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This article describes design, operation and experimental testing of a mechanical DC CB (Circuit Breaker) with parallel capacitors. The topology resembles hybrid DC CB but there are possible advantages in the costs since the main semiconductor valve is replaced with capacitors and in performance since this breaker inserts counter voltage earlier. A detailed PSCAD model is employed to support DC CB design and to analyse operating principles. A 5 kV, 2 kA hardware demonstrator with 1.5 ms disconnector opening time is developed in the university laboratory. The test results demonstrate successful breaking of DC currents, with the measured time for insertion of capacitor voltage of around 290 s. Further experimental analysis evaluates stresses on the key components, optimal timing for opening of LCS (Load Commutation Switch) and the margins for successful current interruption.

Different from typical circuit breakers, breakers used to switch AC filters in convertor stations have to operate frequently according to the real-time operation mode and daily load changes. Therefore, the performance of filter breakers decreases very quickly, which leads to frequent accidents. Both preinsertion resistors and controlled switching devices can suppress switching transients. In this paper, a comparative analysis of whether a controlled switching device and preinsertion resistor should be adopted is carried out using PSCAD. The transient is calculated as the combined result of the switching angle and preinsertion resistor value, and the optimal configurations are proposed. After determining the resistor value and whether a controlled switching device should be included, the reference voltage of the arrester should be reevaluated.

This paper proposes a new modular active injection circuit (AIC) for solid-state circuit breaker (SSCB). The modular AIC is used to achieve soft-switching turn-off during DC current interruption. The proposed AIC presents following contributions: selectable resonant currents are obtained to obtain a reliable artificial zero crossing points in DC currents; current rating scalability is provided; passive components of the AIC are optimized using particle swarm optimization (PSO) algorithm and new proposed objective functions; an external wireless charger is developed to charge the injection capacitor of the AIC to provide voltage isolation, compactness, and flexibility in choosing the pre-charge voltage value on the injection capacitor; the proposed AIC needs no discharge circuits which simplifies the control and accelerates reclosing process. The proposed SSCB is simulated in a 6kV system in PSCAD/EMTDC in interrupting currents of normal and different scenarios . The designed SSCB can interrupt the DC currents up to 200A with the adaptive response time from 3.74s to 6.71s, faster response time in interrupting higher values of DC currents. The effectiveness of the proposed SSCB in practice is validated by experiments of a downsize 380V/20A prototype with only 2.8s response time and 99.91% efficiency.

The high di/dt before zero-crossings easily leads to delayed or failed operations for the active current injection mechanical DC circuit breaker, especially for small direct current interruptions. The pre-charging process also makes this type of circuit breaker hard to realize repeat operations economically in the high voltage DC system. This paper proposes a novel DC circuit breaker and its design method that deeply coordinating a superconducting fault current limiter with the active current injection DC circuit breaker. This method significantly reduces di/dt before current zero-crossings and enables repeat operations economically. Besides limiting fault currents, the superconducting fault current limiter also charges the resonance capacitor flexibly in the circuit breaker, realizing the injected reverse current keep a constant proportion to the arbitrary fault current. Validations of the flexible capacitor charge and repeat operations are made by simulation and low voltage experiments. The charging times are within 2.5 ms and the reverse current keeps 1.2 to 1.7 times over the fault current under arbitrary conditions. Di/dt at current zero is reduced by 80% under 30% of rated interruption capacity. Flexible capacitor charge experiments are consistent with the simulation design. The superconducting tapes can recover within 300 ms to support repeat operations.

The rapid discharge of the dc-link capacitors during the short-circuit fault would cause the transient current with fast propagation speed in the VSC based dc system. It is necessary to limit the dc fault current and lower the requirement of fault detection speed. However, the traditional fault current limitation method with directly installed inductors in the dc line will prolong the fault isolation time, resulting in the system instability during the power flow shifting. In this paper, an adaptive solid-state circuit breaker (SSCB) is proposed for the low and the medium voltage dc system, bypassing the installed inductors during the normal state and connect them into the dc line when the fault occurs. Besides, the energy dissipation circuit and the snubber circuit are applied to release the energy stored in the installed inductors and the dc line inductance after tripping. Hence, the fault isolation speed can be accelerated, and it is not necessary to use the metal oxide varistors in the proposed SSCB. By comparing with other SSCB schemes with the fault current limitation function, the effective fault current limitation, fault isolation and the ride-through of the proposed SSCB is verified in the OPAL-RT based simulation and the hardware test.

High-voltage DC (HVDC) circuit breaker is the necessary equipment for multi-terminal HVDC grids, which is a prospective power transmission method in the future. Therefore, the research about HVDC interruption ushered in an explosive development in recent years. The mechanical DC circuit breaker based on the pre-charged capacitor for current commutation and interruption is considered to be one of the most promising HVDC interruption solution. However, the commutation capacitor requires a complicated pre-charging circuit, especially in high voltage applications, which brings a great challenge to the promotion of mechanical interruption solution. In this paper, a novel self-charging mechanical HVDC circuit breaker is proposed. It utilizes the induced voltage generated by part of current limiting reactor to adaptively charge the commutation capacitor under different fault current conditions without extra auxiliary charging circuit. By investigating the influence of capacitance and inductance on the charging time and current commutation process, the optimized parameters are determined. Then the breaking performance of proposed HVDC breaker under different rising rates of fault current is evaluated in a two-terminal HVDC system. Finally, a low-power prototype is developed to verify the feasibility of the proposed topology and an improved scheme for rated current breaking is discussed.

