High Voltage Vacuum Interrupter Research Articles

Modeling of X-ray Radiation of High-Voltage Vacuum Interrupters and Experimental Verification

Modeling of X-ray Radiation of High-Voltage Vacuum Interrupters and Experimental Verification

Study on arc characteristics and influencing factors of cup-shaped axial magnetic field contact at different gap distances

The cup-shaped axial magnetic field (AMF) contact, integral to high-voltage vacuum interrupters, undergoes innovation by enhancing the slotting rotation angle of the cup wall. This adjustment significantly amplifies the gap magnetic field, promising breakthroughs in handling long-gap arcs within high-voltage vacuum interrupters. Comprehensive vacuum arc experiments were conducted on cup-shaped AMF contacts with varying slotting rotation angles at different gap distances. The research meticulously analysed the evolution of vacuum arc characteristics under diverse breaking currents. Scanning electron microscope (SEM) images of the cathode surface unveiled three distinctive microscopic morphologies: particle gullies, pore platforms, and particle platforms. Notably, the chromium content corresponding to these morphologies exhibited a progressive increase. Integrating the surface distribution of copper and chromium, the study proposed a plausible cathodic erosion mechanism. Extending the investigation, the research delved into the influence of the iron core, contact diameter, and slot number on vacuum arc characteristics, which expected to provide reference for the application of the cup-shaped AMF contact in high voltage vacuum interrupters.

Experimental investigation of vacuum arc characteristics subject to axial magnetic field contacts with different ratios of diameter to gap distance

In this study, to investigate vacuum arc characteristics under different diameter-to-gap distance ratios (D/g), experiments are conducted on axial magnetic field (AMF) contacts with varying D/g. The peak current value ranges from 15 to 35 kA. The experimental results show that the ability of AMF contacts to control the arc decreases with D/g. Furthermore, the 2/3 coil contact can control the arc under long gap distances, whereas the cup-shaped contact cannot effectively control the arc under long gap distances. The arc energy and noisy period duration decrease with increasing D/g. The arc voltage of the 2/3 coil contact at the peak moment is always the lowest compared to the cup-shaped contact and the 1/2 coil contact, and the arc voltage of the 2/3 coil contact at the peak moment has an approximate power function relation with D/g. The simulation results show that the AMF distribution changes from saddle shape to bell shape with decreasing D/g. The 2/3 coil contact is more suitable for high-voltage vacuum interrupters (VIs), while the cup-shaped contact is more suitable for medium-voltage VIs.

Breakdown characteristics of triple vacuum gaps in series under lightning impulse voltage: Effect of floating potential gap

Inside a high-voltage vacuum interrupter, multiple floating shields form the multiple vacuum gaps (VGs) in series. When the number of series VGs exceeds three, there will exist floating potential VGs in which both electrodes have floating potentials. The floating potential VG is important for the dielectric strength of multiple VGs in series. The objective of this paper is to quantitatively determine the effect of the floating potential VG distance on the breakdown (BD) characteristics of triple VGs in series. In the experiments, triple VGs were built up by series-connecting three pairs of sphere-plane electrodes vertically. A negative standard lightning impulse voltage (1.2/50 μs) was applied. The experimental results revealed that a critical gap distance of the floating potential VG was required to support the dielectric strength of triple VGs in series. The distance was approximately 0.7 mm in this experiment. The critical distance of the floating potential VG can be determined by an intersection of the maximum electric field strength at cathode and the 100% BD electric field strength of the floating potential VG. This method can be used to estimate the critical distance of the floating potential VG in a high-voltage vacuum interrupter.

Prediction Method of the Breakdown Probability for Multiple Vacuum Gaps in Series Considering Dielectric Recovery under a Lightning Impulse Voltage

The objective of this article is to propose a novel prediction method of the breakdown (BD) probability for multiple vacuum gaps (VGs) in series considering their dielectric recovery under a lightning impulse voltage. Based on the experimental data of the BD probability for each single VG and the calculated voltage distribution of multiple VGs, the BD probability of multiple VGs in series could be calculated by the proposed prediction method. By dielectric tests under the lightning impulse voltage, we see that the calculated BD probability distributions fit well with the experimental results for double VGs and triple VGs in series. Under sphere–plane electrode VGs, the prediction error was approximately 15% in the whole range of BD probabilities. The errors of the 50% BD voltage were 11.4% and 12.9% for double VGs and triple VGs in series, respectively. Therefore, the reliability of this prediction method considering the dielectric recovery was validated. This prediction method could be used to estimate the dielectric strength of multibreak vacuum circuit breaker (VCB) and multiple floating shields inside high-voltage vacuum interrupters.

