Binxiong Yu’s research while affiliated with Northwest Institute Of Textile Science And Technology and other places

Rogowski coil is an effective tool, which is capable of testing kA-class nanosecond-scale pulsed current. The basic principle is the Faraday Law of electromagnetic induction. In practical application, it is found that the test current waveform of a Tesla-type generator via the Rogowski coil is strongly distorted. It is conjectured that the width of coupling slot in the generator contributes to the distortion. A circuit model including the slot of the Rogowski coil is proposed. Via this model, the conjecture about the slot is verified. In addition, it is found that the oscillation superimposed on the measured waveform becomes large as the slot becomes narrow. To further study the effect of the slot width on the measurement waveform, the practical 3-D model of the Rogowski coil assembled on the generator is also established and the oscillation dependent on the capacitance of the slot is obtained. In the end, an empirical formula to design the width of the coupling slot of the Rogowski coil is presented. With this formula, the new width of coupling slot is calculated out and the ideal measurement waveform of the Rogowski coil in the Tesla-type generators is obtained.

Multi-stage gas switches (MSGSs) are widely used in megavolt pulsed power systems due to their advantages of high withstand voltage, fast establishing time and relatively high operating frequency. Multiple operation modes, which are induced by the different breakdown sequences at each stage, are found to affect the breakdown characteristics of the gas switch. Based on the theoretical analysis of the working principle, the classification of the operation mode and the factors determining the operation mode of the MSGS are proposed. Methods for investigating the output waveform for MSGS are established by simulating lumped parameters and studying the breakdown time sequence of individual stages. In comparison with the intended mode of operation, the disadvantages of the unintended modes of operation for MSGS, including error-breakdown and non-triggering mode, are revealed. For unintended modes, the distortion of the output waveform, which determines the efficiency of energy transmission through the switch and the increased delay time jitter, which determines the synchronization of the gas switch, are further investigated. The possibility of non-triggering and its mechanism on surface flashovers induced by drifting electrons are also analyzed. Based on this study, design principles and methods are proposed to ensure the intended operation of the MSGS.

The miniaturization, lightweight, and solidification of pulse forming lines (PFLs) are of prime significance during the evolution of pulsed power technology. In this paper, an all-solid-state annular pulse forming line (APFL) based on film-insulated coaxial transmission lines is developed to generate fast-rise time quasi-square pulses. First, a coiled coaxial transmission line (CCTL) comprised of multilayer polypropylene films with outstanding insulating properties is constructed. It can withstand direct current voltages up to 200 kV, with a cross section diameter of 7.4 mm. In addition, in order to turn the pulse transmission direction from circumferential to axial, a compact insulated terminal with a 90° bend structure is designed for CCTL. Although single terminal inductance can slow down the rising edge of the output pulse, their parallel connection in an APFL can weaken such an effect. The APFL, with a characteristic impedance of 2.95 Ω and a transmission time of 13 ns, is composed of three CCTLs with six terminals, which can run over 100 thousand times under the pulse voltage of 75 kV. Finally, 15 series APFL modules are employed to assemble a multi-stage PFL for the Tesla-type pulse generator. When charged to a voltage of 1 MV, the mixed PFL consisting of a coaxial line and the multi-stage PFL outputs quasi-square pulses with a voltage amplitude, rise time, and width of 510 kV, 4 ns, and 41.5 ns, respectively, and the fluctuation of the flat top is about 6%.

This article presents the research on repetitive-frequency V/N-type gas switch triggered by high-voltage photoconductive semiconductor switch (PCSS). The working states of V/N-type gas switch in three cases are analyzed theoretically. At underdamping case, the V/N-type gas switch has a shorter trigger delay and a large overvoltage, with a larger triggering current. While at critical-damping case and overdamping case, it has a longer trigger delay and a smaller overvoltage, with a smaller triggering current. Simulations of the working states of the V/N-type switches in three cases were carried out, and the simulation results were consistent with the theoretical results. A V/N-type gas switch triggered by PCSS at the underdamping case was designed. The experimental result of the switch showed that the switch working at the mode of 50 Hz/70 kV/1000 pulses had a trigger delay jitter of 988.7 ps, corresponding operating coefficient of 0.7. After 60 000 pulses, there was a continuous breakdown chain, which connected the electrodes of the PCSS. The damage leading to the breakdown occurred after the close stage of the PCSS, including the damage caused by large conduction current and the damage caused by the energy releasing from the reversal inductor during the insulation recovery of PCSS.

