Swagata Das

Bio: Swagata Das is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Fault (power engineering) & Fault indicator. The author has an hindex of 7, co-authored 11 publications receiving 251 citations.

Impedance-Based Fault Location in Transmission Networks: Theory and Application

Abstract: A number of impedance-based fault location algorithms have been developed for estimating the distance to faults in a transmission network. Each algorithm has specific input data requirements and makes certain assumptions that may or may not hold true in a particular fault location scenario. Without a detailed understanding of the principle of each fault-locating method, choosing the most suitable fault location algorithm can be a challenging task. This paper, therefore, presents the theory of one-ended (simple reactance, Takagi, modified Takagi, Eriksson, and Novosel et al. ) and two-ended (synchronized, unsynchronized, and current-only) impedance-based fault location algorithms and demonstrates their application in locating real-world faults. The theory details the formulation and input data requirement of each fault-locating algorithm and evaluates the sensitivity of each to the following error sources: 1) load; 2) remote infeed; 3) fault resistance; 4) mutual coupling; 5) inaccurate line impedances; 6) DC offset and CT saturation; 7) three-terminal lines; and 8) tapped radial lines. From the theoretical analysis and field data testing, the following criteria are recommended for choosing the most suitable fault-locating algorithm: 1) data availability and 2) fault location application scenario. Another objective of this paper is to assess what additional information can be gleaned from waveforms recorded by intelligent electronic devices (IEDs) during a fault. Actual fault event data captured in utility networks is exploited to gain valuable feedback about the transmission network upstream from the IED device, and estimate the value of fault resistance.

Distribution Fault-Locating Algorithms Using Current Only

Abstract: Traditional impedance-based fault-locating methods implemented in modern overcurrent protection relays require voltage and current measurements to provide reasonable fault-location estimates. Although they capture voltage and current, depending on field condition or due to equipment failure, relays may record current measurements only. Voltage measurements are thus missing or unavailable. The objective of this paper is to develop practical impedance-based fault-locating algorithms with current data (magnitude or phasors) as the only input and demonstrate the efficacy of the algorithms with simulated and actual field data. These algorithms use the circuit model of the distribution feeder and Kirchhoff's circuit laws in estimating the fault voltage at the relay location and then use impedance-based methods for fault location. Based on the analysis conducted on actual fault data, error in estimation is generally less than 0.5 mi from the actual location of the fault.

Time-Domain Modeling of Tower Shadow and Wind Shear in Wind Turbines

Abstract: Tower shadow and wind shear contribute to periodic fluctuations in electrical power output of a wind turbine generator. The frequency of the periodic fluctuations is 𝑛 times the blade rotational frequency 𝑝, where 𝑛 is the number of blades. For three-bladed wind turbines, this inherent characteristic is known as the 3𝑝 effect. In a weak-power system, it results in voltage fluctuation or flicker at the point of common coupling of the wind turbine to the grid. The phenomenon is important to model so as to evaluate the flicker magnitude at the design level. Hence, the paper aims to develop a detailed time-domain upwind fixed speed wind turbine model which includes the turbine's aerodynamic, mechanical, electrical, as well as tower shadow and wind shear components. The model allows users to input factors such as terrain, tower height, and tower diameter to calculate the 3𝑝 oscillations. The model can be expanded to suit studies involving variable speed wind turbines. Six case studies demonstrate how the model can be used for studying wind turbine interconnection and voltage flicker analysis. Results indicate that the model performs as expected.

Effects of distributed generators on impedance-based fault location algorithms

Abstract: Impedance-based fault locating algorithms assume a radial distribution feeder when computing the distance to a fault. With increased penetration of distributed generators (DGs) to the distribution grid, this assumption is violated. Short-circuit current to a fault comes from two sources, the utility substation and DGs. Ignoring the latter term when the fault is located downstream from DGs will adversely affect the accuracy of location estimates. Therefore, this paper aims to evaluate the impact of DGs on the accuracy of existing impedance-based fault location algorithms. The goal is to understand how different factors such as DG technology, MVA size of the DG unit, DG interconnect transformer, tapped loads, location of the fault from the DG unit, and fault resistance affect fault location in the presence of distributed generators.

