Dc Breaker Research Articles

Analysis Methodology for Differential Mode Interference in Energy Supply System of Hybrid DC Breaker

High di/dt during the close-open operation process of hybrid dc breaker will cause differential mode interference (DMI) in the energy supply system of the breaker's driver units due to their inductive coupling. The generated DMI may lead to false action of the breaker, which is an important issue that should be carefully considered in design stage. A method to analyze DMI based on time-domain wideband circuit simulations is proposed in this article. First, a time-domain waveform expression of DMI voltage source is derived, and then wideband equivalent circuit models of major components in the energy supply system are established. Furthermore, a standardized design methodology to reduce DMI is suggested. Applying the method to a high-frequency energy supply system of a ±200 kV hybrid dc breaker, simulation results show that the DMI level for two DMI mitigation measures is reduced by about 90% and 80% of the initial value, respectively.

Improving Low-Voltage DC Circuit Breaker Performance Through an Alternate Commutating Circuit

Current interruption in dc circuits is more challenging than in their ac counterparts due to the absence of natural current zero-crossing and resistive nature of the dc grids. This article summarizes the current dc breaker technologies and proposes new alternate methods for low-voltage applications. The proposed mechanisms utilize two switches, of which one generates zero crossing with an alternate oscillatory circuit for the other one, which can be a conventional ac breaker and is used in the main circuit. This is different than the conventional single-switch commute-and-absorb method used in high-voltage dc systems. It is shown that the proposed oscillatory circuit improves the fault current extinction and significantly reduces the voltage slew rate of conventional mechanical and solid-state switches. Thus, the proposed mechanism is capable of interrupting high dc currents with a minimal arc through a less expensive ac circuit breaker. Simulation and hardware results are provided to show the efficiency of the proposed breakers.

Bidirectional Power Flow Control in AC/DC Hybrid System under AC and DC Fault Conditions

This paper presents a hybrid AC-DC microgrid to reduce the process of multiple conversions in an individual AC microgrid or DC microgrid. The proposed hybrid microgrid compose of both AC microgrid and DC microgrid connected together by bidirectional interlink converter (BIC). Utility grid, 150kVA diesel generator (DG) and 100kW AC load are connected in AC microgrid. DC microgrid is composed of 100 kW photovoltaic array (PV), 20kW battery energy storage system (BESS) and 20kW DC load. The droop control technique is applied to control the system for power sharing within the sources in AC/DC hybrid microgrid in proportion to the power rating. When the faults occur at AC bus, protection signal applied to breaker for isolating the healthy and faults system. DC faults occur at DC bus, DC breaker isolate the AC and DC bus. The system performance for power flow sharing on hybrid AC-DC microgrid is demonstrated by using MATLAB/SIMULINK.

Modular Design Methodology of DC Breaker Based on Discrete Metal Oxide Varistors With Series Power Electronic Devices for HVdc Application

Different from the continuous-switching behavior of series power electronic devices in converters, the single-switching attribute of dc circuit breakers (DCBs) provides opportunities to integrate metal oxide varistors (MOVs), balancing circuits, and series power devices. This paper proposes a modular design methodology based on discrete MOVs of a DCB with series power electronic devices. The modular dc circuit breaker (MDCB) topology and voltage balance issues, the steep front effect and solution, and the design method are proposed and analyzed in this paper. Compared with the traditional DCB, the MDCB has a self-balancing ability, thereby removing the voltage-balancing circuit and reducing the number of series modules. The standard designed cell can be operated as an independent DCB or compose a high-voltage DCB in series flexibly, which decreases the difficulty of design and commission. Finally, a series experimental platform based on an insulated-gate commutated thyristor, an insulated-gate bipolar transistor, and an injection-enhanced gate transistor is built to verify the correctness and effectiveness of the proposed design methodology.

Development and Application of a 10 kV Mechanical DC Circuit Breaker

A DC circuit breaker is piece of core equipment for DC grid construction and can achieve fast isolation of DC faults in the grid. In this paper, based on the fault characteristics and protection requirements of an AC/DC hybrid distribution network, the technical parameters and topology structure of an inductance and capacitance (LC) resonant commutation-type mechanical DC breaker are proposed. Furthermore, an engineering prototype of the mechanical DC circuit breaker is developed, then a small current breaking test and a large current breaking test are carried out. The test results show that a 10 kA fault current can be interrupted within 10 ms by the engineering prototype. Finally, the engineering prototype of the mechanical DC circuit breaker is installed in the AC/DC hybrid distribution network project, and a current breaking test is carried out. The test results show that the mechanical DC circuit breaker has good running conditions, and the function and performance meet the engineering design and operation requirements.