Insulation design in pulsed power systems

The layer number effect on electric breakdown strength (EBD) of multi-layer polymer films is investigated using 10-μm polypropylene (PP) films under a dc condition. The layer number, n, of the films during the test is as large as 120. It is observed that the relation between EBD and n conforms to a minus power law, i.e., EBD(n) = E1′n−a, where the power exponent, a, is 0.27, E1′ is a constant. By reviewing the experimental data in references, it is found that the power law holds true for different types of polymers in different test conditions, but the value of a varies from 0.072 to 0.5. The variation of a is explained in perspective of the discontinuous structures within films and those between films. A small value of a means a good purity level of the film, which is due to the decrease of the size of the inter-layer defects. A large value of a means a poor purity level of the films, which is due to the increase of the amount of intra-layer defects. Both factors influence the value of a, leading to the variation of a.

The pulse lifetime characteristics of solid materials have been widely concerned in the field of pulse power technology. In this paper, a repetitive high-voltage pulse lifetime test platform for the pulse lifetime test of insulation materials is set up. The platform contains a closed magnetic-core transformer and a sample cavity. The transformer insulated by transformer oil was stably operated at the 100 kV/50 Hz mode with maximum rise time of 45 µs. The sample cavity insulated by SF6 gas includes a gas switch with an amplitude jitter less than 3% at the 50 Hz mode. The platform has advantages of high efficiency and reliability. First, it can generate three kinds of different pulses simultaneously, which satisfied the insulation test requirements under different pulse conditions. The first kind of the generated pulse is a sinusoidal pulse with an amplitude of 100 kV when the gas switch keeps open. The second one is a unipolar microsecond pulse when the gas switch closes. The last one is a nanosecond pulse generated by secondary capacitor discharge. Second, long-time operation of the platform including the pulse transformer is realized. The platform was stably operated for more than 20 × 10⁶ pulses at the 50 Hz/100 kV mode for pulse lifetime tests of solid pulse forming lines and other solid materials.

In this paper, a shielded Rogowski coil aslo with a return line for measurement of the nanosecond-range current pulse is studied. It is found that the connection mode of the end lead has effect on the output pulse waveform of the coil. When the free end of the coil is connected to the ground earth, the output waveform is distorted unless the sampling resistor matches the parasitic transmission line(PTL) formed by the return line and the shielding box. Besides, a prepulse caused by capacitive voltage dividing occurs on the output waveform. However, problems above solved by connecting the free end of the return line to the ground earth. A coil of this kind is developed. It has a turn number over 3000, with a return line of 4-mm diameter. Calibration result of the coil shows that this coil has a flattop jitter of 3% for measurement of the rectangular pulse with a rise time less than 6 ns when its end lead is properly connected. The developed coil is utilized for measurement of the discharge current pulse of a high-voltage pulse generator. Experimental result shows that the coil has good response for the heavy-current pulse with a rise time as fast as 4 ns.

To shorten the length of the pulse-forming line (PFL) and generate pulses with good flat-top quality, a 5-GW Tesla-type pulse generator based on a mixed PFL is developed in this paper to produce intense electron beams and generate high-power microwaves (HPMs). The mixed PFL is composed of a coaxial PFL and a multistage series annular PFL, which, in turn, consists of 18 coaxial-output capacitor-loaded annular PFL modules in series. The generator can produce quasi-square electrical pulses with a width of 43 ns and a peak power of 5 GW on a matched load. In experiments where it is used to drive a relative backward-wave oscillator to generate HPMs, the results show that the HPM frequency is 16.15 GHz and the power is 1.06 GW with an efficiency of 25% when the voltage of the diode is 620 kV and the beam current is 6.9 kA.