Direct Current Circuit Breakers Research Articles

Closing performance of the Thomson‐coil actuator for a 110 kV FMS

In the 500 kV hybrid high-voltage direct current (HVDC) circuit breaker, there are five 110 kV fast mechanical switches (FMSs) in the nominal current path. When the detection system detects the failure of the hybrid circuit breaker, in order to protect the disconnectors or semiconductors, the FMSs are required to close quickly. The closing drive technology can be divided into two categories, based on the closing speed of the Thomson-coil actuator. One is based on the conventional closing drive, the open−close operating time of which is 20.0 ms. The other type is based on the fast closing drive, which is used under fault conditions and the total time is ∼7.5 ms. A 110 kV/3 kA prototype FMS employing an interrupter with a 30 mm maximum open gap and 4 kg total moving mass has been modelled based on the equivalent circuit method. Through the simulation, the effect of discharging time sequence on open−close operation has been studied, and the general timing control design principle has been provided.

Flexible, Highly Dynamic, and Precise 30-kA Arbitrary Current Source

High-power current sources with high dynamic performance, ultralow current ripple, and absolute reference tracking accuracy are the key elements for magnets (bumper and septum) that are used in accelerators. Similar requirements are also encountered in plasma research applications in fusion reactors, as well as plasma research for the future high voltage direct current circuit breakers. Therefore, the current source must be able to drive resistive/inductive and highly fluctuating loads without any compromise in its performance. In this paper, such a flexible, dynamic, and accurate current source is introduced, which able to provide amplitudes up to 30 kA and bipolar voltages up to 10 kV. The system’s operating concept is presented and its design procedure in order to fulfill a list of demanding specifications is demonstrated. In addition, a detailed description of its near-optimal, advanced control system is presented. Finally, the theoretical considerations are verified by extensive simulation results for various operating scenarios, including driving chaotic arc loads.

Requirement analysis of hybrid direct current breaker in multi‐terminal high‐voltage direct current grids

Hybrid direct current circuit breakers (DCCB) are the most adopted solution to clear high DC fault currents in short time. Existing literature does not analyse recently validated commercial breakers. This article provides an overview about hybrid DCCB and a list of criteria to evaluate and compare the performance of existing or new DCCB designs. Additionally, general measures are proposed to assess the suitability of the DCCB in a specific grid situation. Accordingly, the fault current evolution under pole-to-pole faults in different parts of a multi-terminal DC grid is analysed by means of mesh analysis with matrix differential equations. Finally, a grid parameter variation analysis is carried out through PSCAD-EMT simulations to compare the presented DCCB concepts.

Technical Assessment of Hybrid DCCB With Improved Current Commutation Drive Circuit

Current commutation from the load current path to the commutation path is the precondition to interrupt current successfully for hybrid direct current circuit breakers (DCCB). With remarkable current commutation performance, current commutation drive circuit (CCDC), mainly consisting of air-core transformer, fast-closing switch (FCS), and precharged capacitor, is proposed by us. In this paper, to eliminate the operating losses of CCDC and to avoid unrecoverable damage of FCS, CCDC used in hybrid DCCB for current commutation has been improved. Different submodules (SM) of commutation path in hybrid DCCB are analyzed, and experiments have been carried out on a hybrid DCCB prototype. Theoretical analysis and experiment results have shown that no matter which kind of SM is used, improved CCDC can ensure reliable current commutation in hybrid DCCB. In the end, by taking total cost of CCDC into consideration, a novel optimization method is proposed to design the parameters of CCDC. With this optimization method, CCDC for hybrid DCCBs with different rated voltage and current can be designed individually and its cost could be reduced significantly.

