Triggered Vacuum Gaps Research Articles

A High-Voltage High-Speed Switch with an Adjustable Switching Duration

The design and principle of operation of a high-voltage high-speed switch consisting of two opposite-parallel connected RVU-61 triggered vacuum gaps are described and the results of testing it are provided. The switch is designed to switch capacitor banks with a charging voltage of 0.1–50 kV that operate in the mode of an oscillatory circuit. One specific feature of the switch is the possibility of controlling the duration of the switched pulse, which enables saving energy in the subsequent bank charging.

Switching regimes of compact triggered vacuum gaps

Dynamic characteristics of compact vacuum gaps are studied. Experiments are performed in the microsecond range of current pulses with amplitudes ranging from 50 A to 5 kA and rates of rise ranging from 109 to 1010 A/s at switching voltages ranging from 2 to 10 kV. The most stable operation of the gaps is reached when the cathode is triggered using positive pulses. The instability of the initial stage of burning of vacuum arc leads to an increase in the stabilization time of the main discharge. Electrical valve-like properties of compact gaps are manifested in the stable quenching of vacuum arc at a current attenuation rate of 0.5 kA/μs.

Erosion of a component cathode of triggered vacuum gaps in arc discharges

The erosion of a cathode consisting of plates of different materials was investigated in a triggered vacuum gap. Scanning electron microscope analysis of the cathode surface was made after various numbers of discharges and the evolution of the erosion was studied. The dimensions of the cathode spot tracks were shown to depend on their locations and the number of discharges. Two effects were observed: first, the ‘fully worked out’ place on the vacuum-metal boundary and second, the increase in dielectric strength of a dielectric shim surface with increasing erosion.

Generation of Crowbar Current using the Polarity Effect of the Triggered Vacuum Gaps

The triggered vacuum gap (TVG) is a closing switch for generating large current pulse and can work in the wide range of voltage for several kV to tens kV. Main electrodes are made of Ag-WC. One of main electrode has a hole for trigger electrode (Mo). The switching time is short, if the polarity of the holed-electrode is negative. It is called polarity effect. We devised a crowbar circuit using the polarity effect of the TVGs. The crowbar current of this circuit was investigated experimentally by varying applied voltage, inductance, capacitance, gap length of TVGs, and trigger current duration. A crowbar current, crest of which is 2.4 kA and 4.9/270µs for example, was observed. The probability of generating the crowbar current was more than about 90 %, in the following condition: the trigger current duration of 6.65 µs and the gap length of 2-6 mm.

Switching characteristics of vacuum gap switch employing UV‐laser triggering

The switching time and arc-ignition probability of a sustained main discharge in a laser trigger vacuum gap were measured. The third harmonic beam of an Nd:YAG pulse laser (wavelength 355 nm, energy 5 mJ/pulse, power density 4 × 107 W/cm2) was used to trigger the gap. The main electrodes 85 mm in diameter were made of oxygen-free copper. The gap length was 1.6 mm and the experimental chamber was evacuated to about 1.3 × 104 Pa by a turbomolecular pump. The UV beam from the laser was focused at normal incidence onto the grounded cathode. The switching time decreased and the arc-ignition probability increased with increasing applied voltage. The switching time was 326 ns at 15 kV with a circuit inductance of 107 μH. Its jitter was 24.8 ns. The advantageous results obtained with the UV beam are compared to the previously reported data on triggered vacuum gaps. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 8–13, 2000

Switching characteristics of vacuum gap switch employing UV-laser triggering

The switching time and arc-ignition probability of a sustained main discharge in a laser trigger vacuum gap were measured. The third harmonic beam of an Nd:YAG pulse laser (wavelength 355 nm, energy 5 mJ/pulse, power density 4 × 107 W/cm2) was used to trigger the gap. The main electrodes 85 mm in diameter were made of oxygen-free copper. The gap length was 1.6 mm and the experimental chamber was evacuated to about 1.3 × 104 Pa by a turbomolecular pump. The UV beam from the laser was focused at normal incidence onto the grounded cathode. The switching time decreased and the arc-ignition probability increased with increasing applied voltage. The switching time was 326 ns at 15 kV with a circuit inductance of 107 μH. Its jitter was 24.8 ns. The advantageous results obtained with the UV beam are compared to the previously reported data on triggered vacuum gaps. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 8–13, 2000

