Vacuum Contactors Research Articles

Calculation of the winding data of the on and off coils of a bistable polarized electromagnet for a vacuum medium voltage contactor

Medium voltage vacuum contactors consist of switching and drive modules. When developing or improving the designs of contactors, the switching module must meet the requirements set forth by their manufacturers. In accordance with these requirements, a drive module is being developed, which consists of a mechanical system and an electromagnet. The operation of the mechanical system of the contactor depends on correctly selected contact springs, and the operation of the electromagnet depends on traction forces during switching operations. The design of a vacuum contactor with a bistable polarized electromagnet with two ON and OFF coils is considered in the article. The counteracting characteristic of the mechanical system of the contactor is constructed and the forces acting on the electromagnet in the ON and OFF positions of the contactor are determined. The FEMM model of a bistable polarized electromagnet was developed and the minimum MMF value of the ON and OFF windings was determined. The resulting traction characteristic of a bistable polarized electromagnet is constructed at the minimum MMF value of the ON and OFF winding sand the working gap. It was determined that when performing the switching operation and using the ON and OFF winding at the same time, it was possible to reduce the MMF of the electromagnet operation. The winding data of the ON and OFF coils were calculated at different values of the nominal diameter of the wire and the voltage of the power supply network, and, in accordance with this, the minimum value of the MMF of the windings was determined

EXPERIMENTAL STUDY OF OPTIMAL POWER CONSUMPTION CONTROL DEVICE FOR THE ELECTROMAGNETIC DRIVE OF A CONTACTOR

One of the priority scientific and technological directions of development of the Russian Federation in the field of energy, is energy and resource saving. In this regard, to ensure the competitiveness of the electrical products market, the issue of research and development of low-voltage electromagnetic switching equipment with low values ​​of power consumption and weight and size indicators is relevant. The purpose of the study is to reduce the power consumption of the electromagnetic drive of the contactor in the holding mode and to increase the electrical wear resistance of the main contacts of the contactor. Materials and methods. The basis of the study was the analyzed existing solutions for the schemes and algorithms for controlling the electromagnetic drive in various sources of information. The electromagnetic drive of the vacuum contactor of the КВ1-160 series was adopted as the initial object of the study. Main parameters of the electromagnetic drive of the contactor КВ1-160: nominal control voltage of 220 V DC, winding resistance values ​​preliminarily measured by the universal voltmeter АВМ-4306 and the testing device РЕТОМ-21 are 62 Ohm, the power consumption of the contactor electromagnet with a standard unit in the holding mode is 15.2 W. The research used the methods of analysis and synthesis, measurement, planning and conducting an experiment. Research results. The paper presents the results of the development and study of a control device for electromagnetic drives, which ensures a decrease in the power consumption of the electromagnetic drive in the holding mode, as well as an increase in their electrical wear resistance. A control circuit for a single-winding electromagnetic drive is proposed. A brief description of the operation of the control device prototype based on a microcontroller is given. Experimental studies of the control device prototype are carried out using a three-stage electromagnetic drive control algorithm. Conclusions. The results of the experimental studies showed the operability of the prototype sample of the contactor electromagnetic drive control device according to the proposed circuit. A reduction in the power consumption of the EMF in the holding mode was achieved, which amounted to 25 W. A slight (approximately 10%) reduction in the vibration time of the main contacts was ensured, which will lead to an increase in their electrical wear resistance.

Fault Diagnosis Method for Vacuum Contactor Based on Time-Frequency Graph Optimization Technique and ShuffleNetV2.

This paper presents a fault diagnosis method for a vacuum contactor using the generalized Stockwell transform (GST) of vibration signals. The objective is to solve the problem of low diagnostic performance efficiency caused by the inadequate feature extraction capability and the redundant pixels in the graph background. The proposed method is based on the time-frequency graph optimization technique and ShuffleNetV2 network. Firstly, vibration signals in different states are collected and converted into GST time-frequency graphs. Secondly, multi-resolution GST time-frequency graphs are generated to cover signal characteristics in all frequency bands by adjusting the GST Gaussian window width factor λ. The OTSU algorithm is then combined to crop the energy concentration area, and the size of these time-frequency graphs is optimized by 68.86%. Finally, considering the advantages of the channel split and channel shuffle methods, the ShuffleNetV2 network is adopted to improve the feature learning ability and identify fault categories. In this paper, the CKJ5-400/1140 vacuum contactor is taken as the test object. The fault recognition accuracy reaches 99.74%, and the single iteration time of model training is reduced by 19.42%.

