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High voltage dc (HVDC) transmission, especially voltage source converter (VSC)‐based HVDC transmission requires high‐speed operation for relay protection. However, traditional derivative‐based non‐unit travelling wave‐based protection (TWP) methods are sensitive to the fault impedance, resulting in low protection sensitivity in case of the high‐impedance fault. First, the fault information containing in the fault travelling wavefront is analysed based on the frequency‐dependent parameters of the dc transmission line and the broadband characteristic of the fault‐point initial travelling wave. It can be concluded that the distortion of the fault travelling wavefront depends on the fault distance and the amplitude of the fault travelling wavefront depends on the fault impedance. Then, a principle of non‐unit TWP for dc transmission line based on waveform correlation calculation is proposed. The proposed method is verified in both thyristor‐based HVDC and VSC HVDC PSCAD test systems. The simulation results verify the high‐speed, high fault‐impedance tolerability and correctness of the proposed protection method. [ABSTRACT FROM AUTHOR]

Due to the characteristics of small, nonlinear, random, and unstable current, the high impedance faults (HIF) are not always effectively cleared by conventional over current relays. A new simple and effective algorithm of HIF detection in distribution network based on the wavelet time–frequency entropy is presented in this article. On the basis of analysis, the time–frequency distribution characteristics in the concerned frequency band of HIFs by wavelet transform. The feature sequence developed by the wavelet time–frequency entropy at the time sequence is employed to detect HIF at substation. This criterion is calculated from the sum of wavelet time–frequency entropy at the time sequence every half cycle. If the value of the criterion is more than the threshold during four cycles, the HIF event can be identified. The developed detection method has been tested with real‐world recorded signals from different HIF medium and PSCAD/EMTDC‐generated signals. The result shows that the proposed method is robust to transients generated during normal events such as capacitor bank switching, load switching, and harmonic load. It has good performance for antinoise ability by noise reduction coefficient improved appropriately. And the proposed method has better reliability than the traditional third‐harmonic‐based method. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

A high‐impedance fault (HIF) is mostly associated with the arcing phenomenon, and its main features are low current, randomness, non‐linearity, and asymmetry. The low fault current of an HIF is a major challenge for overcurrent‐based protection system of distribution networks. Power loss, potential fire hazard, and electric shock are consequences of an undetected HIF. This study presents a time‐domain HIF detection algorithm based on monitoring the substation current waveform. Using the Kullback–Leibler divergence similarity measure, the non‐linearity, and asymmetry features of two subsequent half cycles of the current waveform are quantified as the HIF detection criterion. A time duration‐based criterion is also used to distinguish HIFs from the load, capacitor, feeder, and distributed energy resource switchings and the voltage sag and swell events. The proposed scheme satisfactorily works in the presence of non‐linear loads. Also, it does not require the training data set, transformation, and calculation of harmonic/sequence components. Extensive time‐domain simulation case studies using the IEEE 13 and 34 node test feeders demonstrate the merits of the proposed HIF detection algorithm. [ABSTRACT FROM AUTHOR]

Despite the growing deployment of photovoltaic (PV) systems, they are still facing challenges in developing the proper control and protection schemes. One of the main protection challenges of PV arrays is their low fault currents under low‐irradiance, low‐mismatch, and high‐impedance faults. In addition to these conditions, the operation of the maximum power point tracking algorithm may lead to the faults within the PV array remain undetected, resulting in potential fire hazards and power loss. This study presents a fault detection scheme based on monitoring the output power of the PV array. Using the sample entropy‐based complexity, the irregularity of the time series of the normalised fault‐imposed component of PV power is quantified as the fault detection criterion. The proposed protection scheme is capable of distinguishing the line‐to‐line, line‐to‐ground, and open‐circuit faults from the weather disturbances and partial shadings. Also, it does not require the training dataset and the prior information about the PV array and is effective for both grid‐connected and islanded PV systems. Extensive time‐domain simulation results demonstrate high accuracy of the proposed fault detection scheme. [ABSTRACT FROM AUTHOR]

In this study, an adaptive continuous wavelet transform (CWT)‐based overcurrent protection for smart grids is proposed to enhance the overcurrent protection performance encountering high‐impedance fault (HIF) and current transformer (CT) saturation, which are extremely complex phenomena and their impacts often cause mis‐coordination or mal‐operation. The proposed algorithm samples three phase current waveforms and imports them to CWT to extract high frequency coefficients. Afterwards, the sum of absolute values of the coefficients, Scoef, is calculated for each sample during the last cycle. Meanwhile, several simulations related to HIFs with different impedances and CT saturations with different severities are executed and the fault currents and the sum of absolute values of the coefficients are achieved and saved in the relay memory as (X, Y) coordinates of points (IL‐fault, SL‐coef), named 'learning data'. Thereafter, each Scoef is imported to the X −Y plane and, consequently, the occurrence of HIF or CT saturation is detected and the real‐fault current is estimated by both non‐linear interpolation and extreme learning machine approaches. Subsequently, new time dial setting and Ipickup of the relays are computed and reloaded. Security, dependability, and sensitivity of the proposed adaptive protection method are confirmed by numerous simulation studies. [ABSTRACT FROM AUTHOR]

The fault identification process in transmission systems involves three functions: discrimination, classification and phase selection. The current study classifies the methods that applied for each function. Moreover, this study introduces criticism and assessment study that helps the power system protection engineer to choose the best fault identification scheme at responsible indices. Investigated solutions for the drawbacks appeared with the previous methods are suggested. This study also proposes sensitive and automated fault identification scheme to solve the existing challenges such as high‐impedance faults (HIFs), non‐linear modelling of arcing etc. Several simulation studies are employed using alternative transients program/electromagnetic transient program (ATP/EMTP) package on a sample 500 kV test system to ensure the performances of the proposed scheme compared with the previous methods. Simulation results concluded that: the proposed identification scheme has the ability to discriminate correctly between HIF and low‐impedance faults using current signal captured from one end only. Moreover, the proposed scheme alleviates perfectly the problems associated with load variations by adaptive threshold settings and reduces the impacts on the environmental and external phenomena. [ABSTRACT FROM AUTHOR]

The study presents a differential scheme for microgrid protection using time‐frequency transform such as S‐transform. Initially, the current at the respective buses are retrieved and processed through S‐transform to generate time‐frequency contours. Spectral energy content of the time‐frequency contours of the fault current signals are calculated and differential energy is computed to register the fault patterns in the microgrid at grid‐connected and islanded mode. The proposed scheme is tested for different shunt faults (symmetrical and unsymmetrical) and high‐impedance faults in the microgrid with radial and loop structure. It is observed that a set threshold on the differential energy can issue the tripping signal for effective protection measure within four cycles from the fault inception. The results based on extensive study indicate that the differential energy‐based protection scheme can reliably protect the microgrid against different fault situations and thus, is a potential candidate for wide area protection. [ABSTRACT FROM AUTHOR]