Triggered Vacuum Switch (TVS), also known as Triggered Vacuum Clearance (TVG), is a circuit closure device based on vacuum gap and triggered spark gap technology.
It has the advantages of compact structure, excellent performance, low cost, noiseless operation, high reliability, and strong environmental adaptability. Therefore, it is widely used in high power pulse technology. At present, the maximum operating voltage of TVS is up to 40kV, the maximum operating current can reach 200kA, and the maximum repetition frequency is above 1kHz. Increasing the operating voltage that triggers the vacuum switch has significant implications for the further development of high power pulse technology. In order to increase the operating voltage, the length of the vacuum gap can be increased. Therefore, it is necessary to study the operating characteristics of the long gap TVS.
TVS's operating characteristics include work delay and its stability, trigger reliability, time jitter characteristics of multi-machine parallel operation, and triggering the working life of the specific indicators such as the index, this article for some of the long gap TVS, by the DC charging circuit , trigger vacuum switch, trigger control circuit, signal isolation and measurement processing system and other components. After the storage capacitor is charged to the required voltage, a trigger pulse is issued by the control trigger device to make the TVS conductive.
Since the equivalent impedance Z of the loop is small, a pulse current with a short oscillation period and a large amplitude can be obtained.
The physical phenomenon of external insulating quartz glass eliminates the internal metal shield.
3TVS working process theory analysis 3.1TVS work process The TVS work process can be divided into the trigger phase and the main gap conduction triggers the vacuum switch experimental circuit to trigger the vacuum switch structure stage. The triggering stage provides the initial plasma for the primary gap. The initial plasma is generated by field triggering; the initial plasma expands into the primary gap. When the density is sufficiently large, a metal vapor arc can be established in the primary gap to make it the main gap. Turn on. When the main discharge current crosses zero, the arc extinguishes and the switch opens.
It can be seen that the generation and expansion of the initial plasma is the basis of the TVS work and has an important influence on the operating characteristics of the TVS.
3.2. Initial plasma generation For the field-triggered mode, the discharge starts with the field electron emission in a vacuum. The electron current density J emitted by the cathode under the electric field E by the formula of Fowler is *2. Think of a constant or lookup table. The electron current formed by the high field strength hits the anode, causing the material to evaporate and ionize. The ions move under the action of an electric field like the surface of the cathode and generate an ion sheath that accelerates the emission of electrons. When the sheath or the electron current density is high enough to produce cathode spots on the surface of the cathode, it has a self-sustained discharge condition. The critical field strength to achieve self-sustained discharge is about 108~109V/m, and the general design triggers the field distortion between the connected electrodes to enhance the local field strength. When the trigger gap is turned on by the high field strength formed by the trigger pulse, the cathode and the trigger electrode constitute an emission source of a dense plasma, and the initial plasma emitted therefrom enters the main gap, resulting in the conduction of the main gap.
39. Plasma Expansion After the initial plasma is formed, there are certain conditions that can cause conduction of the main gap, depending on its further development. Generally, the energy provided by the triggering system is insufficient to maintain the breakdown state of the main gap, and the self-sustained discharge of the main gap must be maintained by the continuous supply of charged ions and metal vapor at the cathode spot on the cathode surface of the autonomous gap. Due to the different polarity of the TVS operating voltage, the trigger states with different positive and negative polarities result in different initial plasma development processes.
In the positive polarity triggering state, due to the effect of the main gap electric field, an ion sheath layer is formed on the electrode surface of the dilation, and a cathode spot is formed on the cathode cathode to form a self-sustained discharge. In the negative polarity triggering state, the charged particles that diffuse into the main gap are mainly ions, and an ion sheath layer is formed on the opposite cathode surface. When the ion density or sheath electric field is sufficiently high, cathode spots are also generated to form a self-sustained discharge. . The research shows that the positive polarity trigger is much easier than the negative polarity and the time required is less. This is because the trigger electrode is close to the cathode and the cathode spot can be formed more quickly and more directly. During the experiment, it was also found that in the positive polarity trigger state, the minimum operating voltage of the TVS is 3 kV, and the lowest working voltage of the negative polarity is 6 kV. The following results are obtained under the triggering condition of the positive voltage of the TVS anode.
4 Trigger reliability The triggering reliability of TVS depends to a large extent on the number of initial plasmas provided by the trigger pulse, so the trigger pulse should have a certain amplitude and duration. In the experiment, a high-voltage, small-current breakdown and low-voltage, high-current continuous-current triggering circuit is used. The high-voltage part (20 kV peak) will breakdown with a high breakdown voltage in the high vacuum condition, and then the low-voltage part will continue to flow. Provide a sufficient amount of initial plasma.
5 trigger delay according to the main gap in the trigger current reaches the maximum Itm breakdown probability when it is set to 1/2 half the sine wave, the working voltage is U0, the discharge loop inductance is L, then the trigger at this time The tdpiXL/tm/U0. delay charged particles in the main gap are dominated by electrons, and the effect of the breakdown of the I-Meng-Meng return shinj gap appears obvious oscillation. In order to trigger the current waveform when the main gap is turned on, it is necessary to increase the amplitude and steepness of the trigger pulse as much as possible to reduce the inductance of the discharge circuit. However, the main gap of up to 6 cm has an inherent delay of 0.7 7.0 W41 from triggering to full conduction. However, the A-level trigger delay is still applicable to various occasions in the power system.
6 Jitter time 1 With the development of high-power pulse technology, the flow rate of a J5VS cannot meet actual requirements, and multiple TVSs must be used in parallel. In this case, the dispersion time of the TVS turn-on time is the jitter time for multiple TVSs. Parallel operation is particularly important. By changing the operating voltage and the amplitude and steepness of the trigger pulse, experiments were conducted on different TVSs. It was found that the jitter time mainly depends on the parameters of the trigger pulse, but depends on the size of the operating voltage and the structure of the trigger electrode. Shapes, materials, etc. The relationship between jitter time and operating voltage.
7 Conclusion The trigger vacuum switch with 60mm gap is stable in performance. Its working voltage can meet the requirements of any occasion. The trigger circuit with high-voltage and small-current breakdown plus low-voltage and high-current freewheeling can effectively ensure the reliability of trigger; long gap trigger The trigger time delay of the vacuum switch is small (about tens of thousands), and the jitter time is short (up to several A), which is suitable for various occasions of the power system and is beneficial to the parallel operation of multiple TVSs.
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