Three-terminal Transmission Lines Research Articles

Comprehensive fault reporting for three-terminal transmission line using adaptive estimation of line parameters

In this study, the post-fault synchronized phasors acquired from the local phasor measurement units (PMUs) are used to provide comprehensive fault reporting in Three terminal transmission line system (TTTL). The reporting data incorporates the classification, section identification, and localization of the fault based on the post-fault measurements of positive, negative, and zero sequence quantities. For accurate reporting, a proposed algorithm computes transmission line parameters, on hourly basis, to account for fluctuations in characteristics caused by temperature influences arising from either the loading factor or the climatic vagaries. Upon fault occurrence, the algorithm firstly determines fault classification and faulty section. Thereafter, localization of symmetrical faults is achieved via the positive sequence quantities to solve the positive sequence fault loop equation while that of asymmetrical faults is obtained through the negative sequence quantities to solve the negative sequence fault loop equation. The fault localization speed of the reporting proposed algorithm is attributed to the fact that synchronized data are obtained after one and half cycles from the fault onset. PSCAD/EMTDC platform is dedicated for time-domain investigations, while the proposed algorithm is carried out in MATLAB. The proposed algorithm was tested against 1537 fault characteristics at different locations along the TTTL, including varying fault resistances, loading conditions, and network configurations, in addition to assessing its sensitivity to changes in the TTTL parameters. These tests confirmed the algorithm’s reliability to be used with confidence in a variety of scenarios as the only 13 tests were observed with an error of estimation greater than 1%.

Three-Terminal Transmission Line Protection By Considering Effect of Infeed Current

Three-Terminal Transmission Line Protection By Considering Effect of Infeed Current

New ground fault location method for three-terminal transmission line using unsynchronized current measurements

This paper presents a new ground fault location method for a three-terminal transmission line using unsynchronized current measurements. The faulty line section is identified utilizing the polarity of the second traveling wave that arrived at each terminal. Then, the fault is discriminated as either before or after the middle of the faulty line-section by observing the change in polarity among the first two consecutive traveling waves. Finally, the fault location is estimated at a particular terminal on which the faulty line-section is connected. The three-terminal transmission line model is simulated in PSCAD/EMTDC software. Various fault conditions are considered with wide variation in fault and system parameters to authenticate the proposed method. The obtained results depict the effectiveness of the proposed method for locating all types of internal ground faults. Further, the comparative analysis with several existing methods shows the supremacy of the presented method in terms of the fault location error for high resistance faults at different fault locations. Besides, its accuracy is minimally affected by the saturation of current transformers (CTs), errors in line parameters, and noise in the acquired signals.

A new scheme for fault location of three‐terminal parallel transmission lines without transposer

This paper proposes a new scheme for locating the faults of three-terminal double-circuit transmission line without transposer in the phase domain that is not affected by type of fault. Synchronous voltage and current were measured by phasor measurement units (PMUs) installed at three busbars. Considering the coupling effect of parallel lines, the distribution line model was used to obtain more accurate results and third-order Taylor series expansion to decouple distributed line model. The phase and branch of all faults on the transmission lines were effectively identified, and various types of faults were accurately located including normal shunt fault, evolving fault and cross-country fault. The proposed algorithm was tested under different fault locations, resistances, initial angles and types (including cross-country faults and evolving faults). In addition, the effects of different sampling rates, measurement errors, earth resistivities and transmission line parameter errors were also considered. The simulation calculation was performed in MATLAB software and three-terminal transmission lines were simulated in PSCAD/EMTP software. The results indicate that maximum estimated error was less than 1.8631%.

Fault location determination in three-terminal transmission lines connected to industrial microgrids without requiring fault classification data and independent of line parameters

The connection of large industrial microgrids to three-terminal transmission lines greatly complicates the protection scheme of the lines due to the uncertainty in generating renewable energy sources, the probability of unintentional islanding, the abrupt switching of sensitive and critical loads, the influence of supply and demand management programs, and bidirectional active and reactive power flow. This paper presents a fault location algorithm for three-terminal transmission lines connected to an industrial microgrid that does not need the detection of faulty section, fault classification, and transmission line parameters. The proposed method uses voltage and current phasors of transmission lines measured by phasor measurement units (PMUs). One of the salient features of the proposed algorithm is that it does not need to determine the faulty section before the fault location operation. Furthermore, since power transmission lines are always exposed to changing climatic conditions and aging, their electrical characteristics vary over time in the long run compared to their rated value. Hence, this leads to the malfunction of protection schemes. This is solved in this study as the proposed fault location algorithm is independent of line impedances. On the other hand, the dependence of conventional fault location algorithms on fault classification data reduces the reliability of fault location schemes, making these algorithms dependent on fault classification data. However, the present study overcomes this problem as the algorithm is independent of the data of the faulty phase(s) detection. The proposed scheme is fully implemented in the MATLAB software environment, and the performance of the algorithm is analyzed for various fault types under different conditions. The validity of the algorithm is shown by various tests and sensitivity analyses.