Analysis of designs of drive mechanisms of medium voltage vacuum contactors

One of the main elements of medium voltage vacuum contactors is the drive mechanism, which includes an electromagnet. In existing models of contactors, two types of electromagnets are used: monostable non-polarized electromagnets with a return spring or bistable polarized without a return spring. It was found that the use of polarized electromagnets in combination with a microprocessor control system expands the functionality of the contactor and makes it possible to reduce the energy consumption of the electromagnets, their overall dimensions and weight, while achieving significant armature holding forces. The designs of polarized electromagnets, which were developed at the Department of Electrical Apparatus in recent years, are considered. Their shortcomings were identified and a new design of a bistable polarized electromagnet was proposed, a computer model of the contactor developed in the KOMPAS-3D package was built. The counteracting characteristic of the mechanical system of the contactor, which is brought to the axis of the electromagnet and the stroke of the armature, is constructed, the forces that must be created by the electromagnet in the on and off position for reliable operation are determined. The FEMM model of the experimental sample of a bistable polarized electromagnet was developed and the calculation was carried out in the on and off positions. The possibility of using a new design of an electromagnet in a medium-voltage vacuum contactor has been confirmed.

±10 kV DC Vacuum Switch-Fuse Composite Apparatus for Distribution Grid

DC distribution grid is developing fast with the renewable energy industry. For the DC power grid, the DC circuit breakers protect the customers from the short circuit faults but they can't meet all the demands. For those power systems with little short fault probability, this paper provides a potential ±10kV DC composite apparatus, a DC electric fuse parallels with a vacuum switch, an external transverse magnetic field (ETMF) is generated to enlarge the vacuum arc voltage and help the current to transfer. Normally the vacuum switch conducts the rated and overload current, and the short-circuit current can be transferred by the vacuum arc to the fuse which interrupts the current. The ETMF powered by a 2 mF capacitor is more than 200 mT. The electric fuse's design process was supported by finite element simulation to ensure the fuse can interrupt a 5 kA fault current within 5 ms. The experimental results show the DC composite apparatus with a load switch can interrupt 0∼15 kA in 5ms. The interrupting process has been analyzed to understand the characteristics of the breaker, and the vacuum contacts' erosion may cause the interrupting failure. This research enlarged the electric fuse's range of application.

Study of switching overvoltages in electrical networks up to 1000 V

The aim was to study the effect of switching modes on the power of supply transformers in electrical networks up to 1000 V on the multiplicity of switching overvoltages, as well as to develop recommendations for their reduction. The study was carried out during switching of supply transformers in networks up to 1000 V. Vacuum contactors were used to study overvoltages arising during switching of supply transformers. Overvoltages were recorded using an RDN-1000 active divider and a Tektronix TDS2024B digital oscilloscope. The RC circuit capacitance was measured by a Mastech MY6243 digital LC-meter. To limit switching overvoltages, RC quenchers based on RC circuits were used, reducing not only the switching pulse amplitude, but also the rate of the switching pulse voltage rise. In addition, RC quenchers lack fading zones under high-frequency switching pulses. The capacitance of the primary winding of the transformers under study was measured. An increase in the transformer power was found to lead to a decrease in the multiplicity of switching overvoltages, when the transformer is disconnected from the mains. Under a 1.5-fold increase in the power of the transformer, its inductance and wave impedance decreases. As a result, when the same capacitance is connected to the transformer terminals, the wave resistance in more powerful transformers will be reduced to a larger extent (by 3 to 6 times), thus providing a more effective overvoltage limitation. The conducted experimental studies confirmed the effectiveness of RC circuits in limiting switching overvoltages.

