High Voltage Vacuum Circuit Breakers Research Articles

Modelling of electromagnetic transients in multi-unit high-voltage circuit-breakers

High-voltage (HV) circuit-breakers (CBs) often consist of several making and breaking units (MBUs) in series. A multi-unit circuit-breaker EMTP® model is proposed to analyse the effects of non-simultaneity between MBUs of the same pole. The model allows for simulations of high-frequency voltage and current transients during opening or closing operations. The simulations include the non-simultaneity of MBUs of the same pole or differences in dielectric withstand characteristics for vacuum circuit-breakers (VCBs) and SF6 CBs. According to simulation results, the maximum non-simultaneity of MBUs of the same pole, as permitted per international standards, can lead to multiple re-ignitions during opening or excessive overvoltages during closing operations. These phenomena are rarely simulated with conventional CB models. The simulations also highlight the important challenges facing high-voltage VCB design due to the inherent characteristics of vacuum bottle technology. The proposed models serve as useful tools for understanding and studying the effect of multi-unit CBs in various system studies and advanced diagnostics.

Microstructure and arc erosion behavior of WC/CuCr30 composites based on nano-Cr precipitation

CuCr alloys with high contact performance for medium and high voltage vacuum circuit breakers are becoming increasingly urgent. In this work, WC/CuCr30 composites were prepared by SPS process, and nanometer-sized precipitated Cr phases were obtained by subsequent heat treatment. The microstructure and arc erosion behavior were investigated. The results show that nano-Cr phase precipitated in copper matrix can effectively improve the interfacial bonding strength between the Cu matrix and WC particles, and part of the precipitated nano-Cr phase is combined with the C element in WC to form nano-Cr23C6. Both nanophases can improve the resistance to dislocation and sub-grain boundary movement in the deformation process of WC/CuCr30 composite, thus improving the hardness of the copper matrix with a slight decrease in electrical conductivity. The results of electrical contact show that the addition of WC particles and nano-Cr precipitates can not only extend contact life of CuCr material, but also help to disperse the arc to avoid concentrated erosion. The presence of Cr23C6 phase around WC particles effectively improves the interfacial bonding between Cu phase and WC phase and reduces the probability of pore existence at the interface, which is beneficial to vacuum breaking performance.

Strain Analysis of Vacuum Interrupter Bellows

Abstract The vacuum interrupter (VI) is the main part of the vacuum circuit breaker (VCB), and an essential component of its design is the bellows. In future high-voltage VCBs, faster switching speeds will lead to higher dynamic impact-type loads, and the oscillation of the bellows after the contact opening and closing could shorten the mechanical life of the bellows. This article provides a 1D computer-aided engineering (CAE) analysis of the strain of the bellows oscillation in a VI caused by the axial load from the impact of the contact. A formula for the oscillation is derived using the longitudinal vibration response of a mass-spring 1D model, calculated by the convolution integral of the input and the impulse response function of the vibration modes. The proposed 1D analysis was verified and shown to be effective under four different experimental conditions. This article also provides a 1D CAE analysis of the mechanical life of the bellows. These 1D analyses estimate the effect of stress reducing countermeasures on the bellows' lifetime without increasing its size.

Hardware Design of Online Monitoring Device for the High-voltage Vacuum Circuit Breaker

In order to monitor the mechanical structure status of high-voltage vacuum circuit breakers in real time and diagnose faults online, a hardware design scheme of an online monitoring device for 10kV vacuum circuit breakers is proposed in this paper. From the perspective of practical application, this design scheme fully considers the practical working conditions of the monitoring device. The device not only monitors the mechanical vibration of the circuit breaker, the rotation stroke of the spindle and the position signal of the mechanical switch, but also monitors both the voltage and current of the opening (closing) coil, the energy storage motor and the closing lock coil. In this paper, in order to adapt the monitoring device to the actual application conditions, a modular design is adopted, the isolation and protection performance of the ports is strengthened and the integration degree of the device is increased.

