Jiancang Su

Investigation of Thickness Effect on Electric Breakdown Strength of Polymers Under Nanosecond Pulses

The thickness effect on electric breakdown strength (EBD) of four kinds of polymers under nanosecond pulses is investigated. The polymers are polyethylene, PTFE, PMMA, and nylon. The test samples are 0.5-3.5 mm in thickness (d) and are immersed in transformer oil. The nanosecond pulse is based on a Tesla-type generator, TPG200, which is with values of pulsewidth of 8.5 ns and rise time of 1.5 ns. The experimental results show that EBD is 1-2 MV/cm and decreases as d increases. The dependence of EBD on d is analyzed with the Weibull statistical distribution. It is concluded that logEBD versus log d is linear. By replotting the experimental data and by comparing with Martins results, it is found that the slope for the linear dependence is about -1/8. With this conclusion, the breakdown probability is researched. It is shown that, to get a breakdown probability as low as 0.5%, the applied field should be decreased to about half of EBD.

All-solid-state repetitive semiconductor opening switch-based short pulse generator

The operating characteristics of a semiconductor opening switch (SOS) are determined by its pumping circuit parameters. SOS is still able to cut off the current when pumping current duration falls to the order of tens of nanoseconds and a short pulse forms simultaneously in the output load. An all-solid-state repetitive SOS-based short pulse generator (SPG100) with a three-level magnetic pulse compression unit was successfully constructed. The generator adopts magnetic pulse compression unit with metallic glass and ferrite cores, which compresses a 600 V, 10 mus primary pulse into short pulse with forward pumping current of 825 A, 60 ns and reverse pumping current of 1.3 kA, 30 ns. The current is sent to SOS in which the reverse pumping current is interrupted. The generator is capable of providing a pulse with the voltage of 120 kV and duration of 5-6 ns while output load being 125 Omega. The highest repetition rate is up to 1 kHz.

An 8-GW long-pulse generator based on Tesla transformer and pulse forming network

A long-pulse generator TPG700L based on a Tesla transformer and a series pulse forming network (PFN) is constructed to generate intense electron beams for the purpose of high power microwave (HPM) generation. The TPG700L mainly consists of a 12-stage PFN, a built-in Tesla transformer in a pulse forming line, a three-electrode gas switch, a transmission line with a trigger, and a load. The Tesla transformer and the compact PFN are the key technologies for the development of the TPG700L. This generator can output electrical pulses with a width as long as 200 ns at a level of 8 GW and a repetition rate of 50 Hz. When used to drive a relative backward wave oscillator for HPM generation, the electrical pulse width is about 100 ns on a voltage level of 520 kV. Factors affecting the pulse waveform of the TPG700L are also discussed. At present, the TPG700L performs well for long-pulse HPM generation in our laboratory.

Investigation on properties of ultrafast switching in a bulk gallium arsenide avalanche semiconductor switch

Properties of ultrafast switching in a bulk gallium arsenide (GaAs) avalanche semiconductor switch based on semi-insulating wafer, triggered by an optical pulse, were analyzed using physics-based numerical simulations. It has been demonstrated that when a voltage with amplitude of 5.2 kV is applied, after an exciting optical pulse with energy of 1 μJ arrival, the structure with thickness of 650 μm reaches a high conductivity state within 110 ps. Carriers are created due to photons absorption, and electrons and holes drift to anode and cathode terminals, respectively. Static ionizing domains appear both at anode and cathode terminals, and create impact-generated carriers which contribute to the formation of electron-hole plasma along entire channel. When the electric field in plasma region increases above the critical value (∼4 kV/cm) at which the electrons drift velocity peaks, a domain comes into being. An increase in carrier concentration due to avalanche multiplication in the domains reduces the domain...

Insulation Analysis of a Coaxial High-Voltage Vacuum Insulator

Insulation of a coaxial high-voltage vacuum insulator used in the pulsed power generator TPG700 has been studied in this paper. When output voltage is increased from 700 to 800 kV, breakdown happens in the insulator. With transient simulation, the region of the insulator subject to the highest electric strength is concluded. According to the experimental and simulated results, the breakdown strength has been calculated. An electric-thermal model has been proposed in which factors such as local electric field (E-field) enhancement, imperfection in dielectric, and repetition working state are analyzed. A formula to calculate the effects of these factors is suggested. Moreover, the key structures on the coaxial line which influence the E-field distribution are optimized, and useful advice for designing an insulator of this kind is presented.