Synchrophasor based fault location algorithm for three terminal homogeneous transmission lines

This paper presents a new fault location algorithm for three-terminal transmission lines, with the help of synchrophasor data. The algorithm utilizes the information of voltages and currents which are available from all the three ends. The proposed algorithm utilizes positive and negative sequence data for locating asymmetrical faults and only positive sequence data for locating symmetrical faults. The accuracy of the algorithm has been evaluated for various factors, such as fault inception angles, fault resistance, fault location, synchronization errors, measurement errors. The simulation of faults on the system have been carried out using PSCAD® and the algorithm is implemented in MATLAB software. Based on the simulation results it has been observed that the % error is less than 1.5% for 178 test cases out of 180, which shows 98.8% accuracy.

Asynchronous Fault Location Scheme Based on Voltage Distribution for Three-Terminal Transmission Lines

The synchronization of the voltage and current from different terminals is generally unachievable in the power grids at mountainous area, which leads to the fault location method with synchronized data to be impossibly utilized. This paper proposes a voltage distribution based fault location scheme with asynchronous data for three-terminal transmission lines. At first, the faulty section is identified by the voltage computed from each terminal due to the boundaries formed by fault point and tee-point. Since the fault current is stable after the transients decay, the asynchronous calculated voltage and current from the terminals without faults can be synchronized by their angle differences to form the voltage and current at faulty section near the tee-point. Then, the voltage distribution of the faulty section can be obtained from the tee-point and the terminal to find the intersection point of them. In order to fully utilize the fault characteristics in the voltage and current, the earth mode and the minimum of the voltage distribution are applied to optimize the fault location results for grounding faults and multi-phase faults, respectively. Moreover, the robustness of the proposed fault location scheme is thoroughly validated by the simulation of PSCAD/EMTDC. At last, a set of the field data acquired by wave recorders is applied to test the feasibility of the proposed approach.

PMU-based Fault Location Technique for Three-terminal Parallel Transmission Lines with Series Compensation

This study introduces a fault location technique for three-terminal series-compensated untransposed parallel transmission lines utilizing the three terminals’ synchronized data. The proposed technique is applicable for short or long lines as distributed parameter line model is employed and the potential couplings are considered. The fault location for both uncompensated line sections is obtained adopting previously introduced fault location technique. The faulty phases are required initially to be recognized for series-compensated transmission line. The adopted fault location technique for series-compensated line section is derived based on the resistive nature of the fault impedance. The obtained fault locations for each line section are compared with each other to distinguish the faulty branch and obtain the fault location. DIgSILENT Power Factory and MATLAB programs are utilized for simulation studies and required calculations. The obtained results prove the efficacy of the introduced technique.

Fault location in series capacitor compensated three-terminal transmission lines based on the analysis of voltage and current phasor equations and asynchronous data transfer

In this study, a new algorithm for fault location in series capacitor compensated three-terminal transmission lines using the distributed line model is proposed. The proposed algorithm uses the sampled data of currents and voltages of all the three terminals, which are transferred asynchronously using telecommunication lines. All data transmission delays are calculated in terms of line parameters as well as the measured values of currents and voltages of the three terminals. Based on the data received from the three terminals, current and voltage equations of different points of the network are constituted for different types of faults. By solving these equations according to their boundary conditions, accurate locations of faults are estimated. One of the salient features of the suggested algorithm is that the schemed equations are independent of the model of the series capacitor compensator during fault occurrence and its protective circuitry. Also, based on the sensitivity analyses performed in this paper, the presented algorithm works perfectly against the errors caused by measurements and parameters. The test system and the suggested algorithm were realized in MATLAB environment. The obtained simulation results for different fault types occurring in various places in the line verify the accurate performance of the algorithm.

Novel Fault Distance Estimation Method for Three-Terminal Transmission Line

A new faulty section identification and fault distance estimation technique for three-terminal transmission line (TTL) is proposed in this paper. It is based on the derivation of three indices by solving non-linear equations with iterative method utilizing synchronized measurements from three ends of the line. In the absence of synchronization, an angle synchronization operator is derived for building a common reference among the three terminals. The efficacy of the technique is verified by generating several fault cases on an existing Indian 400 kV TTL using PSCAD/EMTDC software. Reported results demonstrate the capability of the presented technique for all types of fault on three-terminal transposed/untransposed as well as the non-homogeneous transmission line. It also provides accurate fault location under comprehensive variation in type of fault, line length, fault inception angle, complex fault impedance, source impedance, and current transformer (CT) saturation condition. Its accuracy remains almost constant despite errors in line parameters, as well as synchronization and noise in the measured signals. The initial guess has a minimal impact on the accuracy and convergence of the presented technique. The attained results reveal higher accuracy and better robustness of the proposed technique in comparison with those of several existing techniques.