Adding a damping unit to a shunt capacitor is an effective way to mitigate capacitor-caused resonance. However, damping units suffer from power loss issues. This shortcoming is amplified further in cases where resonance has a low possibility of occurring. In view of this, an adaptive damping method is proposed to improve the existing scheme. The damping unit is capable of mitigating resonance and eliminating the power loss under the non-resonance condition. The core idea of the proposed approach is to add a breaker so that the damping unit can be switched on or off depending on whether resonance occurs. The design of and control mechanism for the proposed switchable damping unit are presented. The performances of the new resonance mitigation scheme in terms of harmonic mitigation, loading, switching transient and cost are verified for an actual capacitor application case.

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

Protection of microgrids at the Point of Interconnection (POI) is a challenging task. Particularly, single-line-to-ground (SLG) faults on the interconnection line are difficult to detect using the fault current detection relays if the microgrid is ungrounded at utility side of its interconnection transformer; such microgrid contributes very low fault current, which disappears once the utility feeder breaker opens. Other common schemes for protection of microgrid interconnection line against SLG faults include Direct Transfer Trip (DTT) and over-voltage relay (59G). The main challenges associated with these methods are installation and maintenance costs of high-speed communication system, sensitivity of relay settings, and delayed fault clearing time due to selectivity requirements. To address such concerns, this paper proposes the use of a distance relay at the microgrid/LV side of the interconnection transformer to provide protection against SLG faults on the interconnection line at the utility/HV side. The designed distance relay executes an enhanced apparent impedance calculation using residual voltage compensation to correctly identify the fault, properly measure the fault location, and timely isolate the fault. In this paper, various scenarios are analyzed using ASPEN/PSCAD simulators to demonstrate the effectiveness of the proposed method for protecting the microgrid interconnection line under different fault scenarios.

On March 31, 2019, a 500 kV air-core, shunt reactor at a large generating station in BC Hydro was damaged shortly after four unit transformers were simultaneously energized from a 500 kV series and shunt compensated line source. Forensic investigations revealed that the controlled switching system, controlling the instant at which each breaker phase closes during energization to minimize inrush current, had failed. Uncontrolled closing led to under-damped, high-magnitude and sub-synchronous currents. Protection tripped and isolated the four transformers, followed shortly by shunt reactor protection tripping. Before the reactor could be isolated by circuit breakers, a damaging internal fault developed. This paper presents forensic investigation describing sequence of events leading up to reactor damage and shares the lessons learned with the peer utilities having similar installations.

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.

We present the ferroresonance overvoltage mitigation concerning the power systems of the grid-connected wind energy conversion systems. WECS is considered based on a doubly-fed induction generator (DFIG) type. Ferroresonance over-voltage associated with a single-pole outage of the line breaker is mitigated by fast regulating the reactive power (injected/absorbed) using the static compensator (STATCOM). STATCOM controller is introduced, in which two incorporated proportion-al-integral(PI) controllers are optimally tuned using a modified flower pollination algorithm (MFPA) as an optimization technique. To show the capability of the proposed STATCOM controller in mitigating the ferroresonance overvoltage, two test cases are introduced, which are based on the interconnection status of the power transformer used within the grid-connected DFIGs. The results show that the power transformers servicing the wind farms can be under the ferroresonance stress although the transformer terminals are interconnected, and no side of the transformer is isolated. Furthermore, as a mitigation method of ferroresonance overvoltage, the proposed STATCOM succeeds in improving the system voltage profile and speed profile of the wind turbine as well as protecting the system components against the ferroresonance overvoltage.

Smart transformer (ST) based low voltage (LV) meshed hybrid grids provide various power flow paths and ensure continuous power supply to loads. The meshed hybrid microgrid can continue supplying to LV loads even during islanding operation. In such case, the ST LV converter is operational while its medium voltage (MV) converter as well as the isolated dc-dc converter are shut down. This paper proposes a step by step start-up method for these two converters of the ST to establish reconnection of the meshed hybrid LV microgrid to the MVac grid, while keeping the ST LV converter functional. The proposed method involves charging the MVdc bus to 85% of the nominal value from the LVdc bus which is already energized. Next, the ST MV converter is energized to build the MVdc voltage to the final value. Once that is established, the power flow is started and the transition from islanded to grid connected mode of the meshed hybrid microgrid is established. To realize the entire starting process, a centralized controller is proposed. This controller gives the ON/OFF commands to the various converters and circuit breakers in the system as per the proposed partial start-up algorithm. Stability studies of the ST isolated dc-dc converter are carried out to ensure that the system maintains stability during the starting process. Simulation studies and experimental validation have been performed to verify the proposed starting scheme.

Solid-state dc circuit breaker (SSCB) plays a very important role in the dc system protection against fast rising overload and short-circuit faults. Among various SSCB topologies, z-source dc circuit breakers (ZSCBs) have a great ability to interrupt the fault at a much faster rate, without even using a fault sensing circuit. However, ZSCBs suffer from various issues such as: 1) high starting current in the main thyristor (SCR), 2) unwanted power flow in the load during commissioning and reclosing of ZSCBs, and 3) negative current flow through the load at starting/reclosing of the ZSCB. These problems arise due to the fact that the z-source series capacitor stays charged even after the fault is interrupted or cleared. Unwanted power flow, negative current circulation in the load needs special attention especially in unidirectional loads and also in electromechanical systems. Hence, this article proposes a modified ZSCB to address the aforementioned problems. The proposed topology employs power semiconductor devices such as IGBTs to discharge the capacitor before the next interruption cycle. Initially, a detailed analysis, with simulation and experimental validation showing the issues with the existing ZSCB is presented. Later, a detailed analysis of the proposed modified ZSCB is presented, followed by an extensive simulation and experimental validation on a laboratory scale 120-V/3.5-A (400 W) prototype.