Distribution fault location using short-circuit fault current profile approach

Abstract: Impedance-based algorithms do not consider load current and non-uniform line impedance per unit, thus introducing errors in fault location estimates. To minimize these errors, this paper proposes a short-circuit fault current profile approach to complement impedance-based algorithms. In this approach, circuit model of the distribution feeder is used to place faults at every bus and the corresponding short-circuit fault current is plotted against reactance or distance to fault. When a fault occurs in the distribution feeder, fault current recorded by the relay is extrapolated on the current profile to get location estimates. Since the circuit model is directly used in building the current profile, this approach takes into account load and non-uniform line impedance. The approach is tested using modified IEEE 34 Node Test Feeder and validated against data provided by utilities. Location estimates are within 0.8 miles of the actual fault location when the circuit model closely represents the distribution feeder.

Fault Location in Power Distribution Systems via Deep Graph Convolutional Networks

Abstract: This paper develops a novel graph convolutional network (GCN) framework for fault location in power distribution networks. The proposed approach integrates multiple measurements at different buses while taking system topology into account. The effectiveness of the GCN model is corroborated by the IEEE 123 bus benchmark system. Simulation results show that the GCN model significantly outperforms other widely-used machine learning schemes with very high fault location accuracy. In addition, the proposed approach is robust to measurement noise and data loss errors. Data visualization results of two competing neural networks are presented to explore the mechanism of GCN's superior performance. A data augmentation procedure is proposed to increase the robustness of the model under various levels of noise and data loss errors. Further experiments show that the model can adapt to topology changes of distribution networks and perform well with a limited number of measured buses.

A Traveling Wave-Based Fault Location Method Using Unsynchronized Current Measurements

Abstract: This paper presents a traveling-wave-based fault location method for two terminal transmission lines using unsynchronized current measurements from intelligent electronic devices (IEDs) recorded at both ends. In the formulation, the method considers practical implementation issues such as IED hardware and software processing delays, and data synchronization error. In this method, two possible fault location solutions are determined using the first two traveling wave arrival time recorded at both terminals. Then, the correct fault location is identified between the two based on the faulted half-section information. Identification of faulted half-section is accomplished by comparing the rise time of the first traveling wave recorded at both terminals of the line. The proposed method does not require GPS synchronization and field experiments to calibrate the various asymmetrical delays and synchronization error. The method is tested on a 220 kV transmission line using data simulated in EMTDC/PSCAD tool with frequency-dependent phase models. The proposed method can locate faults using unsynchronized data with various asymmetrical delays, whereas classical methods work properly only for synchronized data with symmetrical delays. The performance of the proposed method is evaluated for different fault scenarios. The proposed method demonstrated high accuracy, noise immunity, robustness against fault inception angles, and high impedance faults. Test results are compared with classical two-terminal methods for a transmission line.

A New Fault Location Technique in Smart Distribution Networks Using Synchronized/Nonsynchronized Measurements

Abstract: This paper proposes a new impedance-based technique to locate all fault types in distribution networks with/without distributed generators. A new procedure to form an impedance matrix using only series impedances of the distribution lines is introduced. The impedance matrix along with the prefault and during-fault voltage phasors at few buses is used to estimate the injection fault current via the least-squares technique. Linear least-squares estimator is utilized if microphasor measurement units ${({\mu} \rm{PMUs)}}$ are installed along the network. However, a nonlinear least-squares problem solved by the trust-region-reflective algorithm is used when only the voltage magnitudes are provided by smart meters. The operation of the standard protective devices in the distribution networks is used to reduce the computational burden of the proposed method. Also, a generalized measurement placement algorithm is studied using the discovered features of the impedance matrix. In addition, the Sobol's sensitivity analysis is conducted to quantify the importance of different input factors on the fault location accuracy. The effectiveness of the proposed method is validated on a real 134-bus, 13.8 kV distribution network under several fault scenarios and noisy measurements.

Incipient Fault Location Algorithm for Underground Cables

Abstract: Cable failure process is gradual and is characterized by a series of single-phase sub-cycle incipient faults with high arc voltage. They often go undetected and eventually result in a permanent fault. The objective of this paper is to develop a robust yet practical incipient fault location algorithm taking into account the fault arc voltage. The algorithm is implemented in the time-domain and utilizes power quality monitor data to estimate the distance to the fault in terms of the line impedance. It can be applied to locate both sub-cycle as well as permanent faults. The proposed algorithm is evaluated and proved out using field data collected from utility distribution circuits. The average absolute error in locating incipient faults for three underground cable failures analyzed in this paper was found to be 7.37%, 4.69% and 3.58%, respectively.