Switching Characteristics of Parallel Connected Triggered Vacuum Gaps with Reverse Polarity in Each Gap

Switching Characteristics of Parallel Connected Triggered Vacuum Gaps with Reverse Polarity in Each Gap

Switching Characteristics of Two Parallel-Connected Triggered Vacuum Gaps

Switching Characteristics of Two Parallel-Connected Triggered Vacuum Gaps

Pseudospark discharge in long time current pulse: electrical characterization and recovery phenomena

At high currents, the performance of triggered vacuum gaps is limited by the constriction of the arc discharge on the anode. In a symmetrical system within flat electrodes, a motionless anode spot appears in front of the trigger spark. A pseudo-spark system within electrode cavities and specific gas pressure provides a good mechanism for avoiding anode spot phenomena. It appears possible to obtain a high intensity diffuse discharge. In this paper, we present the experimental measurements of the instantaneous voltage and discharge current, (peak current less than 50 kA, discharge time between 20 and 300 /spl mu/s). These measurements allow us to determine the dynamical resistance, mean voltage and energy lost during the conduction phase. Consequently, we refine our knowledge of discharge development. Additionally, we present a complementary investigation on quenching behavior.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Switching Characteristics of Two Series-Connected Triggered Vacuum Gaps

Switching Characteristics of Two Series-Connected Triggered Vacuum Gaps

The properties of triggered vacuum gaps

The reaction of the trigger plasma of triggered vacuum gaps (TVGs) to the main gap voltage changes with the main gap polarity. The trigger polarity has no influence when the main gap voltage exceeds a certain value. The high current-chopping instability in positive TVG mode is investigated in detail, with the influence of the loop parameters and electrode contamination. In the negative mode, a history effect is found in TVG triggering, associated with the surface condition of the main gap cathode. The trigger delay time in the negative mode depends on the trigger plasma density and the plasma buildup. The general TVG triggering is explained, and the reaction of the trigger plasma to the main gap polarity determines the main-gap polarity dependence of TVG.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Arc voltage of a fast triggered vacuum gap

At high current, the performance of triggered vacuum gaps (TVGs) is limited by constriction of the vacuum arc. Several concentrated modes can be defined, i.e., foot point, anode spot, and intense arc mode. In all cases, small, luminous, high-temperature spots (from melting to boiling temperature) appear on the anode surface. In accordance with the anodic mode, the arc voltage has different characteristics (quiet and low or with high-frequency noise). The arc voltage is measured for different electrode configurations for a conduction time of 27 mu s and for peak current up to 45 kA. For small gap distances (1-1.5 mm), the arc voltage is quiet and low (20 to 30 V) and almost independent of the peak current. For greater distances, the arc voltage increases with the distance and the peak current. If the peak current is higher than the threshold interruption current, the arc voltage is high and noisy. These overvoltages, with a frequency of about one megahertz, can reach more than 1000 V. These overvoltages disappear completely after about 15 mu s, and the voltage decreases. >

The high level chopping phenomena of sink-in type triggered vacuum gaps

In the positive mode of the main gap with both triggering modes, it was found that the discharge is quite unstable. This instability has a strong influence on the precise control of the triggered vacuum gap (TVG) and gives rise to high transient voltage across the main gap. This unstable phenomenon is investigated in detail. The influence of triggering pulse type, residual pressure, contamination and main gap polarity on the chopping phenomena is described. The experimental setup is described, and results are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Switching characteristics of the triggered vacuum gap for a high-repetition-rate pulse-power source

Switching characteristics of sealed-off triggered vacuum gaps (TVGs) were examined from the viewpoint of a high repetition rate at high current discharge. With a triggered energy of 11 J, it was possible to fire the main gap in both the anode and cathode modes of operation. In repetitive discharge experiments, the TVG-tube was put in the center of the cylindrical conductor and the switching tube inductance was about 27 nH. The TVG-tube was confirmed to have capabilities for 1000 shots with a pulse current of 120 kA and a high repetition rate of 5 Hz. These experimental results indicated that the TVG-tube is a potential repetitive closing switch for the plasma X-ray source. >

