Vacuum Breaker Research Articles

Superconducting fault current limiter for railway transport

A resistive switching superconducting fault current limiter (SFCL) for DC networks with voltage of 3.5 kV and nominal current of 2 kA is developed. The SFCL consists of two series-connected units: block of superconducting modules and high-speed vacuum breaker with total disconnection time not more than 8 ms. The results of laboratory tests of superconducting SFCL modules in current limiting mode are presented. The recovery time of superconductivity is experimentally determined. The possibility of application of SFCL on traction substations of Russian Railways is considered.

Negative pressure difference evaluation of Lungmen ABWR containment by using GOTHIC

Negative pressure difference of the pressure suppression containments means that the wetwell pressure is greater than the drywell pressure and is an undesired effect to the containment safety. The Wetwell-to-Drywell Vacuum Breakers (WDVBs) are check valves used to mitigate this adverse effect. The Lungmen Nuclear Power Plant in Taiwan is a twin-unit Advanced Boiling Water Reactor (ABWR) plant. There are totally 8 WDVBs in the ABWR containment. In this study, a GOTHIC model is developed to evaluate the negative pressure difference of the Lungmen plant. Sensitivity study on the operable WDVB number is also performed. The results show that there is sufficient margin against the negative pressure difference for the ABWR containment. The design value will not be exceeded unless only one WDVB is operable. Furthermore, the effect of the WDVB leakage on the drywell pressure is evaluated by performing the short-term containment analyses. The peak drywell pressure will be greater than the design value with leakage area greater than 50% of one WDVB area. Based on the results of this study, the current requirement that all WDVBs shall be closed and operable during normal operation ensures the Lungmen containment safety.

Experimental Research on Speed Control of Vacuum Breaker

For phase-controlled vacuum breakers, the acting time of the actuator should be precise. The variation of capacitor voltage, capacitance, and environmental temperature impact the dispersion of closing time seriously. A new technology has been put forward in this paper. It is the speed control of the vacuum breaker. This technology can be used for phase-controlled operation of vacuum breakers. By using this technology, the deviation of displacement can be corrected in real time. So the permanent-magnetic actuator (PMA) can move along with the given displacement curve. Also, the closing time is stable when the external factors, such as capacitor voltage, capacitance, and environment temperature change. The closed-loop system has been established in this paper. The proportion-differentiation (PD) algorithm and fuzzy algorithm are used in the system. The PD algorithm adjusts the coil current to ensure that different actuators have the same excitation time. And the fuzzy algorithm is used to adjust actuator displacement. With the use of the algorithm, the closing time of the breaker is stable, and mechanical properties are optimal. Based on the aforementioned theory, many experiments have been performed when external factors change, such as environment temperature, capacitance, and so on. The results prove that the displacement deviation can be corrected using this method and the closing time can be stabilized within ±0.5 ms. Therefore, not only can the accuracy of phase-controlled operation can be ensured, but the lifespan of the circuit breaker can also be prolonged.

Medium-Voltage Switching Transient-Induced Potential Transformer Failures: Prediction, Measurement, and Practical Solutions

During commissioning of a large data center, while switching medium-voltage circuit breakers without any appreciable load, several potential transformers failed catastrophically. A detailed investigation, including a computer simulation, was performed. Ferroresonance produced by switching transients associated with opening and closing the vacuum breakers was determined to be the cause. The analysis also determined that the close-coupled power transformers were also in jeopardy. Field inspections involving grounding improvements coupled with solution simulations were made. High-speed switching transient measurements were performed to verify the analysis and the surge protective device solution (arresters and snubbers). This paper walks the reader through problem recognition, simulation, field measurements, and solution implementation. Special focus will be made on the field measurement verification.

