DC Circuit Breaker Research Articles

Fault protection of multiterminal HVDC networks: Impact of inductance

Multiterminal Voltage Source Converter (VSC) High Voltage Direct Current (HVDC) networks are developing rapidly worldwide, especially in China with urgent needs of long-distance power transmission. Currently, the interrupting capacity of available DC circuit breakers (DCCBs) is a key obstacle to the development of multiterminal VSC HVDC networks. Superconducting fault current limiters (SFCLs) can compensate for the limitation of DCCBs. Conventionally, a resistive SFCL is regarded as essential and sufficient, while an inductive one is less related and optional. However, pure resistance cannot effectively suppress the rising rate of fault current at the very early stage of a fault, resulting in unnecessary blocking of the converter. Adequate inductance is required for such SFCLs to curb rapidly increasing fault currents within the first few milliseconds, which is critical to DCCBs to isolate fault without interrupting other DC transmission lines. In this paper, we compared and analyzed the performances of SFCLs with different resistances and inductances in a four-terminal VSC HVDC network using PSCAD/EMTDC software. The results indicate that even resistance and inductance show different current limiting effects, but they are both necessary to realize effective SFCL function for multiterminal VSC HVDC networks. The outcomes of this paper are of significance in FCL design for multiterminal VSC HVDC networks.

LC DC Circuit Breaker based on Pre-charged Capacitor Commutation

To overcome limitations of the peak DC fault current with previous LC DC Circuit Breakers, this paper studies using a pre-charged capacitor in the auxiliary branch which enables rapid commutation of the fault current from the disconnector in the main branch. The analysis on the theoretical model concludes that the pre-charged capacitor should ideally have high capacitance and low voltage. The design for the practical test case of 5 kV, 2 kA LC DC Circuit Breaker is presented and shows that the pre-charged capacitor voltage requirement is low, at 10% of the DC CB rating. Both, film and electrolytic (lower size and cost) pre-charged capacitor are considered, and the experimental tests demonstrate successful DC current commutation of 2 kA at 5 kV. Successful breaking is also demonstrated on hardware for negative DC fault current and for very low currents, which represent difficult operating conditions. The experimental study further evaluates robustness to the change of timing of the current injection and the pre-charged capacitor voltage. The mechanical LC DC CB commutates DC fault current in very short time of 320 µs, and the use of pre-charged capacitor makes this topology good candidate for applications in medium voltage DC systems.

Hybrid DC Circuit Breaker with Integrated Self-charging and Current Limiting

With the rapid development of DC power systems in recent years, more stringent requirements have been put forward for the fast reliability of DC circuit breakers. At present, in the medium voltage DC circuit breaker, the mechanical switch commonly uses an external secondary power supply to charge the mechanism drive capacitor, which has the problems of large breaker size and high cost. In this paper, we propose a DC circuit breaker topology that uses short-circuit current to charge the mechanism drive capacitor of the mechanical switch. When the short-circuit current rises, a voltage drop is formed across the series inductor, and this voltage charges the drive capacitor in parallel through a diode, avoiding the use of a secondary power supply to charge the drive capacitor and reducing the complexity of the DC circuit breaker system. The operating principle of the circuit breaker is analysed and the rationality of the proposed scheme is verified by simulation calculations.

A Novel DC Circuit Breaker With Counter-Current Injection and IGCT Combined

The fast fault clearance in medium voltage direct current (MVDC) grids requires the DC circuit breakers (DCCBs) with high breaking capability and low cost. The traditional hybrid DCCB realizes large current interruption relying on several insulated gate bipolar transistors (IGBTs) in parallel, which results in difficulty of cost reduction. In this paper, a novel DC circuit breaker with counter-current injection and integrated gate-commutated thyristor (IGCT) combined is proposed and analyzed. By combining forced commutation and IGCT, the large current breaking capability can be realized and the low cost is guaranteed. The simulation of the proposed DCCB is performed to evaluate the fault current breaking capability and influence of circuit parameters consisting of stray parameters and pre-charged capacitors on current commutation processes. Furthermore, a prototype of the 10 kV MVDC circuit breaker with 20 kA breaking capability is developed, then the fault current breaking test is carried out to verify the validity of the proposed topology which can cut off current within 2.5 ms. 1

A Novel DC Circuit Breaker with Fast Breaking Capability in Full Current Range

With the rapid development of DC power system in recent years, more stringent requirements have been put forward for the rapid reliability of DC circuit breakers. At present, most hybrid circuit breakers widely used create artificial zero crossing by injecting current opposite to short-circuit current. However, when it comes to the small current, the injected current may reverse puncture the contacts of the high-speed mechanical switch. And this results in the difficulty of extinguishing the arc between the contacts of the high-speed mechanical switch during disconnection, prolonging the disconnection time and adversely affecting the system. This paper presents a double break DC circuit breaker structure based on double capacitor structure. In the process of current breaking, the capacitor with small capacitance is used to commutate for small current, and the double capacitor parallel method is used to complete the current transfer for large current. The working principle of the circuit breaker is analysed, and the appropriate parameters are selected through simulation.

