Current-limiting Reactors Research Articles

Time-Domain Fault Detection and Location Scheme for Flexible DC Distribution Networks

Accurately detecting and locating the fault point of the DC line is significant for eliminating the fault and restoring the power supply of the flexible DC distribution network as soon as possible. Firstly, a direction pilot protection scheme for a complex DC distribution network is proposed based on the integral of the current superposition to identify the fault direction. Then, an online time-domain fault location method based on the least square (LS) method to solve the overdetermined equations is proposed by analyzing the fault loop circuit after the DC line fault. The proposed location scheme utilizes fault data at both ends of the line to eliminate the theoretical impact of fault resistance, and the calculation of the current difference method is discussed to reduce the location error of whether the fault current-limiting reactor (CLR) exists. Finally, various simulations by PSCAD/EMTDC V4.5 demonstrate that the proposed scheme has high protection reliability and location results after different fault positions and resistances. The proposed scheme has low requirements for the sampling rate, fault data length, and implementation costs, which can meet practical application requirements.

Fault Localization in Multi-Terminal DC Distribution Networks Based on PSO Algorithm

Flexible DC power grids are widely recognized as an important component of building smart grids. Compared with traditional AC power grids, flexible DC power grids have strong technical advantages in islanding power supplies, distributed power supplies, regional power supplies, and AC system interconnection. In multi-terminal flexible DC power grids containing renewable energy sources such as solar and wind power, due to the instability and intermittency of renewable energy, it is usually necessary to add energy storage units to pre-regulate the power of the multi-terminal flexible DC power grid in islanded operation. Aiming at the important problem of large current impact and serious consequences when the flexible DC distribution network fails, a combined location method combining an improved impedance method (series current-limiting reactors at both ends of the line to obtain a more accurate current differential value) and a particle swarm optimization algorithm is proposed. Initially, by establishing the enhanced impedance model, the differential variables under the conditions of inter-electrode short-circuit and single-pole grounding fault can be obtained. Then tailor-made fitness functions are designed for these two models to optimize parameter identification. Subsequently, the iterative parameters of the particle swarm optimization algorithm are fine-tuned, giving it dynamic sociality and self-learning ability in the iterative process, which significantly improves the convergence speed and successfully avoids local optimization. Finally, various fault types in a six-terminal DC distribution network are simulated and analyzed by MATLAB, and the results show that this method has good accuracy and robustness. This research provides strong theoretical and methodological support for improving the safety and reliability of DC distribution systems.

Novel Fault Protection Method for Flexible DC Power Systems

A fault protection method is proposed for flexible direct-current (DC) power systems based on the cosine similarity of currents in current-limiting reactors. The typical characteristics of external and internal faults in a flexible DC power system were analyzed. The principles of cosine similarity and the fault current characteristics of current-limiting reactors were used to distinguish between internal and external faults. The ratio of the average positive and negative voltages of the current-limiting reactor was then used to distinguish the fault types and fault line. Finally, a simulation model of a circular flexible DC power system was constructed using MATLAB/Simulink software (2018b). The simulation results show that the proposed protection scheme can quickly and accurately identify the location and type of faults, and has a strong ability to withstand fault resistance and is less affected by distributed capacitance, noise, and communication delay.

A Cost-Effective Current-Limiting Hybrid DC Circuit Breaker Based on Hybrid Semiconductors

DC circuit breakers (DCCBs) are the key equipment to rapidly interrupt the fault current in high-voltage DC power grids and ensure the safe operation of the system. However, most DCCBs do not take current-limiting measures and rely solely on current-limiting reactors in the system to limit the rate of current rise during the interruption process. The extensive use of fully controlled power electronic devices in circuit breakers (CBs) results in high costs. To address the issues above, this paper proposes a DCCB topology with a current-limiting function based on thyristors and diodes, which can reduce the cost of CB while ensuring reliable interruption. The impact of various parameters on CB performance is analyzed using numerical calculations to optimize the parameters. Then, a simulation model of a 500 kV/16 kA DCCB is built in PSCAD/EMTDC, and the performance of the proposed CB topology is compared with the other CB topologies. By comparison, the proposed DCCB topology can reliably isolate fault currents and reduce the amplitude of fault currents and the cost of CBs. Significantly, the energy absorbed by the metal oxide varistor (MOV) during the interruption process decreases by 64.2%, reducing the cost and volume of the MOV. Finally, the feasibility of the CB is further verified in the ±500 kV 4-terminal high-voltage DC power grid simulation model. The results show that the proposed DCCB topology can limit the fault current rise rate, interrupt and isolate the fault reliably, and reduce the cost.