Impulse breakdown voltages of triggered multistage vacuum gap

Several sealed-off triggered vacuum gaps are connected in series to improve hold-off voltage. The characteristics of impulse breakdown voltage of these series-connected gaps are investigated experimentally. The sum hold-off voltage of series-connected gaps decreases to a unit hold-off voltage when the maximum value of voltage division ratio across the gaps increases to unity. Self-breakdown probability of the series-connected gaps is always higher than that of a single gap under the same conditions. Hence, stage efficiency of the multistage gap decreases with increasing number of stages. Its value is 90 percent with 2-stage gap and 75 percent with 5-stage gap, respectively, under the same voltage division ratio and the same gap length (2.0 mm) in each stage. Triggered breakdown voltage of 2- or 3- stage gap is several hundred volts when all gaps are triggered simultaneously at the peak of the main impulse wave and a working voltage range is nearly 100 percent in this case. The working voltage range decreases with number of stages. Its value is 45 percent with 3-stage gap and 15 percent with 5-stage gap, respectively, when one triggered gap is fired for switching.

A Reignition Installation with Triggered Vacuum Gaps for Synthetic Fault Interruption Testing

A Reignition Installation with Triggered Vacuum Gaps for Synthetic Fault Interruption Testing

A Reignition Installation with Triggered Vacuum Gaps for Synthetic Fault Interruption Testing

In a high power single-phase synthetic test circuit sealed-off triggered vacuum gaps (TVG's) are applied as fast switches. To discharge both capacitor banks (150 kV, 30 kJ) in the reignition installation of that test circuit two switching elements are used with four TVG's in series each. The four TVG's are fired simultaneously by means of two trigger circuits which supply the trigger energy of 2 J each TVG requires. Both trigger circuits in the switching element are fired by two laserdiodes at ground potential. since 1980 both switching elements have been in service in the 30,000 MVA synthetic test plant at KEMA High Power Laboratories

Triggered Vacuum Gaps in a High Power Three-Phase Synthetic Test Circuit

In a three-phase synthetic test circuit triggered vacuum gaps (TVG's) are applied as fast switches. To discharge the six capacitor banks (50 kV, 12.5 kJ) of the reignition installation in that test circuit, sealed-off TVG's are used with a glass-ceramic surface trigger. To switch on a low oscillating current in each phase of the voltage injection installation, three continuously pumped TVG's are used with a polyacetal evaporating trigger. Because of a selfgenerated axial magnetic field of 10 mT/kA this TVG is also capable of switching a high current of 14 kA rms (50 Hz) during the first 4 ms. Since 1982 both types of TVG's are operational in a 145 kV, 50 kA three-phase synthetic test circuit at KEMA High Power Laboratories.

Triggering mechanisms in triggered vacuum gaps

Experiments were conducted on a vacuum gap with a trigger electrode mounted in one of the main electrodes. Waveforms under various circuit conditions, photographic and visual observations, probe measurements, and various trigger materials were studied to investigate the triggering mechanisms. Different mechanisms are proposed according to the polarity of the remote main electrode. For positive polarity, the trigger arc establishes its own cathode spots, which then supply current to the main discharge, dividing to form new spots as needed. For negative polarity, the plasma produced by the trigger produces a concentration of the main electrode potential difference across a thin sheath adjacent to the surface of the remote main electrode.

Anode Phenomena in Triggered Vacuum Gaps

Arc voltage - current characteristics and threshold current densities occuring during the formation of anode spots in triggered vacuum gaps are reported. Single pulses of 1.65 ms arcing time, which correspond to switching surge currents, are used in the study with copper and aluminum anodes. The threshold values are 1.75 times the values reported earlier using the longer, 8 mis, arcing time. They are found to depend upon the duration of arcing time as well as upon electrode material, surface conditions, electrode size and contact separation. Lateral inhomogenity in the electrode geometry appears to reduce the threshold value by promoting early formation of anode spots.