This letter presents a new low-voltage direct-current fault current bypass-based solid-state circuit breaker (SSCB) using silicon-carbide mosfet s. The proposed SSCB provides the possibility to select the clamping voltage of metal–oxide varistors (MOVs) close to the nominal voltage of the dc system. This reduces voltage overshoots across the main switch and snubber components and extends the maximum allowable dc bus voltage on the SSCB. The MOVs are removed from the power line, and their leakage currents are completely eliminated. The clamping voltage of the MOV and its surge energy rating is considered to optimize the MOV. The dv/dt across the main switchis controlled by an auxiliary capacitor, where a design procedure is presented to optimize its value. Also, the stored inductive energy of the line inductor in dc systems is bypassed using an auxiliary branch and prevented from flowing through the faulty section to enhance the safety. LTspice simulations are presented to show the significance of the proposed SSCB. The experiments of 375 V/170 A/2.4 μs and 600 V/163 A/2.4 μs verify the effectiveness of the proposed design in practice.

In this article, a novel isolated circuit breaker (ISCB) that realizes robust interruption capability is proposed for direct current microgird protection. First, the proposed ISCB isolates the main current path and the commutating circuit during the fault-clearing state, thereby not causing fault current surges on both the input and output sides, and effectively protecting the source and load. Second, the ISCB can automatically charge the commutating capacitor to offer interruption capability before the reclosing of the breaker, which ensures a safe restart of microgrids after faults (especially temporary faults). Third, due to the introduced voltage clamping circuits, the ISCB can successfully interrupt faults without being effected by parasitic parameters on microgrids. Finally, the use of the insulated gate triggered thyristor with strong tolerance to current and voltage surges can also enhance the robustness of the ISCB. Consequently, the ISCB features higher fault interruption robustness than the existing breakers. Moreover, design guidelines are provided through mathematical modeling, and then based on the design guidelines, a laboratory prototype is developed to validate the feasibility of the ISCB.

The low voltage DC distribution networks are emerging as a great development trend for their flexible access to photovoltaic energy. However, there is no mature DC circuit breaker to protect DC fault. T-source circuit breakers can quickly and automatically cut off a fault current in a very short time. Compared with Z-source circuit breakers, T-source circuit breakers have greater advantages of zero reflected current, common ground, and capability of low-pass filtering. However, as a result of the high power loss of semiconductor devices, transmission efficiency is reduced. Therefore, this paper proposes a new efficient bidirectional T-source circuit breaker. The number of semiconductor devices that conduct in steadystate is reduced and therefore the on-state loss is reduced by more than 40% compared to the existing bidirectional T-source circuit breakers. The new circuit breaker can be manually turned off by reusing the capacitors. The soft starting circuit is also integrated into the circuit breaker. Finally, it is verified by simulation and experiment that the new circuit breaker has the capabilities of fault clearing, manual tripping, and soft starting.

Two key challenges in meshed multi-terminal dc (MTdc) grids are line power flow management and fault current interruption, which can be solved by current flow controllers (CFCs) and hybrid dc circuit breakers (HCBs), respectively. However, the power losses and the implementation costs of CFCs and HCBs are relatively high. In order to overcome these drawbacks, a combined HCB (CHCB) is proposed in this article by fully utilizing the core ideas of the interline dual H-bridge CFC and the HCB. The proposed device can substitute multiple HCBs at a dc bus with greatly reduced cost. In addition to the fault current interruption capability, the current flows in the adjacent lines can be controlled by the embedded multi-line CFC in the CHCB expanded from the existing interline dual H-bridge CFC. The system-level behavior of the proposed CHCB is similar to the separate solution of the typical HCB and the multi-line CFC. Extensive simulations and experiments verify the effectiveness of the proposed device. Besides, a comparison of the proposed CHCB and the separate solution is presented.

In vacuum interrupters, an insulation ability is degraded immediately after high current interruption, because of thermal electrons, metal vapors, and residual plasma. Thermal electrons and metal vapors are produced from the electrode surface, which is heated by the arc between electrodes. Therefore electrode temperature is affect insulation ability. It is important to measure the transient of temperature distribution at anode surface after current zero, for explication of interruption phenomenon in vacuum. Hence, two color pyrometer method with a high-speed camera for temperature measurement of electrode in vacuum was developed, and temperature of Cu-Cr spiral test electrode was measured after current zero by its method and time change of temperature distribution at anode wad obtained. Also, relationship between interruption current and time change of anode temperature was investigated.

Rapidly growing power demands account for an increasing level of short circuit fault current in recent years. It is difficult for the conventional circuit breaker to meet the capacity requirements for fault current limiting. However, a high temperature superconducting fault current limiter (SFCL) can instantaneously protect power grids by using the HTS quench properties. The wide application of SFCL gives a new avenue for power grid protection. Therefore, SFCL have advantages in reducing the capacity of circuit breaker. A novel self-triggering SFCL with magneto-biased field was proposed in this paper. This SFCL has a non-inductive high temperature superconducting module, a reactor with two split symmetrical windings and a circuit breaker. The experimental platforms for test of the transport characteristic of SFCL unit are set up. A high-speed Data Acquisition (DAQ) System based on LABVIEW produced by NI Corporation is applied for experimental tests. The critical current and AC loss characteristics of a SFCL unit have been tested and compared considering the effects of joints. This SFCL has been validated and its technical feasibility in power grids is verified by experimental investigations.

