Coordinated Control of DC Circuit Breakers in Multilink HVDC Grids

High voltage DC grids are developing in more terminals and with larger transmission capacity,thus the re-quirements for DC circuit breakers(DCCB)will continue to rise.Conventional methods only use the faulty line DCCB to withstand the fault stress,and therefore this paper presents a coordination method of multiple DCCBs to protect the system.As many adjacent DCCBs are tripped to interrupt the fault current,the fault energy is shared,and the requirement for the faulty line DCCB is reduced.Moreover,the adjacent DCCBs are actively controlled to help system recovery.The primary protection,backup protection,and reclosing logic of multiple DCCBs are studied.Simulations confirm that the proposed control reduces the energy dissipation requirement of faulty line DCCB by approximately 30%-42%,the required current rating for IGBTs is reduced,and the system recovery time is also reduced by 20-40 ms.

Fluid-chemical modeling of the near-cathode sheath formation process in a high current broken in DC air circuit breaker

When the contacts of a medium-voltage DC air circuit breaker(DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column's diameter gradually becomes wider. The 11.14 V–12.33 V drops along the17 μm space charge layer away from the cathode(65.5 k V/m–72.5 k V/m) when the current varies from 20 k A–80 k A.The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core,but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.

Novel Fast Operating Moving Coil Actuator with Compensation Coil for HVDC Circuit Breakers

DC circuit breakers are major enabling components for multi-terminal HVDC systems.Their key design targets are operating speed and efficiency.This paper proposes a novel moving coil actuator using a compensation coil topology to operate mechanical circuit breakers.This topology aims to significantly improve the magnetic field saturation and reduce the system inductance,so that the operating speed is increased.Four possible connection methods for the compensation coils are proposed and analyzed using finite element modeling,ensuing simulation results are compared and discussed.The operating speed of the moving coil actuator with compensation coils is significantly improved compared with the original moving coil actuator.The moving coil actuator with compensation coils can open a distance of 5 mm within 2.8 ms and the peak efficiency is 47%.

Circuit Model with Current Interruption for Hybrid High Voltage DC Circuit Breakers to Achieve Precise Current Experiments

The current interruption test based on an LC resonance circuit for hybrid DC circuit breakers(HVDC CBs)is widely employed to characterize the current interruption capability of CBs.In order to ensure a high-fidelity replica of the fault current in a high voltage application,this paper first proposes an equivalent model of the test circuit,where not only parasitic resistances but also the threshold voltages and on-state resistances of various semiconductor devices are considered.Moreover,the analytical formula of the test current is derived by including the working principle of the HVDC CB.Secondly,the parameter extraction method,which combines finite element analysis and measurements by an impedance analyzer,is given in this paper.The extracted result implies that,in current interruption transients,equivalent resistances of 500 kV CB are as large as 535 mS,which have a significant influence on current waveforms.Thirdly,the 34 kV/25 kA current interruption test for the 500 kV CB is conducted.The measured results are proved to be consistent with the analytical results obtained from the proposed model,and the relative error is less than 2%.

Key stress extraction and equivalent test method for hybrid DC circuit breaker

Firstly, relevant stress properties of millisecond level breaking process and microsecond level commutation process of hybrid HVDC circuit breaker are studied in detail on the basis of the analysis for the application environment and topological structure and operating principles of hybrid circuit breakers, and key stress parameters in transient state process of two time dimensions are extracted. The established digital simulation circuit for PSCAD/EMTDC device-level operation of the circuit breaker has verified the stress properties of millisecond level breaking process and microsecond level commutation process. Then, equivalent test method, circuits and parameters based on LC power supply are proposed on the basis of stress extraction. Finally, the results of implemented breaking tests for complete 200 kV circuit breaker, 100 kV and 50 kV circuit breaker units, as well as single power electronic module have verified the accuracy of the simulation circuit and mathematical analysis. The result of this paper can be a guide to electrical structure and test system design of hybrid HVDC circuit breaker.

A Fault Current Limiting Hybrid DC Circuit Breaker

Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC grid.In order to suppress the rising speed of the fault current and reduce the current interruption requirements of the main breaker(MB),a fault current limiting hybrid DC circuit breaker(FCL-HCB)has been proposed in this paper,and it has the capability of bidirectional fault current limiting and fault current interruption.After the occurrence of the overcurrent in the HVDC grid,the current limiting circuit(CLC)of FCL-HCB is put into operation immediately,and whether the protected line is cut off or resumed to normal operation is decided according to the fault detection result.Compared with the traditional hybrid DC circuit breaker(HCB),the required number of semiconductor switches and the peak value of fault current after fault occurs are greatly reduced by adopting the proposed device.Extensive simulations also verify the effectiveness of the proposed FCL-HCB.

