High-speed Charge-coupled Device Video Camera Research Articles

The Characteristics of Vacuum Arc in the Process of Transition to Diffuse Mode Under Transverse Magnetic Field

The motion of arc between the transverse magnetic field (TMF) contacts gradually slows down and transits to the diffusion mode before the current zero crossing. The process of arc transition to diffusion mode seriously affects the contact surface ablation. However, the influence on vacuum arc transition to diffuse mode has not been deeply studied to date. In this paper, TMF contacts with different structures were investigated in a demountable vacuum chamber that contained a high-speed charge-coupled device video camera. It was found that current, arcing time, and axial magnetic field (AMF) components had significant effects on arc appearance, arc column diameter, and moment and current at which the arc transited to diffuse mode. The transition moment to diffuse mode exhibited a linear relationship with the peak current. The arc energy accumulated before diffuse mode would increase and the transition moment would be advanced when the peak current was increased. The range of the transition current to diffuse mode and small-current diffuse mode remain unchanged with peak current and arcing time. The arc column in the contacts with larger axial self-magnetic field had larger diameter while transiting to diffuse mode and also transited to the diffuse mode earlier and accumulated less energy during the transition.

Transformation Characteristics of High-Current Vacuum Arcs With Still-Spaced Contacts Under TMF–AMF Combined Magnetic Fields

A novel double-type contact system with still-spaced contacts was proposed to offer a better arc control and a electric field shielding effect to the eroded inner contacts, especially during the capacitive interrupting process. The experimental double-type contact system consisted of the inner moving transverse magnetic field (TMF) contacts and the outer still-spaced axial magnetic field (AMF) contacts, which was called as TMF–AMF contacts. The objective of this paper is to determine the transformation characteristics of high-current vacuum arcs with still-spaced contacts under TMF–AMF combined magnetic fields. The experimental investigation includes the vacuum arcing behaviors, the arc voltage, and the arc current transformation characteristics. The arc current in the tests varied over a range from 0 to 30 kA at 50 Hz. The contacts material was CuCr25 (25% Cr). A high-speed charge-coupled device video camera was used to record the vacuum arc appearance. The experiments indicate that the vacuum arc current can transform successfully from the inner TMF contacts to the outer still-spaced AMF contacts for the novel TMF–AMF double-type contacts. The partial arc current flowed through the outer still-spaced contacts was mainly at the latter half of the vacuum arc duration and less than 50% of the total arc current. The value and polarity of the arc current also play a significant role in the arc current transformation characteristics of the TMF–AMF contacts with still-spaced contacts. Moreover, with the vacuum arc expanding to the still-spaced contacts, the variation of the Lorentz force of the arc column would weaken the rotation of the arc column and strengthen the transformation characteristics of the vacuum arc column to the still-space AMF contacts significantly.

Prestrike Inrush Current Arc Behaviors in Vacuum Interrupters Subjected to a Transverse Magnetic Field and an Axial Magnetic Field

The objective of this paper is to determine the influences of the transverse magnetic field (TMF) and the axial magnetic field (AMF) on prestrike inrush current arc behaviors in vacuum interrupters (VIs) during capacitive making processes. Two types of cup-type VI contacts were used: TMF contacts and AMF contacts. The contact diameter of the VIs was 48 mm. The insulating envelopes of the VIs were transparent, and there was no metal vapor shield inside the VIs, which were arranged for the observation of the prestrike arcs. The inrush current arc behaviors were recorded by a high-speed charge-coupled device video camera. The experimental results revealed that the VIs of cup-type AMF contact showed a higher dielectric strength than those of cup-type TMF contact during the making operations of inrush current. In addition, the arcs in VIs of cup-type TMF contact tended to be intense arcs that caused serious welding than those of VIs of cup-type AMF contact. Moreover, the cup-type AMF contact effectively reduced the prestrike arc erosion on the contact surfaces than those of TMF contact during the prestrike process of inrush current.

