Mechanical DC Circuit Breaker Research Articles

A Novel Thyristor-Controlled Voltage-Source-Based Forced Resonant Mechanical DC Circuit Breaker

A Novel Thyristor-Controlled Voltage-Source-Based Forced Resonant Mechanical DC Circuit Breaker

Operation Characteristics of a Mechanical DC Circuit Breaker With a Resistive Superconducting Element for High-Reliability HVDC Applications

The issue of DC transmission and distribution systems is increasing due to the increase in DC supply and demand. The fu-ture MTDC (Multi-Terminal HVDC) system is becoming a big issue beyond the general PTP (Point to Point) HVDC system. We live in an era where the super grid is gradually expanding. However, the protection device is required to protect the grid conversion equip-ment from fault currents during line transients to progress from the HVDC stage to the MTDC stage in PTP. The DC fault current, about ten times higher than AC, occurs at a very high speed because of the lack of zero-crossings. We propose a resistive-mechanical DC circuit breaker with a resistive superconducting element is a com-bined model of a resistance-type superconducting element and a me-chanical DC circuit breaker. In detail, it limits the initial fault cur-rent by quenching the resistive superconducting element. Also, it creates an artificial zero-crossing through the LC divergence oscil-lation circuit of the mechanical DC circuit breaker to perform safe fault protection. In this paper, the fault protection of the resistive-mechanical DC circuit breaker with a resistive superconducting el-ement was tested to confirm the current limiting rate of the initial fault current, the artificial zero-crossing, and the total cutoff time. As a result, the initial fault current was limited by about 17.3% by quenching the resistive-superconducting element.

Design and Study of the Key Characteristics of a New DC Vacuum Interrupter With a High Peak and Low Residual Magnetic Field

With the rapid development of multiterminal high-voltage direct current (HVdc) transmission systems, the research and development of high-speed and stable high-voltage dc circuit breakers have received attention. Among them, mechanical dc circuit breakers based on manual zero-crossing dc breaking technology have been applied in practical projects, owing to their small size, low on-state loss, and low price. However, this method adds a high-frequency current, which deteriorates the magnetic field between the poles of the interrupter when the arc is broken. Therefore, the development of HVdc circuit breakers that maintain high peak magnetic fields and low residual magnetic fields at high frequencies has become the key to the development of multiterminal HVdc transmission. To solve this problem, this article proposes a new interrupter for a vacuum dc circuit breaker based on artificial zero-crossing technology and studies its key characteristics, such as temperature rise, electromagnetic field, and arc column plasma distribution characteristics. The results reveal that the new interrupter proposed in this article has a low-temperature rise, uniformly distributed electric field, high peak value and low remanence of the longitudinal magnetic field, and uniformly distributed plasma in the arc column, and exhibits arc diffusion. Its ability to cope with high-frequency current is significantly higher than that of the traditional cup-shaped axial magnetic field (AMF) contact system interrupter, which is conducive to the high-speed and stable breaking of the interrupter.

The Structural and Electromagnetic Comparative Analysis of the Bifilar-Meander-Type Winding Method of Superconducting DC Circuit Breaker

As the utilization of DC systems increases worldwide, the importance of DC cutoff technology is increasing. We proposed a hybrid DC cutoff technology combining an SFCL (superconducting fault-current-limiter) and a mechanical DC circuit breaker. This model can perform a fault-current-limiting operation through the quenching of the SFCL and a breaking operation through an artificial cutoff zero point of a mechanical DC circuit breaker. In particular, the SFCL is responsible for the growth of the initial fault current according to the DC characteristics. As the DC system’s supply and demand increase, the DC system’s capacity also increases. Therefore, the fault-current-limiting capability of the SFCL should be increased according to the increasing DC system breaking capacity. The fault-current-limiting capability can be increased by increasing the superconducting wires used in the SFCL. Current commercially available SFCLs use bifilar-helical-type and bifilar-spiral-type winding methods. These have the disadvantage of increased volume with increased capacity. To compensate for these disadvantages, we proposed a bifilar-meander-type winding method. In this paper, a new bifilar-meander-type winding method was introduced. In addition, the structural and electromagnetic parts of the existing winding method and the bifilar-meander-type winding method were compared and analyzed for differences. The program used for this analysis is the electromagnetic analysis Maxwell program. As a result, it was confirmed that the bifilar-meander-type winding method is superior to the conventional bifilar-helical and bifilar-spiral types.