Magneto-hydrodynamic simulation study of direct current multi-contact circuit breaker for equalizing breaking arc

This work is based on a direct current(DC)natural current commutation topology,which uses load-carrying branch contacts carrying rated current and multiple sets of series arcing branch contacts in parallel to achieve circuit breaking.The proposed topology can meet the new requirements of higher voltage DC switches in aviation,aerospace,energy and other fields.First,a magneto-hydrodynamic arc model is built using COMSOL Multiphysics,and the different arc breaking characteristics of the arcing branch contacts in different gas environments are simulated.Then,a voltage uniformity coefficient is used to measure the voltage sharing effect in the process of dynamic interruption.In order to solve the dispersion of arcing contact action,a structural control method is adopted to improve the voltage uniformity coefficient.The uniform voltage distribution can improve the breaking capacity and electrical life of the series connection structure.

Adaptive Reclosing Scheme Based on Traveling Wave Injection For Multi-Terminal dc Grids

The hybrid dc circuit breaker(HCB)has the advantages of fast action speed and low operating loss,which is an idealmethod for fault isolation ofmulti-terminal dc grids.Formulti-terminal dc grids that transmit power through overhead lines,HCBs are required to have reclosing capability due to the high fault probability and the fact that most of the faults are temporary faults.To avoid the secondary fault strike and equipment damage that may be caused by the reclosing of the HCB when the permanent fault occurs,an adaptive reclosing scheme based on traveling wave injection is proposed in this paper.The scheme injects traveling wave signal into the fault dc line through the additionally configured auxiliary discharge branch in the HCB,and then uses the reflection characteristic of the traveling wave signal on the dc line to identify temporary and permanent faults,to be able to realize fast reclosing when the temporary fault occurs and reliably avoid reclosing after the permanent fault occurs.The test results in the simulation model of the four-terminal dc grid show that the proposed adaptive reclosing scheme can quickly and reliably identify temporary and permanent faults,greatly shorten the power outage time of temporary faults.In addition,it has the advantages of easiness to implement,high reliability,robustness to high-resistance fault and no dead zone,etc.

Circuit breakers in HVDC systems: state-of-the-art review and future trends

High voltage direct current(HVDC)systems are efficient solutions for the integration of large-scale renewable energy sources with the main power grids.The rapid development of the HVDC grid has resulted in a growing interest in DC circuit breakers(DCCBs).A fast and reliable circuit breaker is a necessary requirement in the development of large scale HVDC grids.This paper provides a comprehensive review and survey of the HVDC CBs and discusses potential research directions.Operational principles and the main features of various DCCBs are described and their merits and shortcomings are also highlighted.

Review on Z-Source Solid State Circuit Breakers for DC Distribution Networks

DC technologies will be essential building blocks for future DC distribution networks.As in any DC system,these networks will face crucial threats imposed by short-circuit DC faults.Protection is thus of great interest,and it will likely rely on DC circuit breakers(DCCBs).Among available configurations,Z-source solid-state circuit breakers(Z-SSCBs)are promising candidates for protecting low and medium-voltage distribution networks,as well as DC equipment due to their structural and control simplicity and low cost.In this paper,start-ofthe-art of Z-SSCBs topologies is reviewed.To set the context,the use of DC technologies for grid integration of renewables,DC power transmission,and the main types of DCCBs to protect DC transmission and distribution corridors are discussed.The Z-SSCB topologies are then classified into unidirectional and bidirectional.Advantages and disadvantages of different configurations are compared and analyzed based on existing research.Finally,a perspective on the future development of Z-SSCBs is discussed and potential challenges are elucidated.

Numerical Study on Arc Plasma Behavior During Arc Commutation Process in Direct Current Circuit Breaker

This paper focuses on the numerical investigation of arc plasma behavior during arc commutation process in a medium-voltage direct current circuit breaker （DCCB） contact system. A three-dimensional magneto-hydrodynamic （MHD） model of air arc plasma in the contact system of a DCCB is developed, based on commercial software FLUENT. Coupled electromagnetic and gas dynamic interactions are considered as usual, and a thin layer of nonlinear electrical resistance elements is used to represent the voltage drop of plasma sheath and the formation of new arc root. The distributions of pressure, temperature, gas flow and current density of arc plasma in arc region are calculated. The simulation results indicate that the pressure distribution related to the contact system has a strong effect on the arc commutation process, arising from the change of electrical conductivity in the arc root region. In DCCB contact system, the pressure of arc root region will be concentrated and higher if the space above the moving contact is enclosed, which is not good for arc root commutation. However, when the region is opened, the pressure distribution would be lower and more evenly, which is favorable for the arc root commutation.

