Dc Breaker Research Articles

Hybrid DC circuit breaker based on oscillation circuit

With the rapid development of DC transmission technology, DC circuit breakers, the key equipment for DC fault handling, have become a research hotspot of scholars. This paper proposes a novel hybrid DC circuit breaker topology to improve the shortcomings of traditional hybrid DC circuit breakers. Traditional hybrid DC circuit breakers use too many IGBTs, which results in a large volume and a high cost. The main innovation of this topology is the use of a mechanical switch in series in a solid-state branch, which withstands most of the voltage. An oscillating circuit is in parallel on the mechanical switch, which can generate reverse current to reduce the current flowing through the mechanical switch to zero, to achieve arc free breaking. The feasibility of the proposed topology is verified based on a PSCAD simulation platform. It should serve as a valuable reference for the design of DC distribution systems and DC breakers.

Sensitivity of Cable Model Parameters for Traveling Wave Differential Protections in MTDC Systems

Multi-terminal HVDC systems equipped with multiple DC breakers require a protection system that selectively detects faults within a few milliseconds. In the development and application of such protection algorithms, time-domain simulation studies of various faults are essential when determining the setting and verifying the performance. However, when such protections are applied in practice, it should be expected that the models will not perfectly represent the behavior of the real system or transmission line, thereby possibly causing protections to operate unreliably. This paper presents a simulation process that evaluates the consequences for a protection algorithm when the transmission line parameters are varied. More specifically, the false differential current due to cable model parameter errors is evaluated in a traveling-wave differential protection applied in a multi-terminal HVDC system during an external fault. The purpose is to identify the most critical parameters and evaluate how inaccuracies influence the protection performance when applied in practice. It is shown that the parameters which significantly influence the propagation delay are critical for achieving the ideal performance - a strictly zero differential current during external faults.

An experimental analysis of DC magnetic blowout high-speed circuit breakers’ parameters

High-speed circuit breakers (HSCB) used in DC circuits are one of the basic elements of overload, short-circuit and electric shock protection. Such breakers are used in transport (trams, trolleybuses, subways and railways) in electric power supply facilities and in vehicles. The performance and capability of limiting the current depend on the HSCB design and solutions applied in it. The circuit parameters, particularly its inductance also affect the performance. Additionally, each DC breaking in the RL circuit is accompanied by overvoltages whose level depends on the circuit parameters and breaker design. The paper discussed the process of direct current breaking by magnetic blowout high-speed circuit breakers and factors that affect the HSCB performance, i. e. opening time and arcing time. The influence of the circuit parameters and HSCB design on the value of arc voltage is outlined. The results of laboratory tests of 4 types of high-speed circuit breakers produced in Europe are presented. The test results were used to analyze the effect of current changes in the short circuit on the time of current breaking and the value of switching overvoltages – arc voltage. The results of simulation of the short-circuit breaking in the RL DC circuit made at the rate-of-rise of current in the circuit are presented. Based on the tests and simulations, the current breaking times, values of arc voltage generated in this process and arc energy that is acquired and dissipated by the arc chamber are determined. The objective of the tests and simulations was to answer the question whether it is possible to turn off direct current quickly without generating high arc voltage values – overvoltages in the circuit and how di/dt changes should be formed by a high-speed circuit breaker to achieve the shortest possible time with the lowest possible arc voltage and its lowest energy

Real-time simulation with an industrial DCCB controller in a HVDC grid

DC breakers and their associated control are seen as important lever for the DC grid expansion. In complement to dynamic studies, as intermediate step towards on-site implementation, factory tests using real control and protection hardware enable to fine tune control sequences, to check the software implementation and then test the coordination and interaction between different devices connected to the same grid.This article presents a hardware-in-the-loop setup for testing industrial DCCB controllers and their interoperability with converter controllers. A hybrid DCCB model suitable for real-time simulation has been developed and then validated against offline model. Industrial DCCB controller functions are described. A set-up of three-terminal DC grid with physical controllers for one MMC converter station and 12 DCCBs is described. The results of two application cases including cable energization and fault clearance are presented and discussed.

