Fig. 1. Structure and triggering mode of the 28-stage LTD device

Fig. 2. Equivalent circuit for single-stage LTD

Fig. 3. Load current in the 28-stage LTD circuit model

Fig. 4. Voltage on gas switches in the 5^th stage module when the 1^st group prefire

Fig. 5. Transmission line voltage caused by cascading failure

Fig. 6. Voltage on gas switches in the upstream and downstream stage module when different groups prefire

Fig. 7. Distribution of peak field intensity of transmission line during normal sequential discharge

Fig. 8. Electric field strength at the transmission line of each stage when different groups prefire

Fig. 9. Electric field strength at the transmission line when the 7^th group prefire

Fig. 10. Negative peak voltage and peak field intensity of cascading failure with different bottom diameters of the 1^st group

Fig. 11. Load current of normal discharging with different bottom diameters of the 1^st group