The diode bridge submodule (SM) is one of the basic units of a hybrid high-voltage dc circuit breaker. This article works on the low inductance design of a single SM and series SMs. For the layout design of a single SM, this article proposes a simple and clear +-shaped SM layout, the low inductance design is simplified to the optimization of two laminated busbars with a simple structure. Based on the +-shaped SM layout, this article further proposes an SM structure with holes in diodes region, the stray inductance is further reduced, and only one integrated laminated busbar is needed in a single SM. For the layout design of series SMs, this article makes full use of the layout of a single SM and the mutual inductances between the SMs, series SMs are alternately connected in reverse. The single SM layout proposed in this article is effective in reducing the stray inductance. The loop stray inductance in stage II reduced from 148.4 to 72.3 nH, a 51.3% reduction. When the two parallel IGBTs turn off a 6 kA fault current in 2 μ s, the voltage spike is reduced from 786.1 to 423.4 V, a 46.1% reduction. And the stray inductance difference of the bidirectional current path is controlled to about 10 nH. The layout of series SMs proposed in this article is effective in reducing the length of the series SMs, the length is reduced by 16.7%. The experimental results show that the SMs layout proposed in this article is effective.

Pre-insertion resistors (PIR) are critical components for suppressing the closing inrush current and operating overvoltage during the closing process of the circuit breaker. And it is widely adopted in 800kV and above transmission lines and alternating current filters of converter substations. These special application environments lead to higher failure rates than other electrical components. However, in the daily operation and fault diagnosis of PIR, there is no systematic method to analyze whether there are defects in PIR and the cause of failure after the PIR fails. Based on two PIR failure in series and parallel structures, this paper proposes methods such as dynamic resistance fitting, acoustic and vibration signal detection, insulation performance test, and heat capacity test during operation. In the aspect of fault diagnosis, methods such as PIR splicing based on Iterative Closest Point , stress analysis, and electric field simulation are proposed. Finally, proposed methods can be adjusted to estimate the operating state of PIR through the disassembly inspection to avoid the GIS breakdown accident during the operation of the circuit breaker.

The high conduction loss of solid-state circuit breakers blocks the HTS electrical system implementation for future aircraft. An LN2 switch marries the low conduction loss with good DC interruption performance in the cryogenic circumstance. It shows a fascinating prospect in the HTS electrical system. However, the possible applications of such a novel switch have never been discussed. This paper proposed two potential strategies for applying the LN2 switch into the HTS electrical system. A low voltage experiment is conducted to validate the combination of the SFCL with an LN2 switch. Heat loss is also calculated based on the experimental results. Same level solid-state circuit breakers with cryogenic parameters are set as a fair comparison. A 10 kA prospective short circuit current is limited to 1.4 kA by SFCL within 580 μs and then interrupted by the LN2 switch within 12 ms. The fast response of SFCL compensates for the long clear time of the LN2 switch. Heat loss of this combination is 1/120 of the heat generated by the same level SSCB in an assumed 2-hour flight. With proper design, such a combination could meet the protection requirements of any specific HTS electrical system. Refrigeration system size and weight can be significantly reduced.

Medium-voltage dc (MVdc) distribution systems have the advantages of high power density, low line loss and fast system response. However, the high rise rate and large peak value of short circuit current make the fault current interruption a critical problem in MVdc systems. To solve this problem, a novel circuit breaker scheme based on integrated gate-commutated thyristor (IGCTs) current sharing integrated with freewheeling is proposed in this article, which not only can ensure a high breaking capacity and short interruption time in the full current range, but also have superior vacuum interrupter recovery performance and high breaking reliability. The analysis of key factors, including stray parameters, inductance-capacitance (LC) parameters and arcing time, on the current commutation characteristics is presented, and the optimal design principle of the circuit breaker parameters is obtained. Finally, the proposed MVdc circuit breaker is verified with a 64.2 kA/10 kV fault current interruption experiment.

Currently, we are developing an AC/DC conversion technology with the development of power semiconductors. Accordingly, DC is attracting attention because it is advantageous in the current transmission system. However, it has a problem that the cut-off technology required for DC system operation has not been secured yet. We are researching and developing a DC cut-off technology in several ways. We proposed a model that combines a superconducting fault current limiter and a DC circuit breaker. This is a configuration which a superconducting fault current limiter and a mechanical DC circuit breaker are connected in series. The superconducting fault current limiter limits the initial fault current and the mechanical DC circuit breaker cuts off the fault current. The mechanical DC circuit breaker consists of a high-speed DC switch, a LC divergent oscillation circuit and a surge arrester. This creates an artificial zero-point by affecting the blocking of the DC fault current according to the LC diverging oscillation circuit. In this paper, we analyzed the effect of the LC divergent oscillation circuit on the superconducting DC circuit breaker according to Reactor (L) and Capacitor (C). As a result, we analyzed the operating characteristics of the superconducting DC circuit breaker according to the application of the LC divergent oscillation circuit using the PSCAD/EMTDC program. Also, we confirmed the characteristics of the initial fault current limit rate of the superconducting fault current limiter and the possibility of controlling how the LC divergent oscillation circuit affects the DC arc generated at the opening of the mechanical DC contacts.

Switching transients arises due to random switching of power apparatus results in degradation of thermal and dielectric health of equipment and system as a whole. Controlled switching or point on wave control has emerged as excellent solution for minimizing the charging transients and can aid the better condition monitoring of circuit breaker. Different switching strategies are in place based on different design and connection configurations. Each methodology has certain advantages and dis-advantages. The performance of control switching is dependent on the dielectric performance of insulating medium and circuit breaker performance. The effect of variations in insulation dielectric properties and breaker mechanical performance has been discussed in depth in this paper. Selection and performance of feedbacks used in controlled switching also play a major role in target evaluation and needs proper assessment. Review of different controlled switching methodologies in respect of transformer and shunt reactor have been discussed in paper augmented with field cases. Based on the review of available controlled switching methodologies and field experience, the acceptance criteria have been proposed.

