Xueling Yao

An Experimental Investigation on Initial Plasma Characteristics of Triggered Vacuum Switch

The trigger characteristics of triggered vacuum switch are significantly influenced by initial plasma. An RC charge collector is designed based on the frequency spectrum characteristics of the initial plasma current, and the emission charge characteristics of the initial plasma are analyzed. The experimental results indicate the following: The RC charge collector is suitable to collect the charge of the initial plasma at R = 5 Ω and C = 300 nF, the charge of the initial plasma includes electrons and ions, the electrons are slightly more than the ions, the charge of the initial plasma increases linearly at the beginning with the increment of the charging voltage of the trigger circuit and the trigger current and then ascends gradually to a plateau under a gap space of 4 mm, and the charge of the initial plasma exponentially decreases with the increment of the gap space below 4 mm and then tardily drops to a stable value with the gap space continuingly increasing.

10/350-

This paper presents a novel crowbar system of 10/350-μs pulse current. The crowbar pulse current system includes a crowbar pulse current waveform forming circuit, a controlling unit, and a measuring unit. The crowbar pulse current circuit consists of a main air triggered switch, a triggered vacuum switch (TVS) which is used as the crowbar switch, and two trigger signal generators. A kind of TVS is designed and fabricated. Its triggering characteristics are tested, and experimental results show that, compared with other reported similar switches, the TVS has excellent characteristics such as wide operating voltage scope from 1.3 to 120 kV, short discharging delay time with maximum delay time at 400 ns, and its jitter at ±10 ns. Based on the TVS, the crowbar 10/350-μs pulse current circuit and its controlling circuit are designed. With a 36-μF storage capacitor C and a 6-μH waveform forming inductance L, a 10/350-μs pulse current waveform with a maximum of 150 kA can be generated.

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High-power and high-current test technology has many requirements for a discharging switch, such as high hold-off voltage, wide operating voltage scope, short discharging delay time and jitter, strong charge transfer ability, and long lifetime. A high-voltage and high-current triggered vacuum switch (TVS) with a surface flashover trigger device has been designed, and the trigger device is made from a material whose relative dielectric constant εr is around 2500. The experimental circuits are set up, and the experiments are performed. The experimental results showed that the TVS can be used at a maximum voltage of up to 120 kV, the minimum operation voltage is 1.3 kV, the maximum discharging delay time is less than 400 ns, and the minimum discharging delay time and jitter reach to 100 and 10 ns, respectively. The maximum current switched is about 180 kA, and the maximum transfer charge per shot is larger than 2.5 C. The switch can satisfy the main demands of crowbar circuit applications and can be used on high-voltage and high-current application situations.

Crowbar Pulse Current System

Conditioning is one of the important producing techniques for enhancing GDT (gas discharge tube) performance and stability. Based on the study of traditional AC and DC conditioning, the paper proposed the periodic oscillatory damping pulse current conditioning. Experimental results obtained that periodic oscillatory damping pulse current conditioning is superior to AC conditioning or DC conditioning. Through Comparison of conditioning effect of different structural GDT (including gas pressure and spacing etc), it is found that the conditioning energy is the uppermost factor, and with discharge voltage of GDT increasing, the required conditioning energy showed a downward trend. By controlling conditioning energy, the jitter of breakdown voltage of GDT filled with nitrogen gas is less than 10% and less than 5% for GDT filled argon gas.

A High-Voltage and High-Current Triggered Vacuum Switch

An auto impulse current measuring system for surge protective device (SPD) with power source was studied, the system was composed of impulse current generator, programmable logical controller (PLC), couple and decouple network (CDN), power tracking circuit and intelligent digital peak measuring instrument. It can carry common and different mode tests for SPD, the maximum impulse current amplitude is up to 200 kA, the accuracy of measuring impulse peak is less than plusmn1%, and the accuracy of phase tracking power frequency is less than plusmn3deg

Periodic oscillatory damping pulse current conditioning of gas discharge tube

High rate A/D, data acquisition unit and industrial personal computer (IPC) were integrated together, the virtual measuring instrument of pulse peak (pulse current and voltage) and energy under high voltage pulse current discharging environment was realized by the mean of Visual Basic text programmable software in this paper. It was a new application field of virtual instruments in a pulse high-voltage environment. The technique can be used in measuring for varistors and arrestors and other similar circumstances.

200kA Impulse Current Measuring System for SPD

A surge protective gap (SPG) with an active energy-coupling-triggered circuit is designed, and its discharge characteristics are studied. The experimental results show that the SPG with active-energy-coupling-triggered circuit and flashover trigger device has excellent surge protective characteristics. The gap distance is 5 mm, and the produced p · d is 90 Pa · mm. Moreover, with no active-energy-coupling-triggered circuit, the dc breakdown voltage is 2.32 kV, and the pulse breakdown voltage is 5.75 kV. Therefore, the voltage ratio, which is defined as the specific value of the pulse breakdown voltage and the dc breakdown voltage, is 2.48. When using the BaTiO3 flashover trigger device and the capacitor-coupling-triggered circuit and with 5-mm gap distance and p · d = 90 Pa · mm, the pulse breakdown voltage can reduce to 2.16 kV, the voltage ratio is close to one, and the response time is less than 100 ns. The results of the study lay a theoretical foundation for further research on enhancing the voltage protection level of the SPG.

An automatic measuring instrument of pulse peak and energy

The effects of pulsed current electromagnetic fields (PCEMF) on human peripheral lymphocytes sister chromatid exchanges (SCE), and micronuclei (MN) frequencies were investigated. PCEMF were produced by 8/20 μs pulsed current generation with two model types, a long straight wire and a solenoid. Human peripheral lymphocyte samples were exposed to PCEMF (a pulse per min, and continuing for 1 h). SCE and MN assays were used to evaluate the genotoxic effects. The results indicated that SCE and MN incidences correlated positively with B m and dB/dt. For the long straight wire model, as B m reached 8.48 × 10−2 T and dB/dt = 1.06 × 104 T s−1, the effect was significant. As B m reached 1.70 × 10−1 T and dB/dt = 2.13 × 104 T s−1, the effect was marked. For the solenoid model, the conditions of significant effect were B m = 0.264 T and dB/dt = 3.30 × 103 T s−1 and B m = 1.32 T and dB/dt = 1.650 × 104 T s−1. Data indicated that dB/dt was an important factor in increasing the frequencies of MN and SCE in human peripheral lymphocytes.