The rated current and short-circuit current of the large-capacity generator circuit breaker (GCB) far exceed the limit of a single vacuum circuit breaker (VCB). In this paper, a large-capacity GCB scheme based on multiple VCBs in parallel was proposed, focusing on the parallel current-sharing characteristics. Firstly, the current-sharing path and current transfer path were clarified, and a complete and specific circuit model was established. Secondly, the product variability of the vacuum interrupter (VI) and the action dispersion of the operating mechanism would cause the “current unbalance” problem. The influence rule of impedance matching, arc voltage, arcing synchronization, and other factors on the current-sharing characteristics was studied in detail, and the method that can effectively improve the static and dynamic current-sharing was proposed. In addition, the phase-to-phase electromagnetic field would cause the current of each VI in single-phase GCB to have an obvious phase difference, which greatly reduced the current-sharing effect. The electromagnetic shielding shell (ESS) installed on the GCB could effectively shield the external electromagnetic field and significantly improve the current-sharing effect. The improved ESS significantly reduced phase-to-phase magnetic leakage and avoided magnetic field pollution. Finally, the current-sharing experiment of the prototype proved that the proposed scheme could achieve a better parallel current-sharing effect, which may initially solve the problem of the insufficient current carrying capacity of the VCB.

This study investigated lightning-induced damage of optical fiber overhead ground wires (OPGWs) through damage measurements, numerical simulations and influencing factor analysis. A high-precision damage measurement method was proposed to calculate the lightning damage volume based on laser profile scanning and a developed data processing program. The time-and-space-varying current and heat flows obtained from an arc magnetohydrodynamic model were loaded on OPGWs by stepwise segmental injection to establish a coupled arc-thermal-electric model and simulate the heating and damage behavior of OPGWs. The comparisons indicated that the simulated metal phase transition region agreed well with the actual damage distribution, and the area surrounded by the aluminum melting point isotherm provided a good prediction of the arc sweep damage. The hysteresis of the temperature rise suggested that lightning damage was dominated by heat flow conduction rather than the Joule heating effect. Furthermore, the continuing current was the main cause of severe damage. The damage volume increased linearly with increasing charge transfer. As the discharge gap increases, the arc loading intensity decreases, but the damage volume undergoes a non-monotonic change, which is due to the complex variations in the arc attachment area regulated by the discharge gap and current intensity.

The lightning test method with a single lightning component C was found to be inappropriate to simulate the lightning effect on optical-fiber overhead ground wires (OPGWs). This study establishes a multiple lightning current test system, including intermediate current component B and continuing current component C, to investigate the lightning test method for OPGWs. The lightning characteristics and damage performance of OPGWs with different test conditions under multiple sequential lightning currents were experimentally evaluated via visual inspection and infrared temperature measurement. The test results indicated that the lightning damage of OPGWs was not only related to the parameters of the applied lightning current but also the experimental method. The lightning erosion degree and surface temperature of OPGWs increased as the transfer charge of current component C increased. When the transfer charge was approximately 200 °C, the surface temperature exceeded 3600 °C. Moreover, as the discharge gap increased from 5 cm to 6 cm, the temperature decreased, and the lightning damage degree, particularly the number of broken strands, decreased accordingly. The research on the lightning test method in this paper may provide experimental support and a theoretical basis for a proper evaluation of the lightning protection performance OPGWs and the study of the lightning effect mechanism.