An adaptive reclosing scheme for MVDC distribution networks with mechanical DCCBs

The DC distribution network is an effective solution to distributed renewable energy applications. After a fault occurs in the network, it is necessary to quickly identify and isolate it to protect system components. Subsequent to fault isolation by DC circuit breakers (DCCBs), power transmission should be swiftly restored by reclosing to improve system reliability. However, conventional reclosing schemes risk a second strike on the grids and endanger the safety of the networks. Given those drawbacks, an adaptive reclosing scheme for medium-voltage DC (MVDC) networks is proposed in this paper. An additional signal injection branch with a simple control strategy is appended to the existing commutation branch of a mechanical DCCB for reclosing. The fault nature can be identified by analyzing the magnitudes of one know frequency of the voltage signals injected into the faulty lines while fault locations under permanent faults can also be calculated before reclosing by applying this scheme. Compared with currently widely used methods, this scheme is characterized by its simplicity in structure and affordability in costs. Simulation results by PSCAD/EMTDC verify the efficacy and robustness of the proposed scheme.

A Passive Thyristor-Based Hybrid DC Circuit Breaker

DC circuit breaker (DCCB) is one of the most important technologies for safe and reliable operation of dc grid. And the hybrid DCCB (HCB) is obviously promising in high-voltage application area, because it combines both the advantages of mechanical DCCB and solid-state DCCB. At present, insulated gate bipolar transistors (IGBTs) are generally used for configuring the main breaker branch in the HCB. Compared with IGBTs, thyristors have the merits of ability to bear higher surge current, higher reliability, and lower cost, thus being more economical and reliable when used to replace IGBTs. Right now, several topologies of thyristor-based HCBs have been proposed, but the economy, reliability, control complexity, as well as the operation performance, can still be improved. In this article, a novel passive thyristor-based HCB is proposed. Compared with existing IGBT-based HCBs, the proposed HCB has significant advantages on economy and reliability, due to the application of thyristors for replacing IGBTs. In addition, in the proposed scheme, the required thyristors count is reduced and the additional power supply for capacitor precharging is saved, so the investment and control complexity are both cut down. The feasibility and superiorities of the proposed HCB are validated with scaled-down experiment test and 500-kV-level simulation case study.

Experimental Evaluation of 5 kV, 2 kA, DC Circuit Breaker With Parallel Capacitor

This article describes design, operation and experimental testing of a mechanical DC CB (Circuit Breaker) with parallel capacitors. The topology resembles hybrid DC CB but there are possible advantages in the costs since the main semiconductor valve is replaced with capacitors, and in performance since this breaker inserts counter voltage earlier. A detailed PSCAD model is employed to support DC CB design and to analyse operating principles. A 5 kV, 2 kA hardware demonstrator with 1.5 ms disconnector opening time is developed in the university laboratory. The test results demonstrate successful breaking of DC currents, with the measured time for insertion of capacitor voltage of around 290 μs. Further experimental analysis evaluates stresses on the key components, optimal timing for opening of LCS (Load Commutation Switch) and the margins for successful current interruption.

Comparison and Analysis of Impedance According to the Winding Method of Superconducting Element Connected to DC Circuit Breaker

DC Interruption technology is essentially required as DC systems and microgrids have increased. The Interruption technology also includes current limiting technology. Until now, many hybrid Interruption technologies have been proposed in which a semiconductor element or a superconducting element is combined with a mechanical DC circuit breaker. In this paper, an interrupting test was performed by combining a superconductor and a DC circuit breaker. The advantage of circuit breakers combined with superconducting elements is that they do not cause losses and effectively limit the fault current. When the fault occurs, if the fault current exceeds the critical value of the superconducting material, resistance occurs in the superconducting element. The fault current is limited by the resistance generated during quenching and resonates due to the LC divergence oscillation circuit. The current flowing through the mechanical circuit breaker reaches zero-point by resonance. After that, the mechanical breaker is completely opened, and the fault current is interrupted. Superconducting elements exhibit different characteristics depending on their winding method, material, and length. The purpose of this study is to comparatively analyze solenoid and toroid coil type superconducting elements. Both types are made with the same number of turns, permeability, and length. As a result of the experiment, the toroid coil has generated more impedance than the solenoid coil.