Electrical Life of Vacuum Interrupters for Load Current Switching

While the short-circuit current of vacuum interrupters (VIs) is a key performance parameter, very high current operations rarely occur in actual applications. In contrast, switching load and/or capacitive currents comprise virtually all the practical operations. Load current switching requires a low contact erosion and low metal vapor generation of the arc to achieve a long electrical life and is achieved by contacts in vacuum. However, the excellent performance of contacts in vacuum makes the testing and determination of the ultimate electrical life at load currents challenging. Tests on Cu–Cr and Cu–W contacts in VIs were performed at 2500–2700 A rms with 20 000–30 000 switching operations. The VIs with both types of contacts retained their dielectric strength, contact shape and composition, and low contact resistance. Even after arcing operations with total transferred charges >200 kA <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> s per interrupter, the contacts could continue providing good dielectric and switching performance with low resistance. Contact erosion was minimal and of limited practical significance. These results demonstrate the very long electrical life of VIs when the vacuum arc is naturally diffuse.

TRIEX-II: an experimental facility for the characterization of the tritium extraction unit of the WCLL blanket of ITER and DEMO fusion reactors

The experimental qualification of the tritium extraction unit (TEU) from the LiPb eutectic alloy (15.7 at. % Li), the breeder material of the water-cooled lithium–lead breeding blanket concept, is one of the fundamental items for the demonstration of tritium balance sustainability for ITER and DEMO fusion reactors. Several technologies have been proposed as TEU, but the selection of the reference technology can be carried out only after the experimental measurement of the tritium extraction efficiency. For this purpose, a dedicated facility, called TRIEX-II, was designed and installed at ENEA Brasimone Research Centre, Italy. The facility is able to qualify gas–liquid contactor (GLC), permeator against vacuum and liquid-vacuum contactor technologies at different temperatures, lithium–lead mass flow rates and hydrogen isotopes concentrations. In TRIEX-II, the hydrogen or deuterium, used to simulate tritium, are solubilised inside the LiPb with a dedicated saturator and are then extracted from the liquid metal in the GLC mock-up, which uses pure helium or a mixture constituted by helium and hydrogen as stripping gas and works in the temperature range between 300 and 500 °C.

Development of new analytical tools for tritium transport modelling

Tritium technologies, in particular tritium extraction from lithium-lead (LiPb, 15.7 at. % Li) and tritium concentration measurement in the eutectic alloy, are among the most challenging aspects of the R&D activities envisaged for the development of ITER and the European DEMO reactor. For instance, to efficiently design the systems devoted to the extraction of tritium, such as Gas-Liquid Contactors (GLC), Permeators Against Vacuum (PAV) or Liquid-Vacuum Contactor (LVC), theoretical models for the evaluation of the permeation flux are strictly necessary. In general, the same needs arise for the description of tritium permeators, which can find their application as Hydrogen isotopes Permeation Sensors (HPS) for the measurement hydrogen/tritium solubilized in the LiPb of either the Test Blanket Systems (TBS) or the Breeding Blanket. In this paper, new mathematical tools to describe the different permeation regimes both in the gas phase and in the presence of hydrogen isotopes monoatomically dissolved in a liquid phase, thus substantiating the theoretical background of hydrogen isotopes transport modelling throughout a membrane, is presented. For the sake of completeness, theoretical models in case of absence of a membrane (LVC) are also reported.

Electromagnet with magnetic memory for controlling vacuum contactors for rated currents of 160, 250, 400 A

The results of the development of a universal control circuit for a triggering polarized electromagnet for a low voltage vacuum contactor are presented. The circuit is implemented in the form of a printed wiring block and is unified with an element base with a control circuit for the KV2-160, KV2-250 vacuum contactors commercially produced by the domestic industry. The developed design of an electromagnetic drive with magnetic memory based on high-coercive permanent magnets is described. The working cycle of an electromagnet with a ferromagnetic shunt for the implementation of a manual return unit for the purpose of its use in emergency or necessary technological modes is considered. A block for manual return of contacts of a vacuum contactor using an eccentric transmission has been developed and implemented, which makes it possible to significantly reduce the effort of manual operation when returning the shunt to its original position for the operation of the contactor in normal mode. The classical graphical-analytical method for calculating magnetic circuits with permanent magnets has been modernized. The fundamentals of the modernized method for calculating magnetic circuits with permanent magnets are considered. The positive results of approbation of the developed calculation methods, which were implemented in the development of a vacuum contactor with magnetic memory and the function of manual return of the electromagnet armature and opening of the main contacts for the serial production of contactors, are noted.

