Actual evapotranspiration (ET_a) plays a crucial role in the water and energy cycles of the earth. An accurate estimate of the ET_a is essential for management of the water resources, agriculture, and irrigation, as well as research on atmospheric variations. Despite the importance of accurate ET_a values, estimating and mapping them remains challenging due to the physical and biological complexity of the ET process. As a novel approach for rapid and reliable estimation of ET_a, the present study develops automated deep learning (AutoDL) models that incorporate a metaheuristic optimization algorithm for image processing, architectural design, and hyperparameter tuning. The proposed AutoDL models integrate three different spatial and channel attention mechanisms, including a novel activated spatial attention mechanism (ASPAM), with the U-Net architecture. Bypassing the need for meteorological inputs, the proposed framework uses Moderate Resolution Imaging Spectrometer (MODIS) products and Digital Elevation Model (DEM) data as inputs. To evaluate the performance of the models, they are applied to three study areas in the United States with various climatic characteristics. According to the results, during the spring and summer, when the target values have higher certainty, the estimations are highly promising, with R² as high as 0.91 and MAPE as low as 6.40%. Furthermore, the proposed ASPAM module improves the accuracy of ET_a estimations compared to attention gate (AG) and squeeze and excitation (SE) attention modules. The results also indicate that the MODIS raw products and derived vegetation and water indices can predict ET_a within a reliable range of accuracy, with the addition of DEM data marginally enhancing the models' performance. The automatic workflow of this model makes it significantly easy to use, contributing to its applicability and generalizability for enhancing atmospheric research.

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To promote the integration of renewable energy resources into modern energy systems, high-voltage dc (HVdc) and circuit breaker (CB) technologies have become critical to achieving secure and efficient energy transmission. This article reviews the technical development of the related areas, compares diverse breaker concepts and topologies, investigates possible coordination and testing solutions, and points out the remaining challenges as well as future needs. The time-domain simulation and comparative analysis are adopted in this article to analyze and compare the performances of different HVdc CBs. By making use of different selectivity levels of multiterminal HVdc (MTdc) grids, the suitable planning and placement of HVdc CBs can be conducted. Furthermore, by providing insights into the performance of HVdc CBs, the work presented in this article can serve as a useful asset for the upcoming standardization and industrial application process of HVdc grid and CB design and testing.

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This paper presents a non‐unit protection method for long transmission lines of multi‐terminal HVDC (MTDC) grids based on the magnitude and direction of modal voltage and current travelling waves. The method overcomes the difficulty resulting from high attenuation and distortion as reported in previous methods using fault‐generated transients for protection of long HVDC lines. The proposed method determines the faulted pole using multi‐resolution morphological gradient of the pole voltage. Then, the multiplication of multi‐resolution morphological gradient of the modal travelling waves is utilised as a criterion to discriminate between internal and external faults and non‐fault events. The criterion is a negative high value for internal faults, a negative low value for forward external faults and events, and a positive value for backward external faults and events. A four‐terminal HVDC grid with modular multilevel converters including long HVDC lines is modelled using the PSCAD/EMTDC software. The simulation study validates effectiveness of the method for detection and discrimination of high resistance faults on long lines, as well as stability against external DC and AC faults, and DC circuit breaker opening and reclosing transients. The proposed method uses a relatively low sampling frequency and local data, i.e. no requirement for a communication link.@en

In order to test protection performance of future multi-terminal HVDC grids where DC circuit breakers (DC CBs) play an important role, a DC CB model in real time test environment should be developed. It is well known that a DC CB needs to interrupt DC faults very quickly in order to avoid converter damages and to ensure security of supply. The total current interruption time consists of a fault detection time, which is needed for the DC protection to provide a trip command to the DC CB, and a DC CB interruption time. Thus, it is necessary to demonstrate the performance of associated protective devices through real time simulations, before these devices can be implemented and commissioned in practice. This paper presents a detailed modeling of the voltage source converter assisted resonant current DC circuit breaker (VARC DC CB) in real time simulation environment based on RTDS. The proposed model provides sufficient representation of the circuit breaker for system level studies. External current-voltage characteristics of the proposed VARC DC CB models replicate the ones of the device in the real world. The proposed model of the breaker is tested in a simple test circuit including a DC voltage source and a T-scheme HVDC cable. Additionally, a case study has been presented by making use of a protection algorithm in a multi-terminal HVDC grid with frequency dependent parameters of the HVDC cables to show both protection performance and current interruption.

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eAssessment The application of multiterminal (MT), high-voltage dc (HVdc) (MTdc) grid technology requires test procedures for the operation and implementation of the protection solutions. The test procedures are usually derived from experience and from extensive measurement data, which, at present, are still not widely available. Based on a hardware-inthe- loop (HIL) method, advanced dc protection testing strategies, utilizing existing experience for ac grids and requirements for MTdc grids, may overcome this gap.@en