An adaptive reclosing strategy for high-voltage DC grids with mechanical DC circuit breakers

After fault isolation, the timely reclosure of DC circuit breakers (DCCBs) can improve the reliability of high-voltage DC (HVDC) grids. In previous studies, many adaptive reclosing strategies have been proposed to reclose hybrid DCCBs without a second fault shock. However, the reclosure of mechanical DCCBs is much different from that of hybrid DCCBs and has only received little attention. During permanent faults, further research is needed to make full use of the internal capacitor of a mechanical DCCB to suppress the second fault shock. In this paper, an adaptive reclosing strategy is proposed for a mechanical DCCB, which has the following merits: 1) the second fault shock is effectively suppressed during permanent faults; and 2) the power transmission is restored without significant voltage oscillations during temporary faults. In the preparation stage, the internal capacitor is discharged to a high residual voltage. The HVDC grid injects a traveling wave (TW) into the isolated line through the internal capacitor, and the permanent and temporary faults are distinguished using the TW characteristic. The adaptive reclosing strategy is presented in detail and compared with several existing strategies. Finally, the proposed strategy is validated using PSCAD/EMTDC simulations.

An integrated multi-port hybrid DC circuit breaker for VSC-based DC grids

DC circuit breakers are of great significance for the reliable and flexible operation of VSC-based DC grids. The hybrid DC circuit breaker (HDCB) combines the advantages of low on-state loss of the mechanical DC circuit breaker and fast breaking speed of the solid-state DC circuit breaker, showing excellent application prospects. However, the cluster of two or more HDCBs connected to the same DC bus could significantly increase the total project investment. At present, the solution based on multiport HDCB (M-HDCB) has been proposed to practically reduce the construction cost, but the power transmission among adjacent healthy DC lines will also be interrupted after the isolation of DC bus fault, which is still a challenging problem. Therefore, in order to solve this problem, a novel integrated multiport HDCB (IM-HDCB) is proposed in this paper. In addition to the shared transfer and energy dissipation branches, the key auxiliary units composed of diode-stacks and thyristor-stacks are also integrated into the IM-HDCB to enhance the overall performance. Compared with existing solutions, it is shown that the proposed IM-HDCB has more excellent performance. Finally, the capabilities of the proposed novel IM-HDCB are validated by simulations in PSCAD/EMTDC.

Flexible Fault Current Adaptation Features of a Novel DC Circuit Breaker Assisted by Superconducting Fault Current Limiters

The high d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> before zero-crossings easily leads to delayed or failed operations for the active current injection mechanical DC circuit breaker, especially for small direct current interruptions. The pre-charging process also makes this type of circuit breaker hard to realize repeat operations economically in the high voltage DC system. This paper proposes a novel DC circuit breaker and its design method that deeply coordinating a superconducting fault current limiter with the active current injection DC circuit breaker. This method significantly reduces d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> before current zero-crossings and enables repeat operations economically. Besides limiting fault currents, the superconducting fault current limiter also charges the resonance capacitor flexibly in the circuit breaker, realizing the injected reverse current keep a constant proportion to the arbitrary fault current. Validations of the flexible capacitor charge and repeat operations are made by simulation and low voltage experiments. The charging times are within 2.5 ms and the reverse current keeps 1.2 to 1.7 times over the fault current under arbitrary conditions. D <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> at current zero is reduced by 80% under 30% of rated interruption capacity. Flexible capacitor charge experiments are consistent with the simulation design. The superconducting tapes can recover within 300 ms to support repeat operations.

Study on Overvoltage Rise Rate Suppression Method for DC Interruption

DC circuit breaker is the key equipment for control and protection in the medium and high voltage DC system. Mechanical DC circuit breakers have transient overvoltage in breaking, which may lead to re-breakdown of the breaker or even breaking failure in severe cases. In this paper, the transient overvoltage in the breaking process of typical mechanical DC circuit breakers is studied. An improved topology which can supress the transient voltage is propose. The effect of different capacitance and resistance parameters on weakening the transient voltage is investigated, and the adaptability of the proposed method to different breaking currents is studied.

The Modeling of the LC Divergence Oscillation Circuit of a Superconducting DC Circuit Breaker Using PSCAD/EMTDC

We proposed a superconducting DC circuit breaker that can reliably cut off the fault currents in preparation for the DC system. It consists of a superconducting element and a mechanical DC circuit breaker. The mechanical DC circuit breaker is connected in parallel with a mechanical high-speed switch, an LC divergence oscillation circuit, and a surge arrester. This provides stable cutoff operation due to the fault-current-limiting operation of the superconducting element and the artificial current zero point of the mechanical DC circuit breaker. In this paper, the operating principle of the LC divergence oscillation circuit that creates an artificial current zero point was reviewed based on the theory. We used experimental data to model the time constant of the initial fault current, the arc model generated by the mechanical high-speed switch, and the experimental equipment. As a result, the LC divergence oscillation circuit was confirmed in the simulation, and simulation modeling was reviewed based on the theoretical principle of generation.