A Novel Flexible Fault Current Limiter for DC Distribution Applications

As an effective carrier of new energy collection, DC power grid has characteristics of low inertia and weak damping, which makes DC fault propagate extremely fast. However, the existing protection and DC circuit breaker (DCCB) technique still could not match its fault propagation speed. Therefore, to solve this problem, a novel of flexible fault current limiter (NFFCL) is presented in this paper. Under normal operation condition, NFFCL is connected to DC line in series without negative influence. When a fault occurs to DC line, NFFCL’s rectifier circuit, according to the protection criterion, provides cascade inductor, which is connected to DC line in series, with a set-slope linear current. In this case, the voltage drop between both ends of inductor can be clamped flexibly, which can even completely isolate the fault area. A controlled voltage source (CCVS) is applied to generate inverse flux to prevent the cascading inductor from magnetic saturation. When the fault disappears, the energy of current-limit inductor can be released and transferred to AC power grid through NFFCL’s converter. Finally, simulation cases are carried out to verify the working principles and practicability of proposed NFFCL.

Study on Overvoltage Rise Rate Suppression Method for DC Interruption

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

A global fault current limiting strategy for the MMC-HVDC grid with a reduced DC reactor

The large current limiting reactor (CLR) and DC circuit breaker (DCCB) are required in the half-bridge modular multilevel converter (HB-MMC) project to isolate the DC fault. To limit the fault current and reduce the CLR, a global virtual impedance-based fault current limiting (VIFCL) control strategy is proposed in this paper. This strategy includes two parts: the first part is a simplified adaptive fault current limiting control for limiting the DC fault current by reducing the arm modulating voltage of the MMC adaptively. The second part is a virtual impedance control for limiting the AC currents and the arm currents of the MMCs by mapping the virtual impedance to the reactive power control. The effectiveness of the proposed VIFCL control strategy is verified in the PSCAD/EMTDC using a four-terminal HVDC grid. The proposed global VIFCL control can limit the interrupted currents of the DCCBs and reduce the CLR. The proposed strategy is beneficial for the MMCs to ride through the DC faults safely without a significant influence on the power recovery of the HVDC system.

A Contribution to the Development of High-Voltage dc Circuit Breaker Technologies: A Review of New Considerations

To promote the integration of renewable energy resources into modern energy systems, high-voltage dc (HVdc) and circuit breaker (CB) technologies have become critical to achieving secure and efficient energy transmission. This article reviews the technical development of the related areas, compares diverse breaker concepts and topologies, investigates possible coordination and testing solutions, and points out the remaining challenges as well as future needs. The time-domain simulation and comparative analysis are adopted in this article to analyze and compare the performances of different HVdc CBs. By making use of different selectivity levels of multiterminal HVdc (MTdc) grids, the suitable planning and placement of HVdc CBs can be conducted. Furthermore, by providing insights into the performance of HVdc CBs, the work presented in this article can serve as a useful asset for the upcoming standardization and industrial application process of HVdc grid and CB design and testing.

A Novel High-Power Hybrid DC Breaker Based on Compound Power Electronic Switch With Integrated Commutation Ability

Medium voltage dc power system has the characteristics of low line impedance, resulting in high peak and fast rise rate of the fault current. For example, the current in an onboard 10 kV dc grid can rise to more than 40 kA in 3 ms after the failure. Therefore, it is necessary to configure dc circuit breaker with high current breaking capacity. In this letter, a novel high-power hybrid dc breaker based on integrated commutation compound power electronic switch is proposed. By giving full play to the complementary advantages of insulated gate bipolar transistor (IGBT) and integrated gate-commutated thyristor (IGCT), and skillfully integrating the commutation function into the power electronic switch, the proposed dc breaker has the characteristics of low cost, compact, high performance, and can also play a role in current limiting. The working principle of the proposed scheme is described in detail, and a 10-kV prototype with 40 kA current breaking ability is built to verify its feasibility.