A New Protection Scheme for MMC-Based MVdc Distribution Systems With Complete Converter Fault Current Handling Capability

DC fault handling is a critical aspect for designing and operating dc distribution systems. DC distribution protection must be rapid to avoid the damages caused by the fast growth of dc fault currents. For medium-voltage dc (MVdc) distribution systems, low-cost high-speed dc breakers are still challenging. A hybrid modular multilevel converter (MMC)-based dc fault protection and restoration method is proposed for a cost-effective dc fault protection solution for MMC-based MVdc systems. In the proposed protection solution, the converter topology and associated fault handling can bypass and interrupt the fault currents from both ac and dc sources, and thus allowing fast dc fault isolation by low-cost no-load dc disconnectors. Furthermore, the proposed dc protection solution facilitates converter fault ride-through and system restoration after fault removal. Simulation results of the pole-to-pole fault protection show the satisfactory performance of the proposed protection solution and scheme.

Degradation characteristics of SiC power devices for DC circuit breaker by repetitive unclamped inductive switching test

This paper investigates the degradation of SiC power devices for DC circuit breaker through repetitive unclamped inductive switching (UIS) tests. The ON resistance of SiC power devices such as MOSFET and JFET are lower compared with Si devices. Therefore, SiC power devices are suitable for use as DC circuit breakers. Several papers have discussed degradation of SiC power devices; however, few studies have determined a suitable power device for a DC breaker from a degradation standpoint. In this paper, four types of SiC devices were subjected to repetitive UIS tests. Our research demonstrated SiC-JFET to be suitable for a DC breaker.

Coupled Inductor-Based Zero Current Switching Hybrid DC Circuit Breaker Topologies

This paper proposes a coupled inductor-based hybrid dc circuit breaker topology with zero current switching for fast fault interruption in dc systems. A series resonant circuit comprising of the secondary winding of a two-winding coupled inductor and a charged capacitor (commutation capacitor) is switched on during fault to inject a counter-current pulse, and, consequently, force a zero crossing of fault current. Proposed solution facilitates arcless breaking for a mechanical circuit breaker due to zero current turn- off . The proposed circuit breaker exhibits fast fault response ( $\sim$ 30 $\mu$ s), and the response time is programmable based on the design of the coupled inductor and commutation capacitor. Furthermore, presented solution mitigates the requirement of energy-absorbing elements for demagnetizing the dc network following fault interruption, in contrast to conventional dc breakers. The paper also presents two modified circuit-breaker topologies to achieve unipolar voltage profile on the capacitor, which will enable the use of electrolytic capacitors for commutation so that the capacitor stack size is reduced in high-voltage applications. Detailed analysis and design equations are presented to explain the operation of the proposed topologies. Functionality of the proposed circuit breakers is verified through simulation, and experimental results are based on two laboratory prototypes.

Design of a Solid-State Circuit Breaker for a DC Grid-Based Vessel Power System

Electric propulsion and integrated hybrid power systems can improve the energy efficiency and fuel consumption of different kinds of vessels. If the vessel power system is based on DC grid distribution, some benefits such as higher generator efficiency and lower volume and cost can be achieved. However, some challenges remain in terms of protection devices for this kind of DC grid-based power system. The absence of natural zero crossing in the DC current together with the fast and programmable breaking times required make it challenging. There are several papers related to DC breaker topologies and their role in DC grids; however, it is not easy to find comprehensive information about the design process of the DC breaker itself. In this paper, the basis for the design of a DC solid-state circuit breaker (SSCB) for low voltage vessel DC grids is presented. The proposed SSCB full-scale prototype detects and opens the fault in less than 3 µs. This paper includes theoretical analyses, design guidelines, modeling and simulation, and experimental results.

DC Fault Current Blocking With the Coordination of Half-Bridge MMC and the Hybrid DC Breaker

In this article, a modified hybrid dc breaker and a half-bridge modular multilevel converter (MMC) are employed to interrupt the dc fault current in a high-voltage direct current transmission system. In the hybrid dc breaker, parallel to the main branch, a series connection of an energy-absorbing capacitor and a Thyristor stack is employed. When a dc fault current is recognized, the Thyristor stack is triggered and the load commutation switch in the main branch is turned off. In addition, in the fault clearing state, the MMC is programmed to generate zero voltages at all arms. Using this mechanism, a second-order RLC circuit with zero input is formed, and the fault current is cleared in a very short time. A freewheeling path is provided to bypass the dc line when the equivalent inductance seen from the dc line is large. In contrast to conventional approaches, the peak of dc fault current is limited to a specific limit and the necessity to ultrafast mechanical switches is avoided. In addition, the amplitude of arms currents and corresponding insulated-gate bipolar transistors are kept in the safe operating area. A detailed circuit analysis of the new method is given and design formulas are extracted. Simulation results are provided in PSCAD/EMTDC environment, and experimental results are presented for a scaled-down prototype.