DC microgrids have received remarkable interest in both the academia and the industry for over a decade, yet the protection of dc microgrids remains as a major challenge. This challenge is rooted in the nonexistence of natural zero-crossing point in dc microgrids which rapidly increase the fault current. In this article, a novel bidirectional dc solid-state circuit breaker (dc SSCB) to reinforce the bidirectional flow of energy which significantly boosts the overall efficiency of the power supply of dc microgrids is presented. The proposed topology can perform the operating duty of reclosing and rebreaking, and the commutation capacitor is charged and recharged naturally without any complex control of the main or auxiliary thyristors, which is considered atypical of existing topologies. A clear and detailed analysis of the operation of the proposed topology is presented. Finally, the experimental results are presented to confirm the effectiveness of the proposed novel bidirectional dc SSCB.

A mechanical switch can be used instead of a power electronic load commutation switch in orderto reduce the losses during normal power flow in standard hybrid DC circuit breakers. The success of current commutation in such hybrid breakers depends on the arc voltage formed across the contacts in the mechanical switch. The behaviour of rapidly elongated, wall constricted arcsgenerated during the opening of an ultra-fast mechanical switch in the air is studied here. The voltage-current characteristics of the generated arcs are obtained for steady state contact opening velocities of 6, 11 and 21 m/s. It is found that the arc voltage at a given current and contact separation increases with the contact opening velocity. It is shown that stationary,zero-contact-velocity characteristics can not be used to accurately quantify the voltage build-up in fast elongating arcs in hybrid breakers. A best-fitting black-box equation for the dynamic arc characteristics is presented for the tested velocities. The obtained voltage-current characteristics are used as input to simulate the current commutation process in a 12 kV hybridDC circuit breaker case-study. Different scenarios of current commutation failure related to the arc voltage build up are identified. It is shown that these failures scenarios can be avoided by increasing the contact opening velocity.

Hybrid circuit breaker (HCB) has shown good performance for interrupting dc fault current. However, a massive number of IGBTs in series is needed. These will lead to high costs and significant difficulty in balancing IGBT dynamic voltage. This paper proposes a bidirectional hybrid circuit breaker based on a cascaded half-bridge submodule structure to reduce the overall costs and implementation difficulty of HCB. The number of IGBTs is reduced by 50%, and the operating speed is fast enough. A model of a four-terminal modular multilevel converter (MMC) system with a proposed hybrid circuit breaker in different stages is developed to describe the fault blocking process more clearly. The performance of the proposed HCB is validated and compared with other HCB structure through both theoretical derivation and time-domain simulation.

The installed capacity of renewable energy resources in dc format is increasing in modern power systems, and thus, the protection of high-power dc power delivery from fault is critical in HVdc transmission and MVdc distribution networks. Based on thyristors, Z-source circuit breaker (ZCB) is a promising device for high-power protection, with the capabilities of bidirectional power flow and automatic/controllable turn- off function. In this article, a new specific method for calculating Z-source capacitances is developed based on the reverse-recovery characteristics of SCR, which was not considered in the prior-art solution properly. The proposed method can ensure the turn- off action of SCR in ZCB's practice for realistic dc network protection. At first, it is revealed that the problem in the prior-art solution of ZCB parameter identification, which does not handle the SCR's reverse recovery well, and thus, could result in a failure of tripping action. To solve the problem, the specific method is proposed to adjust the Z-source capacitances, in order to accumulate enough electrons for the postfault depletion region buildup in SCR, and thus, guarantee the SCR's turn- off for a successful dc circuit protection. In the specific derivation, the required tripping time of ZCB is also considered and can remain unaltered after Z-source capacitance adjustment. Finally, experimental tests have verified the problem solving by comparing the proposed to the prior-art solution and proven its accuracy. The proposed method can be added as a supplement to the prior-art solution for the practical design of ZCB. This research article helps to increase the technology readiness level of ZCB solution and practice in realistic dc network protection.

A reliable protection coordination system between the power electronic converters and solid-state device-based fast protection unit in a standalone dc microgrid supplied by a wave energy converter (WEC) and an energy storage unit is presented. A system model with solid-state circuit breakers is developed in Piecewise Linear Electrical Circuit Simulation (PLECS) to analyze the steady-state operation as well as faulted conditions. The effect of both resistive and constant power loads on a current-limited bus controlling converter behavior during an overload event is analyzed theoretically. Also, the variation in the WEC power output and its effect on bus voltage during overload are investigated. The analysis has led to a novel dual current–voltage feedback-based protection coordination system. The method does not require any communication between the solid-state circuit breakers and converters and eliminates the need for adaptive updating of the overcurrent threshold with varying renewable generation output. Bus capacitor discharge during a short-circuit is analyzed theoretically as well to formulate an instantaneous trip threshold selection utilizing device gate driver functionality. The proposed protection coordination system ensures rapid fault isolation and continued power delivery to the healthy segments. An SiC-based bidirectional, solid-state dc circuit breaker prototype is designed and fabricated, which has been used to implement the proposed protection method with a 380-V dc bus-based system.

Pre-insertion resistor (PIR) is an important component of circuit breaker. The healthiness of the circuit breaker (CB) depends upon that of PIR contact. With the increasing demand of uninterrupted ...