First-Principles Calculation of Conductivity of Ce-C Codoped SnO2 Contacts

The contact is the core element of the vacuum interrupter of the mechanical DC circuit breaker. The electrical conductivity and welding resistance of the material directly affect its stability and reliability. AgSnO2 contact material has low resistivity, welding resistance, and so on. This material occupies an important position of the circuit breaker contact material. This research is based on the first-principles analysis method of density functional theory. The article calculated the lattice constant, enthalpy change, energy band, electronic density of state, charge density distribution, population, and conductivity of Ce, C single-doped, and Ce-C codoped SnO2 systems. The results show that Ce, C single doping, and Ce-C codoping all increase the cell volume and lattice constant. When the elements are codoped, the enthalpy change is the largest, and the thermal stability is the best. It has the smallest bandgap, the most impurity energy levels, and the least energy required for electronic transitions. The 4f orbital electrons of the Ce atom and the 2p orbital electrons of C are the sources of impurity energy near the Fermi level. When the elements are codoped, more impurity energy levels are generated at the bottom of the conduction band and the top of the valence band. Its bandgap is reduced so conductivity is improved. From the charge density and population analysis, the number of free electrons of Ce atoms and C atoms is redistributed after codoping. It forms a Ce-C covalent bond to further increase the degree of commonality of electrons and enhance the metallicity. The conductivity analysis shows that both single-doped and codoped conductivity have been improved. When the elements are codoped, the conductivity is the largest, and the conductivity is the best.

Characteristics of a Superconducting DC Circuit Breaker According to L and C Elements of LC Divergent Oscillation Circuit

Currently, we are developing an AC/DC conversion technology with the development of power semiconductors. Accordingly, DC is attracting attention because it is advantageous in the current transmission system. However, it has a problem that the cut-off technology required for DC system operation has not been secured yet. We are researching and developing a DC cut-off technology in several ways. We proposed a model that combines a superconducting fault current limiter and a DC circuit breaker. This is a configuration which a superconducting fault current limiter and a mechanical DC circuit breaker are connected in series. The superconducting fault current limiter limits the initial fault current and the mechanical DC circuit breaker cuts off the fault current. The mechanical DC circuit breaker consists of a high-speed DC switch, a LC divergent oscillation circuit and a surge arrester. This creates an artificial zero-point by affecting the blocking of the DC fault current according to the LC diverging oscillation circuit. In this paper, we analyzed the effect of the LC divergent oscillation circuit on the superconducting DC circuit breaker according to Reactor (L) and Capacitor (C). As a result, we analyzed the operating characteristics of the superconducting DC circuit breaker according to the application of the LC divergent oscillation circuit using the PSCAD/EMTDC program. Also, we confirmed the characteristics of the initial fault current limit rate of the superconducting fault current limiter and the possibility of controlling how the LC divergent oscillation circuit affects the DC arc generated at the opening of the mechanical DC contacts.

A Novel Forced Resonant Mechanical DC Circuit Breaker by Using Auxiliary Oscillation Switch for Zero-Crossing

A low-cost mechanical circuit breaker (MCB) is an important solution in the field of dc breaking. However, the zero-crossing points in the breaking process of the existing MCBs are either insufficient in number or slow in generation, which limits the breaking performance of MCBs. This letter proposes a novel forced resonant MCB (FR-MCB). A large number of zero-crossing points can be generated in a short time by utilizing a resonant circuit and a power electronic-based auxiliary oscillation switch. Thus, the FR-MCB can exhibit more reliable and faster breaking performance while maintaining the low cost. After the detailed analysis of current oscillation and breaking process in the FR-MCB, a prototype experiment of up to 10 kV/8 kA is conducted to verify its feasibility.

기계식 DC 차단기에 적용 가능한 초전도 벌크 및 와이어 유형의 비교 분석

The core technology of the DC grid system is to protect the system in the event of a transient and to cut-off the faults current in a trouble line, quickly. We sat down to analyze to implement the DC breaking technology of mechanical DC circuit breaker on the faster and more safely. However, the mechanical DC circuit breakers have limitations on the opening speed and the components of the break contact. To solve this problem, we applied a superconducting electromagnet to a mechanical DC circuit breaker and proposed a method to reduce the DC Arc energy generated during the breaking operation. In this paper, we proposed the application of superconducting bulk-type magnet and superconducting wire-type electromagnet to the conventional mechanical DC circuit breaker and analysed the breaking characteristic. We designed a mechanical DC cutting-off contact, a superconducting bulk-type magnet, and a superconducting wire-type electromagnet through the Maxwell 3D program. As a result, the Lorentz force was generated between the mechanical DC cutting-off contacts each applied the superconducting bulk-type magnet and wire-type electromagnets. The superconducting bulk-type magnets produced a magnetic force of about 269.3 A/m and the superconducting wire-type electromagnet produced a magnetic force of about 610 A/m affecting DC arc blowing.