A Microscopic Study of Before-Arc Process in Metal Vapor Plasmas Proximal Cathode Region. Part I Formation of the Proximal Cathode Region

Metal vapor arc in vacuum breaker is a very complex phenomena and the researches on the process of arc creating are the effective method to improve breaking ability. By the theoretical study and numerical simulation, exploring the formation of plasma sheath near the cathode, charged particles energy distribution and influence elements in before-arc process are the fundamentals of this paper. Before-arc process is the fundermental of arc energy and the proximal cathode region is the important area for vacuum arc forming, so before-arc process of metal vapor arc was simulated here. The modification to electron motion produced by the interaction between charged particles and plane electrodes and both elastic and charge exchange collisions between electrons and neutral gases were considered here. The copper cross section adopted here was related to the particle energy. The tracks of electrons were traced until they reached to the anode surface. Based on this method, the formation of proximal cathode region and some microscopic parameters were simulated here. The results show that the collision between charged particles with the electrodes is the necessary condition in proximal cathode regions formation.

Simulation on Before-Arc Process of Large Current Breaking in Vacuum Circuit Breaker

Arc breaking at the function of large current is one of the bottlenecks for the development of vacuum breaker to higher voltage level. Simulation on arc is one of the most effective methods in this field. Before-arc process model of vacuum circuit breaker (VCB) whose breaking current is 20kA current and clearance is 10mm is developed here based on Boltzmann equation. Collisions between charged particles and metal vapor and electrodes are considered in the simulation. The physical nature of the sheathe and arc columns formation, the space charge densities and their effects on electric field strength before the steady state of arc plasma are simulated here.

A Microscopic Study of Before-Arc Process in Metal Vapor Plasma's Proximal Cathode Region. Part II the Influence of Macroscopic Parameters on the Proximal Cathode Region

The moment of vacuum breaker contacts opening to arc creating process is an unbalanced gaseous breakdown process. This before-arc process is the foundation of studying arc process. The mechanism of the metal vapor arc is different from other gas medium and contains complex electrode process. The proximal cathode region is the important area for vacuum arc forming and it is affected by many factors. The influences of the different electrode separations, different secondary emission coefficient on electronic density, electronic temperature and electric potential, were analysed in this paper. The simulation results show that the change of electrode separations barely impacts the thickness of sheath and the decrease of electrode separations will lead to the decrease of electronic energy near the cathode sheath. The increase of secondary electron emission will increase charged particles energy, which is the important condition of forming cathode sheath.

Optimal hydraulic design of new-type shaft tubular pumping system

Based on the characteristics of large flow rate, low-head, short annual operation time and high reliability of city flood-control pumping stations, a new-type shaft tubular pumping system featuring shaft suction box, siphon-type discharge passage with vacuum breaker as cutoff device was put forward, which possesses such advantages as simpler structure, reliable cutoff and higher energy performance. According to the design parameters of a city flood control pumping station, a numerical computation model was set up including shaft-type suction box, siphon-type discharge passage, pump impeller and guide vanes. By using commercial CFD software Fluent, RNG κ-ϵ turbulence model was adopted to close the three-dimensional time-averaged incompressible N-S equations. After completing optimal hydraulic design of shaft-type suction box, and keeping the parameters of total length, maximum width and outlet section unchanged, siphon-type discharge passages of three hump locations and three hump heights were designed and numerical analysis on the 9 hydraulic design schemes of pumping system were proceeded. The computational results show that the changing of hump locations and hump heights directly affects the internal flow patterns of discharge passages and hydraulic performances of the system, and when hump is located 3.66D from the inlet section and hump height is about 0.65D (D is the diameter of pump impeller), the new-type shaft tubular pumping system achieves better energy performances. A pumping system model test of the optimal designed scheme was carried out. The result shows that the highest pumping system efficiency reaches 75.96%, and when at design head of 1.15m the flow rate and system efficiency were 0.304m3/s and 63.10%, respectively. Thus, the validity of optimal design method was verified by the model test, and a solid foundation was laid for the application and extension of the new-type shaft tubular pumping system.