Low-loss and Compact Hybrid DC Circuit Breaker Scheme Using Self-commutated Semiconductor Switch Module

In traditional hybrid DC circuit breakers(HCBs)schemes,complex equipment is usually required to ensure current commutation from mechanical to semiconductor switches,which cause not only additional construction costs and volume but also additional losses and maintenance work.Different from this condition,a low-loss and compact HCB scheme that does not use separate current commutation equipment is proposed in this study.By rationally using the charge and discharge of the snubber capacitor,the self-commutated semiconductor switch(SCS)module can integrate both the current commutation and shutdown functions,thereby greatly reducing cost and volume.The working process is discussed and analyzed in detail,and then a 10-kA prototype is developed and tested,which verifies the feasibility and effectiveness of the proposed scheme.Index Terms-HVDC circuit breakers,hybrid DC circuit breakers(HCBs),self-commutated semiconductor switch(SCS).

Research on arc root stagnation when small current is interrupted in self-excited circuit breaker

The self-excited DC air circuit breaker(SE-DCCB)has been widely used in urban rail transit due to its excellent stability.It can realize forward and reverse interruption,but has difficulty interrupting small currents due to the phenomenon of arc root sticking at the entrance of the arc chamber in the splitting process,which is known as arc root stagnation.A coupling model of the self-excited magnetic field and magnetohydrodynamics is established for the SE-DCCB with the traditional structure.The magnetic field,temperature and airflow distribution in the arc chamber are investigated with an interrupting current of 150 A.The simulation results show that the direction and magnitude of the magnetic blowout force are the dominant factors in the arc root stagnation.The local high temperature of the arc chamber due to arc root stagnation increases the obstruction effect of the airflow vortex on the arc root movement,which significantly increases the arc duration time of small current interruption.Based on the research,the structure of the magnetic conductance plate of the actual product is improved,which can improve the direction and magnitude of the magnetic blowout force at the arc root so as to restrain the development of the airflow vortex effectively and solve the problem of arc root stagnation when the small current is interrupted.The simulation results show that the circuit breaker with improved structure has a better performance for a small current interruption range from 100 A to 350 A.

Simulation Analysis of DC Fault Interruption Characteristics of Superconducting Electric Aircraft Propulsion

Environmental issues associated with the aviation industry are getting more attention as air traffic increases.Stringent standards are imposed for fuel consumption and pollution emissions for next-generation aircraft.Superconducting electrical propulsion aircraft(SEPA)have been seen as an efficient way to achieve this goal.High-temperature superconducting(HTS)devices are extensively used in the power system to supply enormous energy.Power is distributed to the different loads via a DC distribution network.However,it will generate an inrush current over ten times higher than the rated current in short-circuit state,which is very harmful to the system.Therefore,it is essential to adopt an appropriate protection scheme.This paper discusses one protection scheme that combines DC vacuum circuit breakers(DC VCB)and resistive superconducting current limiters(RSFCL)for superconducting aircraft applications.Considering problems of cost and loss,the auxiliary capacitor is pre-charged by system voltage,and mechanical elements extinguish the arc.Furthermore,combined with RSFCL,the interrupting environment is fully improved.RSFCL limits fault current,and then the VCB breaks this limited current based on creating an artificial current zero(ACZ).The prospective rated power is 8MW,rated voltage and current are 4 kV and 1 kA,respectively.In this paper,we discuss and simulate switching devices that protect SEPA.The interrupting performance of the circuit breaker is analysed in the DC short-circuit fault that occurs on the transmission line.Finally,the residual energy consumption of different situations is calculated.A comparison is made between using RSFCL with metal oxide varistor(MOV)and just using MOV.The scheme with RSFCL shows a significant advantage in energy consumption.

Study on Clamping Type DC Circuit Breaker with Short Fault Isolation Time and Low Energy Dissipation

The development of DC grids faces challenges from DC fault protection.The conventional DC circuit breaker(DCCB)employs metal-oxide varistor(MOV)to isolate the faulted line,in which the fault isolation process is coupled with the energy dissipation process.In this study,a clamping type DCCB(CTCB)using internal capacitors to clamp the converter voltage is proposed.Thanks to the proposed configuration,fault isolation and energy dissipation are decoupled,resulting in a fast fault isolation and low energy dissipation compared to the conventional DCCB.The working principle of the proposed CTCB is presented and verified in a DC grid simulation model.A comparison is made with the traditional DCCB.The fault isolation time can be reduced by 34.5%.The dissipated energy can be reduced by 17.4%.The energy dissipation power can be reduced by 76.2%.

