Chaobin Bao

Analysis of breakdown mechanism in trigatron switches

Analysis of breakdown mechanism in gas-insulated trigatron switches is important for the engineering design and function prediction. Based on the gas discharge theory, a physical model was proposed to estimate the breakdown time for gas-insulated trigatron switches. And the model can explain the breakdown in the trigatron switches with two modes of the breakdown mechanism, i.e., fast breakdown mode (FBM) and slow-breakdown mode (SBM). Based on Raether breakdown criterion, this paper discussed the factors affecting on the E-field enhancement. The E-field is composed of the static E-field and the dynamic E-field, which leads to transformation of breakdown mechanism. Some coefficients could be determined by experiment and simulation, which are helpful to get the quantitative solution of breakdown time.

Analysis on Triggering and Discharge Characteristics of Three-Electrode Trigatron Gap

The development of a three-electrode trigatron gap with the trigger electrode inside the main electrode is discussed in this paper. Two models of the operation mechanism are proposed to explain the breakdown in the trigatron gap. In addition, a mathematical model was proposed to calculate the breakdown time based on the theoretical analysis. The influence of different parameters on the breakdown time is discussed. Some characteristics in dry air have been experimentally determined such as the influence of the air pressure and the influence of the undervoltage ratio on the spark gap operation. The experimental results show that the operating voltage range between 0.5 and 0.7 might be reasonable. Then, the experimental results and analysis demonstrate that there are three regions divided by two inflection points, and the corresponding values of the undervoltage ratio are threshold values presenting different breakdown processes.

Erosion Model of Trigger Electrode Based on the Theory of Microexplosion

This paper discusses the normal working mechanism of trigatron gap which leads to the erosion of trigger electrode. The theory of microexplosion is based on the gas discharge theory, explosive electron emission theory and thermodynamical theory, and the erosion model of trigger electrode can be obtained by microexplosion theory. The specific action is an important physical quantity in the theory of microexplosion, which could be determined by current density and phase-transition time. The model demonstrates that the erosion of trigger electrode is related to material parameters, discharge current waveform, and charge transfer. Due to the results of experiments, there exists no erosion under the action of trigger current, while under the action of main current, the measured erosion height is 0.51 mm after 4000 shots. Based on the theoretical analysis, it can be calculated that after 4000 shots, the erosion height is 0.54 mm. experimental and numerical results match within 5%.

Study of characteristics and performance optimization of a three-electrode spark gap

Working characteristics of a three-electrode trigatron spark gap is discussed in this paper. Breakdown probability is proven to fit a Weibull distribution. For an engineering application, the lower limit of undervoltage ratio depends on breakdown probability, and the upper limit of undervoltage ratio depends on self-breakdown probability. Some characteristics have been determined experimentally, such as the influence of the air pressure and the influence of the undervoltage ratio on spark gap operation. Curve fitting and quasi-data mining are good methods for research on triggering characteristic in the paper. Therefore, a maximum operation range curve and a boundary line of expected delay time could be determined by application requirements, theory calculation, experimental data and curve fitting. On this basis, optimization operation range could be obtained, which represents a preferable performance of breakdown with expected delay time. It may provide guidance for engineering application.

Study on the Performance of High-Voltage Trigger Generators in Pulsed Power Conditioning System

Two-electrode graphite spark gap switch (TGSGS) is used as the main discharge switch and triggered by a reliable trigger generator in pulsed power conditioning system (PPCS). There would be 108 energy modules in PPCS working at the same time. The reliable operating and jitters of the trigger generators will have impact on the PPCSs performance. In this paper, the working modes of the TGSGS are discussed and the performance of trigger generators in PPCS is tested and presented. A protection strategy of the trigger generator in PPCS is introduced, and effect of the blocking capacitor on the trigger pulse transmission is analyzed and tested. The protection strategy of the trigger generator based on blocking capacitor and fuse can effectively prevent the energy anti-irrigation failure when the pulse transformer core saturated. The blocking capacitor has some effect on the trigger pulse transmission, and has the larger capacitance, getting the higher peak amplitude on the cathode of the TGSGS. It is tried to discuss the working characteristics of the thyristors, and proposes a selection reference of the thyristors in this and other similar applications. The combination of analysis and measurement would be useful for the selection of thyristors and other components.

Development of a long-lifetime spark gap switch and its trigger generator for 2.0 MJ capacitive pulsed power supply module

Starting from the updated requirements of an advanced laser system, a switch-trigger system for a 2.0 MJ pulsed power supply module has been developed. This paper discusses the design, construction and testing of this switch-trigger system. The two-electrode construction for the spark gap switch was selected due to the superiority in long working life, high peak currents and fast rise-time of currents. The trigger generator based on resonant charging of pulse transformer was constructed. A magnetic isolator and a pressure controller were the auxiliary equipments of this system. In the section about the mathematical principles, the equations of the lifetime and stability of this spark gap switch with graphite electrodes are given. These expressions can be regarded as the design basis of the same type switch. As for the trigger generator, the analysis states that an appropriate ratio can be obtained when using the resonant charging based on core-type pulse transformer. The charging time is dependent on the leakage inductance and the capacitance of the primary and secondary capacitors. Extensive testing has proved the operating parameters of the switches and trigger generator. The measured discharge current waveform of 2.0 MJ capacitive pulsed power supply module is demonstrated to be over 500 kA peak-current and 500 µs pulse-width. And the life test has proved that the switch-trigger system can support more than 200 kC transfer charge. Via replacing the electrodes, the lifetime of this switch can be extended more.

Estimation model of switching delay for gas-insulated trigatron switches

Based on the gas discharge theory involving distorted E-field enhancement, a physical model is proposed to estimate the switching delay for gas-insulated trigatron spark gaps with a trigger pin inside the main electrode. Two discovered breakdown modes, i.e., fast-breakdown mode (FBM) and slow-breakdown mode (SBM), can be unified in this model. Raether criterion can distinguish these two modes. If the main E-field and enhanced E-field near the trigger pin tip are great enough, FBM forms easily. Otherwise, if streamer development needs to rely on the second ionization process and relevant distorted E-field enhancement, the breakdown of the main gap would turn into SBM. The enhanced E-field near the trigger pin tip may affect the threshold main E-field of FBM. The distorted E-field enhancement may affect the switching delay length of SBM.

Discussion of breakdown mechanism in trigatron spark gap

Based on the gas discharge theory involving distorted E-field enhancement, a physical model was proposed to estimate the breakdown time for trigation spark gap. Two models of the breakdown mechanism, i.e., fast-breakdown mode (FBM) and slow-breakdown mode (SBM), are used to explain the breakdown in the trigatron gap. Based on Raether breakdown criterion, this paper discussed the factors affecting on the E-field enhancement. The E-field is composed of the static E-field and the dynamic E-field, which leads to transformation of breakdown mechanism. Some coefficients could be determined by experiment and simulation, which are helpful to get the quantitative solution of breakdown time.