A new topology for current limiting HVDC circuit breaker

With the high voltage direct current Transmission (HVDC) booming, HVDC grid has received wide attention. As an essential component in HVDC grid, high voltage direct current circuit breakers (DCCB) requires urgent and intensive study. A novel topology for current limiting DCCB (CL-DCCB) is proposed in this paper. The topology consists of several units which are divided into two classes: main circuit breaker (MCB) and branch circuit breakers (BCBs). The number of inductor branches can be flexibly selected to enhance the current limiting effect. The CL-DCCB can start current limiting operation when a suspected fault occurs. When the detection circuit reveals what has happened, it can be determined whether to implement breaking operation or recover to normal state. This mode allows longer fault detection time and circuit breaker operation delay while guaranteeing the fault current within the maximum limit of the system. Finally, Simulation model and experiment prototype are built to study the design criteria for CL-DCCB. It is observed that the maximum detection delay can be extended to 12 ms. Moreover, the current limiting effect can be enhanced when the number of inductor branches or the inductance of each branch is increased.

Electric Field Characteristics of an Arc-Induction-Type DC Circuit Breaker Combined with a Magnet for Stability in the DC Power Grid

For stability in the direct current (DC) power grid, it is very important to limit the current of the fault section and to protect the system in the fault condition. That is the core technology of the DC power grid. This paper suggests characteristics and a limited range of the fault current for the new model as the significant protecting technology in the DC power grid. Such new model is the arc-induction-type DC circuit breaker (CB) combined with a magnet. The magnetic arc-induction-type direct-current circuit breaker (DCCB) consists of a neodymium magnet, an induction needle, and electrical contacts. During fault operation, the arc occurring between the contacts is induced to the induction needle. To increase the induction effect, Lorentz force is applied to blow the arc. A magnet was applied to reduce the initial fault current and to induce magnetic flux. The simulation data were analyzed using the Maxwell 3D software program. The electric field included the electric force and the electric charge. Therefore, it could analyze the arc as the electric field. The simulation was performed based on the preceding study on induction needle. As a result of the simulation, it was confirmed that the electric field value of the induction needle increased when the DCCB was combined with a magnet.

Centralised busbar differential and wavelet‐based line protection system for multi‐terminal direct current grids, with practical IEC‐61869‐compliant measurements

This study presents a method for discriminative detection of direct current (DC) faults on voltage source converter-powered multi-terminal high-voltage direct current transmission systems using two fundamental guiding principles, namely instantaneous current-differential and travelling waves. The proposed algorithm utilises local voltage and current measurements from all transmission lines connected to a DC busbar, and current measurement from the DC side of the converter. The scheme operates at a sampling frequency of 96 kHz, which conforms with IEC 61869-9. No long distance communication is involved while measurements and signal exchange within DC substations are enabled by the utilisation of IEC 61850. Performance is assessed firstly through detailed transient simulation, using verified models of modular multi-level converters, hybrid DC circuit breakers and inductive DC-line terminations. Furthermore, practical performance and feasibility of the scheme are evaluated through laboratory testing, using the real-time Opal-RT hardware prototyping platform. Simulation and experimental results demonstrate that the proposed protection algorithm can effectively, and within a very short period of time (i.e. <;1 ms), discriminate between busbar and line faults (internal faults), while remaining stable during external faults. Additionally, it has been demonstrated that IEC 61869-9 is suitable for enabling fast DC protection schemes incorporating travelling waves.

Effects of arc ablation on surface electrical performance of epoxy resin insulation