Operation Characteristics of Mechanical DC Circuit Breaker Combined with LC Divergence Oscillation Circuit for High Reliability of LVDC System

DC systems are modernly starting to come into the spotlight again due to the carbon-neutral policy, the development of semiconductor devices for power, and the increase in digital loads. We need to prepare in advance solutions to problems that may arise from fault currents due to transients for future DC power grid models. In the case of DC, there is no current zero-point because there is no frequency. Therefore, a large switching surge is generated when the circuit breaker cuts off the fault current. The possibility of insulation breakdown is greater than that of AC in severe cases. We consider power semiconductors or superconducting current limiters as an alternative. However, DC breaking cannot be safely achieved by itself. For reliable DC breaking, mechanical circuit breakers must be used with them. Among the mechanical shut-off methods, we adopted the divergence oscillation method. It has the biggest advantage compared to other methods in that it has a simple structure by composing passive elements and can artificially create zero current. In addition, it can be applied to a power semiconductor and a superconducting current limiter to perform a high-reliability cut-off operation. In this paper, we conducted simulation analysis by configuring the DC power grid and DC cut-off system through the PSCAD/EMTDC program. Results confirmed that the application of the LC divergence oscillation circuit can reduce the cut-off time and reduce the power burden of the mechanical DC circuit breaker (MCB).

PSCAD/EMTDC를 활용한 초전도 소자의 유무에 따른 기계식 DC 차단기 분석

With the announcement of a policy to reduce carbon emissions, the range and technologies of renewable energy sources are increasing. In new renewable energy, the amount and range of solar power generation is relatively gradually expanding[1]. Based on the high-speed DC circuit breaker used in the solar power generation, we combined the LC divergence oscillation circuit and the superconducting element that this research team is working on. This is to protect peripheral equipment against an increase in solar power generation and unspecified disturbances. The DC circuit breaker, we propose is a mechanical DC circuit breaker with a superconducting element applied. The superconducting element can lower the initial fault current within about 2 ㎳ through the quenching operation. However, it takes a large power burden and a long time to cut-off the fault current. In the mechanical DC cut-off part, the existing high-speed mechanical circuit breaker, LC divergent oscillation circuit and Surge Arrestor are connected in parallel to safely and reliably cut off fault current. The characteristics of the cut-off operation that appear when a superconducting element and an LC divergent oscillation circuit are combined with a conventional mechanical DC circuit breaker were analyzed. As a result, through the application of the superconducting element, the speed at which the artificial zero-point of the fault current occurs was reduced, and the time to complete the shutdown was shortened.

초전도 소자에 의한 DC 차단기의 동작 특성

Superconducting current limiting impedance selection method according to the DC circuit breaker operation characteristics for economic gain with the HVDC hybrid type superconducting DC circuit breaker is attracting attention globally. Due to the development and expansion of renewable energy sources and the development of power semiconductors, HVDC has the advantages of high system transmission efficiency and asynchronous connection. HVDC is currently being developed and commercialized as a pole-to-pole system. As the development of MVDC, LVDC and HVDC progresses, DC grid systems capable of exchanging DC power with each other will be built. A circuit breaker that can increase the reliability of the DC system operation should therefore be developed. HVDC, hybrid, semiconductor and reverse-current-type circuit breakers have been studied as potential circuit breaker options, with many papers being published to demonstrate their respective performances. In this paper, a hybrid superconducting DC circuit breaker was proposed. It consists of a superconducting fault current limiter, a mechanical cut-off contact, an LC circuit and a SA(SA). The rapid rise of the fault current was limited by using the impedance of the superconductor, while the fault current was interrupted by the cut-off operation of the mechanical DC circuit breaker. If the superconducting element shows higher fault current than the breaking capacity level of the DC circuit breaker and the burden on the superconductor will increase. Therefore, efforts were made to confirm the appropriate cut-off capacity level of the DC circuit breaker and the current limiting impedance of the superconductor through experiments. As a result, we proved that the current limiting impedance of the superconductor could be analyzed based on the tripping operation of the DC circuit breaker.