Synchrophasor Based Novel Fault Location Algorithm for Three- Terminal Transmission Line

A fault detection and location algorithm on three-terminal transmission line is proposed. Vast literature on fault location shows that to simplify the analysis, line charging currents are often ignored. To improve the accuracy of fault location, synchronized current and voltage measurements from three ends of the three-terminal line are utilized to detect and locate distance to fault while considering the line charging currents. The method first detects the zone at which the fault has occurred and then locates it from the respective line ends. Since three-terminal lines provide solutions for connecting existing system to the grid, facilitating bulk transfer of power, thus the fault detection and location on the same is important to maintain reliability and security of the system. Performance of the proposed algorithm is tested for various fault types, fault locations, fault resistances and fault inception angles. The 200-kV system is simulated in ATP/EMTP; however, the algorithm is developed in MATLAB. The extensive simulation studies demonstrate accuracy of the proposed scheme.

Fast & adaptive fault location technique for three-terminal lines

This paper presents a fast and adaptive method to locate faults in three-terminal transmission lines, based on the synchronized measurements within the half-cycle data window. First, the voltage and current data are processed by two sets of half-cycle Fourier filters at three terminals in order to extract the main component of the voltage and current phasors quickly and with a high accuracy using a novel method. The proposed algorithm uses the calculated phasors and works without any need to transmission line’s data or the Thevenin equivalent of the system at each terminal. For making sure of considering the real operation conditions of the network, transmission line’s parameters are determined adaptively using the calculated phasors. The voltage at the tapping point is calculated separately using three-terminal data and consequently the faulty section is identified and then, the precise location of fault in the faulty section is accurately calculated using the nodal current unbalance method. Performance of the proposed algorithm is evaluated under different fault conditions. The simulation results show the high convergence speed and the excellent accuracy of the proposed method under various operating conditions and various fault types.

Accurate fault location and faulted section determination based on deep learning for a parallel‐compensated three‐terminal transmission line

Parallel flexible AC transmission systems (FACTS) devices affect the performance of protection relays and conventional phasor-based fault location schemes in transmission lines. This study focuses on both multi-terminal and parallel-compensated lines, not investigated simultaneously in previous works. An algorithm based on deep neural networks is proposed for fault location in a three-terminal transmission line with the presence of parallel FACTS device. The line model and fault occurrence are simulated in SIMULINK and features are extracted from voltages at the three terminals by wavelet transform. The generated features are used to train a deep neural network which determines faulted line section and fault distance simultaneously. The adopted intelligence-based approach has the advantage of not requiring pre-knowledge of line specifications, FACTS devices modelling and the uncertainty in compensator parameters. A large number of fault scenarios are investigated. The faulted section is recognised correctly in 100% of test cases. The algorithm performance is acceptable for both symmetrical and unsymmetrical fault types, small fault inception angles and high fault resistance. The accuracy of fault location is improved compared to previous schemes (total mean error of 0.0993%). The proposed algorithm provides an accurate, fast and robust tool for fault location in parallel-compensated three-terminal transmission lines.

Estimating zero-sequence impedance of three-terminal transmission line and Thevenin impedance using relay measurement data

Current and voltage waveforms recorded by intelligent electronic devices (IEDs) are more useful than just performing post-fault analysis. The objective of this paper is to present techniques to estimate the zero-sequence line impedance of all sections of a three-terminal line and the Thevenin equivalent impedance of the transmission network upstream from the monitoring location using protective relay data collected during short-circuit ground fault events. Protective relaying data from all three terminals may not be always available. Furthermore, the data from each terminal may be unsynchronized and collected at different sampling rates with dissimilar fault time instants. Hence, this paper presents approaches which use unsynchronized measurement data from all the terminals as well as data from only two terminals to estimate the zero-sequence line impedance of all the sections of a three-terminal line. An algorithm to calculate positive-, negative- and zero-sequence Thevenin impedance of the upstream transmission network has also been presented in this paper. The efficacy of the proposed algorithms are demonstrated using a test case. The magnitude error percentage in determining the zero-sequence impedance was less than 1% in the test case presented.