Along with the rapid development of technology and the development of civilization, electrical energy is very important in all fields. This research will conduct a study on the electrical protection system design of PT Semen Padang's Indarung VI Cement Plant using the ETAP 12.6 software. PT Semen Padang's Indarung VI Cement Plant uses three transformers of 150 / 6.3 kV of 30/35 MVA (ONAN / ONAF) and each Main Substation has substations that will supply all the loads to be used. The power flow study shows that the addition of a capacitor bank and a tap changer setting will improve the power factor and voltage of the system, thereby reducing the power supply sent by PLN. The short circuit study shows that the largest short circuit current, which is 35 kA, can be protected by a circuit breaker with a breaking capacity of 40 kA. The protection system coordination study shows that the results of the overcurrent relay setting can protect the electrical system of Indarung VI Cement Plant selectively and safely.

An optimized configuration of bidirectional Z-source circuit breaker using a coupled inductor is introduced for the fault isolation in low-voltage dc microgrid. The proposed circuit breaker is designed to operate with a single coupled inductor for bidirectional power flow. Use of the single coupled inductor for the power flow in both the directions reduces the component count. In this article, the operating principle of the breaker is explained for a short-circuit fault condition and breaker design criteria are derived. The performance of the circuit breaker is evaluated by carrying out a MATLAB simulation study. The functional prototype is developed to validate the breaker capabilities. Experimental results show that the fault is cleared within few microseconds. Additionally, the breaker is tested under the step load change condition for a current five times the steady-state rated current of the breaker and results are satisfactory.

Isolation is a separator between conductors in electrical equipment that prevents flashover, resulting in a short circuit or electrical failure. Isolation is critical in electrical appliances, exceptionally High Voltage Power Equipment (HVPE), to ensure the safety of circuit breakers, capacitors, and transformers. In addition to being an isolator, the insulating liquid material also serves to cool the heat generated by electrical appliances. Isolator with mineral oil-based transformer has various environmental issues, including non-biodegradability, non-renewability, and rarity. Because it is environmentally safe and extensively used, virgin coconut oil (VCO) is an alternative transformer oil insulation. This study aims to determine the properties of Virgin Coconut Oil (VCO) breakdown voltage using the IEC 156 standard and oil temperature conditioning. According to the test results, the oil breakdown voltage before heating (at room temperature) is 14 kV, which is much below the IEC 156 standard, and the breakdown voltage after heating at 90 ° is 35 kV, and 110 ° is 40 kV, which is even higher than the IEC 156 requirement

The extended grading capacitor (EGC) is a cost‐effective technique to suppress secondary arc. However, whether the use of EGC would weaken the interrupting capability of circuit breakers (CB) or not is still undetermined. In this work, an equivalent circuit model for ultra‐high voltage transmission line was established. The expressions of transient recovery voltage (TRV) across the contact gap of CB are derived, and hence the rate of rise of recovery voltage (RRRV). Then, a series of simulations have been performed, including the long‐line fault, the short‐line fault (SLF) and the terminal fault. It is found that the RRRV had approximately linear downward trend with the increase of the capacitance of EGC under long‐line fault but had approximately index downward trend under SLF. The SLF poses the strictest requirements to the CB. In addition to suppressing secondary arc current, the use of EGC would mitigate the interrupting severity and enhancing the interrupting performance of CB.

Ferroresonance often occurs in power systems during system switching, which creates overvoltage situations and poses great risks to the equipment safety. In this article, a single-phase ferroresonance incident during a system energization process is presented, which occurred at a single-phase station service transformer in an ungrounded system, causing a surge arrester's failure. This incident is investigated through the PSCAD simulation and the analytical analysis. To validate the PSCAD simulation model, the relay field record is compared with the PSCAD simulation results. Several case studies are conducted using PSCAD simulation to evaluate contributing factors to this ferroresonance incident. The root cause is found to be lack of ground in the system during energization. Field practices are recommended to avoid such incidents, which were proved to be effective by successfully energizing the system in the field.

The emerging interconnections of renewable energy sources that generate DC power have resulted in demands on DC grid systems. In this situation, a low-voltage DC (LVDC) grid system could be a solution for these DC power sources. For the reliable operation of a LVDC grid, DC faults are an issue and DC circuit breakers (DC CBs) are appropriate devices to clear fault current. However, there are some difficulties in terms of breaking DC faults such as the absence of zero crossing of the current and voltage, and the high di/dt of the fault current. This paper proposes a hybrid circuit breaker (HCB) with a new structure for a LVDC grid system. The main switch consists of a vacuum interrupter (VI) and a permanent magnetic actuator (PMA). Some improvements are proposed to enhance the performance of the PMA. A bi-directional commutation loop consisting of a minimum number of power electronic devices is suggested. To absorb fault energy, a capacitor and a diode loop are applied. The principle of the proposed HCB and the design methods for all of the components are analyzed. Through a simulation model, the designed components are selected and verified. Experimental results with a realized prototype (750 V/300A) verify the design method and its performance.

