In high-voltage power systems, overload or short-circuit accidents occur frequently owing to the failure of the user equipment, leading to the occurrence of power accidents. Therefore, protective relays must be installed before and after each feeder to isolate the occurrence of faults and thus reduce damage to the power system. However, when the working power supply of the protective relay loses power, it will not be possible to isolate the accident feeder, and the failure of the power system will expand, severely affecting the reliability of the system power supply. Therefore, it is expressly stated by the Taiwan Power Company that a capacitor trip device (CTD) must be installed to ensure a power supply to the protective relay for high-voltage users. However, CTDs currently on the market often fail to ensure the proper operation of the protective relay owing to an insufficient capacitance or a low output operating voltage. Therefore, we propose a high-capacity CTD capable of performing self-tests and instant notification for network monitoring. Compared with the conventional CTD, our CTD can prevent instantaneous large current transfer to the powered device, ensuring that the power supply of the powered device is uninterrupted. It can accomplish the real-time monitoring of the power status, provide a stable power supply, prevent overcurrent, and protect equipment. It is a very important contribution to the protection of the relay system.