# Fault Diagnosis of HV Cable Metal Sheath Grounding System Based on LSTM
###### Abstract  
At present, the metal sheath of high voltage (HV) cables generally adopts the cross-bonded grounding method, which brings many types of faults and challenges the monitoring and diagnosis of the operation status of the cables. In order to effectively diagnose various types of faults in the metal sheath grounding system of HV cables, this paper proposes a fault diagnosis method for the metal sheath grounding system of HV cables based on long and short-term memory (LSTM). Firstly, the grounding system model of HV cable metal sheath is established. Secondly, the sheath currents of four faults are analyzed. Based on the sheath current amplitude ratio and phase difference of the same loop and the same grounding box, 14 feature vectors reflecting the operation state of the metal sheath grounding system are constructed. Then, the operation state of 18 kinds of metal sheath grounding systems is simulated, and the fault database is established. Finally, the LSTM algorithm is used to accurately identify the fault of HV cable grounding system. The results show that the LSTM algorithm can effectively diagnose and identify the faults of the HV cable metal sheath grounding system, and the accuracy rate is 100%. metal sheath; fault diagnosis; cables +
Footnote †: journal: Applied  
doi:10.3390/app13042453  
ratio of maximum to minimum single-phase grounding current <3\", [9]. The standard is relatively single and cannot directly reflect the connection between grounding current and grounding system fault. At present, scholars at home and abroad have made some research results on fault diagnosis of HV cable cross-bonded grounding systems. [PERSON] et al. [10] established an HV cable sheath circuit model and analyzed the change of sheath current of coaxial cable monitoring in cross-bonded box under sheath circuit open circuit, link box flooding, and joint epoxy prefabricated breakdown fault, based on this, a set of diagnostic criteria is proposed for the diagnosis and location of cable faults, but involved fewer fault types and lacked a comprehensive classification of grounding system faults. [PERSON] et al. [11] built the sheath current calculation software, which can calculate the sheath current, and compare the calculated value of cable sheath current with the actual measured value under different load operations throughout the day, and the deviation between them is more than 10%, then the cable may be determined to have insulation fault; however, the diagnostic accuracy of this method is not accurate enough, and it is easy to have a false alarm and missed alarm. It is proposed that sheath circulating currents can be used for sheath fault diagnosis. Examining the possibility of detecting cable sheath faults in HV and ultra-high-voltage (UHV) cable sheath cross-bonded systems by monitoring sheath-to-ground currents at the connection end [12]. By collecting the sheath currents at the first and last ends of the HV cable grounding system and constructing a two-dimensional Lissajous graph, the obtained feature parameters include the long axis length, short axis length, eccentricity, rate of change of tilt angle, and sheath currents at the first and last ends of the cable in a total of 6-dimensional feature vectors to diagnose cable sheath faults [13]. However, the method has high sampling requirements for the acquisition device and the data analysis is complicated, which is difficult to be applied to engineering practice. To sum up, the various types of diagnostic schemes proposed have good diagnostic effects in their respective ranges and are not able to diagnose faults outside the range quickly and accurately. After comparing with the existing diagnostic methods in Table 1, this paper proposes a fault diagnosis method based on the LSTM algorithm for metal sheath grounding systems of HV cables is proposed. Firstly, a model of HV cable grounding system is established.