Разработка вакуумной дугогасительной камеры для одноразрывного вакуумного выключателя на 110 кВ

Requirements for high-voltage vacuum circuit breakers for networks with a grounded neutral, which are stemming from the prospects of using vacuum circuit breakers in networks with the solidly grounded neutral are formulated. The arch chute design for a 110 kV single-break vacuum circuit breaker that takes into account the occurrence of repeated breakdowns is developed. The shielding system equalizes the voltage over the chute casing, decreases the electric field intensity at the “triple point”, protects the casing dielectric from becoming dusted with metallic contact parts erosion products, prevents the occurrence of cascade breakdown between the contact parts and central shield, and eliminates a possible decrease of the chute electric strength as it gradually works out its switching life. It is shown that the chute design includes measures to prevent the possibility of repeated breakdowns during disconnection up to class С1 according to GOST 52565-2006. It has been proven that for vacuum arc chutes for class С2 (for switching a capacitive load) it is necessary to develop a chute with two breaks between the contact parts or to connect two vacuum chutes in series. The shielding system adopted in the chute rules out the possibility of ceramic casing to become metallized, which decreases the chute electric strength as it gradually works out its switching life, and the vacuum arc transfer to beyond the inter-contact gap boundaries onto the central shield, the burnout of which results in that the vacuum arc chute loses its tightness and fully loses its functional properties.

Multi-Objective Optimization of a Permanent Magnet Actuator for High Voltage Vacuum Circuit Breaker Based on Adaptive Surrogate Modeling Technique

A novel mono-stable permanent magnet actuator (PMA) for high voltage vacuum circuit breaker (VCB) and its optimal design method are proposed in this paper. The proposed PMA is featured with a structure of separated magnetic circuits, which makes the holding part and closing driving part work independently without interference. The application of an auxiliary breaking coil decreases the response time in the initial phase of opening operation, and an external disc spring is adopted to accelerate the opening movement, which makes the PMA meet the fast-breaking requirement of high voltage VCB. As calculating the characteristics of the PMA accurately through numerical simulation is a time-consuming process, a multi-objective optimization (MOO) algorithm based on surrogate modeling technique and adaptive samples adding strategy are proposed to reduce the workload of numerical simulations during optimization. Firstly, initial surrogate models are constructed and evaluated, and then iteratively updated to improve their global approximating abilities. Secondly, according to the approximate MOO results obtained by the global surrogate models, additional samples are added to constantly update the surrogate models to gradually improve the models’ local accuracies in optimal solution regions and finally guide the algorithm to the true Pareto front. The efficiency and accuracy of the proposed algorithm are verified by test functions. By applying the optimization strategy to the design of the proposed PMA, a set of satisfying Pareto optimal solutions, which improve the overall performance of the PMA obviously, can be derived at a reasonable computation cost.

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

Overheating limits the development of high voltage vacuum circuit breakers (HVVCB) toward large current and compact size. In this paper, an electromagnetic-thermal simulation model is proposed to investigate the thermal characteristics of a 126 kV/40 kA HVVCB. This model is first validated using experimental data. Then it is used to evaluate the thermal performance of the HVVCB with the 2/3 coil-type and horseshoe-type electrodes, respectively. The comparison results showed that the resistance and temperature of the horseshoe-type electrode are much lower than those of the 2/3 coil-type electrodes. The temperature rise in the HVVCB with the horse-type electrodes is also much lower than that in the HVVCB with the 2/3 coil-type electrode. Based on the analysis, a new structure of the HVVCB is proposed by replacing the spring finger connection between the static conductive rod and its conductive support with a fixed connection. The temperature distribution in the new structure and conventional structure is analyzed and compared. The results showed that the temperature reduction at the upper end of the connection is about 23 °C and at the contact surfaces of the two electrodes is about 20 °C in the HVVCB at a current of 2500 A.

