In transportation infrastructure, lighting systems in highway tunnels and rail transit directly affect operational efficiency and travel experience. Traditional AC lighting systems suffer from high energy consumption, prominent safety risks, and complex management challenges. Delta has applied its high-voltage DC technology—originally developed for data centers—to deliver DC lighting solutions for the Kezhu Expressway Tunnel and Ningbo Rail Transit Line 8. These implementations address key industry pain points and create significant value.

Building smart tunnels: Kezhu Expressway lighting failure rate reduced by 40%, energy efficiency improved by 30%
The Kezhu Expressway is a key infrastructure project in Zhejiang province, featuring seven tunnels along its route, with bridges and tunnels accounting for as much as 72.5% of the total length. Traditional lighting systems often face issues of high energy consumption or poor stability in such complex terrain. Delta has implemented a 400V DC intelligent lighting solution across all seven tunnels, equipping them with 16 units of 400V DC cabinets and 5,000 DC lighting drivers. This setup fully leverages the advantages of centralized DC power supply and precisely meets the lighting needs of tunnels.
Delta has implemented a 400V DC intelligent lighting solution across all seven tunnels on the Kezhu Expressway.

Tunnel clusters have a large lighting load, and when using traditional light sources, energy costs can account for over 80% of total operating expenses. Delta’s centralized DC power supply offers higher reliability and efficiency, improving power conversion efficiency by about 6% under the same conditions. The enhanced lighting at tunnel entrances and exits adjusts automatically to the external brightness, achieving an energy-saving rate of over 30%. The system requires only positive and negative lines, eliminating the need for a ground wire and thereby reducing the risk of electric shock. Designed to withstand the high humidity, dust, and corrosive conditions inside tunnels, the luminaires feature excellent durability, effectively extending service life and ensuring operational stability. Dimming is achieved through low-frequency DC carrier control without additional wiring, which not only lowers installation costs but also enables precise energy management. Multi-channel input/output and a 1+ bypass mode ensure continuous lighting operation, while standard interface protocols support remote monitoring and management. Furthermore, each DC circuit requires only two cables, cutting construction costs by approximately 50% compared with AC systems.

Delta 400V DC centralized power supply system architecture diagram

Innovative rail transit application: Ningbo Metro Line 8 achieves over 20% energy savings with first large-scale deployment of DC lighting
Phase I of Ningbo Rail Transit Line 8 spans 23.3 kilometers and includes 19 stations. As a GoA4-grade fully automated line, it places higher demands on its supporting lighting systems. Delta applied its high-voltage DC modules—originally developed for data centers—integrated with DC carrier dimming, floating power supply, and insulation monitoring technologies, achieving overall energy savings exceeding 20%. Delta has deployed more than 500 DC power cabinets, 19 sets of control hosts with backend management software, and 50 sets of DC low-voltage distribution cabinets, providing comprehensive coverage for key areas such as station entrances and exits, platforms, showrooms, maintenance depots, and equipment levels.

The DC power system converts 380V AC mains power into a centralized, regulated 200–300V low-voltage DC supply. Through high-efficiency DC-DC conversion, it minimizes energy loss, achieving an overall system efficiency exceeding 92%. The innovative DC carrier dimming technology enables signal transmission directly through power cables, eliminating the need for additional control wiring and further enhancing energy efficiency. The floating DC power supply and insulation monitoring technologies fundamentally reduce the risk of electric shock while providing real-time safety alerts. The management platform supports automatic dimming and multi-scenario customization, allowing one-click switching between different lighting zones to achieve refined management and efficient operations.

These two major projects not only provide replicable models for upgrading lighting in the transportation industry but also mark Delta’s successful extension of high-voltage DC technology into transportation applications, injecting new momentum into the sector’s green and intelligent transformation.
Delta provides DC lighting solutions for the Ningbo Metro, achieving overall energy savings exceeding 20% across the entire line.