Operation of a high-voltage, direct current circuit breakers can cause irreversible damage to the surface electrical performance of insulation due to arc ablation. To analyze the failure mechanism, the epoxy resin (EP) insulation was ablated under experimental arcs of different energy values. The rated current of the experimental arc is 5 A, and the ablation energy values were set as 0 J, 31.3 J, 78.2 J, 109.6 J and 156.5 J respectively by changing the arc duration. The destruction of the EP surface molecule structure was investigated by using x-ray photoelectron spectroscopy and gas chromatography. Furthermore, the surface potential decay and distribution characteristics of surface traps were studied by using the isothermal surface potential decay (ISPD) method. The test results indicate that when arc energy reaches 156.5 J, the DC flashover voltage of EP decreases by 64.7% and the surface conductivity increases by 3.22 times, compared with that of the virgin sample. Reductive groups in EP molecules are oxidized when suffering arc ablation, thereby leading to the breakage of molecular chains and severe carbonization, forming amorphous carbides with high conductivity on EP surface. ISPD results show that the density of deep traps and the center energy level of traps on the EP surface increase when the arc energy increases. These traps can form multiple charge centers and distort the electric field distribution on the EP surface. Thus, the partial discharge is promoted and flashover finally occurs, thereby decreasing the surface electrical strength of EP.

Quench Protection of the Central Solenoid Model Coil for the CFETR

The China fusion engineering test reactor is a new tokamak device. The central solenoid (CS) model coil, which is responsible for developing and verifying the key manufacturing methods of a superconducting magnet, is now under engineering design. The rating current of the coil is 47.65 kA and total magnetically stored energy reaches 407 MJ, so a quench protection is required to discharge this huge stored energy. This paper gives a description of the quench protection of CS model coil. The circuit of the quench protection system is designed, which consists of the direct current circuit breaker, discharge resistor, diode, and fuse. The main parameters of these components were selected. The control system of quench protection is also introduced.

Development of HVDC system-level mechanical circuit breaker model

The main goal of the paper is the modelling of the mechanical direct current circuit breaker (DC CB) with active current injection that includes different circuit breaker characteristics. System level models provide adequate representation of the circuit breakers for system analysis studies. The performance characteristics of the DC CB in those proposed models replicate the ones of the devices in practice. The developed mechanical circuit breaker model is realized for a 320 kV demonstration circuit in PSCAD environment and its limitations and robustness are analyzed. The performance of the model is investigated by different cases. The obtained results show that the DC CB model can be used with full success for both to simulate DC fault interruptions and to be used for different protection studies.

Reducing Peak Current and Energy Dissipation in Hybrid HVDC CBs Using Disconnector Voltage Control

Peak fault current and energy dissipation in high-voltage direct current (HVdc) circuit breakers (CBs) are very important parameters that impact dc grid protection development. This paper analyzes a hybrid DCCB (HCB) control that reduces peak current and energy dissipation by regulating the voltage across contacts of the ultrafast disconnector (UFD). This is achieved by manipulating the number of inserted surge arresters while contacts of the UFD are moving apart. The controller is seamlessly integrated with the current controller of HCBs. An analytical model for current and energy calculation is presented, verified, and employed for parametric studies. A PSCAD simulation with 320-kV, 16-kA test circuit confirms that the proposed voltage control reduces the peak current and energy dissipation by around 20%-30%. A 900-V, 500-A HCB laboratory hardware is described and the experimental results are shown to corroborate simulation conclusions.

A Direct Current Circuit Breaker With the Grid Method

This paper describes the developed direct current circuit breaker with the grid method (DC CBG). The simplified DC CBG was designed and constructed. It comprises the third electrodes, as the grid of a triode, installed between the main contact electrodes. Moreover, the special-designed transformer (SDT) was designed and constructed to supply a damping high-voltage pulse to the grid electrode for suppressing the arc current. The experiment was conducted to verify the performance of the designed DC CBG. Experimental results show that the amplitude of the arc current was significantly reduced by approximately 94% after the damping high-voltage pulse generated from the SDT was applied to the third electrode. Therefore, the proposed DC CBG has the ability to be developed for practical use in the future.

