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Application of the Vacuum Interrupter for Switching Load Currents
Published in Paul G. Slade, The Vacuum Interrupter, 2020
As I have previously discussed in Section 4.3.1.2 in this volume, interrupting a capacitor circuit is a relatively easy task for the vacuum interrupter, especially as the currents involved are typically less than 1000A and the resulting vacuum arc is in the diffuse mode. Also, the initial recovery voltage across the contacts is zero and its initial rate of rise is very slow. However, its value reaches from about 2PU to 2.5PU. The resulting voltage appearing across the contacts is unidirectional. That is the voltage will be fully offset as is shown in Figure 5.45. For the most part, a well-designed vacuum capacitor switch will withstand this unidirectional voltage during the time it takes for the charge residing on the capacitor bank to leak away and for the normal bidirectional system ac voltage to be impressed across the open contacts. The initial unidirectional voltage across the open contacts does, however, impress an unusual stress on the withstand ability of the contact gap. For most of a vacuum capacitor switch’s operating life it will hold off the unidirectional voltage, but once in a while, a restrike will occur. This phenomenon is not unique to vacuum switching technology. Restriking can also occur with all other switching technologies such as SF6 and oil. In fact, one study by the Kansas City Power and Light Utility states that there have been so many problems with their installed base of oil capacitor switches that they are gradually replacing them with vacuum capacitor switches [72].
Preventing RF System Failures
Published in Jerry C. Whitaker, The RF Transmission Systems Handbook, 2017
Transmitting capacitors — mica vacuum and doorknob types — should never run hot. They may run warm, but usually as the result of thermal radiation from nearby components (such as power tubes) in the circuit. An overheated transmitting capacitor is often a sign of incorrect tuning. Vacuum capacitors present special requirements for the maintenance technician. Care in handling is a prime requisite for maximum service life. Because the vacuum capacitor is evacuated to a higher degree than most vacuum tubes, it is particularly susceptible to shock and rough handling. Provide adequate protection to vacuum capacitors whenever maintenance is performed. The most vulnerable parts of the capacitor are the glass-to-metal seals on each end of the unit. Exercise particular care during removal or installation.
RF System Maintenance and Troubleshooting
Published in Jerry C. Whitaker, Power Vacuum Tubes, 2017
Transmitting capacitors—mica vacuum and doorknob types—should not run hot. They may run warm, but usually as the result of thermal radiation from nearby components (such as power tubes) in the circuit. An overheated transmitting capacitor is often a sign of incorrect tuning. Vacuum capacitors present special requirements for the maintenance technician. Care in handling is a prime requisite for maximum service life. Because the vacuum capacitor is evacuated to a higher degree than most vacuum tubes, it is particularly susceptible to shock and rough handling. Provide adequate protection to vacuum capacitors whenever maintenance is performed. The most vulnerable parts of the capacitor are the glass or ceramic-to-metal seals on each end of the unit. Exercise particular care during removal or installation.
Numerical and Experimental Investigation of the Channel Expansion of a Low-Energy Spark in the Air
Published in Combustion Science and Technology, 2019
K. V. Korytchenko, S. Essmann, D. Markus, U. Maas, E. V. Poklonskii
The electrical discharges under investigation were created with the electrical setup shown in Figure 1. To generate a low-energy discharge, a high-voltage source (FUG HCP 35-35000) was used to charge a variable vacuum capacitor (3-30 pF, Jennings CADC-30-10S) across a 180 MΩ resistor. The resistor limited the current in such a way that continuous discharges could not occur. The voltage and current were measured by means of a high-voltage probe (Tektronix P6015A) and a current transformer (Bergoz CT-B5.0), respectively. These signals were recorded on an oscilloscope (Yokogawa DLM6054). The discharge energy was assumed to be the energy stored on the capacitor and in stray capacitances prior to the discharge, , where represents the capacitance of the setup and denotes the voltage applied before the gas breakdown. The capacitance was measured using a handheld LCR meter (Sourcetronic ST2822). The capacitance was 15.4 pF. The resulting voltage and current of such a discharge is shown in Figure 2. We did not use the voltage and current waveforms to estimate the energy deposited in the gas because the calculated energy includes the energy deposited in the gas as well as the energy losses in near electrode. For the low energy investigated in this study, the fraction of energy remaining on the capacitor is negligible (Hattwig and Steen, 2004).