Conventional applications of vacuum interrupters cover a broad operating frequency range from 60 Hz down to 16.7 Hz, as typically found in power networks and railway electrical systems. With the increasing integration of alternative power sources and the growing complexity of decentralized power networks, new requirements are emerging for vacuum interrupters. Under these evolving grid conditions, fault events may occur at significantly lower frequencies than in traditional systems. Such low-frequency operation can lead to extended arcing times, higher transferred charge, and increased thermal stress on the interrupting contacts. To address these challenges, the present work investigates the arc behavior at frequencies between 2 and 4 Hz and current levels ranging from 70 to 2000 A, using a combination of optical diagnostics and electrical measurements. In addition to high-current experiments, several synthetic test series incorporating transient recovery voltages (TRVs) were conducted to evaluate interruption performance under realistic fault conditions. Furthermore, key aspects of current interruption, such as transferred charge, thermal loading, and contact erosion, were analyzed through numerical simulations and compared with established data obtained at conventional power frequencies. Both the experimental results and the simulation studies demonstrate that vacuum switching arcs exhibit excellent stability and interruption characteristics, confirming that vacuum remains a highly suitable medium for low-frequency current interruption in future power system applications.

As a consequence of sulfur hexafluoride’s global warming potential, the external insulation of vacuum interrupters (VIs) is an important area of research. The VI is an insulation system with a cylindrical structure, with vacuum as the internal and air as the external insulation medium. This article intends to discuss the question of how the flashover phenomena on a VI can be characterized. Continuing on previous works, VI specimens with variations in metal vapor condensation shields are simulated and tested with lightning impulse voltage (LIV) using the up-and-down method. External flashovers are tracked using a high-speed camera and a supplementary mirror arrangement. The flashover images show different discharge paths and collateral discharges. Based on these discharge paths, flashover patterns are created and classified into categories of different flashover phenomena. Based on the 50% breakdown voltage, the characteristic voltage curves at voltage collapse and the flashover pattern, various flashover phenomena are described and discussed.

Vacuum circuit breakers (VCBs) are favored in the medium voltage range due to their gas- and $\mathbf{S F}_{6}$ - free, environmentally friendly operation and relatively low maintenance costs compared to other interrupters. To increase the operational voltage level, a common approach is to use a single or double break device. A classical solution for symmetrizing the voltage distribution over a single contact gap vacuum interrupter (VI) is to use a floating one-part or multipart shielding solution, even on floating potential, along with external grading capacitors. Similarly, for a double contact gap vacuum interrupter, a floating one-part or multi-part shielding solution is given, even on floating potential, and external grading capacitors can be used to balance the voltage distribution. This approach enhances the symmetry of the voltage distribution across the vacuum interrupter and the floating shielding [1]. To enhance overall dielectric performance, this paper presents the integration of additional field grading and shielding electrodes within single and double-breaking vacuum interrupters to symmetrize the voltage distribution [2, 3]. First, the shielding behaviour of the arrangement is analysed as such and “free-standing” and using a grounded flat metal electrode placed at 50 to 100 mm to disturb the symmetric field distribution [4, 5, 6]. Second, the symmetrizing behavior is analyzed through detailed electric field simulations of the grading components within the vacuum interrupter, both before and after implementing the novel design. The basic modular design of the novel vacuum interrupter arrangement is presented and investigated in detail using the EField simulation method. This paper explains how the design improves voltage distribution along the vacuum interrupter and maintains robustness even when an earthed environment is placed close to the interrupter.

Current interruption tests were conducted up to 31.5 kA for frequencies of 50 Hz and 35 Hz. Thereby, two contact design were used: transverse magnetic field (TMF) and axial magnetic field (AMF). The key focus for TMF contacts involved the analysis of arc rotation and operational arc modes, while the study of AMF contacts concentrated on the formation of non-constricted arcs at similar higher gaps. For these investigations 8 test series for TMF and 3 for AMF-conducted to examine the influence of larger gaps, material and current. The results show, that both contact design are feasible for current interruption of gaps up to $\mathbf{4 5 ~ m m}$ and current up to $\mathbf{3 1. 5}$ kA. Thereby, differences in the contact design were found in the analysis of the charge density of anode surfaces

