Back Feeding Energization Transients in a 500 kV Gas-Insulated Switchgear: Field Tests and Electromagnetic Transient Analysis

The special back feeding energization process involves several stages, including tie-transformer energization, GIS-busbar energization, and no-load line energization. These operations can generate transient overvoltages and impose considerable stress on equipment insulation. To investigate the associated transient characteristics, field tests were conducted at a 500 kV GIS substation. Transient signals were recorded during tie-transformer energization and GIS-busbar switching, and the responses at different stages were analyzed. An electromagnetic transient model was subsequently developed in PSCAD/EMTDC and validated against the field measurements. The validated model was then used to investigate the key factors affecting no-load line energization through a GIS outgoing bay. The results show that tie-transformer energization is dominated by nonlinear core excitation. As the system operating state is progressively established, the transient responses during GIS-busbar and transmission line energization are governed mainly by network parameters and switching conditions. During no-load line energization, the closing phase angle and closing resistor condition are the dominant factors affecting switching overvoltage. Degradation of the closing resistor weakens transient suppression and increases the insulation stress on connected equipment. These findings provide a technical basis for evaluating energization transients and optimizing operating conditions during the commissioning of 500 kV GIS installations.