Comparative Study of the Properties of Cu-Cr-Mo System Electrical Contact Material by Sintering and Infiltration Methods

Contact materials in high-voltage vacuum interrupters require properties such as high conductivity, density and hardness to minimize arc heat damage. In this study, Cu–Cr–Mo alloy contact materials were examined for their usage as high-voltage contact materials. Ball milling was performed after analyzing the raw materials of the Cu, Cr and Mo powders. A green compact was produced using high pressure with a mixed powder. Subsequently, the composite was produced by sintering via the temperature and infiltration method according to the Cu content in the green compact. The composite sintering method produced a density of 8.55 g/cm3 (relative density 93%), a hardness of 217 HV and an electrical conductivity of 40.7% IACS at 1200 °C. The composite of 10 wt.% Cu produced by the Cu infiltration method exhibited a density of 8.7 g/cm3 (relative density 94%), hardness of 274 HV and electrical conductivity of 39 IACS% at 1300 °C. The measurements of the physical properties of our newly established method demonstrated a new possibility of using the Cu–Cr–Mo alloy as a contact material for high-voltage vacuum interrupters.

A novel approach for basic insulation-level (BIL) enhancement of vacuum interrupters

This article introduces a newly developed design method that may be utilized in modern high-voltage vacuum interrupter (VI) design. At first, a typical 24 kV vacuum chamber is modeled using finite-element method. Potential and electric field profiles are derived and analyzed in detail. To continue, the proposed approach which consists of twin metallic rings placed in the porcelain tubular insulator is added to the previous model and the new model is analyzed in three steps: short-, medium- and long-course scenarios. The achieved patterns illustrate the severe reduction in electric field value of the contacts' surface especially for long-course prototype (up to 74.2%). This phenomenon is discussed in detail. Considering the Fowler–Nordheim quantum tunneling equation; a reduction in electric field intensity brings to lower field emission current value which is the most important factor of breakdown during BIL tests. It is important to note that any reduction in electric field value results in decrease in micro-discharge value and microparticle movement, which are the additional reasons for vacuum insulator failure during high-voltage pulse insertion. This means that the inception voltage of the proposed VI can be increased so that higher BILs like 63 kV insulation high voltage requirements are achieved. The reduction rate of field emission current density is reduced to 4.9% of its initial value for or 120-mm course which expresses the effectiveness of this new approach.

Laser-induced plasma imaging for low-pressure detection.

A novel technique based on laser induced plasma imaging is proposed to measure residual pressure in sealed containers with transparent walls, e.g. high voltage vacuum interrupter in this paper. The images of plasma plumes induced on a copper target at pressure of ambient air between 10-2Pa and 105Pa were acquired at delay times of 200ns, 400ns, 600ns and 800ns. All the plasma images at specific pressures and delay times showed a good repeatability. It was found that ambient gas pressure significantly affects plasma shape, plasma integral intensities and expansion dynamics. A subsection characteristic method was proposed to extract pressure values from plasma images. The method employed three metrics for identification of high, intermediate and low pressures: the distance between the target and plume center, the integral intensity of the plume, and the lateral size of the plume, correspondingly. The accuracy of the method was estimated to be within 15% of nominal values in the entire pressure range between 10-2Pa and 105Pa. The pressure values can be easily extracted from plasma images in the whole pressure range, thus making laser induced plasma imaging a promising technique for gauge-free pressure detection.

Mechanism of impulse voltage breakdown in high voltage vacuum interrupters with long contact gap

The objective of this paper is to propose a breakdown mechanism of lightning impulse voltage in high voltage vacuum interrupters (VIs) with long contact gap by complementing the Cranberg "clump" hypothesis with an impulse voltage and a non-uniform field. The Cranberg "clump" hypothesis assumed that the vacuum breakdown was due to the loosely adhering microscopic particles under a DC voltage and a uniform field. The microscopic particles might be torn from an electrode surface at a critical voltage. We considered the microscopic particles located at the area with the maximum electric field had the highest possibility to be accelerated. Therefore, the transit process of the micro-particles to the opposing electrodes was under a non-uniform field distribution driven by an impulse voltage. The rise rate of the impulse voltage applied was also considered. As a result, it was found that the breakdown voltage of a vacuum gap depends upon a 0.76 power of the gap length for the plate-to-plate contacts. The diameter of the contacts was 60 mm. The contact radius of curvature was 6 mm. In the same conditions, our previous experimental results showed that the impulse breakdown voltage was in a range of 0.70 to 0.79 power of the contact gap. So the experimental results supported the Cranberg hypothesis in its extension to the impulse breakdown under non-uniform field in high-voltage VIs. Thereafter, this proposed breakdown mechanism is a complement to the Cranberg "clump" hypothesis in terms of impulse voltage breakdown under a non-uniform field in high voltage VIs.