For most applications in medium voltage switchgears, vacuum interrupters are used. The switching arc during interruption processes in vacuum appearing at the mechanical contact separation is evaporated from the contact electrodes. Near the current zero crossing the arc gets instable due to decreasing energy input and can chop abruptly [1], [2]. This can be critical especially at low currents in inductive load circuits: The high current gradient induces transient overvoltages at the load, which can exceed the insulation strength and cause damages [3]. Also, secondary effects like disturbance emissions might affect safety-relevant components like protection relays in terms of electromagnetic compatibility (EMC). The arc chopping is characterized by the chopping current Ich, which represents the instantaneous value of the power frequency current before its interruption. To reduce this current two measures are considered in more detail. By a proper choice of the switching contact materials the arc should be maintained until current zero crossing. For the material properties this means a lowered evaporation temperature of the contact material. Optimized copper-based contact materials with additives of carbide and carbon show chopping values between $I_{\mathrm{ch}}=0.5 \mathrm{~A}$ and $I_{\mathrm{ch}}=3 \mathrm{~A}$. In line with [4]–[7], this work also examines the influence of superimposed (externally generated) axial magnetic fields on the arc chopping behavior. Measurements for the investigated copper-based materials indicate no optimization (reduction of $\left.I_{\mathrm{ch}}\right)$ due to the additional magnetic field. For a better classification of the chopping behavior a statistical evaluation is performed. This is necessary since $I_{c h}$ shows significant scattering even at constant test conditions. For the statistical analysis each series of measurements under constant flux density is performed with a predefined number of measurements (interruption operations). The median chopping currents and outliers of a vacuum chamber with superimposed magnetic field are evaluated. Additionally, for switching operations without applied magnetic field, a probability distribution of all $I_{\mathrm{ch}}$ values is considered.

The need to protect the climate is enshrined in a number of international agreements and national targets. This requires insulation systems in energy technology to be reconsidered. The replacement of previous insulation materials, such as SF6, with climate-neutral insulation materials requires a lower field strength than before. The brazing seams of the climate-neutral vacuum circuit breaker are critical areas for the external insulation system. In order to minimise the local field strength an industrially manufactured vacuum interrupter is equipped with field control elements on the outside. Different variants of field control elements were investigated with lightning impulse voltage to determine the statistical withstand voltage. The results show, that field control elements increase the withstand voltage of vacuum interrupter up to 26 % and so effectively reduce the maximum electric field strength. There is an indication that the flashover process can be influenced by the design of the field control elements. Due to the effective reduction of the field strength the use of climate-neutral insulation materials is feasible.

As a consequence of sulphur hexafluorides global warming potential the external insulation of switchgear is an important area of research. This paper analyses the influence of internal shields in vacuum interrupters on the external dielectric. For this purpose, vacuum interrupters with variation of metal vapour condensation shield are simulated and tested with lightning impulse voltage. The statistical withstand voltage shows a reduction of up to $\mathbf{1 0} \boldsymbol{\%}$ with positive polarity and an increase of up to $14 \%$ with negative polarity while the flashover path does not change. The maximum electric field strength in the triple points seems to be the most important factor for the achievable withstand voltage by variation of internal shield.

This study evaluates contact erosion in vacuum circuit breakers (VCBs) using two contact designs: Axial Magnetic Field (AMF) and Transversal Magnetic Field (TMF). Six test series were conducted under sinusoidal currents up to 45 kArms and contact separations of 45 mm. Results reveal distinct charge distribution characteristics; AMF contacts generated diffuse arcs, leading to concentrated erosion in the middle of the contact surfaces, as confirmed by charge evaluation, microscopy images and high-speed camera (HSC) observation. In contrast, TMF contacts produced rotating, constricted arcs, resulting in a more uniform erosion distribution. Notably, both designs demonstrated resilience to varying gaps, indicating their suitability for higher voltage applications. The charge estimation technique utilized served as a performance indicator, allowing for comparative analysis of different contact geometries.

Reactive power compensation in power systems is crucial for improving the grid's power factor, reducing line losses, and enhancing the quality of electric energy. Shunt capacitor compensation is widely used in medium-voltage power systems. Typically, the rated current of capacitor compensation devices does not exceed 1000A. Due to daily switching, the opening and closing operations of the compensation circuit are frequent. Medium-voltage power systems commonly use vacuum circuit breakers to switch capacitor banks. During capacitive current switching, the closing inrush current can cause the vacuum interrupter contacts to melt and weld, increasing the likelihood of re-strike. The performance verification process for circuit breakers handling capacitive current switching is outlined in IEC 62271-100, which requires a C2 level of 104 operations. However, vacuum circuit breakers in capacitor bank compensation circuits often exceed this number. The new "K-type" vacuum interrupter was developed for frequent switching of capacitor banks. These interrupter contacts have higher resistance to fusion welding, and the closing inrush current has less impact on the contact surface. Vacuum circuit breakers with "K-type" interrupters have successfully passed three rounds of back-to-back capacitor bank switching tests of class C2 (40.5kV, 1250A), totaling 264 operations, in accordance with IEC 62271-100. This paper details the cumulative frequency of the pre-ignition electric field strength and the form and energy distribution of the inrush current during testing. After 264 tests, the insulation performance of the "K-type" vacuum interrupter meets the relevant GB/IEC standards, and the surface roughness and micro-welding of the contacts are significantly improved.

