Emission Current Measurements Research Articles

Measurement of emission currents immediately after arc polishing of contacts-Method for internal-pressure diagnostics of vacuum interrupters

The inherent high reliability of vacuum interrupters is determined by the maintenance of a high degree of vacuum in the vacuum tube for a long time. Rise of internal pressure exceeding a certain threshold value causes loss of the current switching capability and, at a pressure that is about one or two orders higher, the loss of the electric insulating properties. Pressure measurements after manufacturing and reexamining the internal pressure of vacuum interrupters after several years of service require different procedures, measuring methods, and diagnostic techniques. The fundamentals of a new method based on the measuring of emission currents immediately after arc polishing of the contacts are presented. This method is appropriate for estimating the internal pressure of the vacuum interrupters after long-time service and for giving information about the remaining safety margin. >

Prebreakdown emission current measurements in a 24 kV vacuum interrupter with butt contacts

Commercial 24-kV vacuum interrupters with butt contacts were tested under DC conditions with three different contact materials: OFHC-copper, stainless steel 304 and Cu/Cr (75/25, wt.%). The critical breakdown field was computed at contact distances of 1, 2 and 3 mm, based on the prebreakdown emission current and the breakdown voltage. While the values for the critical breakdown field for OFHC-copper and stainless steel 304 were in agreement with the values found by other authors, no previous data were found for Cu/Cr. >

Monitoring alkali metal adsorption by secondary electron emission current measurements

Abstract The room temperature adsorption of potassium and caesium on Al(111) has been followed as a function of time with AES, work function change measurements and measurements of the secondary election yield and crystal current. For each adsorbate the coverage saturates at one monolayer, due to low heats of sublimation, and it is shown that crystal current measurements can be used for assessing the coverage even in the absence of AES or another coverage determination technique. The crystal current is compared with the work function change and for caesium adsorption the crystal current is also compared with the change in the backscattered electron distribution. Work function changes are not solely responsible for the observed variations in the crystal current and it is suggested that changes in transmission probability above the emission threshold are important.

Monitoring alkali metal adsorption by secondary electron emission current measurements

The room temperature adsorption of potassium and caesium on Al(111) has been followed as a function of time with AES, work function change measurements and measurements of the secondary election yield and crystal current. For each adsorbate the coverage saturates at one monolayer, due to low heats of sublimation, and it is shown that crystal current measurements can be used for assessing the coverage even in the absence of AES or another coverage determination technique. The crystal current is compared with the work function change and for caesium adsorption the crystal current is also compared with the change in the backscattered electron distribution. Work function changes are not solely responsible for the observed variations in the crystal current and it is suggested that changes in transmission probability above the emission threshold are important.

High-voltage test equipment for vacuum interrupters and contacts (‘arc and spark’ testing)

An automated ‘arc and spark’ test method has been developed for economical high-voltage testing of vacuum interrupters, taking into consideration both the physics of vacuum breakdown and realistic service conditions. Each breakdown test is preceded by a well defined but variable switching operation. Test control and evaluation by a computer provide fast and economic execution, even of large series of complex tests. Short descriptions of devices for breakdown detection and prebreakdown field emission current measurement are added. The presented test method concerns the dielectric performance of an open interrupter, but not its dielectric recovery at current interruption.

Methods of measurement of electron emission currents in high-voltage vacuum insulation devices: H Moscicka-Grzesiak and J Skibinski, Elektrotech Biul Inform, 27 (4), 1973, 13–20 (in Polish)

Methods of measurement of electron emission currents in high-voltage vacuum insulation devices: H Moscicka-Grzesiak and J Skibinski, Elektrotech Biul Inform, 27 (4), 1973, 13–20 (in Polish)