This paper presents a fast hybrid fault location method for active distribution networks with distributed generation(DG)and microgrids.The method uses the voltage and current data from the measurement points at the ma...This paper presents a fast hybrid fault location method for active distribution networks with distributed generation(DG)and microgrids.The method uses the voltage and current data from the measurement points at the main substation,and the connection points of DG and microgrids.The data is used in a single feedforward artificial neural network(ANN)to estimate the distances to fault from all the measuring points.A k-nearest neighbors(KNN)classifier then interprets the ANN outputs and estimates a single fault location.Simulation results validate the accuracy of the fault location method under different fault conditions including fault types,fault points,and fault resistances.The performance is also validated for non-synchronized measurements and measurement errors.展开更多
Spatiotemporal analysis of long-term changes in air temperature is of prime importance for climate change research and the development of effective mitigation and adaptation strategies.Although there are considerable ...Spatiotemporal analysis of long-term changes in air temperature is of prime importance for climate change research and the development of effective mitigation and adaptation strategies.Although there are considerable studies on air temperature change across the globe,most of them have been on linear trends and time series analysis of nonlinear trends have not received enough attention.Here,spatiotemporal patterns of monthly and annual mean(Tmean),maximum(T_(max)),and minimum(T_(min))air temperature at 47 synoptic stations across climate zones in Iran for a 40-yr period(1978–2017)are analyzed.A polynomial fitting scheme(Polytrend)is used to both monthly and annual air temperature data to detect trends and classify them into linear and nonlinear(quadratic and cubic)categories.The significant(non-significant)trends in Tmean,T_(max),and T_(min) across all climate zones are 41.1%(58.9%),34.1%(65.9%),and 46%(54%),respectively.The highest magnitude of increasing trends is observed in the annual T_(min)(0.47℃decade−1)and the lowest magnitude is for the annual T_(max)(0.4℃decade−1).Across the country,increasing trends(=37.2%)have higher spatial coverage than the decreasing trends(=3.2%).Warming trends in Tmean(65.3%)and T_(min)(73.1%)are mainly observed in humid climate zone while warming trends in T_(max) are in semi-arid(43.9%)and arid(34.1%)climates.Linear change with a positive trend is predominant in all Tmean(56.7%),T_(max)(67.8%),and T_(min)(71.2%)and for both monthly and annual data.Further,the linear trends have the highest warming rate in annual T_(min)(0.83℃decade^(−1))and Tmean(0.46℃decade^(−1))whereas the nonlinear trends have the highest warming rate in annual T_(max)(0.52℃decade^(−1)).The linear trend type is predominant across the country especially in humid climate zones whereas the nonlinear trends(quadratic and cubic)are mainly observed in the arid climate zones.This study highlights nonlinear changes and spatiotemporal trends in air temperature in Iran and contributes to a growing body of climate change literature that is necessary for the development of effective mitigation and adaptation strategies in the Middle East.展开更多
We present a new algorithm for adaptive single-pole auto-reclosing of power transmission lines using wavelet packet transform. The db8 wavelet packet decomposes the faulted phase voltage waveform to obtain the coeffic...We present a new algorithm for adaptive single-pole auto-reclosing of power transmission lines using wavelet packet transform. The db8 wavelet packet decomposes the faulted phase voltage waveform to obtain the coefficients of the nodes 257, 259 to 262. An index is then defined from the sum of the energy coefficients of these nodes. By evaluating the index, transient and permanent faults, as well as the secondary arc extinction instant, can be identified. The significant advantage of the proposed algorithm is that it does not need a threshold level and therefore its performance is independent of fault location, line parameters, and operating conditions. Moreover, it can be used in transmission lines with reactor compensation. The proposed method has been successfully tested under a variety of fault conditions on a 400 kV overhead line of the Iranian National Grid using the Electro-Magnetic Transient Program (EMTP). The test results validated the algorithm’s ability in distinguishing between transient arcing and permanent faults and determining the instant of secondary arc extinction.展开更多
文摘This paper presents a fast hybrid fault location method for active distribution networks with distributed generation(DG)and microgrids.The method uses the voltage and current data from the measurement points at the main substation,and the connection points of DG and microgrids.The data is used in a single feedforward artificial neural network(ANN)to estimate the distances to fault from all the measuring points.A k-nearest neighbors(KNN)classifier then interprets the ANN outputs and estimates a single fault location.Simulation results validate the accuracy of the fault location method under different fault conditions including fault types,fault points,and fault resistances.The performance is also validated for non-synchronized measurements and measurement errors.
基金supported by the Swedish Research Council (2018-00430)
文摘Spatiotemporal analysis of long-term changes in air temperature is of prime importance for climate change research and the development of effective mitigation and adaptation strategies.Although there are considerable studies on air temperature change across the globe,most of them have been on linear trends and time series analysis of nonlinear trends have not received enough attention.Here,spatiotemporal patterns of monthly and annual mean(Tmean),maximum(T_(max)),and minimum(T_(min))air temperature at 47 synoptic stations across climate zones in Iran for a 40-yr period(1978–2017)are analyzed.A polynomial fitting scheme(Polytrend)is used to both monthly and annual air temperature data to detect trends and classify them into linear and nonlinear(quadratic and cubic)categories.The significant(non-significant)trends in Tmean,T_(max),and T_(min) across all climate zones are 41.1%(58.9%),34.1%(65.9%),and 46%(54%),respectively.The highest magnitude of increasing trends is observed in the annual T_(min)(0.47℃decade−1)and the lowest magnitude is for the annual T_(max)(0.4℃decade−1).Across the country,increasing trends(=37.2%)have higher spatial coverage than the decreasing trends(=3.2%).Warming trends in Tmean(65.3%)and T_(min)(73.1%)are mainly observed in humid climate zone while warming trends in T_(max) are in semi-arid(43.9%)and arid(34.1%)climates.Linear change with a positive trend is predominant in all Tmean(56.7%),T_(max)(67.8%),and T_(min)(71.2%)and for both monthly and annual data.Further,the linear trends have the highest warming rate in annual T_(min)(0.83℃decade^(−1))and Tmean(0.46℃decade^(−1))whereas the nonlinear trends have the highest warming rate in annual T_(max)(0.52℃decade^(−1)).The linear trend type is predominant across the country especially in humid climate zones whereas the nonlinear trends(quadratic and cubic)are mainly observed in the arid climate zones.This study highlights nonlinear changes and spatiotemporal trends in air temperature in Iran and contributes to a growing body of climate change literature that is necessary for the development of effective mitigation and adaptation strategies in the Middle East.
文摘We present a new algorithm for adaptive single-pole auto-reclosing of power transmission lines using wavelet packet transform. The db8 wavelet packet decomposes the faulted phase voltage waveform to obtain the coefficients of the nodes 257, 259 to 262. An index is then defined from the sum of the energy coefficients of these nodes. By evaluating the index, transient and permanent faults, as well as the secondary arc extinction instant, can be identified. The significant advantage of the proposed algorithm is that it does not need a threshold level and therefore its performance is independent of fault location, line parameters, and operating conditions. Moreover, it can be used in transmission lines with reactor compensation. The proposed method has been successfully tested under a variety of fault conditions on a 400 kV overhead line of the Iranian National Grid using the Electro-Magnetic Transient Program (EMTP). The test results validated the algorithm’s ability in distinguishing between transient arcing and permanent faults and determining the instant of secondary arc extinction.