A multiphysics model of processes in electromagnets and actuators of vacuum switching devices taking into ac-count contact interaction of structural elements

The purpose of the work is to improve mathematical models and algorithms of computer modeling of multiphysics processes in electromagnets and actuators of vacuum switching devices by taking into account the contact interaction of structural elements when changing their stress-strain state. In the design of modern vacuum circuit breakers and contactors, there is a significant use of electromagnetic actuators based on high-coercive hard magnetic rare earth composite materials NdFeB and SmCo. The most promising for use as drives of circuit breakers and contactors are polarized electromagnets based on the use of these high-coercive permanent magnets. However, the existing serial designs of electromagnets and actuators need to be significantly improved in order to increase reliability and service life, reduce weight and cost, further reduce energy consumption, improve the manufacturability of the mass production process. Computer simulation is proposed to be performed by the Finite Element Method in 2D formulation using commercial software products and/or software created directly for these investigations. One of the priority areas for improving mathematical models and algorithms for computer modeling of processes in the mechanical circuit of vacuum switching devices of medium and high voltage is to take into account the contact interaction of the structural elements of the devices under consideration. The next step, thanks to the use of an advanced mathematical model, is to perform a set of computational research and based on the obtained numerical results to develop recommendations aimed at creating designs of electromagnets and actuators that would meet world standards and be competitive in the world market.

Vacuum contactor operation with parallel connection of independent consumers

This work presents a model of a transformer substation with parallel connection of independent consumers via vacuum switches. Several options of an electric arc model are considered upon switching off a vacuum switch such as: KEMA model and “black box” model. Modern computer models of vacuum switches were analyzed. Since the model data were not suitable for the conditions of the experiment, a simulation computer model was developed that reflects the specifics of the operation of the substation and of the transition process upon disconnection of one or several vacuum switches. The results of the developed methodology of analyzing transition processes were verified. To check the results of computer simulation, an experimental model was constructed, it consisted of: an electric load (inductive nature), a power supply, two vacuum switches, and a measuring circuit. The circuit is switched on and off using a pneumatic system controlled by a microcontroller. The primary purpose of the work is to check mutual influence of vacuum switches upon parallel disconnection, since there may be a restrike caused by effects of switching overvoltage between neighboring switches upon irregular disconnection. The effects of a transition process in one switch on the total current of the entire system were identified. A stand for a projected trial was demonstrated as well.

2D nano-materials beyond graphene: from synthesis to tribological studies

Continuously increasing global population and, therefore, energy consumption as well as diminishing resources combined with environmental aspects such as global warming ask for more efficient, sustainable and reliable processes/applications of mechanically moving parts. Especially under harsh conditions, such as high temperatures, vacuum or dry contacts, 2D layered nano-materials used as solid lubricants have demonstrated to be promising candidates to ensure low friction and wear over the entire component’s lifetime. Therefore, this review article aims at summarizing the existing state-of-art regarding solid lubricants with a special emphasis on 2D layered nano-material beyond graphene including graphene oxide, reduced graphene oxide, MoS2, WS2 as well as Ti3C2Tx MXene nanosheets. Initially, experimental approaches allowing for a large-scale and layer-dependent synthesis are reviewed for each nano-material. Subsequently, their friction and wear mechanisms at the nano-scale are discussed. Afterwards, the ability to improve friction and wear are reviewed when using the aforementioned 2D nano-materials either as a solid lubricant, lubricant additive under lubricated conditions or reinforcement phase in composite materials. Finally, the existing challenges and shortcomings of each 2D nano-material are discussed before deriving the general conclusions and giving some future research directions.

Effects of Homopolar Magnetic Fields on Low-Current DC Vacuum Arcs

This article deals with the effects of homopolar magnetic fields on the lifetime of low-current dc vacuum arcs. A homopolar magnetic field is a distribution with the axially symmetric radially oriented field in the contact gap. It is produced when two dipole magnets are kept with the same poles facing each other. Switching experiments are conducted using an off-the-shelf ac vacuum contactor, and the ring magnets are used to set up a homopolar magnetic field in the contact gap. The arcing times are measured for currents varying from 1 to 30 A with voltages up to 100 V and magnetic surface strengths from 0.34 to 0.43 T. The tests are performed with the fixed contact of the vacuum contactor connected to positive as well as negative polarity. It is observed that the arcing time values are lesser in the presence of magnetic field with the fixed contact at the negative polarity due to asymmetry in the placement of the ring magnets. Finite element method (FEM) simulations are performed to examine the magnetic field distribution in the contact gap. The ratio of radial-to-axial magnetic field components in the contact gap decreases with increasing strength of magnets in the present experimental arrangement. It correlates well with the observed arcing time trends against the variation in the strength of magnets and the polarity of the fixed contact. The present article shows the potential of homopolar magnetic field in the development of dc vacuum contactors and interrupters without the need to create an artificial current zero using forced commutation.

