The optimized bonding method for long high voltage cable lines under the unbalanced cases

Abstract

In the unbalanced loading (UL) and phase to ground fault (PGF) cases, zero sequence current (ZC) flows on neutral point of power transformer, and the sheath current (SC) and the sheath voltage (SV) increase due to ZC. Thus, overvoltage (OV) and high harmonic distortion (HD) occur in cable termination (CT). OV causes high and imbalanced electric field, and high HD causes increasing of insulation temperature in CT, so CT faults occur. In the literature, bonding methods are used to prevent SC and SV effects, but these methods are not sufficient to prevent ZC effects, so the modified sectional solid bonding (MSSB) is suggested to prevent ZC effects. The aims of this study are minimizations of SV and HD on CT to prevent CT faults, so MSSB parameters are optimized by optimization method. In optimization algorithms of MSSB, the forecasting methods (FM) and optimization methods (OM) are used to optimize MSSB parameters. The best FM is selected according to training and forecasting errors, and the selected FM is used as an objective function of OM. Training and forecasting errors of hybrid ANN are less than the other methods, so hybrid ANN methods are used as FM. When bonding methods that are in literature are simulated under UL and PGF cases, SV and HD values exceed the limits. When the optimized MSSB method is used, HD and SV do not exceed the limits. Therefore, the optimized MSSB is suggested to prevent CT faults for the unbalanced cases.