Cross-country Faults Research Articles

A hybrid intelligent system for protection of transmission lines connected to PV farms based on linear trends

Conventional relays face challenges for transmission lines connected to inverter-based resources (IBRs). In this article, a single-ended intelligent protection of the transmission line in the zone between the grid and the PV farm is suggested. The method employs a fuzzy logic and random forest (RF)-based hybrid system to detect faults based on combined linear trend attributes of the 3-phase currents. The fault location is determined and the faulty phase is detected. RF feature selection is used to obtain the optimal linear trend feature. The performance of the methodology is examined for abnormal events such as faults, capacitor and load-switching operations simulated in PSCAD/EMTDC on IEEE 9-bus system obtained by varying various fault and switching parameters. Additionally, when validating the suggested strategy, consideration is given to the effects of conditions such as the presence of double circuit lines, PV capacity, sampling rate, data window length, noise, high impedance faults, CT saturation, compensation devices, evolving and cross-country faults, and far-end and near-end faults. The findings indicate that the suggested strategy can be used to deal with a variety of system configurations and situations while still safeguarding such complex power transmission networks.

Robust distance protection for cross-country faults in power grids with high penetration of inverter- based resources

Cross-country faults can adversely affect the operation of protection devices. Relays whose pickup is based on overcurrent or impedance elements are more likely to fail during cross-country faults. The failure can be expressed as an unnecessary trip of all phases during a single-phase fault or even blocked relay functions. Relays may also fail to operate due to low fault currents, which is the case when power grids make use of many inverter-based resources (IBR) or when two simultaneous faults occur in the same phase and in different locations. This paper proposes a Recursive Discrete Stockwell Transform (RDST) method for addressing the mentioned challenges. The energy content computed by the RDST is used for fault detection and faulty phase selection. A robust distance relay model is proposed to ensure correct relay performance and is combined with a directional and an impedance trajectory module. The proposed method performance is thoroughly evaluated by applying real-time simulations for 6480 different cross-country faults, including three repetitions, four different generators (Synchronous generators, Wind turbine type-III, Wind turbine type-IV), two rating powers, three different fault distances, five different types of faults, and six grid codes. Ninety cases are also tested with real devices in hardware in the loop. Simulation results confirm the method's ability to detect different fault types, even during low fault currents, and to ensure high accuracy in phase selection.

An advanced graph algorithm-based protection strategy for detecting kilometric and cross-country faults in DC microgrid

Low voltage DC microgrids (LVDC) are on rise, because of increase in usage of electronics-based utility loads. However, the protection and safety aspects of these grids remain unresolved due to the fault current magnitude, unnecessary tripping, and blinding of protection. In this paper, an adaptive differential protection system incorporated with an advanced graph algorithm is proposed for DC microgrid. This graph algorithm is a combination of Fenwick tree and Bidirectional Dijkstra algorithm. Fenwick tree algorithm is used to determine the network configuration and Bidirectional Dijkstra algorithm is used to determine the least distance from the fault location to the nearest distributed generations. The developed protection scheme is applied to a 7 bus, 400 V DC microgrid setup using Real Time simulator (control hardware in loop) to detect and clear the faults such as kilometric faults, and cross-country faults. In terms of efficiency, the proposed algorithm demonstrates superiority over the conventional algorithm by detecting and rectifying faults in 384 μs.The results depict the robustness of the protection setup in clearing the faults rapidly with minimum network disconnection.

Formulation of Fault-Branch Currents During Cross-Country Faults on Asymmetrical Double-Circuit Transmission Lines Considering Status of Line-Ground Faults’ locations

Formulation of Fault-Branch Currents During Cross-Country Faults on Asymmetrical Double-Circuit Transmission Lines Considering Status of Line-Ground Faults’ locations

A new differential protection scheme based on Synchro-squeezing transform applied to AC Micro-Grid

In recent years, the protection of a microgrid has been a substantial challenge. This paper performs a differential protection scheme for the micro-grid based on Synchro-Squeezing Transform (SST). The proposed scheme protects the micro-grid in different modes i.e. islanded or grid-connected mode. Also, it is investigated in the ring and radial configuration. In the proposed scheme, currents on two sides of the line are measured by current transformers (CTs), and then differential current (IDiff) is calculated. This current is applied to extract the absolute value of the summation of the square root (ASSR). In this stage, transient and external faults without CT saturation and different switching such as connected or disconnected load/capacitor/distributed generation are detected from different internal faults. In the next stage, the frequency components of SST (FCSST) are extracted. By this feature, external fault and cross-country fault with CT saturation are detected. The proposed scheme is evaluated in noisy conditions, fault in different section of line with high resistance fault (HRF), and high impedance faults (HIF) of line. The micro-grid is simulated in PSCAD/EMTDC by various distributed generation (DG) like wind generation and photovoltaic systems penetrated at different buses. The proposed protection scheme is coded in MATLAB. The simulations represent the proposed protection scheme is correctly discriminate external and internal faults. At the same time, the method is immune to CT saturation and cross-country faults.