Engineering the interface chemistry for scandium electron contacts in WSe2 transistors and diodes

Sc has been employed as an electron contact to a number of two-dimensional (2D) materials (e.g. MoS2, black phosphorous) and has enabled, at times, the lowest electron contact resistance. However, the extremely reactive nature of Sc leads to stringent processing requirements and metastable device performance with no true understanding of how to achieve consistent, high-performance Sc contacts. In this work, WSe2 transistors with impressive subthreshold slope (109 mV dec−1) and ION/IOFF (106) are demonstrated without post-metallization processing by depositing Sc contacts in ultra-high vacuum (UHV) at room temperature (RT). The lowest electron Schottky barrier height (SBH) is achieved by mildly oxidizing the WSe2 in situ before metallization, which minimizes subsequent reactions between Sc and WSe2. Post metallization anneals in reducing environments (UHV, forming gas) degrade the ION/IOFF by ~103 and increase the subthreshold slope by a factor of 10. X-ray photoelectron spectroscopy indicates the anneals increase the electron SBH by 0.4–0.5 eV and correspondingly convert 100% of the deposited Sc contacts to intermetallic or scandium oxide. Raman spectroscopy and scanning transmission electron microscopy highlight the highly exothermic reactions between Sc and WSe2, which consume at least one layer RT and at least three layers after the 400 °C anneals. The observed layer consumption necessitates multiple sacrificial WSe2 layers during fabrication. Scanning tunneling microscopy/spectroscopy elucidate the enhanced local density of states below the WSe2 Fermi level around individual Sc atoms in the WSe2 lattice, which directly connects the scandium selenide intermetallic with the unexpectedly large electron SBH. The interface chemistry and structural properties are correlated with Sc–WSe2 transistor and diode performance. The recommended combination of processing conditions and steps is provided to facilitate consistent Sc contacts to WSe2.

APPLICATION OF THE COMPUTING ENVIRONMENT MAPLE TO THE CALCULATION OF THE DYNAMICS OF THE ELECTROMAGNETS IN THE COMPLICATED SYSTEMS OF FORCED CONTROL

General description of the research topic. The authors propose a technique for calculating the dynamics of electromagnets operating in complex forced systems. Such forced electromagnets are widely used in electromechanical switching devices, in particular in vacuum contactors, to reduce their size, energy consumption and to increase speed, which indicates the relevance of this topic. A mathematical model of the dynamics of a forced electromagnetic system, which takes into account the peculiarities of behavior in transients of its individual elements – the mechanical system, the magnetic and electrical circuits, taking into account the interaction of the electromagnet with a control device when the apparatus is activated, contains certain signs of scientific novelty and is the purpose of the paper. The technique of calculating the dynamics of forced electromagnets uses the computing environment Maple. The calculation is based on a mathematical model, which is a system of nonlinear differential equations of the magnetic and electric circuits, supplemented by the equations of motion of the elements of a mechanical system. The use of the computing environment Maple, applied here to automatically perform the mathematical transformations, allows avoiding the complicated processes of choosing the numerical integration method, programming of complex and cumbersome equations and numerical integration procedures, to obtain results of calculations in convenient tabular and/or graphic form. This specifically indicates the practical significance of this work. The results of the comparison of calculations with previously published experimental data presented in the paper indicate the high efficiency of the proposed models and techniques.