HV isolated power supply system for complex multiple electrical potential equipment in 500 kV hybrid DC breaker

High-voltage direct current circuit breakers (HVDC CB) are one of the key technologies of multi-terminal DC systems and DC grids. Different from other equipment that use a large number of power electronic devices, the HVDC CB cannot obtain its power from the primary system at high potential, making the power supply of the complex multiple electrical potential equipment in HVDC CB a challenge. In this study, the authors propose an HV isolated power supply system based on the multi-output high-frequency isolated power supply unit and the cascaded isolation transformer network. This power supply system can support the 500 kV CB to turn-off 25 kA current with 800 kV overvoltage.

Bridge‐type fault current limiter and hybrid breaker for HVDC grids applications

The fast raising nature of DC fault currents and sensitivity of high-voltage DC (HVDC) power converters to DC faults is critical protection issues. On the other hand, DC fault current does not meet zero; which causes DC to fault current breaking process become more challenging. Specifically, to protect HVDC grids against DC fault currents, the development of very fast breakers is crucial. This study proposes a DC fault current limiter and breaker, which is able to protect the HVDC system/grid in a very fast and safe manner. The main goal of this study is to enhance the performance of already in the market hybrid DC circuit breakersincluding the magnitude of fault current and breaker operation speed. In the proposed HVDC fault current limiter and breaker, the fault current is limited in two stages by an inductive and resistive current limiter, which drastically decreases the main breaker dissipated energy. The functionality of the proposed HVDC fault current limiter and breaker is mathematically analysed, and then verified by PSCAD and Matlab/Simulink. Finally, simulation results are validated by scaled-down laboratory examinations.

Study on the Alliance between SFCL and Hybrid DC Circuit Breaker for Protecting HVDC Grid

Breaking the DC fault in HVDC grid is the greatest challenge for DC grid protection system. Although there are many scientific researches investigating the high voltage DC breakers, yet, there is still always a trade-off between the interruption time and the breaking capability. Therefore, combining between the superconducting fault current limiter (SFCL) technology with a fast DC circuit breaker could bring a solution to this limitation. In this work, an accurate model of resistive-type SFCL (r-SFCL) considering the electro-thermal behaviour, is proposed to be placed in series with ABB proactive hybrid DC circuit breaker (PHCB). To test the viability of the system, a pole-to-pole DC fault scenario was imposed in a HVDC grid. The numerical analysis was undertaken with (EMTP-RV®) software, while the simulation results show how effectively the SFCL can reduce the fault current below the maximum breaking capability. Also, it is concluded that there is a positive interaction between the r-SFCL and PHCB.

A Novel Converter-Breaker Integrated Voltage Source Converter Based on High-Surge IGCT and Fault Self-Clearing Strategy for DC Grid

Existing multiterminal voltage source converter based high voltage dc projects are constructed by separate modular multilevel converter (MMC) and dc breaker (DCB) utilizing insulated gate bipolar transistors. However, the MMC requires high-surge thyristors and the DCB should be equipped with very large turn- off solid-state switch against fault. Their independent operations are complex and unreliable by two separate control systems. In this letter, a novel converter-breaker integrated voltage source converter (IVSC) based on high-surge integrated gate commutated thyristor is proposed, and to integrate the converter and breaker operation, the fault self-clearing strategy is developed. IVSC can get rid of thyristors and replace DCB with small turn- off capability load switch. This converter-breaker integration can result in advantages including lower manufacturing cost and volume.