Partial discharge detection method for vacuum leakage diagnosis of a vacuum interrupter

Vacuum circuit breakers (VCBs) have been widely used in the medium distribution voltage range of 12–38 kV for more than half a century. Recent interest for them is because of the loss of vacuum in a vacuum interrupter (VI). Generally, the leakage is an improbable event during the expected lifetime of typically 20–30 years, while there are some reports that VIs beyond their expected lifetime have a significantly higher leakage rate. To keep the high reliability of middle voltage VCB, even for the high voltage VCB, it is necessary to develop the earlier detection method of vacuum leakage from VI. In the present study, an experimental setup with a partial discharge (PD) detecting system for detecting vacuum leakage from a test VI was constructed. The internal pressure of VI was arbitrarily regulated in the range of 0.02–100 Pa through an insulating tube using several valves. A detecting resistor of 1 kΩ was connected to a plane electrode located outside 115 mm away from VI to measure the PD current due to discharges inside the VI. A current transformer (CT) was also placed below the plane electrode. Sensors with different specification for PD detection, such as a transient earth voltage sensor, a horn antenna, and an acoustic emission sensor, were investigated and characterized. As a result of pressure dependence of PD inception voltage, it follows the left side of Paschen's Law in the pressure range more than 2.0 Pa, while no discharges occurred below 2.0 Pa. To analyze the PD charge and rise time from measured waveforms, the PD mechanism in the medium voltage range inside the VI was discussed. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A Review of the Synergy Effect in Multibreak VCBs

At present, multibreak vacuum circuit breakers (VCBs) have attracted more attention in order to meet the requirement of the environmental protection, high-voltage VCBs, capacitive current switch-off, and the dc current breaking. The advantages and disadvantages of multibreak VCBs are analyzed and discussed according to the research status. Then, the synergy effect of multibreak VCBs is proposed, which is the interaction among the arc memory, current zero characteristic, and the postarc characteristic. The target of the synergy effect is the synergy between the dynamic dielectric recovery strength and the postarc dynamic voltage distribution. The maximum breaking capacity can be obtained in the above-mentioned synergy control. Finally, the optimization design, key technology, basic theory, and application of multibreak VCBs are discussed. With the development of multibreak VCBs, it will be widely used in high-voltage level, HVdc, and pulsed-power switchgear in the future.

Breaking Capacity Test of 126kV/2500A/40kA Double Breaks Vacuum Circuit Breaker

High-voltage vacuum circuit breakers are intended for breaking the short-circuit current, and the breaking capacity is the major performance indicator. In the paper， the Weil synthetic circuit was built, and by using unit testing method and referring to standard GB/T 1984-2014, the breaking capacity of 126kV/2500A/40kA double-break vacuum circuit breaker developed by Central Research Institute of Tianjin Benefo Machinery Equipment Group Co., LTD was tested. Result showed that this vacuum circuit break can meet the breaking capacity requirement for grid integration

Analysis and design of a high‐speed permanent magnet characteristic actuator using eddy current effect for high‐voltage vacuum circuit breaker

This study proposes a high-speed permanent magnet actuator (HSPMA) for high-voltage vacuum circuit breaker (VCB). The HSPMA comprises mainly of an eddy current repulsion force actuator and a permanent magnet (PM) actuator. The structural saliency of HSPMA is described and its control principle is elaborated in details. Finite element method is used and the eddy current is included in the computation of the electro-magnet fields of the HSPMA. The system equations, which couples the magnet field to circuit and mechanical equations, are built in ANSOFT Maxwell and Circuit Editor in this study of the making and breaking procedures of the HSPMA. The simulated characteristics show the design meets the requirement of the high-voltage VCB. The optimal thickness of the eddy current plate is 10 mm. The capacitor also has an economic optimal value of 10,000 µF. The simulated results indicate that the HSPMA has a sound characteristic when compared with circuit breakers with only PM actuator.