DC fault current limiting effect of MMC submodule capacitors

DC short-circuit fault is a crucial issue in DC grids because the DC fault current increases rapidly with accompanying high fault energy. Limiting the DC fault current is a promising solution to simplify the design of the DC breaker and DC protection. The majority of existing DC fault current limiting (FCL) approaches relies on extra devices, such as DC line inductors. However, the control ability of modular multilevel converters (MMCs) is not optimized. In this study, the submodule (SM) capacitor dynamics during the short DC fault procedure was considered a new control objective, and its effect on the limiting DC fault current was analyzed and revealed. The complex time-varying DC fault transient circuit was comprehensively represented by introducing two base circuit structures and one duty cycle index D. The averaged circuit model was proposed on the basis of the state–space averaging method, which can intuitively show the relation between SM capacitor and DC fault current. The analytical expressions of the DC fault current was given, which can guide the design of the DC FCL control of MMC. The duty cycle index D can represent the discharge of SM capacitors, and the increasing speed of the DC fault current declines with the decrease in D. Accordingly, a feasible FCL control strategy was proposed by choosing D as a tool for affecting and controlling the DC fault current. The proposed FCL control strategy can evidently reduce dc fault current, and avoid the drawbacks of the conventional block or bypass approaches. The simulation results validated the effectiveness of the proposed analysis method and corresponding conclusions.

Optimal Design of Diode-Bridge Bidirectional Solid-State Switch Using Standard Recovery Diodes for 500-kV High-Voltage DC Breaker

At present, it is usually necessary to use fast recovery type diodes to cooperate with the fast switching actions of fully controlled devices such as insulated-gate bipolar transistors (IGBTs). However, the specific nature of the working conditions of the diode-bridge bidirectional solid-state switch (DBSS) provides an opportunity to apply standard recovery diodes for this purpose, which helps to reduce the cost of the bidirectional switch. This letter presents the self-oscillation phenomenon that is caused by the recovery processes of the diodes in a DBSS. Then, the recovery effects of these diodes in different topologies are analyzed from the perspective of the DBSS and optimized designs for both the snubber circuit and the energy-absorbing circuit are proposed. A 500-kV dc breaker is realized based on the proposed DBBS using the standard recovery diodes, which can work reliably with IGBTs, and the cost of the resulting dc circuit breakers is greatly reduced.

A Novel Mixture Solid-State Switch Based on IGCT With High Capacity and IGBT With High Turn-off Ability for Hybrid DC Breakers

Hybrid dc circuit breakers (HCBs) usually require a large number of insulated-gate bipolar transistors (IGBTs) with high turn- off capability for series and parallel connections. This requirement entails excessive cost. Compared with IGBTs, integrated gate-commutated thyristors (IGCTs) are another kind of fully controlled power device with high surge current and voltage capability but are low cost. However, the weak turn- off capability of IGCTs hinders their application to high-powered HCBs. On the basis of the complementary advantages of IGBTs and IGCTs, this paper proposes a mixture solid-state switch (MSS) for HCBs that uses the switching action of several IGBTs to create a low-current condition that favors the turning off of large-scale series-connected IGCTs. The MSS topology can significantly reduce cost while maintaining the excellent performance of traditional solid-state switches. This study also introduces two different turn- off modes for MSS, namely, single oscillation and multiple oscillations. Finally, 25 kV/20 kA prototypes in both modes are developed to verify the effectiveness of the MSS topology.

Protection Coordination for Assembly HVDC Breakers for HVDC Multiterminal Grids Using Wavelet Transform

A major challenge in a multiterminal high-voltage direct current (MT-HVdc) system is the detection and subsequent removal of dc faults, i.e., line–line or line–ground faults. This technology is crucial to make emerging MT-HVdc systems reliable and stable. Current detection solutions are either too sensitive to load variations causing false positives or are too slow to detect faults before the equipment is damaged. This paper proposes a framework and case examples for fault detection based on features derived from the wavelet transform of the grid current. The algorithm is intended to control new high-speed dc breakers (such as assembly HVdc breaker) for improved fault protection. This paper customizes the detection strategy to specific fault frequencies using multiresolution analysis, whose magnitudes are significant in the vicinity of the fault, and are attenuated at remote grid terminals. A model of a three-terminal MT-HVdc system is developed in power systems computer aided design/electromagnetic transients including dc. The results have been post processed in matrix laboratory and simulation results verify the effectiveness of the proposed solution for preventing dc faults on an HVdc system.