A solid-state circuit breaker for DC system using series and parallel connected IGBTs

MVDC systems have attracted a lot attention for the integration of renewable energy and electrification of transport due to their superior system operational performance and high power quality. DC circuit breakers are of significant importance for the development of MVDC systems because they offer fast protection from fault conditions compared to mechanical equivalent. However, unlike AC systems, there is no zero-crossing for the current in DC systems, this makes the DC circuit breakers design more demanding. This paper presents the design of a solid-state DC circuit breaker (SSCB) in details using series and parallel configurations of IGBTs to increase the voltage and current ratings. The operation, electrical design and thermal design of the SSCB are presented and analysed. A PLECS model is developed to simulate the operation of the SSCB. A 1 kV SSCB prototype is built and experimentally tested under both static and dynamic conditions. The prototype demonstrates even current sharing and voltage balancing in the experimental tests. The prototype can carry 150 A current continuously without overheating and demonstrates successful interruption of 1 kA DC current.

A current‐limiting DC circuit breaker with power flow control capability

Power flow controller (PFC), fault current limiter (FCL) and DC circuit breaker (DCCB) are important equipment in the DC grid. There are a large number of power electronic components in these equipment, resulting in high cost. In order to reduce the use of additional components, a current-limiting DC circuit breaker with power flow control capability is proposed here, which integrates the PFC, FCL, and DCCB into one equipment. Further, the main breaker in the proposed circuit breaker is shared by all lines connected to a DC bus to reduce cost. The topology and operating principle of the circuit breaker are introduced. Theoretical analysis and parameter design are carried out. Besides, the proposed circuit breaker is verified in PSCAD/EMTDC. Finally, the performance and cost are compared with existing schemes. The simulation results show that the proposed circuit breaker can effectively realize power flow control, current limiting and fault isolation at a lower cost.

Fault current calculation in MTDC grids considering MMC blocking

In this paper, a generic fault current calculation method based on coupled differential equations is proposed which is valid for both blocked and unblocked states of the MMC. The first part of the paper concerns the modeling aspects of MMCs in blocked and unblocked states, while the second part focusses on the representation of the DC grid. Overhead lines are modeled as lumped RL-elements, whereas cables are represented by an adapted π-model in order to consider the capacitor discharge. A simplified DC Circuit Breaker model is integrated into the set of coupled differential equations, which allows to estimate the energy absorption requirements during fault current suppression. The results of the method are compared to EMT simulation results and validated throughout different fault scenarios. The method enables the representation of temporary MMC blocking for a large timeframe of tens of milliseconds after fault occurrence and is convenient for the sizing of DC Circuit Breakers and DC reactors in MTDC grids.

Stability Control of Flexible High Voltage Direct Current (HVDC) Transmission Based on DC Circuit Breaker Protection

In order to control the stable operation of flexible DC transmission system and ensure the uninterrupted power supply of flexible DC transmission system, the stability control method of flexible DC transmission system based on DC circuit breaker protection is studied. Taking support vector machine as the basic classifier, the two parameters of support vector machine classifier and support vector machine classifier are optimized by bird swarm algorithm, The sample weight is adjusted in real time according to the classification error of support vector machine classifier; The corresponding kernel function is selected and the bird swarm algorithm is used to find the optimal parameters; Through the fault location method of flexible DC transmission system based on wemtr, the fault location of flexible DC transmission line is realized; According to the fault location of flexible DC transmission system, the optimal coordination strategy of DC circuit breaker based on protection line is adopted to realize the stability control of flexible DC transmission system. The simulation results show that this method can realize the stability control of flexible DC transmission in a short time. Under the control of this method, the fluctuation amplitude of voltage and current of flexible DC transmission system becomes smaller, which has application value.

A Low-Loss Integrated Circuit Breaker for HVDC Applications

Hybrid dc circuit breakers (HCBs) are recognized as suitable devices for protecting high-voltage direct-current (HVDC) systems, along with other dc circuit breakers (DCCB). However, compared to mechanical circuit breakers, HCBs exhibit higher conduction losses. Such losses are inevitable under no-fault conditions as current may flow through some of the semiconductor switches. An integrated circuit breaker (ICB) minimizing these losses is presented in this paper, and this is achieved by replacing semiconductor switches by mechanical components in the current path. For completeness, the topology design, operating sequence and a mathematical analysis for component sizing of the device are provided. In addition, an estimation of the conduction losses is quantified. It is estimated that the power losses of an ICB are 2 to 30% of an HCB only. The ICB has been implemented in PSCAD/EMTDC to demonstrate its effectiveness for isolating dc faults, with simulations conducted on a three-terminal HVDC grid.