Control and suppression of impulse surface flashover in vacuum based on discharge development mechanisms

Surface discharge on solid insulator in vacuum is one of the significant issues for the development of vacuum circuit breakers (VCBs) and vacuum interrupters (VIs). For the development of higher voltage VCBs and VIs, control and suppression techniques of the surface flashover are required. The aim of present study is to suppress the surface flashover, based on physical mechanisms of flashover development. Impulse surface flashover in vacuum, starting with explosive electron emission (EEE) from cathode, develops with the formation of transient charge on the insulator as well as the development of secondary electron emission avalanche (SEEA) along the surface toward anode. To reduce the EEE current from the cathode and the SEEA development, we changed the electrode geometry such as thickness of alumina ceramics and tip radius of cathode rod, respectively, and installed a plane electrode as the back electrode of the cathode rod. As the results, EEE current was reduced by the field relaxation effect of transient charging due to EEE, and SEEA was also suppressed by the perpendicular electric field of the plane electrode. When the flashover was suppressed by using the cathode back electrode, transient charge amount was smaller on alumina dielectrics at the end of the plane electrode area. From the above results, it would be an effective technique for the control and suppression of surface flashover in vacuum to enlarge the perpendicular electric field for the insulator.

Impulse surface flashover development associated with transient charging by explosive electron emission in vacuum

Surface discharge on solid insulator in vacuum, which is one of the most significant issues under high electric field, prevents the development of higher voltage vacuum circuit breakers and vacuum interrupters. To clarify the mechanism of the surface discharge in vacuum, charge activities on solid insulators in the development process of the surface discharge should be investigated. By using electrostatic probes behind the alumina dielectrics and measuring fast-framing images of the surface discharge, in the present paper, we clarified that the impulse surface flashover starts in developing with explosive electron emission (EEE) on cathode, which is specific phenomenon on the electron emission site exploding due to extreme field emission current density. Experimental results revealed the characteristics of transient charging by EEE in the surface flash over development as follows: (1) the probe current due to EEE increases with the EEE inception electric field on the cathode, and also depends on the work function of the cathode material, (2) the transient charge distribution on the alumina dielectrics is determined by the EEE spot on the cathode, (3) EEE occurs several times due to the erosion and the regeneration of electron emission sites. (4) the successive EEE makes the transient charge distribution smooth on the alumina dielectrics.

Transient Charging Characteristics in Surface Flashover Development Process due to Explosive Electron Emission in Vacuum

SUMMARYFor the development of higher voltage vacuum circuit breakers and vacuum interrupters, surface discharge in a vacuum is one of the most significant issues. We measured the charge activity on alumina dielectrics in a vacuum through ultrahigh‐speed optical and electrical measurements. We found that surface flashover in a vacuum starts with an explosive electron emission (EEE) with higher current density, which consists of electron emission from the cathode, and results in surface flashover development. The transient charge on the alumina dielectrics formed by electrons emitted by EEE influences the distortion of electric field distribution around the cathode rod and then the subsequent flashover development. In particular, in the case of a shorter gap between the cathode rod and the alumina dielectrics, the electron emission may be suppressed by the relaxation effect of the electric field due to transient charge accumulation.

An Approach for Minimum Percussion Welding in Closing Operation of a 126-kV Vacuum Circuit Breaker

SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> circuit breakers are widely used, to safely and reliably protect the high-voltage (72.5-1000 kV) power system. However, SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> is a greenhouse gas. It is necessary to develop high-voltage vacuum circuit breakers (VCBs) instead of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> circuit breakers above 110-kV power systems. To obtain the optimum performance from a high-voltage VCB design, the mechanism design must be perfectly matched to it. For a closing operation of a 126-kV VCB, most of the arc energy for performing percussion welding is from the prestrike arc and the bounce arcs if contacts close in vacuum when a high current passes through the contacts. An approach for minimum percussion welding in the closing operation of a 126-kV VCB is investigated by reducing both the prestrike arc duration and the bounce open duration. The breakdown phenomena in 126-kV vacuum interrupters are investigated to obtain a prestrike gap of 4 mm. The bouncing-open time of a prototype of a 126-kV VCB is measured in the prestrike closing velocity range of 0.7 to 2.0 m/s. The results show that the total arcing duration (including the prestrike arc and bouncing arc duration) is a function of the prestrike closing velocity (an average closing velocity in the prestrike gap (d) before the contacts touched each other). According to the function, the optimized prestrike closing velocity is 1.15 m/s, which can minimize the total arcing duration to 4.91 ms in the 126-kV VCB. The prototype of the 126-kV VCB passes the full-voltage synthetic making test successfully by applying the closing characteristic.