Concept design of 100 kA hybrid DC breaker on China fusion engineering test reactor

• High current DC breaker is the key problem of quench protection system design for superconducting Tokamak. • This paper describes a new of hybrid breaker composed of three-levels contacts mechanical switch, and a solid-state switch in parallel. • The new hybrid breaker is more effective to realize high-power DC interruption and fast energy transfer. • A principle prototype experiment was done to verify the conceptual design. China Fusion Engineering Test Reactor (CFETR) is the next device for the Chinese magnetic confinement fusion program, which is now under conceptual design phase. This paper describes the concept design of the high current hybrid breaker for the quench protection of superconducting magnets. The rated currents and maximum reapplied interruption voltages for breaker are 100 kA and 20 kV. The concept solution design of DC breaker is presented, which is mainly composed of a mechanical main switch with three levels contacts for conducting the continuous current, and a solid-state switch in parallel for current transferring. The design principles of each part and the preliminary results are given respectively. Finally, two test platforms were built to verify the calculation and design. Compared with the traditional oscillation zero-point DC breaker, the hybrid breaker topology can improve the dielectric strength recovery speed of mechanical switch and reduce the whole operation time. It is more suitable for fast current interruption at heavy DC current level.

A Novel DC Fault Ride-Through Method for Wind Farms Connected to the Grid Through Bipolar MMC-HVDC Transmission

Modular multilevel converter based high voltage direct current (MMC-HVDC) transmission is the prospective technology for large-scale wind farms integration. In this paper, a comprehensive coordinated control strategy for DC fault ride-through (FRT) of wind farms connected to the grid through bipolar MMC-HVDC transmission is proposed. To reduce the requirement of breaking speed and capacity of DC breakers, an active current-limiting control method is proposed to limit the rise rate of DC fault current, and the principle of parameter selection is designed. After DC breakers isolate fault, the control mode switching methods of bipolar MMC are designed to make the fault pole MMC operate as a STATCOM to support the AC grid and improve the active power transmission capability of the healthy pole MMC, which can reduce the impact range of unbalanced power between wind farms and converter station. In addition, a coordinated control strategy for wind farms load-shedding considering speed constraints is designed to realize the optimal distribution of load-shedding power among wind turbines, which can regulate unbalanced power together with the healthy pole MMC to realize DC FRT. Finally, the effectiveness and feasibility of the proposed control methods are verified by simulation results.

Analysis of Black Start of a Microgrid with PV, DG, and BESS

Different combinations of operating scenarios for a microgrid with distributed energy resources and energy storage system is considered to understand the operation of a microgrid. An operational strategy analysis of a microgrid system consisting of photovoltaics, diesel generator, and battery energy storage system during a black start in islanded mode is considered in this paper. BESS under study consists of a bidirectional converter and a battery system. BESS is assumed to be active as a solution provided in all the scenarios. The various capabilities of BESS in a microgrid system is also discussed. Microgrid system provides reliable power supply and hence black start capability for such a system is essential in keeping intact the advantages of a microgrid. Performing a black start requires a sequential process to be followed to avoid fluctuations in bus voltage, frequency, and protecting the fuses/ contactors from blowing. To black start the system under study, the DC breaker connecting the battery and the bidirectional converter needs to be closed. Closing the DC breaker results in high inrush current from batteries at the DC output of the bidirectional converter. A DC arrangement is envisaged in the battery energy storage system to avoid arcing due to high inrush current.

A Multi-Terminal HVdc Grid Topology Proposal for Offshore Wind Farms

Although various topologies of multi-terminal high voltage direct current (MT-HVdc) transmission systems are available in the literature, most of them are prone to loss of flexibility, reliability, stability, and redundancy in the events of grid contingencies. In this research, two new wind farms and substation ring topology (2WF-SSRT) are designed and proposed to address the aforementioned shortcomings. The objective of this paper is to investigate MT-HVdc grid topologies for integrating large offshore wind farms with an emphasis on power loss in the event of a dc grid fault or mainland alternating current (ac)grid abnormality. Standards and control of voltage source converter (VSC) based MT-HVdc grids are defined and discussed. High voltage dc switch-gear and dc circuit topologies are appraised based on the necessity of dc cables, HVdc circuit breakers, and extra offshore platforms. In this paper, the proposed topology is analyzed and compared with the formers for number and ratings of offshore substations, dc breakers, ultra-fast mechanical actuators, dc circuits, cost, flexibility, utilization, and redundancy of HVdc links. Coordinated operation of various topologies is assessed and compared with respect to the designed control scheme via a developed EMTDC/PSCAD simulation platform considering three fault scenarios: dc fault on transmission link connecting the wind farm to mainland power converters, dc fault within substation ring of VSC-HVdc stations, and ultimate disconnection of grid side VSC station. Results show that 2WF-SSRT is a promising topology for future MT-HVdc grids.