Design and Implementation of a High-Power DC/DC Converter for HVDC Interconnections With Wide DC Voltage Range and Fault-Blocking Capability

Highly efficient and lightweight high-voltage high-power dc/dc converter is one of the key equipments needed by future HVDC grid. In order to satisfy the technical requirements of interconnecting HVDC lines with different voltage levels, this article develops a thyristor-submodule hybrid dc/dc converter (TSDC) by combining the merits of low cost, low conduction loss, and high robustness of thyristors with the high controllability of the cascaded half-bridge submodules (SMs). The proposed converter presents the attractive features of efficient dc/dc conversion, reliable turn-on and turn-off of the thyristors, wide dc voltage operation range, and above all, the dc fault-blocking capability which avoids the installation of dc circuit breakers. The circuit structure, operating principle, and control schemes are discussed. The validity and effectiveness of the TSDC are verified by 150-MW, 100-kV/300-kV simulation case study as well as the experimental tests from a 4.5-kW, 300-V/450-V scaled-down prototype.

Operation Characteristics of a Superconducting LC Resonant DC Circuit Breaker According to Pole-to-Pole and Pole-to-Ground

DC technology has become an issue as it is applied to DC distribution systems, due to the acceptance increment of the renewable energy. For this reason, research on DC circuit breaker to be applied to Medium Voltage Direct Current(MVDC) or higher is active and various cut-off technologies are being developed. In this paper, we propose a fast and reliable superconducting LC resonant DC circuit breaker in DC system. It reduces the initial fault current through the superconducting element and the fault current reaches zero-point by LC resonance and is interrupted. We designed Pole-to-Pole(PTP) and Pole-to-Ground(PTG) simulation circuits using the PSCAD/EMTDC program. Also, we analyzed and compared the cut-off operation characteristics in the circuit. We confirmed that the superconducting element reduced the initial fault current and the power burden. It is expected that the deterioration of the protective devices and the surrounding equipment can be reduced.

A New Design of MP-HDCCB Topology Based on Hybrid Switching Device

Since each branch of the multiterminal DC circuit system relies on the DC circuit breaker for breaking and fault isolation, the prohibitive cost and huge volume of the Hybrid DC Circuit Breaker (HCB) limit its development and broad application in multiterminal flexible DC systems. Multiport hybrid DC circuit breaker (MP-HDCCB) based on device and branch sharing reduces the configuration cost of the circuit breaker to a certain extent. In order to further reduce the cost of MP-HDCCB, a novel MP-HDCCB topology based on hybrid switching devices is proposed, adopting full controlled switching devices to achieve rapidity of breaking fault current, and using semi-controlled switching devices in series to withstand the transient interruption voltage (TIV), so as to reduce the construction cost and technical difficulty. In this paper, the working principle and fault breaking strategy of the topology are introduced in detail, then the parameters of the major circuit are analyzed theoretically, and the parameter design of each branch is given. In the end, the rationality and validity of the proposed topology is tested and verified by simulations and experimental tests.

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

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

Parallel breaking characteristics of diode-bridge power electronic switch for DC circuit breaker

With the improvement of the breaking-current level of the DC circuit breaker, the current level of the existing power electronic devices cannot meet the demand of breaking the DC current. However, it can realize high-power DC breaking through the power electronic devices in parallel. In order to reveal the influencing factors and laws of parallel breaking characteristics of power electronic devices suitable for DC breaking, and to break through the parallel technology of power electronic devices suitable for DC breaking, the influence of stray inductance of power electronic switch branches, driving performance of power electronic devices, technical parameters of buffer branches and characteristics of switching current on the characteristics of parallel breaking are studied in this paper, which are based on the Injection Enhanced Gate Transistor (IEGT) and the diode bridge type topological structure of power electronic switches. And then a parallel method of power electronic devices suitable for DC breaking is proposed. Lastly, a power electronic switch module suitable for DC breaking is developed, and a parallel power electronic switch module test is carried out. The experimental results show that the two parallel power electronic switching modules can break 50kA current within 10 μs, and the maximum non-current sharing of the four IEGTS is 2.1kA. The current sharing characteristics are good, which verifies the effectiveness of the parallel method of power electronic devices suitable for DC breaking. The research results of this paper lay a technical foundation for the engineering application of power electronic switch suitable for DC breaking.