Transient Charging Characteristics in Surface Flashover Development Process due to Explosive Electron Emission in Vacuum

For the development of higher voltage vacuum circuit breakers (VCB) and vacuum interrupters (VI), surface discharge phenomenon in vacuum is one of the most significant issues. We measured the charge activity on alumina dielectrics in vacuum through ultra-high speed optical and electrical measurements. We found out that the surface flashover in vacuum starts with an explosive electron emission (EEE) with the higher current density, which is the electron emission from the cathode, and results in the surface flashover development. Transient charge on the alumina dielectrics formed by electrons emitted by EEE influences the distortion of electric field distribution around the cathode rod and then the subsequent flashover development. Especially, in the case of the shorter gap between the cathode rod and the alumina dielectrics, the electron emission could be suppressed by the relaxation effect of the electric field due to the transient charge accumulation.

Development and Application of Distributed Multilayer On-line Monitoring System for High Voltage Vacuum Circuit Breaker

On-line monitoring system is important for high voltage vacuum circuit breakers (HVCBs) in operation condition assessment and fault diagnosis. A distributed multilayer system with client/server architecture is developed on rated voltage 10kV HVCB with spring operating mechanism. It can collect data when HVCB switches, calculate the necessary parameters, show the operation conditions and provide abundant information for fault diagnosis. Ensemble empirical mode decomposition (EEMD) is used to detect the singular point which is regarded as the contact moment. This method has been applied to on-line monitoring system successfully and its satisfactory effect has been proved through experiments. SVM and FCM are both effective methods for fault diagnosis. A combinative algorithm is designed to judge the faults of HVCB's operating mechanism. The system's precision and stability are confirmed by field tests.

Influencing Factors of Breaking Capacity of Double-Break Vacuum Circuit Breakers

Using a series arrangement of two vacuum interrupters (VIs) has been proved to be an effective way of developing higher voltage vacuum circuit breakers (VCBs), which are known as double-break VCBs. The uniform distribution of the transient recovery voltage (TRV) across each VI is very critical for the breaking capacity of double-break VCBs. In this paper, the TRV distribution characteristics of double-break VCBs was studied by the synthetic test and the PSCAD/EMTDC simulation based on a vacuum arc interruption model. The results show that the bias of the TRV distribution ratio is caused by the stray capacitance and the imbalanced post arc plasma characteristic in each VI, which is consistent with the theoretical analysis. Moreover, the negative effect of grading capacitors was discussed. The results show that it is advisable to limit the value of grading capacitors to those ranges which can guarantee sufficiently improve the voltage distribution. DOI: http://dx.doi.org/10.11591/telkomnika.v11i6.2140

Heat transfer in a high-voltage vacuum circuit breaker

Thermal performance is one of the key issues of the high-voltage vacuum circuit breaker (HV VCB). However, temperature rise of a HV VCB cannot be estimated easily. This article studied heat transfer of a 126-kV/2500-A single break VCB. A three-dimensional electro-thermal coupling model of the VCB was built, where the power loss was calculated by the electro-magnetic field analysis, and was then used as the input data to predict the temperature rise for the thermal analysis. The heat transfer coefficients on the boundaries were numerically calculated by a commercial software. The electrical contact resistance as well as the thermal contact resistance was taken into account in the electro-thermal coupling model. The simulated results were validated experimentally. The results showed that power losses of conductors enveloped in the vacuum interrupter took up 63.3 per cent of the total power loss of the VCB. Thermal resistances of conducting rods were the highest. The second highest was thermal resistance of a pair of main contacts. The thermal contact resistance significantly affected temperature at two conductors where there is a contact guaranteed by springs. However, temperature of the conductors exposed in the air was only affected by the natural convection and radiation.

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.