System Fault Currents Research Articles

PMU placement and fault elimination in power system using hybrid Iwd-Goat algorithm

Power system fault currents are crucial since they determine the system's capacity to survive the failure. The fault currents may be measured in several methods. Phase voltages and phase currents are measured using the Phaor Measurement Unit (PMU). The faults that occur in power systems are more often unsymmetrical, and Line to line-to-ground faults are the ones that happen there the most frequently. In this study, a technique to compute fault currents in a PC and discover fault currents by monitoring the phase currents using PMU has been provided. If the computed fault current is higher than the stated limit, the relay coil is triggered. The outcomes of the simulation demonstrate the output's perfection.

신재생에너지 보급률 증가에 따른 지역적 태양광 수용 용량 추정에 관한 연구

Due to eco-friendly policies, the use of distributed generation, which is a renewable energy, in the existing power system is increasing. Such renewable energy has advantages of voltage drop compensation and power loss reduction, but has disadvantages such as reverse current phenomenon, overvoltage, and increased complexity. For this reason, research on the effect and stability of the power system when a distributed power supply is connected is becoming important, and it is necessary to calculate the maximum allowable distributed generation supply capacity. To this end, this study analyzed the effect on the transient state when the distributed generation supply is connected to the power system through simulation, and presented the maximum allowable distributed generation capacity by analyzing frequency, rotor angle, convergence time, voltage magnitude, etc. In this study, the IEEE 37-bus test feeder and IEEE 9-bus test feeder were set as the test bed as the simulation system, and the simulation was conducted including the photovoltaic system installation, fault current, and events such as switch opening and closing.

Active Fault Current Limitation for Low-Voltage Ride-Through of Networked Microgrids

With the continuously increasing penetration of networked microgrids (MGs) on the local utility grid (UG), MGs face the challenge to avoid increasing system fault currents during low-voltage ride-through (LVRT). To solve this challenge, an active fault current limitation (AFCL) method is proposed with three parts: 1) a novel phase angle adjustment (PAA) strategy is conducted to relieve the impact of MGs output fault current on system fault current; 2) the current injection (CI) strategy for LVRT is formulated to fit the function of PAA; 3) a novel converter current generation (CCG) strategy is developed to achieve a better voltage support ability by considering network impedance characteristics. The proposed AFCL method is applied to the back-to-back converter, as a connection interface between MGs and UG. Extensive tests and pertinent results have verified the improvements of proposed AFCL method with better LVRT performance, while the networked MGs output fault current does not increase the amplitude of system fault current.

Calculation method of steady-state fault current for offshore wind farm

In order to improve the efficiency of solving the steady-state fault current of the offshore wind farm current collection system, In this method, the equivalent model of the PMSG and the VF control converter is established by taking into account the low-voltage ride-through in the case of failure. The Newton-Raphson method is used to iteratively calculate the fault equivalent network. By establishing a simulation model under PSCAD, the symmetric and asymmetrical faults in the collector system of a grid-connected permanent magnet wind turbine connected to the VSC-HVDC are simulated. Simulation results verify the effectiveness and accuracy of the calculation method.

Research on the Multiphysics Field-Circuit Coupling Model of Press Pack IGBT Considering the Application of Hybrid HVDC Breakers

Press pack insulated gate bipolar transistor (PP IGBT) is suitable for the hybrid high voltage direct current (HVdc) breaker to clear the fault current of the flexible HVdc transmission system with its advantages of double-side cooling, short-circuit failure mode, and easy to connect in series. However, it should have the ability to transmit the fault current, which is up to five or six times of its rated current, within several milliseconds depending on the distances between two stations without external cooling system. The junction temperature of PP IGBT will increase sharply and it is not possible to be measured during that situation. Therefore, the accurate prediction of junction temperature is extremely important for the packaging design of PP IGBT according to its working condition. In this article, an electro-thermo-mechanical multiphysics field-circuit coupling model of PP IGBT, which is coupled with the electrical, thermal, and mechanical fields, is proposed to predict the collector current, clamping force, and junction temperature. The 3-D mechanical model is decoupled with the 1-D electro-thermal Cauer network model to simplify this multiphysics model without reducing its accuracy. Both the normal and worst working conditions are analyzed through this multiphysics field-circuit model.

