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  1. Free, publicly-accessible full text available May 1, 2024
  2. Power system equipment presents special signatures at the incipient stage of faults. As more renewables are integrated into the systems, these signatures are harder to detect. If faults are detected at an early stage, economical losses and power outages can be avoided in modern power grids. Many researchers and power engineers have proposed a series of signature-specific methods for one type of equipment's waveform abnormality. However, conventional methods are not designed to identify multiple types of incipient faults (IFs) signatures at the same time. Therefore, we develop a general-purpose IF detection method that detects waveform abnormality stemming from multiple types of devices. To avoid the computational burden of the general-purpose IF detection method, we embed the abnormality signatures into a vector and develop a pre-training model (PTM) for machine understanding. In the PTM, signal "words," "sentences," and "dictionaries" are designed and proposed. Through the comparison with a machine learning classifier and a simple probabilistic language model, the results show a superior detection performance and reveal that the training radius is highly related to the size of abnormal waveforms. 
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  5. The security of active distribution systems is critical to grid modernization along with deep renewable penetration, where the protection plays a vital role. Among various security issues in protection, conventional protection clears only 17.5% of staged high impedance faults (HIFs) due to the limited electrical data utilization. For resolving this problem, a detection and location scheme based on μ-PMUs is presented to enhance data processing capability for HIF detection through machine learning and big data analytics. To detect HIFs with reduced cost on data labeling, we choose expectation-maximization (EM) algorithm for semi-supervised learning (SSL) since it is capable of expressing complex relationships between the observed and target variables by fitting Gaussian models. As one of the generative models, EM algorithm is compared with two discriminative models to highlight its detection performance. To make HIF location robust to HIF impedance variation, we adopt a probabilistic model embedding parameter learning into the physical line modeling. The location accuracy is validated at multiple locations of a distribution line. Numerical results show that the proposed EM algorithm greatly saves labeling cost and outperforms other SSL methods. Hardware-in-the-loop simulation proves a superior HIF location accuracy and detection time to complement the HIF's probabilistic model. With outstanding performance, we develop software for our utility partner to integrate the proposed scheme. 
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  6. The high impedance fault (HIF) has random, irregular and unsymmetrical characteristics, making such a fault difficult to detect in distribution grids via conventional relay measurements with relatively low resolution and accuracy. This paper proposes a stochastic HIF monitoring and location scheme using high-resolution time-synchronized data in μ-PMUs for distribution network protection. Specifically, we systematically design a process based on feature selections, semi-supervised learning (SSL), and probabilistic learning for fault detection and location. For example, a wrapper method is proposed to leverage output data in feature selection to avoid overfitting and reduce communication demand. To utilize unlabeled data and quantify uncertainties, an SSL-based method is proposed using the Information Theory for fault detection. For location, a probabilistic analysis is proposed via moving window total least square based on the probability distribution of the fault impedance. For numerical validation, we set up an experiment platform based on the real-time simulator, so that the real-time property of μ-PMU can be examined. Such experiment shows enhanced HIF detection and location, when compared to the traditional methods. 
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  7. Under the trend of deeper renewable energy integration, active distribution networks are facing increasing uncertainty and security issues, among which the arcing fault detection (AFD) has baffled researchers for years. Existing machine learning based AFD methods are deficient in feature extraction and model interpretability. To overcome these limitations in learning algorithms, we have designed a way to translate the non-transparent machine learning prediction model into an implementable logic for AFD. Moreover, the AFD logic is tested under different fault scenarios and realistic renewable generation data, with the help of our self-developed AFD software. The performance from various tests shows that the interpretable prediction model has high accuracy, dependability, security and speed under the integration of renewable energy. 
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  8. For accommodating more electric vehicles (EVs) to battle against fossil fuel emission, the problem of charging station placement is inevitable and could be costly if done improperly. Some researches consider a general setup, using conditions such as driving ranges for planning. However, most of the EV growths in the next decades will happen in the urban area, where driving ranges is not the biggest concern. For such a need, we consider several practical aspects of urban systems, such as voltage regulation cost and protection device upgrade resulting from the large integration of EVs. Notably, our diversified objective can reveal the trade-off between different factors in different cities worldwide. To understand the global optimum of large-scale analysis, we studied each feature to preserve the problem convexity. Our sensitivity analysis before and after convexification shows that our approach is not only universally applicable but also has a small approximation error for prioritizing the most urgent constraint in a specific setup. Finally, numerical results demonstrate the trade-off, the relationship between different factors and the global objective, and the small approximation error. A unique observation in this study shows the importance of incorporating the protection device upgrade in urban system planning on charging stations. 
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