Fault location on a series‐compensated three‐terminal transmission line using deep neural networks

In this study, discrete wavelet transform (DWT) and deep neural network (DNN) are utilised for fault location in a series-compensated three-terminal transmission line. The series compensation causes challenges in fault location schemes of the three-terminal transmission lines. The presented fault location method has been extensively tested using the SIMULINK model of a three-terminal transmission line. Features extracted from synchronous measurements of fault currents at the three terminals using DWT are fed to the DNN. Faulted section determination and fault distance calculation are carried out using a single intelligent network simultaneously. Faulted section is determined with 100% accuracy, and the efficiency of algorithm is validated for symmetrical and unsymmetrical faults, and different values of fault resistance, inception angle, and location. The accuracy of the algorithm is acceptable for large fault resistances (above 100 Ω) and fault inception angles near zero. Total mean error for test data is 0.0458% which is much improved with respect to other similar works.

New fault detection and localisation technique for double‐circuit three‐terminal transmission line

This study proposes a new technique which detects fault on the line, identifies faulty circuit/line-section and estimates location of fault (fault localisation) on the double-circuit three-terminal transmission line. The fault detection and faulty circuit/line-section identification has been carried out by estimating the superimposed components of current at remote end with reference to all the three terminals. Subsequently, the estimation of fault distance is performed by utilising phase angle of voltage and current at the fault point. The performance of the proposed technique has been evaluated by simulating 400 kV double-circuit three-terminal transmission line network using PSCAD/EMTDC software package. The results indicate that the presented technique is able to detect as well as recognise the faulty circuit/line-section correctly even in case of occurrence of a high resistance ground fault near the tap point. At the same time, it is also capable of estimating the precise value of fault location as the percentage error remains within ±1.3%, even under wide variation in system and fault parameters. The proposed technique is also valid for cross-country faults and its accuracy remains consistent even with considerable errors in the measurement of current transformers and capacitive voltage transformers.

Unsynchronized fault-location technique for two- and three-terminal transmission lines

In this work, a novel fault-locator technique for two- and three-terminal power transmission lines is introduced. Unsynchronized three-phase current and voltage measurements of all line ends are processed for estimating the required synchronization angle/s and the fault location via exploiting the initial conditions of each fault type. To realize this target, the computations of the required synchronization angle/s are initially accomplished independent of the fault location via considering a lumped charging current at the reference terminal which is selected arbitrarily. Consequently, the initial fault location is determined via equating the deduced equations of the positive-sequence voltage at the faulty point from two sides of the faulted segment as a function of the measured data after their correction. The previous obtained fault location is, then, utilized as an input for the next iterative computations, where the distributed line model is used to update the charging current. This process is repeated until the change rate of the obtained fault location becomes negligible. The proposed technique has been examined and assessed under different fault scenarios simulated using MATLAB. The sample results of the assessment are declared and discussed.

Dynamic state estimation‐based fault locating on transmission lines

Accurate fault locating minimises labour and outage time. Efforts to increase the accuracy of fault locating methods are on-going. In this study, a dynamic state estimation-based fault locating (EBFL) method is proposed. Best implementation requires GPS synchronised sample value measurements at both ends of the line. The dynamic state estimator operates on the sampled values using a detailed dynamic model of the line, which includes the fault location as a state. Specifically, the dynamic line model is represented as a multi-section transmission line model, inclusive of phase conductor type and size, shield wire(s) type and size, and tower ground impedances, integrated with the fault model. This study presents extensive numerical experiments demonstrating that the method has higher accuracy than traditional fault locating methods for different fault types, locations and impedances. Additionally, the method works for both two-terminal and three-terminal transmission lines.

A new faulty section identification and fault localization technique for three-terminal transmission line

Owing to mal-operation of the conventional scheme during high resistance ground fault near tap point, a new faulty section identification and fault localization technique for three-terminal transmission line is presented in this paper. The proposed technique utilizes time-synchronized voltage and current signals from all the three terminals. Initially, fault detection based on estimation of superimposed voltage of tap point with reference to all three terminals has been carried out. Subsequently, utilizing the above three estimated superimposed voltages; faulty section identification criterion is formed. Finally, fault localization i.e. estimation of the value of fault distance and resistance has been performed. The authenticity of the proposed technique has been verified by simulating an existing 400kV Indian three-terminal transmission network in PSCAD/EMTDC software. The simulation results point out that the proposed technique is able to identify the faulty section correctly. Moreover, it precisely estimates the value of fault distance and fault resistance as the percentage error for fault location and resistance remains within ±1.5% and ±3.5%, respectively. Likewise, its performance remains unaffected during wide variation in fault and system parameters. At the end, comparative evaluation of the proposed technique with the existing protection scheme clearly shows its superiority.

Generalized Alpha Plane for Numerical Differential Protection Applications

In this letter, a new generalized alpha plane (GAP) is proposed for numerical differential protection applications. Its performance is thoroughly evaluated for a wide variety of faults simulated in a 500 kV three-terminal transmission line using the Alternative Transients Program. The obtained results reveal that in comparison with the only other GAP reported in the literature, the proposed formulation may lead the differential protection function to have a more well-behaved response in the alpha plane, besides having a rather simpler formulation.