Modeling and Analysis of Short-Circuit Fault Current for MMC-HVDC Grid with DC Circuit Breaker

DC line fault is one of the important factors restricting the development of flexible DC system. DC circuit breaker is an effective means to realize the short circuit fault isolation on DC side of flexible DC system. Therefore, it is necessary to add DCCB into the short-circuit current calculation and modeling of MMC-HVDC power grid for comprehensive analysis. Firstly, the external characteristics of the hybrid HVDC circuit breaker and the modular multilevel converter (MMC) are modelled. Then, the modeling of short-circuit fault current in different stages was analysed. The analysis method of short circuit fault current of four-terminal MMC system with DC circuit breaker is obtained. Finally, the simulation results and the calculation results are compared and results show the effectiveness of the short-circuit calculation method proposed by this paper.

Short-Circuit Fault Current Calculation Method for the Multi-Terminal DC Grid Considering the DC Circuit Breaker

The analysis and calculation of the short-circuit fault current in the DC grid is of great significance to the design and configuration of the converter station and DC circuit breaker parameters. The existing flexible DC system not only includes the modular multilevel converter (MMC) converter, but also needs power equipment such as the fault current limiter and DC circuit breaker. Therefore, the system modeling and short circuit calculation of the multi-terminal DC system after adding the DC circuit breaker are also of great significance for the design of DC power system parameters and the grid troubleshooting ability. In this paper, firstly, the parameters of the four-terminal DC system of the modular multilevel converter (MMC) are simplified, and the analytical solution of the short circuit fault current of the multi-terminal DC system is given. Then, the external characteristics of the cascaded hybrid DC circuit breaker are modeled. Based on the equivalent circuit of the fault current in different stages, the short circuit calculation method of four-terminal MMC system with DC circuit breaker is obtained. This method can effectively describe the overall trend of fault current and provide the basis for the configuration of DC line protection settings and DC circuit breaker related parameters.

A DC fault identification scheme for multi-terminal VSC-LVDC system based on voltage of current-limiting reactor

The rapid and effective identification of DC faults is one of the key technologies for the development of multi-terminal DC (MTDC) system based on voltage source converter (VSC). The DC system fault current is characterized of high increasing speed and wide influence range. At present, the peak current and the rising speed of the fault current can be limited by current-limiting circuits, which are serially connected at both ends of the DC line. In this paper, the DC fault characteristics of a three-terminal DC system with DC line current-limiting reactors are analysed. On this basis, a fast identification method for DC faults in MTDC system according to the voltage across the line current-limiting reactor is proposed. The proposed scheme can quickly identify the fault location, the fault type and the fault pole. Finally, the effectiveness of the proposed fault detection scheme is verified by simulations. The simulation results show that the proposed method is still effective when the fault resistance and fault distance change, and is able to realize the rapid and accurate detection of DC faults.

Transient Inrush and Fault Current Signal Extraction Using Discrete Wavelet Transform for Detection and Classification in Shunt Capacitor Banks

An unbalanced current protection relay (60C, 51NC) cannot operate fast enough to avoid catastrophic failure against high system fault currents within capacitor units because a traditional unbalanced current protection relay is not capable of classifying the transient fault current and switching inrush current. This article proposes a new algorithm for the detection and classification of these transient current signals. Simulations are performed using PSCAD/EMTDC programs. The outputs of the current signals are used as inputs for the discrete wavelet transform (DWT) process. The wavelet-based fault and inrush current detection and classification unit receive the captured transient current signals and use DWT to detect and analyze these signals. Actual inrush current signals from an experimental setup and shunt capacitor banks of 115 kV, 22 kV, and 6.6 kV are used to verify the proposed algorithm. The results show that the proposed algorithm provides good performance and accuracy in identifying faults and inrush currents.

Fault Current Negative Contribution Method for Inverter-Based Distributed Generators Under Grid Unbalanced Fault

With the rapid increase of embedded inverter-based distributed generators (IBDGs), the active distributed network (ADN) is facing security and protection challenges because IBDGs will contribute extra fault current. In contrary to the existing method that IBDGs provide varying degrees of positive contribution to system fault current, in this article, a fault current negative contribution (FCNC) method is proposed for IBDGs to reduce the system fault current lower than the situation where without IBDGs embedded. In the proposed method, a maximum current phase angle adjustment (MCPAA) strategy is conducted for IBDGs to maximize its negative contribution, thus to minimize the system fault current. In order to obtain a more precise current phase angle, a voltage phase angle determination (VPAD) strategy is also formulated by considering the voltage angle difference on the electrical distance between IBDGs and fault bus. Extensive tests and relevant results have validated the feasibility of FCNC method to achieve a negative contribution of IBDGs on system fault current.