Electric Contact Material Selection for Medium and High Voltage DC Circuit Breakers

Medium and high voltage DC grids are increasingly proposed for terrestrial, shipboard and aircraft power systems. However, multi terminal DC networks can only be realized with the development of a DC circuit breaker. Due to the difficulty in breaking DC currents, hybrid circuit breakers—which consist of a non-arcing fast mechanical disconnect switch (FMS) in parallel with a solid state switch—is the most promising solution. The stresses experienced by the electric contacts of FMS are different from those of AC and low voltage DC breakers and disconnect switches. The choice of contact material has a significant impact on the performance of the DC circuit breaker. The Ashby method is used to systematically identify the best suited contact materials by translating the requirements of FMS contacts into objectives and constraints and deriving material indices for each objective. Minimizing power loss, wear and overheating of contacts are identified as the key objectives. The results suggest that copper-based alloys and compounds are more suitable than silver based alloys and compounds and other contact materials.

Optimum Design Operation Principles and Simulation Results of DC Breakers in High Voltage DC System

The feasibility DC power applied in distribution system is discussed. The efficiency and topologies of applying DC distribution for different purposes are investigated as well. For applying DC distribution, there are two key components, AC/DC converters and DC breakers. This thesis investigates the specification of converters suitable for applying in DC distribution system. In those converters, power losses are calculated as an index to compare their overall efficiency. Voltage control on the DC side and power factor correction on the AC side are also the primary requirements. Due to the absence of natural zero crossing current, the design of DC breakers is different from AC ones, therefore, in this thesis, the design rules of different DC breakers are investigated and their performance are also compared as a reference when selecting suitable DC breakers.

Damping HVDC Circuit Breaker With Current Commutation and Limiting Integrated

The fault current limiting in high-voltage dc (HVdc) grids is critical to reducing the breaking stress of dc circuit breaker and improving the breaking reliability. However, the existing HVdc circuit breakers rarely consider the rapid limiting of fault current in the breaking process. In this article, a novel HVdc circuit breaker integrating current commutation and damping is presented, which can realize fast current limiting and interruption while preserving large breaking capability and low cost. Simulation analysis of current commutation capability is carried out to determine the optimal parameters in the current damping module. Then, the fault current breaking performance of the proposed HVdc breaker is evaluated and compared with conventional hybrid HVdc breaker theoretically. Finally, a low-power prototype of the current damping dc breaker is built and tested to verify the validity of the proposed topology.

Optimized Protection Strategies for HVDC Grid with Fault-blocking Modular Multilevel Converters for Overhead Line Applications

The high-voltage direct current (HVDC) grid has been recognized as an effective solution for renewable energy integration. Currently, two main development trends for HVDC grids are being studied: a DC breaker based HVDC grid and fault-blocking converter based HVDC grid. Although the former has a perfect performance for fault clearance, its development is still highly constrained by the cost and maturity of DC breakers. The latter can extinguish DC faults by the fault-blocking converters. Without using DC breakers, there is no bottleneck in its technical feasibility. Nevertheless, in fault scenarios, such types of HVDC grids will be blocked at length for air-deionization, which is its main drawback. The aim of this paper is to minimize its power interruption time, by optimizing protection coordination strategies. To cover the most complex cases, the overhead line applications, in which the reclosure actions are required to be implemented, are considered. In this paper, the protection requirements of HVDC grids are first discussed, then the benefits of fault-blocking modular multilevel converters (MMCs) and their fault features are analyzed. Based on this, a control function is designed to reduce the air-deionization time. To minimize the influence of the DC faults, a separation methodology for restarting the system is proposed. The effectiveness of the proposed protection coordination schemes is validated by PSCAD/EMTDC simulations.