Design and Experimental Tests of a Superconducting Hybrid DC Circuit Breaker

Direct current (DC) circuit breakers are a key enabling technology for fault management in multiterminal high-voltage DC (HVDC) systems. DC fault isolation is challenging due to the high rate of rise of the fault current and the lack of natural current zero-crossings found in ac systems. In this paper, we present a novel superconducting hybrid dc circuit breaker that utilizes the intrinsic characteristics of the superconductor material. The automatic quench of the superconductor coil as a result of a high fault current transfers the current from the mechanical switch to the semiconductor switch. The isolating mechanical switch is able therefore to open at low current and recover its dielectric capability rapidly. A low voltage DC circuit breaker prototype has been built using a multistrand magnesium diboride (MgB2) coil, a vacuum interrupter, and an insulated-gate bipolar transistor module. This prototype successfully demonstrated interruption of 500 A DC within 4.4 ms. This paper presents the design of the superconducting hybrid breaker prototype and a detailed analysis of the experimental results. This superconducting hybrid dc circuit breaker has significant potential for scaling up the high-voltage and high-current applications.

Transient Current Interruption Characteristics of a Novel Mechanical DC Circuit Breaker

With the rapid development of multiterminal direct current (MTDC) grids, high-voltage direct current circuit breakers (HV-DCCB) capable of interrupting currents within 5 ms are in urgent demand. The mechanical DCCB has always been one of the main proposals for HV-DCCBs. The current commutation is the prerequisite for mechanical DCCBs to interrupt currents successfully. Focused on the current commutation difficulty, a novel mechanical DCCB has been investigated in this paper. A simulation model of the novel mechanical DCCB in MTDC system for fault current interruption was established in PSCAD. By analyzing the simulation results, the detailed transient varying patterns of current, voltage, and energy in the novel mechanical DCCB during its interruption process are revealed. To verify the feasibility of the novel mechanical DCCB, a prototype was developed in the lab, and current interruption tests were carried out on the prototype. Experimental results have shown that a current of 5.3 kA can be interrupted by the prototype within 3 ms. In the end, failures that occurred in initial experiments are discussed and relative protection measures have been proposed. By adopting these measures, failures are successfully avoided and the normal operation of the novel mechanical DCCB are ensured.

A Novel Topology of Hybrid HVDC Circuit Breaker for VSC-HVDC Application

The use of high voltage direct current (HVDC) circuit breakers (CBs) with the capabilities of bidirectional fault interruption, reclosing, and rebreaking can improve the reliable and safe operation of HVDC grids. Although several topologies of CBs have been proposed to perform these capabilities, the limitation of these topologies is either high on-state losses or long time interruption in the case bidirectional fault current interruption. Long time interruption results in the large magnitude of the fault current in the voltage source converter based HVDC (VSC-HVDC) system due to the high rate of rise of fault current. This paper proposes a new topology of hybrid CB (HCB) with lower conduction loss and lower interruption time to solve the problems. The proposed topology is based on the inverse current injection method, which uses the capacitor to enforce the fault current to zero. In the case of the bidirectional fault current interruption, the capacitor does not change its polarity after identifying the direction of fault current, which can reduce the interruption time accordingly. A switching control algorithm for the proposed topology is presented in detail. Different operation modes of proposed HCB, such as normal current mode, breaking fault current mode, discharging, and reversing capacitor voltage modes after clearing the fault, are considered in the proposed algorithm. The proposed topology with the switching control algorithm is tested in a simulation-based system. Different simulation scenarios such as temporary and permanent faults are carried out to verify the performance of the proposed topology. The simulation is performed in the Matlab/Simulink environment.

Design, Modeling and Control of Hybrid DC Circuit Breaker Based on Fast Thyristors

This paper presents a systematic study on designing a hybrid direct current (dc) circuit breaker (CB) based on fast thyristors. As an illustration, the dc CB main parameters are calculated for a 120 kV, 1.5 kA test breaker with an interrupting current of 10 kA. The studies indicate that the opening time of 2.3 ms can be achieved only if fast thyristors are employed. It is further illustrated that there is a design tradeoff between minimum interrupting current capability and discharge time for the internal capacitors (reclosing speed). The dc CB control system for opening and closing is presented based on different levels of protection and the self-protection. The dc CB is modeled in PSCAD and simulation results are used to evaluate the breaker performance under different operating conditions. It is concluded that the model represents well the dc CB and can be employed for dc grid protection studies. It is further shown that the opening time becomes longer as interrupting current reduces, and it is very long in the case of load current interruption.