A Feasibility Study of Smart High-Temperature Superconducting Cable to Improve Stability of KEPCO System

The Korean power system is a very tightly coupled island system. The installed capacity is about 100 GW and the load demand is gradually increasing. Especially in metropolitan areas where the load is concentrated, the system fault current often exceeds the breaker capacity due to the strong connection. The system operator limits the fault current by bus split operations considering the breaker capacity but this reduces system stability. Therefore, various efforts have been made using a fault current limiter to overcome these problems. A smart superconducting (SC) cable is a type of SC power transmission cable. It has not only standard structure of the existing SC power cable but also a fault current limiter. The cable has a SC characteristic in a normal state, while when a fault occurs, it can limit a fault current through generating impedance that adjusts electrical and thermal properties of SC cable and material and cross-sectional area of SC cable. In this paper, a technique is proposed to reduce system fault current while improving the system stability using a smart high-temperature SC cable. In addition, the appropriate cable capacity and locations are selected to improve the reliability of the Korean power systems using the smart SC cables. The proposed locations and capacities will be applied to the smart SC cable development project that started in May last year

Logistic Regression Based Arc Fault Detection in Photovoltaic Systems Under Different Conditions

This paper investigates direct current (DC) arc fault detection in photovoltaic system. In order to avoid the risk of fire ignition caused by the arc fault in the photovoltaic power supply, it is urgent to detect the DC arc fault in the photovoltaic system. Once an arc fault is detected, the power supply should be cut off immediately. A lot of field experiments are carried out to obtain the data of arc fault current of the photovoltaic system under different current conditions. Cable length, arc gap, and the effects of different sensors are tested. These three conditions are the most significant features of this paper. Four characteristic variables from both the time domain and the frequency domain are extracted to identify the arc fault. Then the logistic regression method in the field of artificial intelligence and machine learning is originally used to analyze the experimental results of arc fault in the photovoltaic system. The function between the probability of the arc fault and the change of the characteristic variables is obtained. After validating 80 groups of experimental data under different conditions, the accuracy rate of the arc fault detection by this algorithm is proved to reach 100%.

A study on application of SFCL in vietnam power distribution system with distributed generators (DGs)

As the power load demand is rapidly increasing nowadays, many new power generation units are continuously connected to the power system such as small hydropower, wind power, solar cell, and so on. However, in a distribution system, the presence of Distributed Generators (DGs) would generally change the distribution system's behavior. This change can affect to the operation and protection of devices in power system and the original parameters will be deviated. Especially, the fault current of power system with DGs is dramatically increasing, and Superconducting Fault Current Limiter (SFCL) has attracted lots of attention as one of the best correctives to solve these issues. This paper proposes a strategy on application of SFCL in distribution system to solve the problems related to excessive short-circuit current and the mitigation of voltage sag due to the introduction of the DGs. Firstly, a Resistive-type SFCL (R_SFCL) is modeled by Matlab/Simulink. Next, a distribution system of Southern Vietnam power system is selected and simulated. Finally, according to the simulation results, the short circuit current and voltage sag improvements can be validated.

A study on application of SFCL in vietnam power distribution system with distributed generators (DGs)

As the power load demand is rapidly increasing nowadays, many new power generation units are continuously connected to the power system such as small hydropower, wind power, solar cell, and so on. However, in a distribution system, the presence of Distributed Generators (DGs) would generally change the distribution system's behavior. This change can affect to the operation and protection of devices in power system and the original parameters will be deviated. Especially, the fault current of power system with DGs is dramatically increasing, and Superconducting Fault Current Limiter (SFCL) has attracted lots of attention as one of the best correctives to solve these issues. This paper proposes a strategy on application of SFCL in distribution system to solve the problems related to excessive short-circuit current and the mitigation of voltage sag due to the introduction of the DGs. Firstly, a Resistive-type SFCL (R_SFCL) is modeled by Matlab/Simulink. Next, a distribution system of Southern Vietnam power system is selected and simulated. Finally, according to the simulation results, the short circuit current and voltage sag improvements can be validated.

Topology and Performance Optimization of a Novel Hybrid Material-Based Direct Current Fault Current Limiter

A novel direct current system fault current limiter (DCSFCL) based on the principle of nonlinear magnetization was proposed to limit fast rising fault current of the dc system. Different materials were also tested to find the iron core material. However, the existing material is not able to obtain both two necessary indexes, namely, a large saturation point and fast demagnetization speed. Hence, the performance is not satisfactory using a single material. In order to obtain the best performance for the DCSFCL, mixed materials were applied to combine the advantages of different soft magnetic materials. Furthermore, magnetic valves were also added to the original DCSFCL topology, which is an effective method to optimize the clipping performance and reduce the usage of materials. The 2-D models were built and finite-element analyses were carried out to verify these assumptions. Compared with a traditional smoothing reactor, the proposed new model not only limits the fault current by 55.4%, but also reduces the usage of both magnetic material and permanent magnets by over 20%.