Research on Reliability and Lifetime of Solid Insulation Structures in Pulsed Power Systems

Based on the Weibull statistical distribution and the thickness effect on dielectric breakdown strength EBD, a formula to evaluate the reliability of solid insulation structures (SISs) in pulsed power systems is derived. By calculating this formula, it is concluded that an increase of 1.4 times in the dielectric thickness d or a 3/4 decrease in the applied voltage U will increase the reliability of SISs by “9.” Moreover, by introducing the variable of pulse number N into the Weibull statistical distribution, a formula to evaluate the lifetime of SISs is also derived. It is concluded that when the time shape parameter a is equal to 1, an SIS is in its normal lifetime stage, and the lifetime can be described by the Martins formula; when a is not equal to 1, the Martins formula should be revised. To verify the lifetime formula, experiments were designed and conducted. In the end, useful suggestions on design of SISs are summarized.

A Low-Energy-Triggered Bulk Gallium Arsenide Avalanche Semiconductor Switch With Delayed Breakdown

This letter presents a low-energy-triggered bulk gallium arsenide (GaAs) avalanche semiconductor switch with delayed breakdown. The actual optical energy contributing to switch triggering is studied with reference to the switching delay. When an optical pulse triggers the cathode of the 0.625-mm thick GaAs avalanche semiconductor switch biased at 5.2 kV, a delay time of 3.7 ns and a switching time of 258 ps are achieved, indicating a low-energy switch triggering energy of 5.6 nJ. The results of a 1-D simulation show good agreement with experimental voltage and optical waveforms.

A low-jitter self-break repetitive multi-stage gas switch

A megavolt low-jitter self-break repetitive gas switch is developed by the use of the corona stabilization and the multi-stage structure in this paper. This switch is multi-stage, consisting of one corona stabilization stage and subsequent rimfire stages. The corona stabilization stage breakdowns first, then the subsequent rimfire stages are self-fired by the over-voltage from the closure of the corona stabilization stage. SF6 is used in the switch. It has been proven by experiment that the multi-stage gas switch, which consists of one 1.3-cm gap corona stabilization stage and five 0.5-cm gap rimfire stages, can operate at repetition rate frequency (PRF) of 50 Hz with a voltage jitter less than 2% in 2000 discharges. The breakdown voltage of this multi-stage switch reaches 770 kV and the single discharge current is 8.50 kA at 4 bars.

Micro-effects of surface polishing treatment on microscopic field enhancement and long vacuum gap breakdown

In this paper, three surface polishing treatments were employed to treat plate titanium electrodes, and microscopic surfaces of the electrodes after polishing were presented. Through comparing the breakdown strength of the 2.5 cm vacuum gap formed by plate titanium electrodes after the three treatments, experimental results showed that the breakdown strength was enhanced by 35% while the micro-surface roughness dropped from 3.5μm to 0.35μm. In view of that, effects of microstructural parameters after polishing on the microscopic field enhancement factor were investigated. The field-uniformity mechanism and the shield effect between micro-protrusions on the rough electrode surface were put forward and demonstrated. Based on the idea that electric field can be shield in a pit, a theoretical model was established to evaluate the maximum field enhancement factor βEmax on the micro-surface. It revealed that 1 ≤ βEmax ≤ 3.96, and βEmax had the maximum decrements of 1.96 and 2.1 both from 3.96 after the mirror p...

A multi-functional high voltage experiment apparatus for vacuum surface flashover switch research

A multifunctional high voltage apparatus for experimental researches on surface flashover switch and high voltage insulation in vacuum has been developed. The apparatus is composed of five parts: pulse generating unit, axial field unit, radial field unit, and two switch units. Microsecond damped ringing pulse with peak-to-peak voltage 800 kV or unipolar pulse with maximum voltage 830 kV is generated, forming transient axial or radial electrical field. Different pulse waveforms and field distributions make up six experimental configurations in all. Based on this apparatus, preliminary experiments on vacuum surface flashover switch with different flashover dielectric materials have been conducted in the axial field unit, and nanosecond pulse is generated in the radial field unit which makes a pulse transmission line in the experiment. Basic work parameters of this kind of switch such as lifetime, breakdown voltage are obtained.