The delayed operation of distance relays zone-2 element for the faults at the end of the line is excessive. It reduces the fault clearing speed and therefore, is one of the main factors that can endanger power system stability. This paper proposes an impedance-based scheme for discrimination between the last 20% of the line length faults and the adjacent line faults, which are covered by the relay zone-2. The suggested non-pilot scheme uses a modified fault location formula for the accelerated zone-2 operation of distance relays. The negative- and zero-sequence components of local signals are utilized to calculate the accurate fault location after the remote circuit breaker (CB) operation. The proposed algorithm is independent of fault resistance, power flow direction, pre-fault condition, and it can clearly distinguish internal faults from the adjacent line faults. Simulation results show that the proposed method can identify the remote CB operation and thus can accelerate the tripping of zone-2 within a very short time for different fault locations, fault types, fault resistances, and load angles. Also, accurate fault location has been achieved under all simulation conditions. 1986-2012 IEEE. Manuscript received December 7, 2019; revised March 12, 2020, May 20, 2020, and July 1, 2020; accepted July 3, 2020. Date of publication July 7, 2020; date of current version May 21, 2021. This work was supported in part by the National Priorities Research Program under Grant 11S-1125-170027, and in part by the Qatar National Research Fund (a member of Qatar Foundation). (Corresponding author: Amir Ghorbani.) Amir Ghorbani is with the Department of Electrical Engineering, Ab-har Branch, Islamic Azad University, Abhar 4561897594, Iran (e-mail: ghorbani.a@abhariau.ac.ir). Scopus 2-s2.0-85099116532

The purpose of this article is to provide a comprehensive and integrated discussion on the basic concept and general design methodology of a gallium nitride (GaN)-based, tri-mode, intelligent solid-state circuit breaker, referred to as iBreaker. The iBreaker concept explores the use of GaN devices in the low-voltage ( on / off switch configuration in order to integrate more intelligent functions without increasing component count. The iBreaker adopts a distinct pulsewidth modulation (PWM) current limiting (PWM-CL) state in addition to the conventional on and off states to facilitate soft startup, fault authentication, and fault location functions. Key design elements, such as use of wide bandgap (particularly GaN) switches, tri-mode operation, combined digital and analog control, and universal hardware/software architecture, are discussed in detail. In particular, the bidirectional buck topology, changes among operation states, variable PWM frequency control, fault locating techniques, GaN FET hardware, and thermal design are discussed. Two iBreaker prototypes, rated at 380 V/20 A and 1000 V/10 A, respectively, are built and tested to validate the proposed SSCB design concept. 99.95% transmission efficiency, passive cooling, and μs-scale response time are demonstrated experimentally.

DC microgrids have attracted more and more attention with its universality, high efficiency, and potential application market. However, dc fault protection is still a challenge to the development of dc microgrids. In this article, a novel bidirectional dc solid-state circuit breaker based on coupled inductor is introduced. It can realize bidirectional energy flow and bidirectional isolation and interruption of short-circuit faults with fewer components. The working principle of the topology and the working process under different conditions are described, and some properties of the novel circuit breaker are explored, including minimum fault current ramp rate and load step analysis, which provide a reference for the selection of component parameters. Finally, the feasibility and performance of the novel bidirectional circuit breaker is evaluated by simulations and experiments.

Circuit breakers (CBs) play an important role in distribution networks. According to IEC standards, protection characteristics need to be investigated to ensure reliability in the manufacturing process. It is required from IEC 60947 that the instantaneous release shall be verified with a test current at least 10 times greater than the rated current. For large-capacity CB testing, converters with large output current, high accuracy and fast response are needed. A large current indirect converter including four converting units and a matrix transformer is proposed. The converting units are synchronized using a complex programmable logic device (CPLD)-based logic control unit. To increase the current accuracy, an adaptive feedforward control strategy is developed to compensate for the influences of CB-dependent resistances and inductances. The equivalent load impedance is adaptively identified from a robust identifier, which is then used to construct the feedforward compensator. Simulation and experimental results show that different CBs create CB-dependent contact resistances and inductances in the testing circuit. The impedance change can be successfully identified by the robust identifier with limited errors. The proposed converter is capable of generating a wide range of current from 100 A to 40 kA with an error no greater than 2.2%.

DC circuit breakers (DCBs) are expected to isolate faults in high-voltage DC grids. Multiple DCBs are required for a DC bus connected to multiple lines, and they form a DCB cluster. To reduce the construction cost, the DCB cluster can be integrated into a multiport DCB (MDCB). The integration of proactive-DCBs has been widely researched. However, in previous articles, only a few MDCBs have been proposed to integrate current-injection-DCBs (C-DCBs), and the interruption reliabilities of these MDCBs are reduced because multiple mechanical switches (MSs) should be opened during an interruption. This article proposes a novel MDCB to integrate C-DCBs. In the proposed MDCB, all ports share one main breaker and one energy absorber. The interruption operations during a port fault and bus fault are detailed, and the backup protection for an MS failure is presented. The parameter designs of the proposed MDCB are discussed. The proposed MDCB is compared with the DCB cluster to show the economic advantage and is compared with the previous MDCB to show the reliability advantage. Finally, the proposed MDCB is validated using PSCAD/EMTDC simulations.

The coordination between protective devices is the process of determining the most appropriate timing of power interruption during abnormal conditions in the power system. The aim of this work is to coordinate the protection of the 33/11 kV power distribution substation in Iraq using the CYME 7.1 software package. In this paper overcurrent and earth fault relays are simulated in two cases, with time delay setting and instantaneous setting, to obtain the Time Current Characteristics (TCC) curves for each Circuit Breaker (CB) relay of Al-Karama substation (2×31.5 MVA, 33/11 kV) in Babil distribution network. The short circuit current at each CB is calculated and accordingly, the protection coordination for Al-Karama substation has been simulated. The TCC curves have been obtained in two cases for overcurrent and earth fault relays; in a case with time delay setting and in the case with the instantaneous setting. The setting takes into consideration the short circuit current at the furthest point of the longest outgoing feeder and the shortest outgoing feeder.