Optimum Selection of Circuit Breaker Parameters Based on Analytical Calculation of Overcurrent and Overvoltage in Multiterminal HVDC Grids

This paper proposes a time-domain method to calculate the fault response in multiterminal dc (MTdc) grids and the performance of hybrid dc breakers. The proposed method, based on traveling waves: 1) provides a sound representation of fault performance by considering all created traveling waves; 2) introduces a new approach to estimate the reflection coefficients; and 3) provides an approximation of the worst case fault location. Then, based on the analytical results, three parameters of the hybrid dc circuit breaker, i.e., current limiting reactor, arrester rated voltage, and time delay are optimally selected with respect to maximum overcurrent, maximum overvoltage, fault clearance time, and energy absorption in arresters through multiobjective optimization. Accuracy and performance of the proposed method are evaluated and verified by time-domain simulation studies in the power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) environment using frequency-dependent models. The results confirm reasonable accuracy of the proposed fault performance calculation and represent a further step towards optimized design of hybrid dc circuit breakers.

Contribution of travelling wave propagation time to the speed of optical link protections in multi‐terminal high‐voltage DC systems

During faults in multi-terminal high-voltage DC systems, the disturbance will quickly become evident throughout the entire system. If DC breakers are included in such systems, the entire fault clearing process needs to occur within a few milliseconds. Therefore, DC line protection schemes based on telecommunication have previously been discarded by some authors as their performance is constrained by the communication delay. However, telecommunication-based detection methods offer some very favourable features, one being that selectivity can be achieved without coordination of settings. In this study, several telecommunication-based protection schemes are evaluated with regards to their minimum possible detection time when considering telecommunication delay. It is shown that they perform best during faults located at the remote end of a line, i.e. fault locations that are difficult to reliably detect using single-ended methods. Therefore, it is reasonable that the most reliable protection system will consist of both single-ended and communication-based methods because they complement each other well. Furthermore, it is shown that the travelling wave differential protection offers the shortest theoretical detection time due to the wave propagation delay being included in the formulation.

Research on Switching Overvoltage of MMC-MTDC System with Hybrid DC Circuit Breaker

The modular multilevel converter based multi-terminal HVDC (MMC-MTDC) system with hybrid DC breakers should consider the influence of the action of the DC breaker on the switching overvoltage, which puts higher requirements on the overvoltage protection of the system. Flexible DC demonstration project in Zhangbei will realize the first engineering application of hybrid DC circuit breaker. Based on this project, an overvoltage protection scheme for MMC-MTDC system is proposed. Firstly, this paper investigates the effect of the operation mode of the DC grid on the switching overvoltage level. Secondly, typical faults and the protection action sequence of various faults are analyzed in detail. The characteristics and laws of various switching overvoltage are deeply studied. Finally, the switching overvoltage of converter station is calculated on the basis of the control and protection system, and the recommended values of the insulation level of converter station equipment for the ±500kV MMC-MTDC system with hybrid DC circuit breaker are given.

A hybrid circuit breaker based on current commutation approach for multi feeders 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.

Experimental results from a Thomson‐coil actuator for a vacuum interrupter in an HVDC breaker

Recent developments in high-voltage direct current transmission technology and the plans for multi-terminals motivate research efforts on the fast DC breaker. A novel concept to interrupt current up to several kiloamperes within a few milliseconds is presently under development, using a vacuum interrupter together with power electronics to create an artificial zero-crossing in the current through the switch. To achieve this objective, one critical component in the concept is an ultra-fast linear mechanical actuator. A prototype has been developed based on a Thomson coil. The experimental results are presented and show how a contact gap in a vacuum interrupter was effectively created in a controlled manner. Current of several kiloamperes was successfully interrupted within 3 ms, thanks to the high-speed operation of the linear actuator.

Study on DC Breaker Fault Current and Its Limiting Method of Multiterminal Flexible DC Distribution System

The multiterminal flexible DC (MTDC) distribution system has become a hot research topic for its advantages such as new energy load accessibility and high reliability of power supply. However, the fault current during short-circuit faults will be more complicated and serious because of the multiple operating modes and specific converter structure in MTDC distribution system. The high fault current will affect the safety of equipment and system operation. As a result, it is necessary to study the fault current generation mechanism and current limiting method of the DC distribution system. In this paper, the generation mechanism, transient characteristics, and the influencing factors of the fault current in the DC breaker during the short-circuit faults are analyzed by theoretical analysis and simulations separately based on a ±10 kV three-terminal flexible DC distribution system. The current limiting devices are analyzed, and its configuration position and parameter calculation method are proposed. On this basis, the parameters of the current limiting reactor and its effects on each position are analyzed by electromagnetic transient simulations. The current limiting scheme is proposed and its reliability is verified. The study results can provide some reference for overcurrent analysis and current limiting measures of the multiterminal DC distribution system.