SiC JFETs Modular Cascaded Method with Active Clamp Control Strategy for DC Solid-state Circuit Breaker

Power semiconductor devices cascaded topology is one of the most common solutions for solid-state circuit breakers(SSCBs)working in medium-voltage DC systems.However,when the number of cascaded devices is large,current series technologies of power semiconductor devices will be difficult to be applied since with uneven voltage sharing problems.Thus,this paper proposes a novel cascade method of multi-SiC JFETs based on modules cascaded.This method consists of two parts:one is a single-gate driver cascaded SiC JFETs topology which is used to form the module,the other one is an active clamp control strategy which ensures that each module is protected from overvoltage when modules are cascaded.The proposed cascade method can effectively suppress voltage overshoot of cascading power devices in the switching process.Based on the proposed cascade method,a 5kV/63A SSCB prototype is designed.Finally,an experiment is conducted based on the designed SSCB.Experimental results validate the effectiveness of the proposed cascaded method for SSCB.

Protection of large partitioned MTDC Networks Using DC-DC converters and circuit breakers

This paper proposes a DC fault protection strategy for large multi-terminal HVDC(MTDC)network where MMC based DC-DC converter is configured at strategic locations to allow the large MTDC network to be operated interconnected but partitioned into islanded DC network zones following faults.Each DC network zone is protected using either AC circuit breakers coordinated with DC switches or slow mechanical type DC circuit breakers to minimize the capital cost.In case of a DC fault event,DC-DC converters which have inherent DC fault isolation capability provide‘firewall’between the faulty and healthy zones such that the faulty DC network zone can be quickly isolated from the remaining of the MTDC network to allow the healthy DC network zones to remain operational.The validity of the proposed protection arrangement is confirmed using MATLAB/SIMULINK simulations.

Topology of Current-limiting and Energy-transferring DC Circuit Breaker for DC Distribution Networks

With the development of power electronic technologies and distributed power generation,DC distribution networks attract increasing attention due to their various advantages compared with traditional AC distribution networks.However,DC fault protection is one of the major issues in DC distribution networks.To improve their reliability and protect the semiconductor devices under DC faults,a current-limiting and energy-transferring DC circuit breaker topology is proposed in this paper.By applying passive components and thyristors,the proposed topology is capable of quickly limiting the fault current and transferring the faulty energy.The working principle,mathematical model and parameter designing method of the proposed topology are presented in this paper.The simulation results verify that the proposed DC circuit breaker could effectively limit the fault current and quickly interrupt the fault current.Cost and conduction power loss evaluation proves the practicality of the proposed topology in medium-voltage DC distribution networks.

Coordination Control of Power Flow Controller and Hybrid DC Circuit Breaker in MVDC Distribution Networks

The two main challenges of medium voltage direct current(MVDC)distribution network are the flexible control of power flow(PF)and fault protection.In this paper,the power flow controller(PFC)is introduced to regulate the PF and inhibit the fault current during the DC fault.The coordination strategy of series-parallel PFC(SP-PFC)and hybrid DC circuit breaker(DCCB)is proposed.By regulating the polarity and magnitude of SP-PFC output voltage during the fault,the rising speed of fault current can be suppressed so as to reduce the breaking current of hybrid DCCB.The access mode of SP-PFC to the MVDC distribution network and its topology are analyzed,and the coordination strategy between SP-PFC and hybrid DCCB is investigated.Moreover,the emergency control and bypass control strategies of SP-PFC are developed.On this basis,the mathematical model of SP-PFC in different fault stages is derived.With the equivalent model of SP-PFC,the fault current of the MVDC distribution network can be calculated accurately.A simulation model of the MVDC distribution network containing SP-PFC is established in MATLAB/Simulink.The fault current calculation result is compared with the simulation result,and the effectiveness of the proposed coordination strategy is verified.

A Hybrid Circuit Breaker Based on Current Commutation Approach for Multi-feeder DC Railway Substations

The paper presents an economic hybrid circuit breaker for limiting and interrupting the faults in DC railways substations. For fast fault current interruption, the hybrid breaker incorporates high speed mechanical contacts actuated by power semiconductor devices. Additionally, to avoid formation of electric arc, a commutation circuit is used to inject a counter current during fault interruption. In a real railway substation, each feeder is connected to the main DC bus through an expensive air magnetic DC circuit breaker and to an auxiliary DC bus through another expensive breaker. This leads to high cost especially in railway substation with multi feeders which are used to energize the vehicle transmission lines. In this paper, all DC breakers in DC railway substations are replaced by the suggested circuit breaker, which consists of a high speed mechanical contact with two semiconductor devices in each feeder and only one commutation circuit for injecting the counter current in all faulted feeders. The fault diagnosis is designed to detect the abnormal condition (current or voltage) in all feeders and direct the injected current from the commutation circuit to the faulted feeder only when the abnormal reaches a predetermine level. The suggested breaker is able to detect and interrupt any cascading of faults.