The electric strength of vacuum interrupters is an important field of research with the aim of replacing environmentally harmful insulating gases in external insulation. When improving insulation systems, particular attention is paid to the triple points where three different materials are connected. As device under test, an industrially manufactured vacuum interrupter is equipped with a field control ring on the outside, which is positioned at the different triple points. The experimental investigations are carried out with positive and negative lightning impulse voltage using the extended up-and-down method to determine statistical withstand voltage. The control of triple points with external field control rings increases the electric strength of vacuum interrupters. The statistical withstand voltage of the vacuum interrupter can be increased up to 18% with a field control ring at right position. An explanation is proposed for the change in the flashover structure caused by the field control ring.

During opening and interruption operations in vacuum chambers, an arc is created during mechanical contact separation, consisting of vaporized contact material. With decreasing current, it becomes an unstable situation, and current can chop before the natural current zero crossing. This transient process, with a high current gradient, can cause high overvoltage in the network, particularly at inductive loads due to resonances. This may result in irreversible damages to the insulation of connected equipment, such as transformers or motors, as well as electromagnetic compatibility (EMC) issues. Switching contact materials for applications in contactors, such as tungsten carbide silver (WC-Ag), show chopping current values ranging from 0.7 to 2.5 A. To reduce chopping currents, different approaches are needed. Specifically, a proper selection of contact materials can minimize chopping currents or, at the very least, shift them closer to the zero crossing. Easily emitting contact materials at low temperatures are favorable. Additional tests cover the superimposition of externally applied magnetic fields during the arc burning phase. This research paper analyzes both the combination of different known and optimized contact materials and the superimposition of axial magnetic fields during interruption operations. Using materials comparable to WC-Ag reduces the chopping current by about 52% without a superimposed magnetic field. Other contact materials show field-dependent characteristics, such as copper chromium (Cu-Cr). Regarding interruption speed, an improvement in chopping behavior is observed with slower movements. Finally, the focus is set on the aging behavior. More than 10 000 switching opening operations are performed in this work, and, with the exception of one material combination, no aging can be observed.

Switching opening operations in vacuum are characterized by an arc, which occurs during mechanical contact separation and is created from vaporized contact material. At low currents it is unstable and can chop before the natural current zero crossing. The result of this transient process is a high current gradient, which can lead to high overvoltage’s e.g. at inductive loads due to resonance phenomena. Damages to the equipment and electromagnetic compatibility (EMC) issues can occur. Contact materials for contactor applications like tungsten carbide silver (WCAg) show a chopping current in the range of 0.7… 2.5 A. Circuit breakers must interrupt high short circuit currents without damaging the contact surface by material erosion. Therefore, zero chopping is not the focus. In circuit breakers the chopping current is between 4 and 6 A with contacts made of copper chromium (CuCr). Different approaches can be used to improve the chopping behavior. The choice of the used contact materials can reduce current chopping or shift it closer to the zero crossing. Lower chopping values with the reduction of transient overvoltage’s at inductive loads are important especially for contactor applications. Therefore, an emission of the contact material at low temperatures is necessary. Another approach is the superposition of an externally applied axial magnetic field during the switching operation. Some publications indicate an influence on the chopping behavior. Thirdly, the switching speed for the selected materials is investigated in more detail. This paper determines both, different contact materials and superimposed axial magnetic fields regarding their chopping behavior. Contact materials comparable to WCAg show a 52% reduction of the chopping current without a superimposed magnetic field. Other materials show a behavior like CuCr. The superimposed magnetic flux density (up to B=200mT) provides higher values for the chopping current with a minimum at approx. B=80mT.

Vacuum interrupters (VI) are primarily used for electrical power applications at frequencies of 50/60Hz. However, other electrical power applications exist at lower frequencies. One key application is in rail power systems that operate at 25 and 16. 7Hz. Vacuum interrupters have successfully performed in these applications for many years. Recently, green energy applications can produce temporary fault conditions with even lower frequencies, such as in wind turbine, pumped storage, solar power DC to AC converters, and shipboard applications. The challenge in low frequency applications stem from the very long arcing times and high transferred charge for a given current level. This paper presents the calculated theoretical boundary of the interruption performance down to frequencies of 0.5 to 2Hz and compares it to the cases at 16.7 and 50Hz. In addition, experiments were performed concerning the arc impact on the VI including metal vapor deposit on the ceramic, and heat build-up in the contacts and shields surrounding the arc chamber. The arc erosion rate of the contacts was also calculated for short-circuit conditions from 10.40kA at 50Hz, and at frequencies of 0.5 to 5Hz with currents of several hundred amperes. Comparison to certain certification test conditions is made, such as the delayed current zero (CZ) and very high DC current offset tests in the generator breaker standard, that are effectively tests at lower frequencies.