Oil-Operated Fixed-Piston Sampler and Its Applicability

AbstractThis paper presents the development of an oil-operated fixed-piston sampler. This sampler includes a vacuum breaker, which prevents the suction between the sample and piston during disassembly, and an improved version of a complex system used for continuous advancement in mechanical samplers. The improvement makes the new sampler easy to operate, similar to the hydraulic sampler. The oil-operated and hydraulic samplers were used at a site in the Nakdong River Delta. Suction, shear-wave velocity, and consolidation tests were performed on 100-mm-long specimens equally divided by the extruded samples, as well as the seismic flat dilatometer and the piezocone tests in the field. The results show that the new sampler gave better sample quality than the hydraulic-type sampler, indicating better recovery ratio. The main difference in sample quality between the two samplers can be attributed to mechanical destructuration, owing to the stepped advancement and the slight tilt of the hydraulic sampler.

Vacuum Circuit Breaker Transients During Switching of an LMF Transformer

Switching transients associated with circuit breakers have been observed for many years. With the widespread application of vacuum breakers for transformer switching, recently, this phenomenon has been attributed to a significant number of transformer failures. Vacuum circuit breaker switching of electric arc furnace and ladle melt furnace (LMF) transformers raises concern because of their inductive currents. High-frequency transients and overvoltages result when the vacuum breaker exhibits virtual current chop and multiple re-ignitions. This paper will present a detailed case study of vacuum breaker switching of a new LMF transformer involving current chopping and restrike simulations using the electromagnetic transients program. A technique that involves a combination of surge arresters and snubbers will be applied to the LMF to show that the switching transients can be successfully mitigated. Additionally, some practical aspects of the physical design and installation of the snubber will be discussed.

Passive containment cooling system (PCCS) response with Drywell Gas Recirculation System (DGRS) activated during a postulated Loss of Coolant Accident (LOCA)

Passive Containment Cooling Systems (PCCS) are characterizing the design of several advanced LWR such as SBWR, ESBWR, ABWR-II, etc. These systems should ensure the mitigation of postulated accidents both under Design Basic Accident (DBA) and Beyond DBA (BDBA) conditions. Some ALWR designs integrated in the PCCS a system called Drywell Gas Recirculation System (DGRS). The DGRS works like a fan, with inlet flow lines connected to the Passive Cooling condenser (PCC) vent lines and the outflow line connected to the Drywell (DW). The present paper presents the experimental results of an integral containment test performed in the PANDA facility. The initial conditions (temperature, pressure, gas composition, decay heat, etc.) for the test represent the containment situation 1 h after a Loss of Coolant Accident (LOCA). The test consists of two phases (6 h each) for a total duration of about 12 h. In the first phase has been simulated the response of the PCCS to a LOCA, in the second phase the DGRS has been activated and has been investigated the effect of such activation on the overall PCCS response. The test shows that the activation of the DGRS has an effect on the overall PCCS characteristics, i.e. composition of gas mixture in the PCC tubes, stratification in the Wetwell (WW), DW–WW pressure differences, timing for the opening of the Vacuum Breakers (VB) and overall containment pressure.

Field emission currents in vacuum breakers after capacitive switching

Field electron emission current measurements during the recovery phase of vacuum interrupters are carried out to understand the origin of restrikes in case of interrupting capacitive loads. A special shunt is designed for this measurement. To compensate the capacitive current component due to the stray capacitance of the interrupter, hardware (electronic, on-line) as well as software (off-line) processing are developed for different applications. Measurement and analysis of field emission currents (0.01-5 mA) from current zero until the moment of restrike are performed both in an experimental circuit as well as in full-power test-circuits with commercially available vacuum circuit breakers (up to 36 kV rated voltage). In this context, the influence of capacitive breaking currents on the dielectric recovery of the vacuum gap and the contacts surface condition is studied. Furthermore, the influence of pre-arcing at contact closing under inrush currents in the range of several kilo-amperes and kilo-hertz on the field emission characteristics after capacitive current switching is investigated. The number of making operations as well as the amplitude of the inrush current is varied. A clear relation between inrush current during closing and field emission current after interruption was established.