Lightning impulse voltage breakdown characteristics of vacuum interrupters with contact gaps 10 to 50 mm

The objective of this paper is to understand the standard lightning impulse voltage breakdown characteristics of vacuum interrupters with contact gaps 10 to 50 mm and how contact parameters influence the breakdown characteristics. The investigated contact parameters include contact diameter 75 and 60 mm, contact surface roughness 1.6 and 3.2 μ m, and contact radius of curvature 6 and 2 mm. Therefore we designed four high-voltage vacuum interrupters in the experiments. The vacuum interrupters were put into a porcelain envelope with SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas as an external insulation of the vacuum interrupters. The contact gaps can be adjusted manually up to 50 mm. Positive polarity lightning impulse voltage (1.2/50 μs) was applied by an up-and-down method. Experimental results revealed the breakdown probability distributions followed Weibull distributions when the breakdown voltage saturated within the investigated contact gaps 10 to 50 mm. Within the contact gaps 10 to 50 mm, U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> of vacuum interrupter with contact radius of curvature 2 mm was higher than that of vacuum interrupter with contact radius of curvature 6 mm. And U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> of contact roughness 1.6 μm was close to that of contact roughness 3.2 μm. U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> of the contact diameter 60 mm was close to that of contact diameter 75 mm. And 50% breakdown voltage U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> depended on the contact gap d (10-50 mm) for four interrupters, can be expressed by an equation U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> =kd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</sup> , where a is a power exponent; k denotes a coefficient which can be determined by experiments. And under our experimental condition, power α lay in a range of 0.6-0.7 for the four vacuum interrupters. The breakdown phenomenon could be due to the micro-particles.

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.

A gravity heat pipe for high voltage vacuum interrupter

To enhance nominal current of high voltage vacuum circuit breakers (VCBs), a gravity heat pipe was proposed to replace stationary conducting rod of a high voltage vacuum interrupter. The heat pipe is composed of two coaxis tubes: the external tube is made of oxygen-free copper and the inner tube is made of stainless steel. The bottom end of the inner stainless steel tube is connected to the external copper tube by holes. Transient and static thermal performance of the heat pipe was measured, and the thermal resistance of it was compared with that of a solid copper rod with the same dimensions. Experimental results showed that thermal resistance of the heat pipe was about 1/3 of that of the copper rod, and it decreased slightly with the rising of the input heat flux. 3D thermal simulation on a 126 kV/2000 A single break VCB was done to compare the thermal performance between the proposed gravity heat pipe and the copper rod serving as the stationary conducting rod of the vacuum interrupter. Simulation results revealed that in the heat pipe case, the maximum temperature between contacts was 67 °C lower than that in the copper rod case.

Magnetism-driven anomalous surface alloying between Cu and Cr

Cu–Cr contact materials are widely used as medium- and high-voltage vacuum interrupters. The microstructure of these materials is critical in their performance: the finer structure they have, the better are their physical properties. A solid solution of Cu and Cr could significantly increase the performance of such contact materials. However, Cu and Cr are practically immiscible in the bulk phase. Based on first principles density functional theory we show here that the solubility of Cr in Cu is dramatically increased on Cu surfaces already at room temperature and Cu–Cr alloys are formed on both the Cu(111) and Cu(100) surfaces. We demonstrate that the origin of this phenomenon is the unique magnetic properties of Cr atoms near surfaces.