Simulation and Experimental Investigation on a New Type of Cup-Shaped Contacts With Iron Cores

Vacuum interrupters, with the advantages of high breaking ability, small volume, low weight, and little pollution, are widely used in medium voltage circuit breakers. The transverse magnetic field (TMF), generated by spiral-type or cup-type contact, moves the constricted arc over the contact surface, which avoid excessive heating on the contact and reduce the erosion of a fixed area. The TMF contacts are slotted to cause current flow diversion, and a radial magnetic field is produced. In this paper, we propose an improved cup-type contact with iron cores. The magnetic field distribution of this new contact was simulated, and the magnetic force acted on arc column was calculated. It was found that the optimized contacts could effectively enhance the radial magnetic field between contacts and reduce the radial force of the arc column. In addition, two different kinds of cup-type TMF contacts were investigated in a demountable vacuum chamber using a high-speed charge-coupled device video camera. The experimental results suggested that compared with the traditional cup-shaped contacts, the new contacts could effectively improve the arc speed and duration of arc movement, accompanied by a more evenly surface ablation and an improved surface utilization.

Rotation Characteristics of Vacuum Arcs Driven by Transverse Magnetic Fields

The objective of this paper is to propose a new method to quantitatively determine the arcing rotation characteristics of the constricted vacuum arc driven by the transverse magnetic field (TMF). This method is based on a split-anode TMF contacts’ system, including a split-anode TMF and a spiral TMF cathode. Experiments were carried out in a demountable vacuum chamber. Both contacts had a diameter of 60 mm. The anode surface was divided into four areas: one central area and three symmetrically peripheral annular areas. The currents of the four split-anode areas were measured using four Rogowski coils situated outside the vacuum chamber. The observed arc behavior was recorded by a high-speed charge-coupled device video camera. This experiment proposes a new method to quantitatively determine the arcing rotation velocity of the TMF vacuum arcs by the current waveforms of the four split-anode areas. After some comparison to the new method, the rotation velocity of the TMF vacuum arcs estimated in the traditional method by the arc photographs seems underestimated. The experimental results indicate that the constricted vacuum arc driven by the TMF should be higher than 471 m/s with the arc current of 16-kA rms. The results also reveal the corresponding anode current distribution characteristics under the TMF in different arc stages during the arcing period.

Inrush Current Prestrike Arc Behaviours of Contact Materials CuCr50/50 and CuW10/90

In the case of back-to-back capacitor banks switching, the inrush current arcs can locally melt the contact surfaces of vacuum interrupters (VIs) during the prestrike process. The contact materials significantly influence the behaviours of the inrush current prestrike arcs. The objective of this paper is to determine the influence of contact materials on prestrike arc behaviours of VIs during capacitive making processes. Six identical 12-kV VIs were used in the experiment after the proposed conditioning. The contact diameter of the VIs was 48 mm, and the insulating envelope was transparent. There were no metal vapour shields inside the VIs to enable the observation of the prestrike arcs. Two different contact materials (CuCr50/50 and CuW10/90) were used in the experiment. Test inrush currents were set to 5-, 10-, and 20-kA peak values, respectively. The inrush current arc features were recorded by a high-speed charge-coupled device video camera. It is discovered that the contact materials have a significant influence on the prestrike gaps. Moreover, the prestrike arcs in VIs with the CuW10/90 contact material tend to be more diffuse than those in VIs with the CuCr50/50 contact material. The results indicate the impact of different contact materials on the prestrike arc behaviours and reveal the contact erosion patterns for different materials.

Effect of an axial magnetic field and arc current on the anode current density in diffuse vacuum arcs

The objective of this paper is to measure the effect of an axial magnetic field (AMF) BAMF and arc current on the anode current density in diffuse vacuum arcs. The experimental geometry included a split anode and a butt-type cathode, both with a diameter of 60 mm. The anode surface was divided into a central area and three symmetrically disposed peripheral annular areas. The central area of the split anode had a diameter of 20 mm. The contact material was CuCr25 (25% Cr). The arc current IARC ranged from 4 to 14 kA (rms) at 50 Hz. The opening velocity was 2.4 m/s. The currents of the four areas on the anode contact were measured using four Rogowski coils situated outside the vacuum chamber. An external uniform AMF BAMF ranging from 0 to 110 mT was applied during the experiment. The observed arc modes were recorded by a high-speed charge-coupled device video camera. The experimental results quantitatively reveal that the current density distribution on the anode surface in the diffuse arc mode was not uniform but concentrated in the central area. The current density in the central anode area at the current peak JPeakArea I decreased with increasing BAMF following a power law. For BAMF of 0–110 mT and IARC of 4–14 kA, JPeakArea I = (2.2 IARC + 0.069 IARC2) BAMF−0.22, where JPeakArea I is in A/mm2, BAMF is in mT, and IARC is in kA. Moreover, the current distribution was uneven in the three peripheral areas.