Analysis on DC Fault Current Limiting Operation of Twice-Quench Trigger Type SFCL Using Transformer Considering Magnetizing Current and Current Limiting Reactor

As the penetration of distributed energy resources (DER) has increased, research on direct current (DC) power transmission and distribution has been actively performed. The DC system has the advantage of high-power transmission efficiency. However, it has a very large and rapid increase in fault current in the DC system directly after a fault occurs. As one of the countermeasures, studies on the application of the superconducting fault current limiter (SFCL) into the DC system have been conducted to protect major facilities from DC fault current, which is expected to alleviate the power burden on the DC circuit breaker through its quench operation. Among the studied DC SFCLs, the trigger-type DC SFCL using a transformer, which can achieve the peak DC fault current-limiting operation, has been suggested. However, the DC fault current-limiting operation, in the case of the DC SFCL with a current-limiting reactor (CLR), was analyzed to not be effectively executed in the steady state since the transient state directly follows the fault occurrence. In this paper, the DC fault current-limiting operation of a twice-quench trigger type SFCL using a transformer considering magnetizing current and its CLR was analyzed. Through DC fault current-limiting experiments according to the inductance of its current-limiting reactor (CLR), the effective current-limiting design of twice-quench trigger type SFCL using a transformer was described.

Fault protection scheme of flexible DC grid based on transient power instantaneous energy difference

The DC line protection is the key to the stable operation of the multi-terminal flexible DC grid, and the current limiting reactor (CLR) as the boundary condition provides great convenience for the design of the flexible DC grid fault protection scheme. Using the boundary condition characteristics of the CLR, the paper proposes a fault protection method for flexible DC grid based on transient power instantaneous energy (IE) difference. First, the equivalent circuit of the DC line of the flexible DC grid under different faults is established. On this basis, the conclusion that the transient power amplitude of internal fault is much larger than the external is deduced from the full-power in the time-domain. The Teager energy operator is used to calculate the maximum IE of the transient power, and then the internal and external faults are identified. Secondly, according to the difference of the transient power amplitude of the CLR on the fault pole and the healthy pole, the ratio of the IE of the positive and negative CLR transient power is used to construct the fault pole selection. The scheme is simple and easy to implement, and does not need to consider the synchronization problem of data at both sides. Finally, the simulation results show that the proposed method can better satisfy the speediness and selectivity requirements of DC grid protection. The scheme can accurately detect faults under different working conditions, and has strong fault resistances capability.

Single-ended DC line protection scheme based on first peak time of current-limiting reactor voltage

Fast and sensitive DC line protection is an important guarantee for the security of the flexible DC grid. However, the reliability and sensitivity of the DC line protection are greatly affected by the high fault resistance. To overcome this problem, this paper proposes a novel single-ended line protection scheme for multi-terminal flexible DC grid. Firstly, the propagation characteristics of traveling wave after the internal and external faults are analyzed. Furthermore, a single-ended protection criterion based on the first peak time of current-limiting reactor transient voltage is proposed to distinguish the internal and forward external faults, which is independent of simulation. Then, based on the change characteristics of fault component current, a fault direction criterion and fault pole identification criterion are constructed to identify the backward fault and fault pole, respectively. Finally, extensive simulations and experiments show that the proposed protection scheme can identify the fault quickly and sensitively even for the internal remote-end fault with high fault resistance.

Study of Short Circuit and Inrush Current Impact on the Current-Limiting Reactor Operation in an Industrial Grid

Current-limiting reactors are widely used in industrial electrical grids to reduce the current amplitude in the equipment and stabilize the voltage on the busbar during short circuits. Their application is distinguished by high technical and economic efficiency. However, mechanical damage to the reactors has been observed within extensive industrial grids with many induction motors and internal synchronous generators. The article analyses a case study of the reactor damage in the true industrial grid during a short circuit. An analysis of the damaged reactor’s previous operation had shown that there was a weakening of the fastenings in the reactor design, caused by the repeated starting currents of the grid motors and generators. A study of grid transients during short circuits was carried out by Matlab/Simulink software. The simulation results showed that the reactor could be damaged by a critical peak current in an unfavourable combination of the grid configuration and the short circuit location. The results of the study prove that, for industrial networks containing powerful induction motors and internal synchronous generators, the standardized procedure for selecting current-limiting reactors should additionally consider such factors as the localization in the grid, the effect of equipment-starting currents and possible grid configurations.