This paper outlines different test methods for investigating electrical strength with lightning impulse voltage. The test methods are compared and contrasts for application to vacuum interrupters. In addition to the procedures for determining the withstand voltage according to standards, the up-and-down method for determining statistical withstand voltage and 50 % breakdown voltage as well as the step-up method are described. For determination of breakdown probability distributions, a classic method and the new always breakdown method are explained. The minimization of the influence of the conditioning effect on the results of the different methods is discussed. Characteristic parameters for the test methods used to generate the breakdown probability distribution are indicated. Thus, the basics of an evaluation procedure for test methods for electric strength using lightning impulse voltage are presented.

Low current vacuum arcs have the natural tendency to interrupt currents before the natural current zero of a system, which is known as current chopping. This paper presents results of investigations comparing the chopping current performance of isotropic and anisotropic WCCu contacts for two compositions (WCCu 60 wt.% and WCCu 79 wt.%). The goal is to show the influence of the contact microstructure, and the role of the associated increase in the electrical and thermal conductivities of the anisotropic material on the chopping current. The results indicate an improved median chopping current value for the anisotropic compositions compared to the isotropic ones. It is lower of about 1A for WCCu 60 wt.% (5.1A vs 6.0 A), while is it is only slightly lower for WCCu 79 wt.% (9.0 A vs 9.4 A). The SEM investigations of the top surface structure do not show significant changes after a few arcing operations at 75A peak current between the two types of microstructures. It is assumed that the current flow localized below the contact surface is affected by the microstructure in a way that favors local heating at the last cathode spots and help to sustain the arc stability.

The vacuum interrupters (VI) are an environmentally friendly alternative to circuit breakers based on sulphur hexafluoride (SF6). The aim is to replace the SF6 interrupters. During the interruption process of a VI a plasma consisting of metal vapour occurs. This plasma must be extinguished as fast as possible to recover the dielectric strength. Therefore, it is necessary to understand the plasma behaviour. The plasma can be described through the voltages and currents during the breaking process. In this paper an analysis of the post-arc current is carried out.The aim is to describe the phenomenon during the current zero crossing (CZC) like chopping current. Limits and appearances will be described by the current and voltage curves at CZC. Thereby, the circuit elements, which generate a circuit response will consider and with a circuit model will verify the plasma behaviour by the current curves. The measurements were taken in a synthetic test field, a Weil-Dobke circuit. High short-circuit current up to 15 kA rms, 50 Hz and transient recovery voltages (TRV) of 60 kV peak were carried out.

The development and testing of vacuum switches with long gap distances or series configurations is mostly focused on AMF-contacts. The advantages of transversal magnetic field (TMF)-contacts are currently confined to medium voltage switchgear. These contacts are inexpensive in production and show lesser contact resistance in closed position. The goal of the contact geometry is the distribution of energy over the contact surface. The derived question is whether this task can be performed at higher distance, where the magnetic field is weaker.This paper tests VIs equipped with TMF-contacts under short-circuit currents and contact gaps above 20 mm. The goal is the analysis of the TMF-effect and the derived energy distribution during the high current phase. In the experimental setup, a programmable servo drive is used to achieve gaps up to 31 mm during 50 Hz interruption at current zero. For even larger gaps, the current frequency is lower to 35 Hz to reach 47 mm at current zero.An image detection in combination with electrical data is used to investigate the high current phase under increasing gaps. Evaluating arc voltage and arc movement in form of speed and rotations, the TMF-contact is not significant affect by increasing gaps. The contact geometry could be feasible for high voltage application.

Currently the detection of an internal arc inside a switchgear is done by means of an optical arc flash sensor. This triggers an external power supplied electronic device with charged capacitor to actuate the active primary arc mitigation device. In several cases the arc sensing is linked with the current threshold value in addition. A new and innovative method to detect, trigger and power the arc mitigation device by means of solar-cells which are energized by the arc flash only, has been worked out. There is no need to have the detection of both current and light together because the arc flash itself is used to generate enough power to tigger the active arc mitigation device. The new method using solar-cell triggers and powers the mitigation device even within less than 4…5ms. This paper presents an innovative way how to detect the internal arc in low– and medium– voltage and to trigger and actuate the active arc mitigation device.