Binglin Wang

This paper proposes a novel phasor domain fault location method for two or three terminal double-circuit transmission lines sharing the same tower without requiring line parameters. First, the models of the two and three terminal double-circuit lines with faults are derived. The line models fully consider the mutual coupling between the two line circuits, distributed line parameters, asymmetry of line structures, and extensive fault types. Through the modeling procedure, the fault location, line parameters, unsynchronized phase angle, fault resistance and other internal states of the line are introduced as unknown variables, resulting in a highly nonlinear problem. Afterwards, the line model is solved via the state estimation algorithm. Compared to the existing least square type algorithms such as Gauss-Newton and Levenberg Marquardt methods, the proposed Unscented Kalman Filter based algorithm greatly improves the convergence region. Compared to the existing parameter-free fault location method on double-circuit transmission lines, the proposed method more accurately presents the physical laws of the line and is compatible with common or split bus configurations. The proposed method is verified via numerous simulation experiments, proving that it can accurately locate faults for different fault resistances, locations and types. The method is also validated via field data experiments.

In this paper, an improved dynamic state estimation (DSE) based protection (DSEBP) scheme is proposed for transmission lines in MMC-HVDC grids. Firstly, a dynamic model of the protection zone (DC line of interest) is constructed using differential and algebraic equations. The impact of frequency dependent line parameters is mitigated through the utilization of the “line mode” transmission line model. Then, a novel Runge-Kutta (RK) discretization scheme is proposed to consider the dynamics of the control variables during electromagnetic transients, yielding reduced discretization error as compared to the conventional RK scheme. Finally, the batch mode regression framework based DSE is developed to formulate the protection logic considering errors of both measurements and historical estimates. Numerical experiments have shown that the proposed DSEBP scheme can dependably detect and trip internal faults, and securely ignore the external faults. The proposed scheme achieves improved reliability and operational speed as compared with the existing DSEBP schemes. The proposed scheme only requires a typical sampling rate of 10k samples per second, has the robustness to measurement noises, and the calculation burden is low enough for practical implementations.

Accurate fault location for underground cables in MMC-HVDC grids reduces the time finding faults as well as the system operational costs. For MMC-HVDC grids, the data window during faults is usually short. During such severe transients, the frequency dependent line parameters of the underground cables have strong influence on the fault location accuracy. In this paper, a novel fault location algorithm for underground cables in MMC-HVDC grids is proposed. First, a multi-layer model for the underground cable using partial differential equations is proposed, which considers the distributed and frequency dependent line parameters in time domain. Afterwards, the numerical finite difference solution of the multi-layer model is proposed to obtain the voltage distributions along the entire cable. Finally, the voltage method is applied to locate faults. Numerical experiments show that the multi-layer model accurately considers the frequency dependency of the cable parameters, and the solution of the model obtains accurate voltage distribution even during system transient. Extensive test cases prove that the proposed algorithm locates faults with less errors than the existing algorithm. The method is also compatible with a relatively low sampling rate (20 kHz) and a short data window (5 ms).

This paper proposes an improved noniterative fault location method on untransposed transmission lines without utilizing line parameters. Two-end three phase voltage and current phasor measurements before and during the fault are typically required. First, the parameter-free fault location problem is formulated through multi-section transmission line models, and the necessary condition of noniterative solutions is carefully investigated to determine the maximum possible section number of the multi-section line model. Afterwards, with the determined section number, the analytical solution of the fault location is derived with full utilization of the inherent characteristics of the line parameter matrices. Instead of solving all the parameters, two key variables inside the parameter matrices are extracted and the fault location is obtained by analytically solving a polynomial equation. The method provides a closed-form analytical solution, and therefore avoids convergence issues of iterative algorithms. In addition, line asymmetry of untransposed transmission lines are fully considered to minimize fault location errors. Extensive numerical experiments show that the proposed method has improved fault location accuracy compared to the existing method, with different fault types, locations and impedances.

This article proposes a parametric fault detection method for switching power converters. The method generates a health indicator to represent the health condition of the entire power converter, and parametric faults are detected with any abnormality of the health indicator. The method first introduces a systematic mathematical modeling framework to describe all the physical laws of the switching power converter during healthy conditions. Afterwards, the dynamic state estimation via batch mode regression is applied to solve the states of the system and to generate the health indicator. The health indicator sensitively reflects the consistency between the actual measurement and the healthy circuit model by taking the statistic characteristics of solution into consideration. The proposed method only requires terminal measurements of the switching power converter, and does not have further assumptions on the topology of the converter. Compared to the existing observer based approaches, the method presents higher sensitivity during parametric faults. Compared to the existing parameter identification based approaches, the method does not need to estimate all the parameters of the converter in order to detect parametric faults. Simulation and experimental results on an example buck converter prove the validity of the proposed parametric fault detection method.

This paper proposes a new fault location method for transmission lines in MMC-HVDC grids based on dynamic state estimation (DSE) and gradient descent. The method only requires a short data window of 5 ms after the occurrence of the fault and therefore is applicable for MMC-HVDC grids with high-speed tripping techniques. The method first builds a high-fidelity linear dynamic model of the DC transmission line, which accurately describes physical laws of the transmission line during the fault. Afterwards, the consistency between the measurements and the linear dynamic model is evaluated through the DSE algorithm. Finally, the actual fault location which corresponds to the best consistency is determined via the gradient descent algorithm. Compared to the existing DSE based fault location methods which solve highly nonlinear DSE problems, the proposed method only needs to solve a series of linear DSE problems, which overcomes the issues such as large numerical error and high computational burden especially for transmission lines in MMC-HVDC grids. Numerical experiments validates the effectiveness of the proposed method, with different fault types, resistances and locations. In addition, the method only requires a relatively low sampling rate of 20k samples per second.

Accurate fault location reduces operating cost and outage time. This paper proposes a time-domain method to accurately locate faults in transmission lines, which only requires a very short data window (several milliseconds) during faults. First, the voltage distribution through the line during faults is accurately obtained by solving the matrix form partial differential equations using the proposed numerical scheme. The proposed numerical scheme is mathematically validated for the transmission line fault location problem, with the optimal selection of time and distance intervals to ensure stability and minimum solution error. Afterwards, the fault location is obtained via the extremum value of the voltage distribution. The method fully considers distributed parameters as well as asymmetry of the line. Extensive numerical experiments validated that (a) the proposed numerical scheme demonstrates advantages towards other numerical schemes; (b) the proposed method presents higher fault location accuracy compared to the existing method, independent of fault types, locations and impedances; and (c) the fault location accuracy is not sensitive towards fault inception angles, loading conditions, measurement errors and parameter errors. The proposed method works with relatively low sampling rates (80 samples per cycle) and is compatible with IEC 61850 standard in present digital substations.