The effect of laser surface melting on grain refinement of phase separated Cu-Cr alloy

Grain refinement and homogenization of Cr phase were achieved by laser surface melting (LSM) method, and the properties of Cu-Cr alloy were significantly improved. In this study, LSM of Cu-50Cr alloy (wt.%) was conducted with a high power density (106–107 W/cm2) laser beam, the microstructure and the properties of melt layer were investigated. The size of Cr phase was effectively refined from hundreds of micron scale to several micron scale, and the average size of Cr particles decreased to a few hundred nanometers. High cooling rate effectively inhibited coarsening effect on the Cr particles during liquid phase separation. Spherical Cr particles were dispersed in the melt layer with a thickness of 165 ± 20 μm. Microhardness was obviously enhanced and the maximum hardness was 232HV, which was 2.8 times that of the substrate. Arc duration of the LSM treated contacts increased up to 18%. The withstanding voltage of the fixed and the moving contact increased to 28.7% and 35.4%, respectively. The results show that LSM is an effective method to refine the microstructure of Cu-Cr alloy, and it is a promising modification method for electrical Cu-Cr vacuum contacts.

Hybrid control system for monostable polarized vacuum contactor drive

The analysis of control systems for medium voltage vacuum contactors is carried out. The shortcomings of electromechanical and microprocessor control systems are revealed. It has been established that a promising direction for improving control systems is the development of microprocessor hybrid control systems for electromagnets winding based on the use of compact electromechanical interface relays. An algorithm of operation and a microprocessor hybrid control system for a monostable polarized single-coil electromagnet are developed. Experimental investigations of the microprocessor hybrid control system operation are carried out, the results of which are the values of the turn-on time of the contactor of 65 ms and of the turn-off of 60 ms. These values are within the corresponding time intervals of operation of the models of medium voltage vacuum contactors from leading world manufacturers. The developed microprocessor control system for a monostable polarized electromagnetic drive has been experimentally tested on prototypes of several contactors.

Investigations of transients in the novel semiconductor device of forced control of the vacuum contactor monostable electromagnet

The analysis of the disadvantages of the existing systems of forced control with buster and holding windings, in which the opening internal control contacts are used, which commute large starting currents, is carried out. The analysis is led to the search for new technical solutions related to improving the reliability of such systems by eliminating the indicated control contacts. A novel semiconductor device of forced control of the vacuum contactor monostable electromagnet is proposed, in which a simple electronic circuit is used instead of an unreliable internal control contact. The experimental investigations of the operating features of the novel semiconductor device of forced control of the КВТн-250/1,14 vacuum contactor monostable electromagnet produced by the Electrodynamics Company are carried out. Two series of experiments are conducted: the first series of experiments was conducted for the semiconductor device of forced control, in which there is no closing internal control contact, and the second series of experiments – for a forced control system in which the closing internal control contacts which commutes the insignificant current in the control circuit is used. The oscillograms of current and voltage in the buster and holding windings are obtained at various voltage values U = 220, 180, 150 V, and when powered from a source of constant voltage, and then from a source of alternating voltage. The conclusions are made and it is recommended to use a closing internal control contact in the forced control system of the vacuum contactor monostable electromagnet, which will operate when the moving part ends moving before the control device triggers, which will not allow a large starting current to flow through the starting windings. The novel semiconductor device of forced control of the monostable electromagnet is used in the products of the Electrodynamics Company and is successfully operating since October 2017 and still at several mining enterprises (mines, processing plants).

Research on the self‐healing failure characteristics and its protection methods of high‐voltage self‐healing capacitors

There are no reliable measures for identifying self-healing failures in capacitors. Therefore, the high-voltage self-healing capacitor have not been widely adopted in power systems yet. It is urgent to study new scheme to protect the self-healing failure of high-voltage capacitors. Simulations tests and experiments were conducted to further assess self-healing of capacitors. The broken-down capacitor samples were connected into the test circuit with a vacuum contactor, and recorded the experimental phenomena and current wave-forms. The impedance changes were measured before and after the test, and calculated the active power dissipated by the sample. The test results showed that the insulation of self-healing failure sample temporarily restores or deteriorates rapidly. No visual defects are observed in the case of temporarily restored insulation, and the capacitor can continue to operate. However, if the insulation was deteriorated, unwanted gas generation, consisting of 85% H 2 , potentially lead to smoke and fire. Our study showed no obvious correlation between impedance change and occurring self-healing phenomena. It is found that the process consumes a lot of active power in case of deterioration. Therefore, a method of capacitor self-healing failure protection based on active power variation was proposed.