At both transmission and distribution voltage ratings, utilities have employed overhead lines that are supported by outdoor insulators. These insulators serve a crucial function of insulating the high voltage transmission line from the steel tower (Ahmed S. Haiba et al. 2019). Although due to their nature operation in overhead transmission and distribution lines, outdoor ceramic insulators are subjected to various defects under operating and environmental conditions. One of these defects is the expansion of cement which can form cracks in the insulator and this expansion can be accelerated under wet conditions leading to insulator failure (Anjum 2014). As a result, Cherney and Hoton (Cherney and Hooton 1987) introduced water expansion tests on the used cement to ensure its quality to be assembled with the insulator. Also, erosion and corrosion of pin and cap hardware in the insulator is another defect that can be occurred due to the salt solution formation on the insulator surface. At wet atmospheric conditions, the formed salt solution may lead to loss in cross-section area and mechanical strength in the insulator pin leading to dropping the overhead conductor (Cherney 1982). Furthermore, contamination flashover is the main problem of overhead insulators (Zhao et al. 2015; Zhang et al. 2013; Krystian Leonard Chrzan 2010; Krystian L. Chrzan, Vosloo, and Holtzhausen 2011). Contaminants, such as salts, chemical particles, dust, sand, and etc, can be accumulated on the surface of the insulator. At wet conditions, the pollution surface layer is converted into a conductive layer and the leakage current passes through these layers on the insulator surface causing heating of that layer. Dry bands are then formed and discharges can continue until occurring of insulator flashover and outage of the power line (He and Gorur 2016). Ceramic insulators may be broken and punctured due to the occurrence of over-voltages from the lightning on the transmission line (Cherney 1982). Also, during manufacturing process, very small internal voids or cracks may be developed within the insulator (Zener and Wills 1934; Polisetty 2019). These voids may cause continuous discharges under operating conditions leading to the insulator failure. As a result, PD growth measurement is the most significant indicator of all the above mentioned defects that occurred for the overhead insulators (Ghosh, Chatterjee, and Dalai 2017). Consequently, many researches have introduced various methods to evaluate the insulators’ condition based on PD signatures (Ahmed S. Haiba et al. 2019). Many detection techniques, based on both electrical and non-electrical methods, have been introduced for the detection, analysis and evaluation of PD activities (IEC Standards 60270 2000; Albano et al. 2016; FRĄCZ 2016; Si et al. 2010; Yaacob et al. 2014; Sahoo, Salama, and Bartnikas 2005). Each technique has benefits and drawbacks and one may be better than the other depending on the application. A brief overview of the widely techniques that used for monitoring the condition of the overhead line insulators will be provided in figure (1) (Hussain, Refaat, and Abu-Rub 2021).
Over time, various parameters have been manually extracted from recorded patterns or signals with the goal of using these parameters to build a classifier capable of differentiating and characterizing faults, partial discharges, defects, or degradation (Mantach et al. 2022). While the process has become somewhat automated, the need for experts to manually select the features presents a challenge, as different features may lead to different outcomes. This relying on selected features manually can adversely affect the classifier's performance.
Deep learning enables the integration of feature selection with the learning process, thereby automating the entire process. In the realm of applications of high voltage, the primary objective has been to localize or classify faults, defects, or partial discharges that could occur in high voltage equipment, or to detect the deterioration of insulating materials. Classification involves differentiating between various sources of faults, defects, or partial discharges, or levels of degradation. Artificial intelligence techniques that applied to classify the condition of insulators holds great promise, as defects could be automatically fixed out of pattern recognition (Stefenon et al. 2022). Deep learning techniques can be utilized to detect the presence of a fluctuating number of missing disks in transmission lines consisting of chain insulators (Sampedro et al. 2019). The main challenge in using computer vision to detect insulator failures is the infrequency of such failures. As a result, training a network to recognize specific conditions becomes challenging due to the limited dataset available. (Sampedro et al. 2019). However, applying engineering constraints for datasets captured through inspections could enhance the model's accuracy, resulting in an accuracy rate of up to 92.86%, as demonstrated in (Shi and Huang 2021).
Many techniques of artificial intelligence have been developed for predicting the stability of smart grids (Arzamasov, Bohm, and Jochem 2018; Aghamohammadi and Abedi 2018; Gupta, Gurrala, and Sastry 2019; Zare, Alinejad-Beromi, and Yaghobi 2019; Chen et al. 2019). Furthermore, researchers have shown the widespread utilization of these techniques such as Artificial Neural Network (ANN) (Dadashizadeh Samakosh and Mirzaie 2019; Belhouchet, Bayadi, and Bendib 2019; A. A. Salem et al. 2020), Support Vector Machine (SVM) (Mahdjoubi et al. 2019), fuzzy logic (FL) (Asimakopoulou et al. 2011), K-means clustering (Farshad 2019), and Hidden Markov Model (HMM) (Lu et al. 2019) in addressing electrical power system and high voltage engineering issues (A. Salem et al. 2021; Tahir Khan Niazi et al. 2020). Intelligent systems can improve the reliability of the transmission and distribution power system, cost savings, and reduce human effort by facilitating effective assessing the state and performance of outdoor insulators during voltage operation (Surya Prasad and Prabhakara Rao 2016). In their study, Salem et al. (A. A. A. Salem et al. 2020) utilized insulator diameter, height, creepage distance, form factor, and Equivalent Salt Deposit Density (ESDD) as input parameters to train a model that combined the Adaptive Neuro Fuzzy Inference System (ANFIS) with ANN. Also, by establishing correlations between leakage current and weather conditions, A. Din et al. (Din et al. 2021) used SVM technique to evaluate the leakage current for outdoor insulators. In another work, Saranya et al. (Saranya and Muniraj 2016) put forward a novel approach for assessment the status and performance of outdoor insulators, which involves recognizing the arc faults of insulators through measurements of phasor angle.
In this current work, detection technique of acoustic emission is used for detection PD signatures resulting in artificial defects in ceramic outdoor insulators. A series of advanced signal processing techniques are performed on the captured signals from the experimental section to extract and select the most significant features to be as input data for the proposed classifier. Finally, artificial neural network (ANN) is proposed in order to assess easily, cost-effectively and accurately the classification of defective insulators.