Anode thermal process in high current vacuum arc under low frequency AC discharge condition

Low frequency AC transmission systems exhibit extensive application prospects in scenarios such as long distance offshore wind power transmission and have garnered significant attention in developing eco-friendly power systems. Compared with conventional 50 Hz AC systems, low frequency systems demonstrate prolonged short-circuit current duration with distinct vacuum arc characteristics. Consequently, this study conducts numerical analyses of arc evolution dynamics and anode thermal processes in 20 Hz vacuum interrupters to evaluate the applicability of standard 50 Hz vacuum circuit breakers under low frequency conditions. Results reveal that reduced frequency alters the coordination between arc current and contact gap, intensifying arc constriction during later arcing stages for 20 Hz vacuum arc, thereby elevating the plasma parameters, including pressure, temperature, and current density. Under specified conditions, namely 60 mm contact diameter, 2.0 m/s contact opening speed, and 10 kArms short-circuit current, the peak anode heat density reaches 5.2 × 108 W/m2 for 20 Hz arcs, exceeding the maximum value of 50 Hz with 4.1 × 108 W/m2 by 26%. The 20 Hz arc anode further maintains elevated temperatures for extended duration, attaining a peak center temperature of 1795 K, which is 64% higher than the 50 Hz value of 1095 K. These findings provide theoretical guidance for designing low frequency vacuum interrupters.