Vacuum arcing behavior between transverse magnetic field contacts subjected to variable axial magnetic field

The objective of this work is to reveal the effects of an axial magnetic field (AMF) on the vacuum arc characteristics between transverse magnetic field (TMF) contacts. These vacuum arc characteristics include the vacuum arcing behavior and the arc voltage waveform. In the experiments, an external AMF was applied to a pair of TMF contacts. The external AMF flux density BAMF can be adjusted from 0 to 110 mT. The arc current in the tests varied over a range from 0 to 20 kA rms at 45 Hz. The contact material was CuCr25 (25% Cr). A high-speed charge-coupled device video camera was used to record the vacuum arc evolution. The experimental results show that the application of the AMF effectively reduces the TMF arc voltage noise component and reduces the formation of liquid metal drops between the contacts. The diffuse arc duration increases linearly with increasing AMF flux density, but it also decreases linearly with increasing arc current under application of the external AMF. The results also indicate that the diffuse arc duration before the current zero is usually more than 1 ms under the condition that the value of the AMF per kiloampere is more than 2.0 mT/kA. Finally, under application of the AMF, the arc column of the TMF contacts may constrict and remain in the center region without transverse rotation. Therefore, the combined TMF–AMF contacts should be designed such that they guarantee that the AMF is not so strong as to oppose transverse rotation of the arc column.

Experimental Investigation of High-Current Vacuum Arc Instability Modes Under Transverse Magnetic Field

The behavior of vacuum arc influences the heat distribution on the contacts and the contact melt and erosion, and thus, it greatly affects the breaking capacity after current zero. In this paper, high-current arc instability modes were investigated in a demountable vacuum chamber with a high-speed charge-coupled device video camera. Three kinds of spiral contacts were used with CuCr50 as the contact material. We observed and summarized three types of arc instability modes: 1) multicolumn arc mode; 2) single stationary jet mode; and 3) single moving jet mode. As the peak current increases, the instability mode will transition from multicolumn arc mode to single stationary jet mode, and then to single moving jet mode. We also found the periodical transition between the plasma jet and the relatively diffuse columnar arc during single moving jet mode. It was shown that the occurrence of arc instability modes, especially the single moving jet mode, is usually accompanied by the increase in mean value and high fluctuations on the arc voltage. Besides, during the instability mode, a large number of droplets and macroparticles will be produced in the gap. These will have a great influence on the interruption capacity of the vacuum interrupter.

Influence of axial self-magnetic field component on arcing behavior of spiral-shaped contacts

The transverse magnetic field (TMF) contact design is commonly used in vacuum interrupters. When arcing occurs between the TMF contacts, the contact structure can create a self-induced magnetic field that drives the arc to move and rotate on the contact, and thus local overheating and severe erosion can be avoided. However, TMF contacts could also create an axial self-magnetic component, and the influence of this component on the arc behavior has not been considered to date. In this paper, five different types of Cu-Cr spiral-shaped TMF contacts with three different structures are investigated in a demountable vacuum chamber that contains a high-speed charge-coupled device video camera. It was found that the contact structure greatly influenced the arc behavior, especially in terms of arc rotation and the effective contact area, while contacts with the same slot structure but different diameters showed similar arc behavior and arc motion. The magnetic field distribution and the Lorentz force of each of the three different contact structures are simulated, and the axial self-magnetic field was first taken into consideration for investigation of the TMF contact design. It was found that contact designs that have higher axial self-magnetic field components tend to have arc columns with larger diameters and show poorer arc motion and rotation performance in the experiments.

