Wu Jianwen

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.

Motion and Splitting of Vacuum Arc Column in Transverse Magnetic Field Contacts at Intermediate-Frequency

Splitting of vacuum arc at intermediate frequency (400-800Hz) were investigated under transverse magnetic field (TMF). The experiment was performed on cup-type TMF contacts with contact diameter of 40 mm and a contact gap of 2 mm in a single-frequency circuit. With high-speed photography the arc appearances at different arc currents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies were characterized. As arc current increases from 3.3 kA-rms to 10 kA-rms the arc appearance changes obviously. When current value is 3.3 kA-rms (current frequency 400-800 Hz), there is almost no splitting arc; when the current exceeds 5 kA-rms (current frequency 400-800 Hz), the arc rotated at a speed above 20 m/s, accompanied by an observable splitting arc. The splitting arc could be observed at different frequencies and the arc-voltage had no noises when splitting occurred. Furthermore, the generations of the split arcs almost have the same features. The split arc formed in the opposite (retrograde) direction, contrary to the Ampere rule. The velocity of split arc is related to the motion direction and the generation position. According to the observation of the split arc at different frequencies, a conclusion can be drawn that the split arc is more likely to occur when the arc almost fills half of the contact surface. The motion direction and the velocity of arc column were studied. Finally, the formation of a split arc was discussed.

The Dynamic Volt-Ampere Characteristics of a Vacuum Arc at Intermediate-Frequency Under a Transverse Magnetic Field

In this study, the changes of a vacuum arcs appearance were observed and the volt-ampere characteristics of the vacuum arc at intermediate frequency were analyzed under a transverse magnetic field (TMF). The TMF and phase shift time were calculated by using the TMF contact model and the large phase shift of the magnetic field at a higher frequency was conductive to the dispersion process of residual plasma. The arc velocity was higher at 800 Hz than at 400 Hz. It can be inferred that TMF will encourage arc movement at 800 Hz. Moreover, the arc movement has an impact on the arc voltage. Because of the increasing length of the arc column with a high arc velocity, the elongated arc causes the arc voltage to increase. Specifically, the volt-ampere characteristics of the vacuum arc are divided into three stages in this paper. The higher the frequency, the greater the initial rate of rise in the arc voltage and the larger the area surrounded by arc volt-ampere characteristics. The correlations between the arc voltage and the amplitude and frequency of the current are also presented.

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.

Study on Dynamic Characteristic in Force Interrupted DC Vacuum Arc

In this paper, the characteristic of 270 V dc forcing interruption is studied. The experiments are performed on a synthetic test circuit, under 1400 and 2000 A current, with the CuCr electrode vacuum interrupter. With a fixed average current rate, di/dt, the arc column shrinks in different situations. In both experiments, the arc diameter changes with three phases. At the beginning of forcing, the arc column seems stable. Consider that the thermal hysteresis plays an important role in it. Then, the arc shrinks with the current decline. Finally, the arc sharply decreases until the arc is quenched. Images of the arc dynamic characteristic are presented.

Plasma Characteristics of DC Hydrogen—Nitrogen Mixed Gas Arc Under High Pressure

In this paper, dc arc characteristics in different high pressure gas atmospheres were studied, both in pure N₂ and in mixed gases of 20%N₂ and 80%H₂ at 5 atm. The experiments were conducted in a demountable arc-quenching chamber with double contacts and a transparent glass shield in a 270 V dc circuit. With a high-speed camera, the arc motion is analyzed. The results indicate that H₂ and N₂ mixed gases have better performance for dc arc extinguishing. Images of pure N₂ and 20%N₂-80%H₂ mixed gas dc arc appearances are presented.

Study of mode transition of long gap vacuum arc

By using a self-made CCD optical transient image system, the arc mode transition of long contact gap is studied. The re-ignition initial location at the side of the electrode is found. Adding an axial magnetic field by an additional coil, the high current arc mode becomes diffuse, and the arc voltage is reduced.

Properties of intermediate-frequency vacuum arc influenced by electrode diameter and material in axial magnetic field

With the development of more-electric and all-electric aircraft technology, it is a trend to unify secondary energy sources, such as mechanical energy, pressure energy, hydraulic energy and so on, into electric energy gradually. Obviously the capacity of power system, distribution system and consumer equipment will experience a giant promotion. The variable-frequency power system has become the most important development orientation for the future aircraft. It is the most advanced technology around the world that intermediate-frequency (360Hz~800Hz) electric power is supplied by the variable-frequency generator which is connected to the engine directly. In this paper, intermediate-frequency (400Hz) vacuum arc in the cup-type interrupter with axial magnetic field (AMF) is generated by the oscillating circuit. In the condition of 3mm opening gap, experiments of different current are carried out in interrupters with the diameters being 41mm and 58mm, and the electrode materials being Cu, Cu-W-WC alloy and CuCr50 alloy respectively. The arc voltage and the transformation of arc performance are analyzed contrastively. It is indicated by the experiment results that breaking capacity of vacuum interrupter and properties of intermediate-frequency vacuum arc are closely related to the electrode diameter and material. With the electrode diameter increasing, arc voltage decreases gradually, and diffuse arc tends to be stable, for which the breaking capacity is better. For the same size of electrode diameter, the breaking capacity in CuCr50 is better than that both in Cu and Cu-W-WC.

Intermediate-frequency vacuum arc movement on TMF contacts

In this paper, the morphological changes at intermediate frequency (400Hz∼800Hz) were investigated under transverse magnetic field (TMF). The experiment was performed on a cup-type TMF contact with a contact diameter of 66mm and a contact gap of 4mm in single-frequency circuit. With high-speed photography, three different arc modes were identified: arc column expansion, arc column movement and diffuse arc. At the arc column expansion mode, the arc column is immobility and the diameter of arc column increases with the increasing current. At the arc column movement mode, arc velocity between 10m/s – 100m/s was observed. The arc column expansion mode plays an important role in the anode erosion in the intermediate-frequency vacuum arc. Furthermore, the arc velocity increases almost linearly with the total current at the same frequency. As the current frequency increase, the arc velocity also increases at the same current.