SIMULATION OF OPERATION PUMP –STATION WATER IN IRAQ AND CHALLENGES FACING ITS OPERATION WITH POWER SYSTEM

This paper’s research focuses on real problems suffered by pump stations during their connection with the national electric network, in our paper, we will take negative effects that appear in the pump stations with power flow parameters, voltage, active and reactive power current loading, and total losses. Using an electric network have 28 Buses (test2) as a simulation of Iraq’s electric network. Firstly, we will connect a pump station has a capacity of power equal to 75 MVA and do an analysis by the Neplan program which uses the Newton Raphson method to calculate load flow, after that we are solving problems by using FACT'S system (SVC, UPFC, and capacitor bank). also taken the problem of power equality as the effect of Harmonic which produced from electronic devices “soft start of the pump station and method treatment by passive filter first order. At last, we are studying the effect of fault current and how to reduce the effect by using the Current Limiting Reactor (CLR).

Current-Limiting Reactors Based Time-Domain Fault Location for High-Voltage DC Systems With Hybrid Transmission Corridors

Accurately locating the fault distance helps in the rapid restoration of the isolated line back into the system. This article proposes a novel time-domain-based algorithm to determine accurate fault location in high-voltage direct current (HVdc) systems with hybrid dc transmission corridors i.e., a combination of underground cables (UGCs) and overhead lines (OHLs). The work gives a fault location method for a two-segment and three-segment hybrid transmission corridor (HTC) and then generalizes the analysis for an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -segment HTC. The algorithm offers flexibility to locate faults ranging from the homogeneous transmission line to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -segment HTC. The algorithm uses a simplified unit resistance–inductance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$RL$ </tex-math></inline-formula> ) representation of transmission lines along with time-domain-based measurements i.e., terminal voltage, current, and voltage across current-limiting reactors (CLRs). Power systems computer-aided design/electromagnetic transients including dc (PSCAD/EMTDC)-based simulations are used to validate robust performance against variation of key implementation parameters like type of faults, fault resistance, fault location, sampling frequency, and white Gaussian noise (WGN) in measurement. Further, the fault location calculation is analyzed under parameter variation i.e., change in the true value of unit resistance and unit inductance of line or cable and the true value of dc link capacitance.

THE EXCESSIVE TECHNICAL LOSSES OF ELECTRICITY IN ELECTRICAL SYSTEMS OF POWER CONSUMPTION

Reducing electricity losses in electrical networks is a complex complex problem that requires significant capital investments necessary for optimizing the development of electrical networks, improving the electricity accounting system, introducing new information technologies in marketing activities and managing network modes, training personnel and equipping them with means of testing measuring devices etc. In reality, in recent years, in connection with the inclusion of normative losses in the tariff for electric energy transmission services, a dangerous trend of adapting these norms to actual losses has emerged. The article analyzes the occurrence of power losses in electrical engineering systems and electrical networks of various voltage classes. Special attention is paid to the so-called excess losses, which are not taken into account during design and operation. These losses occur in insulators, linear fittings, current-limiting reactors, electricity meters, windings of current and voltage transformers, etc. Excessive losses of electricity in electric networks are direct financial losses of electric power companies. Savings from reducing losses could be directed to technical re-equipment of networks; staff salary increase; improvement of the organization of electricity transmission and distribution; increasing the reliability and quality of electricity supply to consumers. Unaccounted losses reach approximately 1% of the total amount. This fact must be taken into account. Because currently we are talking about millions of losses.

An ANN-based protection technique for MTDC systems with multiple configurations

A unified protection technique for different configurations of Multi-Terminal high voltage Direct Current (MTDC) systems is presented in this paper. The technique is based on using positive and negative poles’ currents of one end for each line. The spectral energy of two distinct frequency bands captured from fault currents, together with the fault current initial slope, are used to supply a feed forward Artificial Neural Network (ANN) for identifying fault zone and classifying fault type. Different configurations of MTDC systems are used to train and test the proposed ANN including radial system, meshed system without Current Limiting Reactors (CLRs), and meshed system with CLRs. Different fault types, fault locations, fault inception times, and fault resistances are used to train and test the proposed ANN. The proposed algorithm showed an excellent performance in the identification of the fault zone and the classification of the fault type for various MTDC configurations. Moreover, the algorithm does not respond to non- DC fault abnormal conditions.