Unbalanced Distribution Network Cross-Country Fault Diagnosis Method with Emphasis on High-Impedance Fault Syndrome

Unusual fault scenarios can occur on the utility grid in a power system network. Cross-Country Faults (CCFs) connected to the High-Impedance Fault (HIF) syndrome are more prone to occur in forested areas due to thunderstorms, cyclones, and improper vegetation management and tree pruning. Finding and categorizing CCFs associated with HIF syndrome is a great challenge. This study employed the cross-correlation method to reconstruct the signals produced by CCFs with HIF, which were shown to be complicated, aperiodic, asymmetric, and nonlinear. A decreased sensitivity to random noise means that a given modification might not affect equally all component peaks. This allows for more precise signal recovery. The maximum voltage cross-correlation coefficients were carefully evaluated as distinguishing elements in the development of a suggested fault detection technique. The proposed concept was evaluated on a modified imbalanced IEEE 240 bus system under different case studies. These case studies cover a wide range of scenarios, such as the switching of a capacitor bank, feeder energization, and the effects of nonlinear loads under noisy conditions.

Evolving fault diagnosis scheme for unbalanced distribution network using fast normalized cross-correlation technique.

There has been a lack of a satisfactory solution for identifying and locating evolving faults in unbalanced distribution systems. The proposed approach is based on the cross-correlation technique as a key element for fault detection and location. Evolving faults, in this context, refer to two sequential faults that result in a change of fault phase. The captured QRS value reflects the occurrence of the second fault occurrence. In order to identify Evolving Faults, it makes use of the signal that is currently being monitored at any given point in the network. Typical system occurrences, such as a short circuit fault that grew into another short circuit fault, as well as cross-country faults, are simulated, and according to the suggested technique, they are accurately differentiated from one another. Using a real-time simulator, rigorous simulations are performed on the modified IEEE 240 bus distribution system. The results of these simulations reveal that they have the potential to uncover defects that are constantly changing. Regardless of the fault (location\resistance\inception angle), location of the monitored point, or sample frequency that is selected, the suggested approach is unaffected by any of these factors. In addition, the slime mold optimization approach is utilized in order to get the best monitoring points that accurately identify the bus in which the evolving fault has taken place.

A simple approach for the protection of EHV transmission lines

Due to the geographically widespread nature of the transmission lines, the chances of fault occurrence are more due to outdoor erection. This makes it inevitable to detect and isolate the faulty section of the system as quickly as possible. The existing fault detection and classification algorithms are limited to a specific configuration of transmission lines. This work has proposed a novel and simple methodology to recognize and classify faults on transmission lines by using single-end current data. A Harmonic Phasor Measurement Unit (HPMU) based on a non-recursive DFT algorithm is used to extract the fundamental and second-order harmonic components from current samples. The Equivalent Fundamental Component (EFC) and ΔEFC are estimated from the extracted data. Subsequently, an Index Matrix (P) is derived to recognize the fault. The non-zero value of the determinant of the index matrix detects the occurrence of a fault in the system. Second-order harmonic fault current coefficients are proposed for fault classification based on the second-order harmonic component extracted from HPMU. The proposed method accurately detects and classifies all types of conventional faults and cross-country faults (CCF) for any configuration of transmission network. The proposed method has also been validated under various abnormal conditions in PSCAD/EMTDC to ensure its efficacy.

A random forest based communication-less approach for protection scheme of six-phase transmission line against shunt, series, evolving and cross-country faults

A random forest based communication-less approach for protection scheme of six-phase transmission line against shunt, series, evolving and cross-country faults

Identification of Cross-Country Fault with High Impedance Syndrome in Transmission Line Using Tunable Q Wavelet Transform

The transmission lines of an electricity system are susceptible to a wide range of unusual fault conditions. The transmission line, the longest part of the electricity grid, sometimes passes through wooded areas. Storms, cyclones, and poor vegetation management (including tree cutting) increase the risk of cross-country faults (CCFs) and high-impedance fault (HIF) syndrome in these regions. Recognizing and classifying CCFs associated with HIF syndrome is the most challenging part of the project. This study extracted signal characteristics associated with CCF and HIF syndrome using the Tunable Q Wavelet Transform (TQWT). An adaptive tunable Q-factor wavelet transform (TQWT) based feature-extraction approach for CCHIF fault signals with high impact, short response period, and broad resonance frequency bandwidth was presented. In the first part, the time–frequency distribution of the vibration signal is used to determine the distinctive frequency range. Adaptive optimal matching of the impact characteristic components in the vibration signal was achieved by optimizing the number of decomposition layers, quality factor, and redundancy of TQWT based on the characteristic frequency band. In the last, the TQWT inverse transform was utilized to recreate the best sub-band to boost its weak impact characteristics. The effectiveness of the approach is confirmed by simulation and experimental findings in signal processing. The best decomposition level for signature features that can be extracted has been decided by Minimum Description length (MDL). The IEEE 39-bus system is used to test the suggested approach with reactor switching and the Ferranti effect.

