T. Tamagawa's research while affiliated with Tokyo Electron and other places

... AMF contacts, proposed in the 1970s, generated a magnetic field parallel to the current direction. 7 This kind of magnetic field restrains the radial contraction of vacuum arcs, and then the threshold current for anode spot formation is increased. 8,9 AMF contacts can reduce contact erosion significantly, but the loop resistance of the AMF contact is high due to the long current path. ...

... However, these types of tests are costly and not commercially attractive. Some studies modified AC test circuits to create synthetic test circuits for DCCBs [29][30][31]. This method not only saves investment costs but is also capable of generating a higher peak discharge current with a longer discharge time. ...

... Radio frequency (rf) glow discharges are used in micro-electronic device fabrication and gas laser excitation. For high pressure gas laser excitation, dielectric-covered electrodes are particularly employed to achieve higher stability and homogeneity compared to metallic electrodes with dc discharges [41]. In industrial systems, the rf discharge is driven at 13.56 MHz which is the value regulated by the Federal Communication Commission (fCC). ...

... 13 The former experimental investigations on the high frequency interruption characteristics of VCBs mainly gave statistical results of the interruption ability with relation to di/dt at CZ, [14][15][16] but a further analysis on how di/dt influences the post-arc recovery process is absent. Although a few references investigated the post-arc current in the case of forced CZ interruption, [17][18][19][20] the breaking current and di/dt in those experiments are much lower than the actual interruption duties. 6,8,9 In this paper, we will report our experimental investigations on the post-arc current phenomena of the VCB in an active mechanical DC CB. ...

... These were usually circuit-breakers with sufficiently large breaking capacity, but with long total break times 1 and current limitation coefficients 2 C o ¼ 1. Effective mitigation of the harmful effects of short circuit currents requires effective mitigation of these currents, i.e. breakers as fast as possible with the lowest possible C o . Similar needs exist for medium DC voltages (MVDC) used in DC1 (3 kV) and DC2 (1.5 kV) systems of railway traction and in some propulsion or electrothermal devices, as well as in low voltage systems (LVDC, up to 1250 V) used in all types of city or mining electric traction and numerous industrial systems (converters, propulsions, etc.) [1][2][3][4][5]. ...

... Vacuum interrupters (VIs) are widely used in medium-voltage grid systems due to their advantages of no pollution, small size, and easy maintenance. 1 In VIs, if the current exceeds a critical value, active anode modes will occur, which will increase the probability of reignition, leading to interruption failure. 2 The axial magnetic field (AMF) can effectively improve the breaking capacity of VIs by suppressing the arc contraction and reducing the energy flux to the anode. [3][4][5] AMF is generated by the current flowing through a special contact structure. ...

... Figure 3b shows the traditional schematic diagram of an active resonance MCB. In this scheme, the artificial zero crossings in the main interrupter circuit are produced by using the current injection from the pre-charged capacitor into the commutation circuit [34,35]. This improves the speed and reliability of the system. ...

... Then we have the traditional AMF distribution, a bell-shaped AMF, which has its maximal value near the axis, then decreases towards the contact's periphery, at which point B z is weakest. It has been investigated that for certain AMF strengths, the interruption capacity of a vacuum interrupter is in proportion to the contact's diameter [113]. Furthermore, for a given contact's geometry, the interruption capacity increases with the increase of AMF, whereas, the interruption capacity tends to saturate at a certain B z [114]. ...

... field (AMF) has been proved to have an influence on both the positive ions in the vacuum arc plasma and the plasmaplume overlap region between contacts. The application of the AMF can make the vacuum arc column controlled effectively, which can reform the distribution of the energy flux of the vacuum arcs [4][5][6][7][8][9][10][11][12]. ...

... Although the post-arc current has been studied for years, its physical mechanism still remains unclear in some aspects. [4][5][6][7][8][9][10][11][12][13][14][15] The elaborated measurement of the post-arc current of VCB has been achieved using a high-resolution diagnostic system. 13,16 Besides, numerical simulations also provide a useful approach for in-depth investigation on the mechanism of post-arc current. ...