A novel fault current limiter topology design based on liquid metal current limiter

The liquid metal current limiter (LMCL) is regarded as a viable solution for reducing the fault current in a power grid. But demonstrating the liquid metal arc plasma self-pinching process of the resistive wall, and reducing the erosion of the LMCL are challenging, not only theoretically, but also practically. In this work, a novel LMCL is designed with a resistive wall that can be connected to the current-limiting circuit inside the cavity. Specifically, a novel fault current limiter (FCL) topology is put forward where the novel LMCL is combined with a fast switch and current-limiting reactor. Further, the liquid metal self-pinch effect is modeled mathematically in three dimensions, and the gas-liquid two-phase dynamic diagrams under different short-circuit currents are obtained by simulation. The simulation results indicate that with the increase of current, the time for the liquid metal-free surface to begin depressing is reduced, and the position of the depression also changes. Different kinds of bubbles formed by the depressions gradually extend, squeeze, and break. With the increase of current, the liquid metal takes less time to break, but breaks still occur at the edge of the channel, forming arc plasma. Finally, relevant experiments are conducted for the novel FCL topology. The arcing process and current transfer process are analyzed in particular. Comparisons of the peak arc voltage, arcing time, current limiting efficiency, and electrode erosion are presented. The results demonstrate that the arc voltage of the novel FCL topology is reduced by more than 4.5 times and the arcing time is reduced by more than 12%. The erosions of the liquid metal and electrodes are reduced. Moreover, the current limiting efficiency of the novel FCL topology is improved by 1%‒5%. This work lays a foundation for the topology and optimal design of the LMCL.

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.

Limitation of cross country fault currents in MV distribution networks by current limiting reactors connected between cable screens and primary substation earth electrode

MV distribution networks with ungrounded or grounded neutral by compensating impedance are exposed to Cross-Country-Faults (CCFs). If CCFs occur in cable lines, fault current value can reach that of line-to-line fault current. This is because the large part of the fault current flows through cable screens and only a small amount through grounding systems of secondary and primary substations. Cable screens in the joints can reach very high local temperatures where screen and copper stocking connecting the sectioned screens are not pressed enough each other. In these small areas high electric contact resistances cause large joule losses, potentially leading to insulation burning. Successive temporary/switching over voltages can cause dielectric failure, i.e. faults to ground. A way to prevent the screen insulation thermal damage could be a drastic reduction of CCF currents, especially when they occur in different cable feeders of the MV network. The paper illustrates a countermeasure able to reduce CCF currents: the use of current limiting reactors (CLRs) connecting the cable screens to the earth electrode of the primary substation. The influence of the CLRs on the equivalent earth impedances of primary and secondary substations is investigated. The methodology is applied to an existing MV distribution network.

A pilot protection scheme for flexible HVDC transmission lines based on modulus power

Existing protection methods for Flexible HVDC transmission lines easily fail to detect the fault location fast and reliably. Concerning this problem, a modulus power based pilot protection scheme is proposed. By analyzing the dynamic switching process of sub-modules in flexible DC converter station, the expression of converter station DC voltage taking into account the influence of AC system is derived. On this basis, the modulus voltage and modulus current are calculated by phase-modulus transformation, and the modulus power calculation model containing DC components alone is built. Then, the expressions of modulus power in different fault cases are derived, and a protection criterion based on the polarity difference characteristics of modulus power is established. Finally, the RT-LAB is used to build the model of a flexible DC system for simulation verification. The results of simulation tests verify that, the proposed protection scheme can detect the fault line and fault pole fast and accurately, with easy threshold setting and low demand on communication synchronization. Besides, it is unaffected by the fault resistance and the specific boundary conditions of current-limiting reactor, etc.

