A quasi-coaxial HV rolled pulse forming line

A pulse forming line (PFL) cascaded in the radial direction by multistage rolled strip line units is put forward. With this method, the dielectric thickness of the rolled strip line unit is decreased. So, the reliability of the PFL under a high voltage will increase. At the same time, the difficulty for rolling the PFL will decrease. The factors affecting the pulse lifetime of the rolled PFL are analyzed by theory and simulation, and two improvement methods are put forward. First, the electric field enhance at the edges of the electrodes of the rolled PFL is so large that corona discharge occurs at these positions. The improvement method is to use the combination dielectric layer combined by corona-resistant polyimide (PI) films and polypropylene (PP) films as the dielectric of the rolled strip line unit. With this method, the normal electric field of the electrode edges is decreased. Besides, the corona resistance of the dielectric layer is much improved because the PI film has a good performance under corona discharge. Second, the positions where the output foils are located are the insulation weakness of the PFL because these positions are discontinuous. The improvement method is to increase the insulation thickness of these positions. A rolled PFL is cascaded by 3 stages of rolled strip lines, which has a charging voltage of 90 kV. According to the lifetime test, the pulse lifetime of the rolled PFL reaches 300 000 pulses, which is 100 times larger than the pulse lifetime of a rolled PFL without the improvement method.

Insulation improvement of an all-solid pulse forming line with film dielectric

et al. 2019

Prolonging the lifetime of a compact multi-wire-layered secondary winding in the Tesla transformer

Zhao

et al. 2022

A compact multi-wire-layered secondary winding for the Tesla transformer was proposed by Zhao et al. [Rev. Sci. Instrum. 88(5), 055112 (2017)]. The basic idea is to wind multiple layers of a metal wire around a polymeric base tube. However, the lifetime of this type of winding is only about 200 000 pulses, and thus it fails to meet the requirement of a lifetime of 1 × 106 pulses. In this study, two methods are developed to prolong the lifetime of this winding. One method involves replacing the original three-skin wire with a polytetrafluoroethylene (PTFE) wire. The results of small-scale experiments in different conditions show that the lifetime of the PTFE-covered copper wire is at least ten times longer than that of the three-skin wire. The other method involves improving the local structure of this winding. A strong mechanical stress is concentrated at the small end of the winding, and a highly intense electric field appears in this region, where both reduce the lifetime of the winding. Improving the local structure of the winding theoretically prolongs its lifetime by a factor of 4. Both methods were applied to the original secondary winding of a Tesla transformer and extended its theoretical lifetime by a factor of 40. The modified winding had a lifetime longer than 2 × 106 pulses without any traces of discharge. This is equivalent to a lifetime longer than that of the original winding by a factor of 10 and verifies the effectiveness of the proposed methods.

An annular pulse forming line based on coaxial transmission lines

Qiu,

Su,

et al. 2024

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%.