Anode Erosion Pattern Caused by Blowing Effect in Constricted Vacuum Arcs Subjected to Axial Magnetic Field

The objective of this paper is to investigate the anode erosion pattern caused by the blowing effect in constricted vacuum arcs under an axial magnetic field (AMF). The blowing effect was reflected from the microstructure of the melt layer on the anode. A pair of 42-mm-diameter AMF contacts were installed inside a detachable vacuum chamber. The contact material was CuCr25 (25% Cr). The arc modes were observed with a high-speed charge-coupled device video camera. The anode surface temperature after current zero was measured with a two-color pyrometer. The microstructure of the cross section of the anode surface melt layer was observed by scanning electron microscopy. The experimental arc currents increased from 10.5 to 17.8 kA (rms) with an interval of 2 kA. The results show that the anode erosion pattern in constricted arcs is caused by an interactive process of thermal and mechanical effects. The constricted arc columns melted the anode surface material and blew the molten material from the center to the peripheral region. The redistribution of the anode molten layer caused by this blowing effect formed two erosion regions on the anode surface. The depth of the melt layer in the central region was less than 100 $\mu \text{m}$ , but in the peripheral region it was in the range of 100–400 $\mu \text{m}$ . In these different erosion regions of the anode melt layer, there was considerable variation in both size and shape of the Cr sphere. Moreover, the thermal and mechanical effects of the constricted arc redistributed the Cr content of the molten layer on the anode surface. The Cr content in the central region (Erosion Region I) increased to 31% and in the periphery region (Erosion Region II) it decreased to 18%, respectively, from 25% before the experiments.

Study on Influence of Self-Generated Axial Magnetic Field Upon High-Current Vacuum Arc Behavior at a Long Contact Gap in High-Voltage Vacuum Interrupter

In this paper, the high-current vacuum arc characteristics under self-generated axial magnetic field (AMF) generated by a sinusoidal current flowing through the coil type of AMF contacts are investigated at long contact gaps of 40 and 60 mm. The distributing characteristics of the AMF in the contact gap are studied by a finite-element method, taking eddy current effect into account. Vacuum arc appearance was observed by a high-speed charge-coupled device video camera. The vacuum arc voltage was measured using a high-voltage probe. Capacitor and reactor (LC) discharging-current-interrupting tests were done with a single-frequency oscillating circuit. The vacuum arc behavior of a single coil-type AMF contact and that of a 1/2 coil-type AMF contact were compared. The research results show that both the amplitude and phase shift time of the AMF have great influence upon the high-current vacuum arc characteristics.

Study on High-Current Vacuum Arc Characteristics Under Self-Generated Axial Magnetic Field of Contact at a Long Contact Gap for High-Voltage Vacuum Interrupters

In this paper, the high-current vacuum arc characteristics of the single coil-type AMF contacts, under axial magnetic field (AMF) generated by a sinusoidal current following, were investigated at a long contact gap of 40 and 60 mm. The distributing characteristics of AMF in contact gap were studied by a finite element method, taking eddy current effect into account. Vacuum arcs appearance was observed by a high-speed charge-coupled device video camera. Vacuum arc voltage was measured using a high-voltage probe. Dependence of arc voltage and vacuum arc appearance upon the self-generated AMF characteristics was investigated. The research results show that anode melting phenomena without arc voltage noises could occur both in an unstable arc and in a diffuse arc in a wide range of arc current and AMF strength at a long contact gap. Also, both many small-scale transient spots and several small luminous melting regions on anode could be observed with a diffuse arc column and a quiescent arc voltage.

Study on a New Single Coil-Type Axial Magnetic Field Contact for High-Voltage Vacuum Interrupters

A new single coil-type axial magnetic field (AMF) contact for high-voltage vacuum interrupters is introduced. Its AMF characteristics were studied by a finite element method, taking the eddy current effect into account. Vacuum arc appearance of the new single coil-type AMF contact was observed by a high-speed charge-coupled device video camera. Capacitors and reactors (LC) discharging current interruption tests up to 45.0 kA were done with a single frequency LC oscillating circuit. Vacuum arc appearance of the single coil-type and slot-type AMF contacts was compared. The research results show that the new single coil-type AMF contact is more suitable for high-voltage vacuum interrupters than the slot-type AMF one