Transformer Failure Due to Circuit-Breaker-Induced Switching Transients

Switching transients associated with circuit breakers have been observed for many years. Recently, this phenomenon has been attributed to a significant number of transformer failures involving primary circuit-breaker switching. These transformer failures had common contributing factors such as the following: 1) primary vacuum or SF-6 breaker; 2) short cable or bus connection to transformer; and 3) application involving dry-type or cast-coil transformers and some liquid-filled ones. This paper will review these recent transformer failures due to primary circuit-breaker switching transients to show the severity of damage caused by the voltage surge and discuss the common contributing factors. Next, switching transient simulations in the electromagnetic transients program will give case studies which illustrate how breaker characteristics of current chopping and restrike combine with critical circuit characteristics to cause transformer failure. Design and installation considerations will be addressed, particularly the challenges of retrofitting a snubber to an existing facility with limited space. Finally, several techniques and equipment that have proven to successfully mitigate the breaker switching transients will be presented, including surge arresters, surge capacitors, snubbers, and these in combination.

관로계통 및 가압펌프장 수격에 따른 최적 안정성 확보방안

This paper is performed to find out the stability of water-hammer in pipe line and pump station that is happened when additional water needs demanded. At first, the water supply construction project is planned to supply 6,000 ㎥/day through 17.9 ㎞ pipe line. But additional demand (1,200 ㎥/day) happened from Cheong-ra water reservoir. In this situation, air-chamber(4 ㎥) and vacuum breaker valve(φ100 ㎜) are needed to prevent water-hammer. When the additional water is supplied, the existing facilities (air-chamber, vacuum breaker valve) are sufficient to alleviate shock not changing capacity alteration, judging from the airspace change and rise. Therefore, there is no problem for water-hammer by installing air-chamber(4 ㎥) and vacuum breaker valve(φ100 ㎜) at the top of Yeo-ju hill.

Upgrade of the RFX energy transfer system for a reliable 35 kV, 50 kA DC-current interruption

In the reversed field pinch experiment (RFX), the energy transfer system (ETS) is operated so as to divert the magnetising current into the transfer resistors, in order to ionise the gas and start the plasma current. In the next experimental campaigns, the current in the magnetising circuit will be increased to the design target of 50 kA; this will lead to unbearable conditions for the vacuum interrupters, in terms of specific energy ( I 2 t) that can be dissipated in the closed contacts, before opening; an upgrade of the ETS is therefore necessary. The paper, after giving a survey of possible solutions, discusses the choice made for RFX, which consisted in connecting new vacuum breakers in parallel to the existing ones, so as to increase the interruption capabilities; then, the implementation of the new components is described, in particular with reference to the control and protection upgrade. Finally, the tests carried out on one of the four units are described. The positive results of the tests allowed programming the extension of the modifications to the other units during the experiment shut-down taking place in late summer 2008.

Vacuum Breaker for High DC Current: Experimental Performances and Operational Limits

This paper presents a new method to assess the performances of vacuum circuit breakers (VCBs) for high DC based on the measurement of the energy dissipated in the contacts before the opening of the breaker. This energy is given by the product of the closed-contact resistance times the specific energy ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> ) flowing through the breaker. The results of an extensive experimental campaign on VCB prototypes, customized for special applications in the field of thermonuclear fusion, are reported in this paper, showing that, whenever the energy dissipated before the opening exceeds a threshold, the probability of VCB restrike increases. It is also demonstrated that vacuum tubes need initial training at low current prior to the operation at full performance.

A Database Alternative Transient Program Simulated Waveforms of Shunt Reactor Switching Cases With Vacuum Breakers on Motor Circuits

This paper presents a database Alternative Transient Program (ATP) simulated waveforms for shunt reactor switching cases with vacuum breakers in motor circuits following interruption of the starting current. The targeted objective is to provide multiple reignition simulated data for diagnostic and prognostic algorithms development, but also to help ATP users with practical study cases and component data compilation for shunt reactor switching. This method can be easily applied with different data for the different dielectric curves of circuit-breakers and networks. This paper presents design details, and discusses some of the available cases and the advantages of such simulated data.