A distance Protection/Fault location algorithm for Double-Circuit transmission lines with asymmetrical circuits during Cross-Country faults

The impedance-measuring elements and fault locators in distance relays suffer from measuring the correct fault impedance and fault location when facing cross-country faults (CCFs). During such atypical faults, this paper proposes a distance protection along with a fault location algorithm for double-circuit lines with asymmetrical circuits. This is fulfilled through instantaneous fault-branch currents innovatively derived from the line six-phase circuit model analysis on a time-domain basis. The currents derived lead to the relations that are mathematically linear combinations of designated vectors. This makes the possibility of establishing vector-input adaptive linear combiners (VI-ALC) in accordance with the relations derived. Being fed from the vectors of instantaneous measurements at the relaying side, the VI-ALCs with a distinctive capability of online training would swiftly give an accurate estimation of the fault distances during CCFs. The estimations are exploited in a logical procedure for both of the distance protection and fault location functions, taking account of different position status of the CCFs’ comprising LG faults. The proposed algorithm is feasibly implementable and is independent of the system configuration. It operates robustly in high-ground resistance and noisy conditions. Through extensive simulation studies in PSCAD/EMTDC, performance of the proposed algorithm would be investigated and verified in a variety of fault scenarios.

Countermeasures for reduction of screen currents due to cross country faults in MV cable distribution networks

• Cross-country faults can involve large currents liable to damage MV cable sheaths. • Methodologies to reduce cross-country fault currents in cable screens are presented. • Methods are compared by means of ATP-EMTP simulations on a 20 kV test network. • Additional ground wires are effective but viable only for newly built cable lines. This paper investigates the reduction of Cross-Country-Faults currents in medium voltage (MV) cable networks in order to decrease thermal stress of cable screens, especially inside joints. Four methods are analyzed: 1) disconnection of cable screens from the earth electrode of primary substation (PS); 2) buried ground wire laid near the cable lines and connected to each earth electrode of secondary substations (SSs) and PS; 3) buried ground wire and disconnection of the bonded cable screens from the earth electrode only at sending/receiving end of each cable line between two consecutive SSs; 4) cross bonding of cable screens between two consecutive SSs. Methods are analysed by ATP-EMTP simulations of a 150/20 kV radial test system formed by eight 5 km long cable lines equipped with 50 mm 2 copper conductors per phase and 16 mm 2 copper screen per cable. Compared to the limiting reactors countermeasure presented in a previous paper by the authors, which seems the solution less burdensome both technically and economically for existing lines, method 3 is more effective but its implementation is limited only to newly built lines, whereas the main drawback of method 1 is the increase of ground potential rise at fault locations.

Transformer differential protection scheme based on self‐adaptive biased characteristic curve and considering cross‐country faults

AbstractThe differential protection of transformers sometimes does not have reliable performance facing some faults and events such as saturation of current transformers (CTs) during internal and external faults, inrush currents, and cross‐country faults (CCFs). In this paper, a new transformer differential protection scheme based on the self‐adaptive biased characteristic curve and considering CCFs and various disturbances are used. First, the maximum overlap discrete wavelet transform (MODWT) was used to extract the superior characteristics of sampled differential current of the transformer at different levels. Then, by calculating the duty cycle (D) values of energy coefficients extracted in each periodicity by MATLAB software, a new self‐adaptive biased characteristic curve will be obtained in different operating conditions. Finally, the percentage differential protection operation is adjusted based on the new adaptive characteristic curve zones. Differential current sampling under different operating conditions was performed on a real three‐phase transformer in EMTP software. The simulation results show that the proposed adaptive differential protection scheme can accurately detect various faults and events occurring in the transformer and increase system reliability.

