“…According to the research idea of multi‐feature fusion, many protection algorithms integrating data driven and AI have been published for transformer protection. At present, the differential current is still the main research object, for instance: (i) it is directly used as an input to train machine learning algorithms, such as decision tree [26, 27], random forest [28], artificial neural network (ANN) [29–33], probabilistic neural network [34–36], radial basis neural network [37], and so on; (ii) the features that are extracted from the differential current by the tools, such as wavelet transform [38–44], Clarke transform [45], principal component analysis [46], and so on, are used as the inputs of machine learning algorithms; (iii) the running states are identified through pattern recognition methods such as fuzzy theory [32, 47, 48]; (iv) according to the theory of image recognition, mathematical morphology [49, 50] is used for identifying the running states, in addition, deep learning algorithms such as convolutional neural networks (CNNs) [51, 52] have also received attention in recent years. Besides the methods mentioned above, some scholars put forward the concept of equivalent magnetisation curve [53] whose several geometric features are extracted to train an support vector machine (SVM) for the identification of running states.…”