Design and test of hydraulic vacuum breaker check valve for simplified boiling water reactor

In the current design of the simplified boiling water reactor, the vacuum breaker check valve is an important safety component. The vacuum breaker check valve is the only key safety components which is not passive in nature. Failure of this mechanical valve drastically reduces the passive containment cooling system cooling capability and hence containment pressure may exceed the design pressure. To eliminate this problem novel vacuum breaker check valve was developed to replace the mechanical valve. This new design is based on a passive hydraulic head, which is fail-safe and is truly passive in operation. Moreover this new design needs only one additional tank and one set of piping each to the wetwell and drywell. This system is simple in design and hence is easy to maintain and to qualify for operation. The passive vacuum breaker check valve performance was first evaluated using RELAP5. Then the passive vacuum breaker check valve was constructed and implemented in the PUMA integral test facility. Its performance was studied in a large break loss of coolant accident simulation test performed in PUMA facility.

The duration of arcing following late breakdown in vacuum circuit breakers

Vacuum interrupters occasionally show unexpected (late) breakdowns after current interruption. As a result, the interrupter conducts briefly, carrying a high-frequency current due to the discharge of various capacitances in the vicinity of the interrupter. Thanks to the capability of vacuum interrupters to interrupt such high-frequency current, the conduction period is very short (normally in the order of 10 microsecond). In the discussion around the assessment of such late break- downs (often termed non-sustained disruptive discharges in the standardisation literature) regarding the possibility of generation of overvoltage as a result of late breakdown in capacitive circuits, the duration of the conductive period is an important parameter. Experiments were carried Out, in which discharges of various single frequencies (72 kHz - 1.1 MHz) were generated following breakdown (spontaneous breakdowns as well as pre-strike) of two commercial vacuum breakers, stressed with ac voltages well above the rated value. From a statistical analysis, it is demonstrated that the dura- of the discharge depends strongly on the discharge current frequency. At higher frequencies, the duration of the discharge tends to be shorter than at lower frequencies due to the domi- nance of thermal reignitions of the arc at high values of dl/dt over dielectric reignitions, observed only at lower frequencies. For practical circuits, allowing simultaneous discharge from various circuit parts, it was observed that the highest frequency component determines the arc duration. Durations of up to 15 us were observed. This duration is too short to allow significant overvoltages to develop in standard capacitive circuits, the main candidate switching duty to be troubled with overvoltage generation.

Parameter Measurements to Study Surge Propagation in Induction Machines

Winding failures in induction machines have been a major concern in the past several years, and more so recently with the addition of variable-speed drives (VSDs). Both the introduction of the vacuum breaker, and the use of pulsewidth-modulation (PWM) drives, utilizing fast switching insulated gate bipolar transistors, have resulted in an increase in winding failures in induction machines. Two mechanisms that cause winding failures are steep-fronted surges, like those caused during the opening and closing of vacuum breakers, and transient overvoltages caused by impedance mismatch between the cable and load during VSD operation. There has been a fair amount of work done to date on the propagation of vacuum-breaker-induced steep-fronted surges in the windings of the induction machine. More recently, work has been progressing on overvoltages at the machine terminals as a result of VSDs operating with long cables connecting the drive and machine. However, the propagation of these surges down the coils and the interference of these PWM surges with each other in the coils as well as the coupling between turns and coils have not been thoroughly investigated. Such an investigation would allow more benign PWM strategies to be developed, which do not build up in the machine to unacceptably high levels. The relevant parameters to be used are unknown and difficult to calculate and measure. To this end, this paper presents a measurement technique to determine the machine parameters for surge studies in machines. Detailed parameter measurements are made of each turn section (slot versus overhang), which are then used to determine the surge impedance of each section. Also included are the mutual capacitive and inductive couplings. Reflection and refraction coefficients are calculated which may then be used for further analysis of surges in machines.