Pole-to-Ground Fault Analysis and Fast Protection Scheme for HVDC Based on Overhead Transmission Lines

Flexible direct current (DC) transmission network technology is an effective method for large capacity clean energy access to power grids, but the DC short-circuit fault detection for it is a difficult problem. In this paper, the pole-to-ground fault transient characteristics in a multi-terminal DC power grid, based on overhead transmission lines and DC circuit breakers, are analyzed firstly. Then, a fast protection scheme is proposed according to the fault transient characteristics. Only local information is utilized for fault detection and location in the proposed scheme. Moreover, the scheme is verified to have the advantages of fast action speed, high reliability and the ability to resist the transition resistance. A four terminal DC power grid model based on actual engineering parameters is established in PSCAD/EMTDC, and the validity of the protection scheme under different fault conditions is verified by simulation results.

Integrated HVDC Circuit Breakers With Current Flow Control Capability

Two key problems in meshed high-voltage direct current (HVDC) transmission grids are managing line power flows and protection against dc faults. Current flow controllers (CFCs) will be required to balance cable currents in meshed dc grids, in order to prevent individual line power capacity limits restricting overall power flow in the grid. Direct current circuit breakers (DCCBs) will be also required to protect HVDC grids from dc faults. This paper demonstrates that the current flow controller functionality can be added into a hybrid CB's design. This paper proposes integrating an interline CFC into the load commutation switch (LCS) of a hybrid DCCB. The integrated design LCS/CFC is analyzed and a state-space model is derived. The control of the CFC is designed and the performance of the LCS/CFC during normal operation is verified by means of MATLAB Simulink and PSCAD simulations. A comparison of the integrated LCS/CFC and the separate design is given. The case studies show a reduction in total power losses, and improved protection operation times can be achieved.

Test Circuits for HVDC Circuit Breakers

High voltage direct current circuit breakers (HVDC CBs) are necessary for reliable and safe operation of future multi-terminal meshed HVDC grids. So far no commercially mature products of such equipment exist. A few industrial concepts as a result of advances in power electronics have been proposed and prototypes have been built. However, performances of these concepts have never been demonstrated under realistic operation conditions. Since these tests require construction of high power DC sources incurring significant investment costs, alternative test circuits providing equivalent stresses must be considered. In this paper various test methods and circuits used for testing HVDC CBs are investigated and their performance is evaluated against the stresses in a conceptual future HVDC grid. A novel method of testing an HVDC CB using existing installations in a high power ac test laboratory is proposed and its prospective fault current and voltage is experimentally demonstrated. It is concluded that adequate test circuits need to maintain the supply voltage not only up to the current zero in the main interrupter unit of the HVDC CB, but also during the entire energy dissipation phase of the interruption process.

Research on fault protection of DC grid based on hybrid MMC

The protection strategy of overhead direct current (DC) grid is studied based on the hybrid modular multilevel converter (MMC), which is composed of half bridge sub-modules and full bridge SMs (FBSMs). First, the topology, operating principle and DC voltage operating region of the hybrid MMC are analysed. Then, a control framework embedding three-channel control freedom and DC fault ride through control strategy are presented. Two protection schemes based on DC disconnectors and mechanical DC circuit breakers (DC CBs) are designed. In the first scheme, the hybrid MMC controls the DC fault to zero and a current injection method is adopted to restart the DC grid. In the second scheme, the mechanical DC CBs can block the DC fault current and has the ability to reclose for three attempts. At last, the feasibility of two schemes is validated in power systems computer-aided design/electro-magnetic transient design and control.