Energization of the transformer leads to large magnetizing current called inrush current. It results in reduction in transformer life, reduction in circuit breaker life, and power quality issues in the system. For low and medium voltage level systems in generation and distribution, usually, gang operated circuit breakers are employed, which do not allow independent pole operation. This makes controlled switching more challenging in such systems. This paper proposes a controlled switching technique to minimize the inrush currents for a 3-phase transformer using gang operated circuit breaker. Optimum points for controlled closing and opening are obtained from a flux error function calculated from residual and prospective fluxes of the transformer. Practical challenges due to error in voltage measurements, variation in mechanical closing time, transients in flux, etc. and their solutions are also discussed in this paper. The proposed technique is validated by Controller Hardware-In-Loop (CHIL) test and a scaled-down laboratory test on 5 kVA, 210/400 V, Delta-Star transformer. In both cases, the inrush current is limited to 1pu, demonstrating the effectiveness of the proposed scheme. Furthermore, a field test is carried out on a 500 kVA, 6.6 kV/433 V, Delta-Star distribution transformer to confirm the viability of the developed switching technique.

To ensure the reliability and flexibility of direct current (dc) system, direct current circuit breakers (DCCBs) are in urgent demand. Compared with solid-state and hybrid DCCBs, mechanical DCCBs have features of low operating losses and investment, showing bright application prospects. Until now, without concern about transient operating voltages (TOV) in the whole dc system, the reclosing of DCCB is still an open problem, and it is the emphasis of this article. First, overview of TOV in typical pseudobipolar dc system is introduced. Then, focused on hardware, electrical characteristic of a novel mechanical DCCB is analyzed, and verification tests are carried out in our laboratory. By taking interaction between the dc system, DCCB, and lines into consideration, distribution patterns of TOV under different faults and its mechanism are revealed. Based on TOV, novel reclosing strategy is proposed for mechanical DCCBs, and case studies are conducted in PSCAD/EMTDC for verification. Remarkable advantages of novel reclosing strategy are: fault type could be identified without operating any component of DCCB after fault current interruption; no risk of reclosing a permanent fault point; an explicit time could be reserved for the dielectric recovery of temporary fault point.

When the fault current in high voltage direct current (HVDC) systems rises to a higher level, the DC circuit breakers will have either insufficient capacity or will require larger sizes with increased costs. Fault current limiters (FCLs) can reduce the turn-off stress and the stringent requirements on breakers, thereby also lowering their cost. The use of saturated core FCLs, which have fast response times and low power loss, is a promising approach for this issue. However, the parameter design principles for this kind of FCL has so far not been discussed in the literature. The design is often based on reactors that does not consider the transient performance. In this study, an optimized design method for permanent magnets saturated core FCLs in HVDC transmission systems, is proposed. The constraint conditions, parameter optimization and modification steps are discussed, and an optimized FCL design is obtained with the lowest cost and expected current-limiting function. Both simulations and experiments are conducted, and the results demonstrate the validation of the proposed method. Finally, a cost evaluation among main types of inductive FCLs is carried out and suggestions for scaling up saturated core FCLs to HVDC applications are given.

Grading capacitors are required to balance the voltage distribution of the double-break vacuum circuit breaker. However, large grading capacitors increase the magnitude and duration of the reignition current. To reduce grading capacitors, a synthetic circuit with double vacuum breaks was set up to study the effects of arcing time on voltage distribution. The voltage distribution of the upper break decreases from 61% to 52% with arcing times of two breaks decreasing from 6.6 to 3.4 ms synchronously. The experimental results demonstrate that reducing the arcing times can balance the voltage distribution during the transient recovery voltage (TRV) rising phase. The unbalance of TRV distribution can be further improved by adopting appropriate arcing times in the two breaks with grading capacitors having a capacitance of 3000 pF.

Power grid failure is very costly to any modern society, and preventing upheavals like the blackout in eastern US and Canada in the summer of 2003 is extremely important. Complete power grid failure may be triggered by the failure of a transformer, underground cable, overhead line insulator or any other component of the power grid. While close monitoring of expensive, centrally located assets like transformers, generators and circuit breakers is feasible and economically justified, it is extremely difficult to continuously monitor assets that are spread over long distances, and in some cases very difficult to reach, like overhead lines accessories and outdoor insulators. Condition monitoring of outdoor insulators is prohibitively costly, time consuming and unsafe. To overcome these problems, the use of machine learning (ML) in outdoor insulators condition monitoring and diagnostics could be a viable solution.

Difficulties of low sensitivity, being affected by CT saturation, capacitive current, fault resistance, low inception angle, close-in faults, remote up faults, and adjacent lines, demanding information about circuit breakers, needing synchronization devices, overreach, and the impact of compensation with a series capacitor faces the traditional protection methods. This paper presents innovative Cos-Sin features for double-circuit transmission lines protection without communication channels to overcome such drawbacks. The suggested design extracts a group of information from the creative Cos-Sin variation relaying signals. This information is the magnitude and polarity of the innovative Cos-Sin variation relaying signals. The suggested design measured the current signals at only the relay location. It applies a simple formula to merge the three-phase current signals into one to decrease the computational burden. The research uses the ATP software to generate fault cases and MATLAB to implement the suggested design. Besides, the paper validates the simplicity of the experimental implementation of the proposed Cos-Sin variation relaying a signal using physical data. The software employed to record physical data is LABVIEW software. Also, the article compares the proposed method with conventional methods and compares it with a new existing one. The results show that the suggested design succeeds in overcoming such difficulties in addition to its experimental building is simple. Moreover, this article records the success of the proposed method under the different transmission line length and system voltage. The results demonstrate that the suggested design is sensitive, selective, secure, dependable, and reliable for double-circuit transmission line protection.