Impact of dc grid protection strategies on frequency stability of the connected ac system: a quantitative analysis

Various options for dc grid protection strategies are currently investigated which differ in terms of speed and selectivity. In order to compare these options fairly, the impact on the connected ac grid needs to be studied. This paper analyzes the ac grid impact in terms of frequency stability and calculates the reserve capacity necessary to retain the stability. Assuming fast frequency reserves as a possible mitigation, a probabilistic method is provided to determine a trade-off between under frequency load shedding and additional reserve requirement. In general, non-selective strategies require higher and faster reserves compared to their fully selective counterparts for both cases analyzed in this paper. Both the selectivity and the speed of protection have an influence on the reserve requirement. The dc grid topology also plays an important role in the reserve sizing by determining the impact of dc contingencies on the ac grid. The concept of reserve sizing based on temporary loss of supply shows value in terms of lower capacity requirement. A grid specific CBA study shows that it is possible to compensate the higher investment cost associated with dc breakers by the benefit of lower reserve procurement cost.

Optimal allocation of fault current limiter in MMC-HVDC grid based on transient energy flow

Economical and reliable protection of dc-side short-circuit faults has become a key technology for promoting the development of module multilevel converter based high voltage direct current grid (MMC-HVDC-Grid). The fault current limiter (FCL) can effectively suppress the rapid development of fault current and reduce the current breaking capacity of the circuit breaker. In this paper, a method based on transient energy flow (TEF) analysis is proposed to optimize the allocation of resistive and inductive FCL in MMC-HVDC-Grid. In the proposed method, the electromagnetic TEF is measured firstly, and then, the TEF suppression rate and suppression efficiency are defined as optimization objectives, and the installation place of the FCL and its impedance parameters as optimization variables. To test the proposed method, a two-terminal and four-terminal bipolar MMC-HVDC-Grids with single-pole-to-ground dc fault are modelled in the PSCAD/EMTDC so that the TEF data can be acquired. The optimal FCLs' location and parameter values are determined through investigating the evolution paradigm of TEF along with changes of FCL position and parameters. The results prove that the selected parameters can effectively slow down the dc fault current rising rate, thus reducing the requirements on tripping current of the dc breaker.

Control-based fault current limiter for modular multilevel voltage-source converters

The sharp rise in short-circuit currents of voltage-source converters is still a challenge for DC grid reliability, which imposes stringent requirements on DC breakers. Therefore, fault current limiters are used for slowing down the rise in short-circuit currents. This paper proposes a control-based fault current limiter (CbFCL) for modular multilevel converters (MMCs). The proposed method reduces the fault current purely by control action, thus not incurring costs and not leading to reduced stability, energy storage, conduction losses or the need for maintenance as impedance-based fault current limiters do. The CbFCL does not affect the system in normal operation, acting only in the presence of a fault. The CbFCL performance was evaluated performing simulations of a four terminal DC grid. The results confirmed that the CbFCL was able to limit the fault current of the MMC while keeping the AC currents within their nominal limits, and thus producing a minor impact on the grid operation.

Modeling a voltage source converter assisted resonant current DC breaker for real time studies

In order to test protection performance of future multi-terminal HVDC grids where DC circuit breakers (DC CBs) play an important role, a DC CB model in real time test environment should be developed. It is well known that a DC CB needs to interrupt DC faults very quickly in order to avoid converter damages and to ensure security of supply. The total current interruption time consists of a fault detection time, which is needed for the DC protection to provide a trip command to the DC CB, and a DC CB interruption time. Thus, it is necessary to demonstrate the performance of associated protective devices through real time simulations, before these devices can be implemented and commissioned in practice. This paper presents a detailed modeling of the voltage source converter assisted resonant current DC circuit breaker (VARC DC CB) in real time simulation environment based on RTDS. The proposed model provides sufficient representation of the circuit breaker for system level studies. External current-voltage characteristics of the proposed VARC DC CB models replicate the ones of the device in the real world. The proposed model of the breaker is tested in a simple test circuit including a DC voltage source and a T-scheme HVDC cable. Additionally, a case study has been presented by making use of a protection algorithm in a multi-terminal HVDC grid with frequency dependent parameters of the HVDC cables to show both protection performance and current interruption.