Intermediate-frequency Vacuum Arc Research Articles

Numerical Simulation of Intermediate-Frequency Vacuum Arc

Numerical Simulation of Intermediate-Frequency Vacuum Arc

Properties of intermediate-frequency vacuum arc in sinusoidal curved contact and butt contact

In this report, two new contact structures of a vacuum interrupter with a sinusoidal curved surface are proposed to improve the capability by increasing the surface area. The experimental investigation of vacuum arc at intermediate frequency (360–800 Hz) was conducted and the results were compared with a butt contact with the same contact diameter (41 mm) and the same material. By analyzing the arc behavior, arc voltage characteristics, arc energy, current interrupting capacity, ablation of the anode contact and condensation of the arc products at a 3 mm gap, the differences in their vacuum arc characteristics were determined. The correlations of their arc energy with the amplitude and the frequency of the current were also achieved. Analysis suggests that the ruled curved contact has strong application potentiality because of its low arc energy, low arc voltage noise and arc voltage peak, light ablation on the surface of the anode contact and high interrupting capacity.

External Excitation of Axial Magnetic Field for Intermediate-Frequency Vacuum Arc Research

In order to the make the magnetic field synchronous with the actual current in the current interruption experiment, an external excitation of axial magnetic field for intermediate-frequency vacuum arc experiment and research is designed and tested in this paper. The excitation system is consisted of intermediate-frequency current transformers (CTs) and Helmholtz coil. CTs are used to induct current in main circuit and the Helmholtz coil can be excited by the secondary current. Thus the axial magnetic field (AMF), which is synchronous with the primary current, is generated inside the Helmholtz coil. And different from traditional magnetic field excitation system, the magnetic field generated by commercial AMF contact can be simulated. The test is implemented to test the excitation system. The phase difference between the primary side and secondary side of the CT is less than 10'. The steady state error of B is within 1% and the dynamic error of B/I is within 1.5% as well. The results turn out to be consistent with the theoretical value, which proves the effectiveness of this external excitation system.

Reignition After Interruption of Intermediate-Frequency Vacuum Arc in Aircraft Power System

Intermediate frequency (IF) electric power supply system has been widely applied in airplanes. Reignition after interruption of 360-850 Hz vacuum arc in axial magnetic field (AMF) is studied in this paper. According to the experimental results, the current interruption ability decreases from 22.4 kA at 360 Hz to 14.0 kA at 850 Hz. With the increase of frequency, the rate of change of current, di/dt, at current zero (CZ) reaches the breaking threshold at a smaller current value. Based on the least squares solution of the Mayr model, the time of decay of arc energy is prolonged when interruption fails, which is disadvantageous to the breaking process. On the other hand, the eddy effect is enhanced by higher frequency, which increases the residual magnetic induction intensity and the hysteresis phase of AMF after CZ. As a result, the diffusion of plasma is blocked. In the experiments, we find that the position of arc reignition always appears at the margin of contacts. It is shown by calculation that the electric field at the marginal area is twice as strong as that inside the contact. The current density is high, where the electric field is strong, leading to the higher probability of field emission. Arc images are analyzed by frame differential method. The sputtering velocity of macroscopic particles is estimated to be 10-20 m/s. The dissipation time of the macroscopic particles is longer than the arc time of IF vacuum arc, and the presence of macroscopic particles leads to the arc reignition. The findings of this paper would be beneficial to the parameter design of IF vacuum circuit breakers, such as the magnetic flux density of AMF, the chamfering of contact margin, and contact materials.

Analysis of the Vacuum Arc Interruption Process in Aviation Intermediate-Frequency Power Supply Systems

In this paper, we present our research into the interruption performance of vacuum circuit breakers in aviation intermediate-frequency (360 Hz to 800 Hz) power supply systems. Intermediate-frequency vacuum arc experiments were carried out in interrupters with a diameter of 41 mm and CuCr50 alloy contact material. The results show that, as the frequency and peak value of the current increase, both the peak value and rise rate of the intermediate-frequency vacuum arc voltage also increase, and the interruption ability decreases. However, compared to the power frequency current at the same value, the erosion of the contacts is weaker over a shorter arc period. When the vacuum arc reignites, metal droplets are emitted from the contacts. The drive force is from the center of the contact to the edge. If the density of the plasmas and metal vapors and the number of the metal droplets reaches a certain level, the arc may break down, which will cause the interruption to fail.