Current-limiting characteristics of saturated iron-core fault current limiters in VSC-HVDC systems based on electromagnetic energy conversion mechanism

A common method to examine the current-limiting performance of saturated iron-core fault current limiter (SI-FCL) in high-voltage direct-current transmission based on voltage source converter (VSC-HVDC) systems is to solve differential equations based on the system fault transient characteristics and the equivalent inductance calculation equation. This method analyzes the fault current of the VSC-HVDC system in the time domain. However, it is computationally complex and cannot directly reflect the relationship between parameters and the current-limiting effect of the SI-FCL. In this paper, the relationship between the magnetic flux density and magnetic field energy of the SI-FCL is analyzed. The energy exchange between the DC capacitor and the SI-FCL in the DC short circuit fault process is analyzed. From the perspective of electromagnetic energy conversion, the criterion for determining the current-limiting ability of the SI-FCL in the transient process is given based on the parameters of the SI-FCL and VSC-HVDC system. On this basis, the characteristics of the DC side fault current and the capacitor voltage when the SI-FCL has current-limiting ability are examined. Based on the parameters of the SI-FCL and VSC-HVDC system, a method for calculating the fault current peak value and capacitor voltage drop time is given. Finally, the accuracy of the analysis of the SI-FCL in the VSC-HVDC system based on the electromagnetic energy conversion mechanism is demonstrated through a case study and simulation results of the VSC-HVDC system with different SI-FCLs.

Waveshape recognition technique to detect current transformer saturation

This study presents a technique to identify current transformer (CT) saturation based on waveshape properties of the CT secondary current. First, a variable-length window, designated as the symmetry assessment window (SAW), is defined. Certain distinctive features of the distorted and undistorted currents inside the SAW are extracted by defining two variance functions. Using the extracted features, a new criterion is introduced to detect CT saturation. The proposed method is unaffected by fault current characteristics and CT variable parameters, such as CT burden, core remanence and its magnetising curve. One major contribution of this method is allowing cheaper measurement systems for busbar protection by easing the relay CT requirements. Analysis of real power system fault currents in a real-time manner using a hardware setup is accompanied by PSCAD/EMTDC simulation results to verify the accuracy and high speed of the proposed technique in various conditions.

IEC 60909에 의한 삼상 고장계산

This paper analyzes how to calculate the three phase short circuit current calculation procedures used in the IEC 60909 short circuit. It presented the new procedure of the fault current for the interrupting capacity of the circuit breaker. This procedure is applied to the future power system and calculates the fault current. Power demands are increased because of the growth of the economy for this reason, the fault current of the power system is largely increased and the fault current procedure for the proper interrupting capacity calculation of the existing or the new circuit breaker is essential. How to calculate the three phase short circuit current for ac electrical system and select the high voltage and low voltage circuit breaker based on IEC 60909 standards.

송전급 초전도한류기의 적용에 따른 선로보호용 비율전류차동계전기의 동작특성 및 보호협조 분석

The fault current of the power transmission system is greater than that of the power distribution system. Therefore, the introduction of superconducting fault current limiter (SFCL) is more needed to reduce the increased fault current. The trigger-type SFCL consists of the high-temperature superconducting element (HTSC), the current limiting reactor (CLR) and the circuit breaker (CB). The trigger-type SFCL can be used to supplement the disadvantages of the resistive-type SFCL. The operation characteristics of the current ratio differential relay which is usually applied to the protection device of the power transmission system are expected to be affected under fault conditions and the applicability of the trigger-type SFCL. In this paper, we analyzed the operating characteristics, by the fault conditions, between the current ratio differential relay for line protection and the trigger-type SFCL in the power transmission system through the PSCAD/EMTDC simulation.

Thermal Analysis of HTS Power Cable Using 3-D FEM Model

Thermal stability is an important issue to put high-temperature superconducting (HTS) power cables into practical use. Cooling system breakdown and fault current are the two major factors that might cause overheating or quench in HTS power cables. In this paper, a dynamical model of the HTS cable is built with the 3-D finite element method (3-D FEM), and the dynamic thermal characteristic under different operation conditions is analyzed. The computational results of this model can be used to evaluate the operation parameters of HTS cables and to set the action time of the relay protection system. The electrical and thermal parameters are based on the HTS cable, which is being manufactured in China.