Fault detection and classification scheme for smart grids considering high impedance evolving and cross-country faults

Fault detection and classification scheme for smart grids considering high impedance evolving and cross-country faults

An algorithm scheme for detecting single-circuit, inter-circuit, and grounded double-circuit cross-country faults in GUPFC-compensated double-circuit transmission lines

An algorithm scheme for detecting single-circuit, inter-circuit, and grounded double-circuit cross-country faults in GUPFC-compensated double-circuit transmission lines

Performance Improvement of Transformer Differential Protection During Cross-Country Fault Using Hyperbolic S-Transform

A cross-country fault is a fault occurring at two different locations of the same circuit, simultaneously or with a short time delay and possibly involving different phases, which is a challenge for the protection system. On the other hand, one of the main problems in transformers’ differential protection is the distinction between inrush current and other faults, such as cross-country faults, internal faults, and saturation of current transformers (CTs) during external faults. In this article, for the first time, external electrical faults and internal mechanical faults, such as radial deformation (RD) and axial displacement (AD) of winding, were considered as cross-country faults in a real winding. The transformers’ winding is modeled based on the detailed model, and the parameters were practically validated in the laboratory. Differential currents are sampled during different disturbances simulations by EMTP software, and feature extraction is performed using hyperbolic S-transform (HST) in MATLAB environment. As a final point, cross-country faults were distinguished from other faults and events by calculating various S-transform indices, including mean square sum absolute deviation (MSSAD), correlation coefficient (CC), and minimum–maximum (MM). The obtained results confirmed that the proposed protection algorithm is very efficient in detecting and distinguishing cross-country faults, even in the presence of noise.

Distance Protection Methodology for Detection of Faulted Phase and Fault Along With Power Swing Using Apparent Impedance

In this paper, a novel distance protection methodology that uses apparent impedance and concentric characteristics to identify faults and faulty phases along with power swing condition is proposed. The rate of change of apparent impedance is used to identify the fault or power swing condition. If a fault is detected, the relative location of the apparent impedance of the six distance elements with respect to their concentric characteristics is used to identify the faulty phases. The distance element(s) that compute the correct apparent impedance is(are) then enabled, which then issues the trip signal if the zone criterion is met. The proposed distance protection methodology is validated in Western System Coordinating Council (WSCC) Nine Bus System in MATLAB/Simulink by simulating various fault and power swing conditions. The results from the case studies proved that the proposed distance protection methodology could enable the right distance elements and issue trip signals during common faults and special kinds of faults like evolving and cross-country faults. Compared to others, the distinguishing feature of the proposed algorithm is its ability to identify the exact faulty phases even during special fault conditions like evolving and cross-country faults. The distance relay using the proposed methodology can issue the trip signal within one cycle for common faults and within one and half-cycle for evolving and cross-country faults.

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.

Identification and classification of cross-country faults in transformers using K-NN and tree-based classifiers

Today, despite the advances made, differential relays still fail to identify cross-country faults and some events. Therefore, in this paper, signal processing techniques and artificial intelligence were used to identify and classify cross-country faults with other events in transformers simultaneously. For this purpose, first, mechanical defects of transformer winding were modeled on a laboratory sample. Then, types of cross-country faults, internal and external electrical faults, and transformers҆ inrush currents were simulated using EMTP software to extract differential current signals. The sampled signals were transferred to MATLAB software. Then, some salient features were extracted from the obtained signals by Time-Time transform. Finally, these features were used to train Random Tree, Random Forest, and K-Nearest Neighbors (K-NN) classifiers in order to identify and classify cross-country faults from other events in the Rapid-Miner software. The results showed that the intelligent combined method can identify and classify cross-country faults from other disturbances in transformers with an appropriate degree of accuracy; which is the main innovation of this research compared to other studies that have been limited to identifying and classifying only some of the mentioned faults.

A Novel Voltage Clamping-Based Overvoltage Protection Strategy to Avoid Spurious Trip of Inverter-Based Resources and Eliminate the Risk of Wildfire Following the REFCL Operation in Compensated Networks

This article investigates the operational performance of the rapid earth fault current limiter (REFCL) that has been employed in Australia to reduce the risk of wildfires and shows that after the REFCL activation, an overvoltage is imposed on the grid which can lead to wildfire by creating a cross-country fault. Moreover, by increasing the penetration level of the inverter-based resources (IBRs), the potential inverter trip on transient overvoltage can become a vital issue. Since the protection functions of the IBRs are very sensitive to any transient overvoltage, their overvoltage or dc reverse current protection functions will trip the IBRs immediately following any overvoltage condition such as those caused during the REFCL operation. To tackle the mentioned problems, a novel voltage clamping-based overvoltage protection strategy is proposed and developed through a smart power electronic topology. The article presents the analytical analysis and the mode of operation of the proposed overvoltage protection strategy. The effectiveness of the proposed overvoltage protection strategy is tested through a comprehensive set of simulation studies in Power System Computer-Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC). The simulation results show that the proposed strategy can immediately limit the magnitude of the overvoltage, thereby it can not only reduce the risk of cross-country faults and wildfires but it can also mitigate the spurious trips of the IBRs.