Interruption Phenomenon in Intermediate-Frequency Vacuum Arc**supported by National Natural Science Foundation of China (No. 51377007), Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20131102130006), and Fundamental Research Funds for the Central Universities of China

In the condition of the 3 mm gap, experiments for 360 Hz intermediate-frequency vacuum arc are carried out in interrupters with the diameters being 41 mm and with the contact materials being CuCr50 and Cu-W-WC alloy respectively. The results indicate that the contacts material is closely related to the breaking capacity of the vacuum interrupters and characteristics of an intermediate-frequency vacuum arc. For contacts with the same diameter, the breaking capacity of CuCr50 is better than that of Cu-W-WC. When the current fails to be interrupted, the arcs overflow the gap and present irregular performances in the first half wave. Consequently a voltage spike appears. More macroscopic metal droplets can be seen in the arc column between CuCr50 contacts because of the lower melting point. It is observed that the droplet emission is much more severe during arc reignition than that in the first half wave. It is much more conspicuous that the high frequency arc voltage noises appear in Cu-W-WC contacts when the vacuum arcs reignite, for higher temperature and stronger electronic emission ability of Cu-W-WC contacts.

Arc Movement of Intermediate-Frequency Vacuum Arc on TMF Contacts

This paper describes the arc behavior in the transverse-magnetic-field (TMF) contacts at intermediate frequency (400-800 Hz). With high-speed photography, three different arc modes were identified: expansion arc column, moving arc, and diffuse arc. In the expansion arc column mode, the arc column is immobile and the diameter of the arc column increases with the current. During this stage, the bright anode spots appear with high amplitude noise of arc voltage at high current. The expansion arc column mode plays an important role in the anode erosion. In the moving arc column mode, the average velocities were observed about 10-100 m/s, and the arc velocity increases with the increased frequency at the same current. The arc voltage expressed by arc current and frequency was obtained in this paper. The cross-section area of the arc column decreases with the increased frequency at the same current. The current density increases with the increased frequency at the certain current. Consequently, it is deduced that the arc velocity increases with the increased frequency at the same current. The mean power input concentrates in a smaller area at a higher frequency. It may be one of the reasons why the anode local melted.

Arc Behavior of Intermediate-Frequency Vacuum Arc on Axial Magnetic Field Contacts

A vacuum circuit breaker has advantages of low maintenance cost and high reliability. It reaches the priority in aviation field. This paper focuses on the arc behavior of intermediate-frequency (400, 650, and 800 Hz) vacuum arc in commercial-type vacuum interrupters with axial magnetic field contacts. With high-speed photography and volt-ampere characteristics, three different arc modes were identified: free-expansion arc column, transition arc, and diffuse arc. At the transition arc mode, the arc column is constricted, twisted, and fast moving, with an increasing number of cathode spots around it, and accompanied by an appreciable arc voltage noise at higher current. At a given current, the arc column is more constricted at higher current frequencies during this stage. The arc voltage increases with the increasing frequency regardless of the arc voltage noise; it implies a larger instantaneous energy input in shorter arc durations. Anode behavior was observed to further investigate the increased instantaneous energy input. It showed that the transient spot on the anode during the transition arc mode becomes a major source of anode erosion, although the anode erosion is slight at very high current. The instantaneous energy input, defined as mean power input, increases with current frequency, and it correlates with the constricted arc column at higher frequency. This explains the anode erosion that happened in short durations in our experiments and others.

Properties of Intermediate-Frequency Vacuum Arc Under Axial Magnetic Field

This paper presents an experimental study of the intermediate-frequency (400-800 Hz) vacuum arc under axial magnetic field (AMF). Arc-voltage noise at the first current semi-wave is inconspicuous even if the current is not interrupted successfully. This fact is attributed to the application of a sufficiently strong AMF provided by the current flowing through a short vacuum gap. The influence of the current frequency on peak arc voltage and the rate of rise of the arc voltage are investigated. Interrupting ability of a vacuum interrupter (VI) with cup-type AMF contacts made from CuCr50 is examined. It is found that the upper limit of current interruption is inversely proportional for frequencies in the range from 400 to 800 Hz. Phase shift of AMF is studied by the finite-element method based on a simplified symmetric model. The results show that the phase-shift angle increases with the current frequency and influences intermediate-frequency current interruption of VI with AMF contacts.