A modular hybrid DC circuit breaker with fault current self-adaptive control and protection coordination

Hybrid DC circuit breaker (HDCCB) takes advantage of both mechanical and solid-state breakers, the low-loss and fast-breaking characteristics are suitable for MMC-HVDC system. Because the existing DC protection cannot act fast enough, the limitation of fault current based on HDCCB has become an prospective technology. This work proposes a modular hybrid DC circuit breaker (MHDCCB) at first which can self-adaptively control current limiting and current clearing according to the protection action signal after fault. The new topology can be switched to primary current-limiting state and backup current-limiting state, which reserves enough time for fault detection and location. After receiving trip signal, current-limiting reactor can be bypassed to accelerate current clearing speed. Then, the cooperation strategy of protection system and MHDCCB is analyzed. Finally, the simulation cases are carried out to verify the working principle, protection coorperation strategy, and superiorities of the proposed MHDCCB. The technology presented in the paper alleviates the speed limitation of protection and benefits the safty operation after fault in high-voltage and large-capacity MMC-HVDC systems with overhead transmission lines.

Research on Improved Fault Current Analysis Method for Flexible Direct Current Power Grid Considering Alternating Current Feed

Flexible direct current (DC) grid can realize large-scale renewable energy, wide-area coordinated complementation, and reliable power transmission. It is an important development that can be used to support high-voltage and large-capacity flexible DC transmission in the future. The short-circuit current of the DC line is one of the important bases for the selection of key main equipment parameters such as converter valves, DC circuit breakers, and reactors in the flexible DC grid. In this paper, a flexible DC grid equivalent circuit network model with alternating current (AC) feed-in is established. Aiming at the monopolar ground fault of the flexible DC grid grounded through the metal loop, an optimized traditional matrix calculation method is proposed to obtain the accurate line fault current value. On this basis, with an actual engineering background, the equivalent circuit model of the four-terminal bipolar flexible DC power grid is established, and the influence of grounding position, grounding parameters, and current-limiting reactor on the fault current of the DC line is analyzed. Finally, simulation using the PSCAD software verifies the effectiveness and accuracy of the proposed method. The method proposed in this paper can provide the necessary bases and references for the selection of flexible DC grid equipment.

An Improved DC Line Fault Detection Scheme Using Zone Partition for MTDC Wind Power Integration Systems

The MMC based DC grids are an effective solution to integrate bulk wind power. Under DC faults, the wind power is continuously fed into DC grids, resulting in large fault currents. To guarantee the uninterrupted and safe operation of healthy parts, DC faults should be detected and isolated selectively. Most existing DC fault detection schemes rely on large current-limiting reactors (CLR) to guarantee high selectivity. The reliability of them will be deteriorated under weak boundary conditions. Besides, some schemes fail to identify close-in faults. Though fault detection schemes independent of CLRs are proposed, they cannot work well for remote faults. Hence, to protect the entire transmission line with smaller CLRs, an improved DC fault detection scheme using zone partition is proposed. Firstly, according to different fault distances, internal faults are partitioned into four zones along the transmission line. The fault characteristics in different zones are analyzed. Then, the polarities and arrival times of traveling-waves are used to design the criteria dedicated to different zones. The proposed method is endurable to fault resistance and noise disturbance. Simulation results show that the MTDC wind power integration systems can operate safely during DC fault isolation.

Impact on Current-Interrupting Characteristic by Parameter Settings of Superconducting Hybrid DC Circuit Breaker

DC faults cause severe disruption in not only the DC system but also the AC system because the fault current is very large and rapidly increases. The DC circuit breaker used to separate the DC faults from the power system is still being researched, but it is very expensive due to the use of multiple power semiconductors to interrupt a large fault current in a short time. However, if the quench characteristic of a superconductor is used, the amplitude of fault current can be reduced. Therefore, it is possible to effectively interrupt a large fault current even if a relatively cheap mechanically passive DC circuit breaker is used. In the current study, a superconducting hybrid DC circuit breaker is proposed, and the limiting characteristics of each element are analyzed. By using two superconducting elements, the quench occurs sequentially twice according to the magnitude of the fault current, and the current-limiting reactor and resistance are used. If a current-limiting reactor is used in the DC system, the fault current rises slowly at the beginning of the fault, and the use of resistance can reduce the magnitude of the fault current. The inductance of the current-limiting reactor and resistance parameter settings of the hybrid DC circuit breaker was analyzed by the step-changing case method, and the interrupting characteristic of the DC circuit breaker was improved.