, and usually only one FVS needs to operate when interrupting fault current. In existing MP-CB, the operating mechanism of each FVS, based on Thomson-coil-actuator (TCA), is configured with an independent drive circuit consisting of capacitor banks and thyristor modules, resulting in large-volume and high-cost. To tackle this problem, a novel centralized drive circuit is proposed for all FVS in MP-CB in this article. The main contribution of this article is by adding thyristor modules to ensure multiple FVSs, whose moving contacts are electrically connected together, could share the capacitor banks in the centralized drive circuit, reducing the cost and volume. Structure, working principle and mathematical model of the proposed drive circuit are presented. Taking three-port dc breaker as an example, experiments on prototype of FVS and the whole MP-CB (transient interruption voltage of 1.5 kV, interruption current of 2.9 kA) are conducted for verification. The research shows volume and cost of drive circuit for the operation of three FVS could be reduced by 58% and 43%, respectively.

Low-voltage direct current power supply system for secondary measuring and controlling devices in substation is a typical single-source multi-loads system, which is protected by air circuit breakers (ACBs) in cooperation with inverse time-lag trip. However, due to the long response time of ACB (≥10 ms), the selectivity of ACB cannot be ensured, enlarging the blackout scope and threatening the reliability of whole substation. To solve this problem, contributions of this article are as follows: First, a novel thyristor based multiport dc breaker (T-MP-CB) with response time less than 1ms is proposed for the ±110 V single-source multiloads power supply system in substation. With special configuration of metal oxide varistor (MOV), transient interruption voltage can always be limited within ∼1.6 p.u., avoiding the potential degradation of MOV caused by leakage current. Second, it is proved by experimental data that extinguishing of thyristor is closely related with reverse recovery time (t_r) and uncertain zone of (t_r) exists; by taking both reliable extinguishing of thyristor and economic performance into consideration, parameter optimization design method for T-MP-CB is proposed. Simulation and experiments validate the proposed T-MP-CB.