Abstract : A stable and reliable control and voltage regulation power supply system is crucial for the safe, stable, reliable, and economical operation of modern hydropower plant automation systems. After technical upgrades, the secondary equipment control and voltage regulation power supply at Lushui Hydropower Plant reduced intermediate links in the power supply system and lowered the failure rate of secondary equipment caused by power supply failures. Keywords : Hydropower plant; Voltage regulation power supply; Inverter; Relay switching; Redundancy; Switching power supply; Bumper-free switching. Control and voltage regulation power supplies are widely used in industry, and their performance directly affects industrial production efficiency and product quality. This issue is even more prominent in power production, where the performance of the secondary equipment control and voltage regulation power supply directly affects the stability of the power system and the quality of power. With the development and rapid advancement of "unmanned" or "minimal" operation in hydropower plants, the application of "4C" technologies (Control, Computer, Communication, CRT) and "5 Remote" technologies (Remote Control, Telemetry, Remote Signaling, Remote Adjustment, Remote Viewing) in modern power systems is becoming increasingly widespread and developing rapidly. This provides a broad development space for power plant automation systems while simultaneously placing higher demands on the automation of hydropower plant production operation and management. Modern hydropower plant automation systems have become integrated systems combining computers, control, communication, networks, and power electronics. Therefore, the control and voltage regulation power supply for secondary equipment in hydropower plants must also adapt to these changing needs. A stable and reliable control and voltage regulation power supply system is a powerful pillar for the safe, stable, reliable, and economical operation of the power plant. The original control and voltage regulation power supply system for secondary equipment at the Lu Hydropower Plant varied depending on the time the equipment was put into operation, the manufacturer, and the type of equipment. To ensure the reliability of the power supply to the secondary equipment, traditional wiring typically used a combination of two or three power sources: 220V plant AC, 220V DC, and 220V inverter AC. Redundancy was achieved using relay switching circuits. Early secondary equipment mostly used a parallel power supply of 220V plant AC and 220V DC, with relay switching circuits providing redundant wiring. The control power was supplied from the plant AC after rectification and filtering. When the plant AC power was lost, the relay normally closed contacts switched to DC power supply. The wiring principle is shown in Figure 1. [b][align=center]For details, please click: Technical Upgrade of Secondary Equipment Control Power Supply at Lushui Hydropower Plant[/align][/b]