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Although vacuum technology is commonly used in power systems, challenges still remain for vacuum circuit breakers (VCBs) to cope with the requirements of capacitor bank switching duties as the insulation performance can deteriorate by inrush current. In order to reduce the restrike probability, vacuum interrupters (VIs) in series are recommended. The objective of this paper is to investigate the field emission current I e characteristics and voltage distribution in series vacuum gaps after making inrush current. The results show that I e of the VI pre-stressed by inrush current is much higher than that of the new one and I e has a conditioning effect. It is found that the insulation performance of two pre-stressed VIs in series is not significantly improved compared to a single VI. But the insulation performance of a new VI and a pre-stressed VI in series is significantly improved. Moreover, the voltage distribution of two VIs in series can be estimated by I e. It is found that each VI only withstands about 50% of the applied voltage when two pre-stressed VIs are in series. However, the new VI can withstand >70% of the applied voltage when a new and a pre-stressed VI are in series. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the effect of a high-frequency high-voltage impulse conditioning technique on the inrush current interruption phenomena. In this paper, the inrush current interruption phenomena referred to the actual interruption and the currentless period following interruption. First, Six 7.2 kV vacuum interrupters (VIs) were conditioned by 400 batches of voltage impulses. The duration of each batch were set to 0.1 s. The peak value of each impulse could reach up to 100 kV. The repetition frequency of the impulse was set to 1000 Hz. The contact gap was 0.8 mm. The VIs were tested for the inrush current interruption performance with inrush current set to 2 kA and 5 kA, with a frequency of about 3800 Hz. The experimental results showed that there were two different types of inrush current interruption depending on high-frequency high-voltage impulse conditioning. The inrush current interruption type I referred to the inrush current interruption during the prestrike process before the contacts touched. This type inrush current interruption could be caused by the erosion of prestrike arc. Moreover, the high frequency voltage impulse conditioning influenced the occurrence frequency, the number of interruptions and the duration of the inrush current interruption type I. The inrush current interruption type II referred to the inrush current interruption during the contact bouncing process after the contacts touched. The inrush current interruption type II occurred only in the case of the VIs after conditioning. Furthermore, the occurrence frequency of the inrush current type II decreased with increasing inrush current. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate an impact of the inrush current on the prestrike and restrike characteristics of vacuum interrupters (VIs) during capacitive current switching duty. Eleven 7.2 kV VIs are used. Their contact parameters are contact gap 4 mm and contact material CuCr25 (25%weight of Cr). A series of 80 CO operations are executed for each test VI. The amplitude of inrush current Iinrush (3800 Hz) is set to 0 kA, 2 kA, 5 kA and 10 kA, respectively. The switching current is less than 1 A rms. The (1-cosωt) shape of the recovery voltage with a peak of 15 kV is applied to the test VI. The experimental results show that the prestrike and restrike phenomena are significantly influenced by the contact surface conditions damaged by the inrush current. The cumulative probability of the prestrike gap dpre follows a 3- parameter Weibull distribution. When Iinrush increases from 2 kA to 5 kA, the prestrike gap increases accordingly. The 10% dpre increases from 0.5 mm to 0.7 mm. The 50% dpre increases from 0.7 mm to 1.0 mm. The 90% dpre increases from 1.0 mm to 1.5 mm. The scale in the Weibull distribution, which can describe the scattering of dpre, is 0.2 mm and 0.6 mm in the case of Iinrush = 2 kA and Iinrush = 5 kA, respectively. It is found that the occurrence frequency of the inrush current interruption increases from 37.9% to 68.3% with the increase of Iinrush from 2 kA to 5 kA. Moreover, the inrush current also has an impact on the restrike types, which are classified into three types according to the waveform features. The average restrike probability increases from 4.6% to 17.9% and further to 30.4% with the increase of the inrush current from 0 kA to 2 kA and 5 kA, respectively. In addition, the higher the inrush current, the restrike tends to occur earlier during the recovery voltage period. [ABSTRACT FROM AUTHOR]