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.

In the dc traction power supply system in subway, over-current tripping device (OCTD) is essential for air circuit breakers as backup protection. At present, current threshold value ( I _th ) of OCTD is adjusted by the cooperation of magnetic circuit regulating block (MCRB) and spring. Depending on MCRB is installed or not, only two-level adjustment can be realized, resulting in low adjustment accuracy of I _th . In this letter, a novel OCTD based on controllable magnetic coupling is proposed. Instead of using MCRB, an auxiliary winding wrapped on the static iron core is added, with different resistors and thyristors attached. By controlling thyristors, a wide-range and multilevel adjustment of I _th can be achieved. Benefits of the proposed method are: reducing the stiffness factor of spring from 55 to 42 N/mm, improving the adjustment accuracy from 0.66 to 0.33 kA/mm, and adjusting I _th online without power supply system interruption.

Air circuit breakers (ACBs) are widely used in the DC traction power supply system to interrupt fault current. To trip ACB rapidly, over-current tripping device (OCTD) and Thomson-coil actuator (TCA) are configured in ACB. However, the response time of OCTD is strongly affected by the fault current and it might be too long for remote or high-resistant faults. To cover the shortcoming of OCTD under these faults, TCA is configured additionally, resulting in extra mechanical devices and increased risks of mechanical failure. To solve the problems of OCTD and TCA, a novel ultra-fast hybrid electromagnetic actuator (UHEA) is proposed in this paper. The proposed UHEA is to add an auxiliary winding (AW) wrapped on the conventional OCTD, with AW connected to a pre-charged capacitor through thyristors. By using multiple thyristors to control the discharge of capacitor through AW, fast tripping of ACB can be obtained under random faults. Advantages of the proposed UHEA are: its response time is only ∼2ms, faster than existing tripping devices by at least 36%, and is hardly affected by fault current, showing low dispersion of response time; it can replace OCTD and TCA inside ACB, simplifying actuators and reducing risks of mechanical failure.

The unique delayed current zero (DCZ) exists in fault current fed by high-capacity synchronous generator (HSG). As current zero is the pre-condition for current interruption, DCZ must be eliminated within 1∼2 power cycle to realize rapid fault interruption. Existing method is using SF6 arc resistance to eliminate DCZ, meaning SF6 interrupter is the inevitable choice for high-capacity generator circuit breaker (GCB). To promote the replacement of SF6 interrupter by vacuum interrupter (VI), mechanism of DCZ is revealed, and novel elimination method of DCZ without using SF6 arc resistance is proposed. Contributions of this paper are: First, based on the existing recognition that different time constants lead to DCZ, it is found the magnetic coupling effect between stator winding and damping winding is the fundamental reason for DCZ, and the stronger the coupling effect is, the more severe the DCZ is. Second, the key constraint of eliminating DCZ is revealed. Instead of using large SF6 arc resistance, changing the material of damping winding can also satisfy the constraint, and eliminate DCZ within 1∼2 power cycles, providing technical premise for the replacement of SF6 interrupter by VI in high-capacity GCB. All these findings are validated by simulations based on finite element method (FEM).

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.