Structure improvement of a 126 kV vacuum circuit breaker using electromagnetic-thermal field coupling simulation

Vacuum circuit breakers are widely used in medium voltage circuit breakers. The 3/4 coil-type axial magnetic field (AMF) contact has passed type test and reaches a nominal rated current of 2500 A. However, there is a higher requirement of the nominal rated current of 3150 A. A new 2/4 coil-type contact was proposed to increase the nominal rated current. But the current interrupting capacity of 2/4 coil-type AMF contact was unknown. The objective of this paper is to compare the vacuum arc characteristics between the 2/4 coil-type AMF contact and the 3/4 coil-type AMF contact to estimate the current interruption capacity of 2/4 coil-type AMF contact. A pair of 2/4 coil-type AMF contact was used in the experiments. Contact diameter was 100 mm, and contact material was CuCr50. Full contact gap was 50 mm, and opening velocity was set as 2.4 m/s within 20 mm after contact separation. A drawn arc experiment was carried out in a L-C discharging circuit. Arcing current was ranged from 5 to 40 kA rms and current frequency was 49.2 Hz. In the experiments, the vacuum arc behaviors were recorded by a high speed CCD camera. The results show that, the resistance of single contact of the 2/4 coil-type AMF contact was $6.29\ \mu\Omega$ , and the contact resistance of the 3/4 coil-type AMF contact was $8.12\ \mu\Omega$ . Besides, the intense arc mode duration and the diffuse arc mode duration before the second current zero of the 2/4 coil-type AMF contact and 3/4 coil-type AMF contact was similar. Therefore, the 2/4 coil-type AMF contact could control the high-current vacuum arc as well as the 3/4 coil-type AMF contact. The results suggested that the 2/4 coil-type AMF contact has similar current interrupting capacity with the 3/4 coil-type AMF contact, with a higher carrying capacity of the nominal rated current.

Comparison of Arc Characteristics between 2/4 Coil-type AMF Contact and 3/4 Coil-type AMF Contact

The results presented in this article relate to the work conducted to verify the existence of anode-induced phenomena, predominantly anode vaporization and consequent prebreakdown (PBD) current enhancement due to the impact of positive ions and microparticles over a relatively larger area at the cathode (presumably ion-assisted field (I-F) emission like). The verification of this hypothesis is attempted using a three-electrode arrangement. One electrode is comprised of a needle insulated from and projecting through a plane electrode (collector) of 40-mm diameter. It was surmised that if the positive ion beam from the anode spot (due to electron beam impact) were to be macroscopically diffuse, at least the collector would gather a part of it. However, no currents could be detected in the collector circuit even at voltages close to breakdown. The needle currents continued to display the typical characteristics of PBD currents under alternating voltages. The needle currents depended on the spacing between the needle tip and the plane of the collector and the polytetrafluoroethylene (PTFE) insulation used to prevent emission from the immediate vicinity of the needle evaporated significantly. Typical broad-area electrode behavior displayed by needle currents indicated that I-F emission, if any, is limited to the needle itself, which is certainly broad compared to the positive ion beam. Dependence of the PBD currents and breakdown voltages on the melting point of the anode material lend support to such anode-triggered electrode phenomena.

Experimental Verification of Anode-Induced Phenomena During Prebreakdown Conduction in Vacuum Gaps Under Alternating Voltages With Special Electrode System

The objective of this paper is to compare mounted angles between a pair of 2/3 coil-type AMF electrodes in a 126 kV single-break vacuum interrupter. Three kinds of mounted angles are assigned, which include 0°, 30°, and 60° slot shift between a pair of contact plates. A comparison of the mounted angles is made from the point of view of the distribution of axial magnetic flux density, the AC and DC resistance, the anode discharge mode, as well as the contact erosion pattern. The axial magnetic flux density, both in the intermediate plane of the electrode gap and on the contact plate under each mounted angle case, is compared. The AC and DC resistance for each case are also analyzed. A high-speed Charge Coupled Device (CCD) camera is used to determine the arc discharge mode under different mounted angle cases. The contact erosion condition is compared between different mounted angle cases, with each case is subjected to 6 interruptions of 40 kA arcing current.

Comparison of mounted angles between a pair of 2/3 coil-type AMF electrodes in a 126 kV single-break vacuum interrupter

With the widely use of vacuum interrupter, there are many methods have used for conditioning. Moreover, some different electric fields have used for conditioning, such as AC power-frequency electric field, DC electric field and a lot of pulsed fields type with different emerged techniques. The field emission current of cathode has been studied extensively by early researchers, such as Fowler, Nordheim, Van Oostrom, and others. But the paper for field emission current of contact conditioning is only a few. In this paper, we used experiment and simulation method to research the field emission current in contact conditioning, by imposing different type of electric field on the electrode model. We have compared the field emission current, and we know that there is a relationship between the contact surface state, the type of conditioning electric field and the field emission current.

Research on the field emission current in contact conditioning with different electric field

The conditioning is widely used to enhance the insulation performance of vacuum interrupter, such as current conditioning and spark conditioning In this paper, we compared the conditioning performance between traditional ones and high frequency voltage impulses conditioning method with their conditioning parameters, such as conditioning voltage, current and times Positive polarity lightning impulse voltage (12/50μs) was applied by an up-and-down method to test the conditioning insulation performance The experiment results showed that, after high frequency voltage impulses conditioning, insulation strength of vacuum interrupter increased by nearly 16% In addition, the melt layer on contact surface is well-distributed

Insulation performance of vacuum interrupter after high frequency voltage impulses conditioning

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Comparison of mounted angles between a pair of 2/3 coil-type AMF electrodes in a 126 kV single-break vacuum interrupter

Research on the field emission current in contact conditioning with different electric field

Insulation performance of vacuum interrupter after high frequency voltage impulses conditioning