Critical Radius of Axial Magnetic-Field Contacts in Vacuum Interrupters

Vacuum circuit breakers (VCBs) are widely used to protect medium-voltage (MV) power distribution circuits. Since SF6 gas is specified as a global warming gas, VCBs are stepping into a higher voltage sector to protect power transmission circuits. Axial magnetic field (AMF) contacts are widely used in vacuum interrupters. In this paper, we propose a concept of critical radius of AMF contacts. When coil width and coil height are fixed, the axial magnetic flux density increases first with increasing contact diameter. Then, it reaches a maximum value. Thereafter, the axial magnetic flux density decreases. The contact radius corresponding to the maximum axial magnetic flux density is critical radius. The concept of critical radius is validated by coil-type AMF contacts and slot-type AMF contacts in MV vacuum interrupters with finite-element analysis. Critical radius is only related to contact geometry parameters and the current has no influence on critical radius. Critical radius increases with increasing contact gap, coil width, coil height, and thickness of the contact plate. In high-voltage AMF vacuum interrupters, axial magnetic flux density per kiloampere increases with increasing contact diameter since the critical radius is typically high with a high contact gap and it is in the rising branch. In an MV AMF vacuum interrupter, interrupting capacity could increase with an increase of the contact diameter with a different rising rate before and after the critical radius. This is expected to be experimentally validated.

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.

A utility optimization method of a high voltage vacuum interrupter design

In this paper, a new method of electric field design of high voltage vacuum interrupters is proposed. According to the multi-gap insulation effect and the vulnerable breakdown spots theory, the symmetrical voltage shields are proved to be effective. So the initial model of a high voltage vacuum interrupter is designed. Next with finite element methods and optimization theory, a mathematical model of electric field intensity in interrupters is given. What's more, by optimizing this model with finite element software, a more symmetrical electric field in vacuum interrupters is obtained and its peak value appear as in the second auxiliary gaps (the two gaps between the center floating shield and the symmetrical voltage shields). The result shows that with this method, the vacuum interrupters can withstand higher static breakdown.

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

The Discharge Development and Arc Modes in Vacuum at A Long Gap Distance in Vacuum Interrupters

The influence of an arc current on the discharge development and thearc modes of a single coil type axial magnetic field (AMF) electrodewere investigated by a high-speed charge couple device (CCD) videocamera in a long gap distance of 40 mm. The distribution of theaxial magnetic field of the single coil type AMF electrode wascomputed. By computational results, the single coil type AMFelectrode could generate higher axial magnetic flux density than theslot type AMF electrode. It was found that the single coil type AMFelectrode could perform better than the slot type AMF electrode withthe same designing parameters. And the development of the arc modesexperienced diffuse mode, constricted but unstable mode, andconstricted and stable mode with the amplitude of the arc currentincreasing. The correlation between the vacuum arc and the noisecomponents of arc voltage was investigated too. The interruptioncapability could be known in a practical commercial vacuuminterrupter by the test results in a demountable vacuum interrupter(DVC) with a electrode diameter of 50 mm and a gap distance of40 mm.The test results could provide reference to design the highvoltage vacuum interrupter adopting the single coil type AMFelectrode.

Research on Vacuum Arc Characteristics of a New Electrode Structure Applied in High Voltage Vacuum Interrupter

In this paper the vacuum arc behaviors of the axial magnetic field (AMF) electrode with single coil structure were investigated at gap distance 10 mm and 40 mm respectively. And the axial magnetic field distribution was computed at 10 mm and 40 mm. A high-speed charge couple device (CCD) video camera was used as a major diagnostics to investigate the arc behaviors. At gap distance 10 mm, the vacuum arc maintained diffuse. With the gap distance increasing from 10 mm to 40 mm, the vacuum arc experienced constricted arc modes only in short time at beginning. In most of time, the vacuum arc kept diffuse. The test results proved that the AMF electrode with single coil structure was feasible to be applied in high voltage vacuum interrupter.

Influence of Gap Distance on Vacuum Arc Characteristics of Cup Type AMF Electrode in Vacuum Interrupters

The greenhouse effect of SF6 is a great concern today. The development of high voltage vacuum circuit breakers becomes more important. The vacuum circuit breaker has minimum pollution to the environment. The vacuum interrupter is the key part of a vacuum circuit breaker. The interrupting characteristics in vacuum and arc-controlling technique are the main problems to be solved for a longer gap distance in developing high voltage vacuum interrupters. To understand the vacuum arc characteristics and provide effective technique to control vacuum arc in a long gap distance, the arc mode transition of a cup-type axial magnetic field electrode is observed by a high-speed charge coupled device (CCD) video camera under different gap distances while the arc voltage and arc current are recorded. The controlling ability of the axial magnetic field on vacuum arc obviously decreases when the gap distance is longer than 40 mm. The noise components and mean value of the arc voltage significantly increase. The effective method for controlling the vacuum arc characteristics is provided by long gap distances based on the test results. The test results can be used as a reference to develop high voltage and large capacity vacuum interrupters.