Power Transmission Infrastructure Expansion and the Reshaping of Manufacturing Agglomeration: Evidence from China’s Ultra-High-Voltage Projects

This study examines how power transmission infrastructure expansion reshapes manufacturing agglomeration and regional industrial systems. Taking China’s ultra-high-voltage (UHV) transmission projects as a quasi-natural experiment, we investigate their impact on manufacturing agglomeration. Using panel data from 282 prefecture-level cities over the period 2006–2020, we adopt a comprehensive empirical strategy centered on a multi-period difference-in-differences (DID) framework, complemented by synthetic DID, propensity score matching, instrumental variable approaches, and double machine learning methods to ensure robust causal inference. The results show that UHV projects significantly promote manufacturing agglomeration, indicating a substantial reconfiguration of regional industrial systems. This effect operates through increased power supply in input areas, the release of resource advantages in output areas, and market scale expansion. Both input and output sides have significant positive effects, with a stronger impact from the input side. Moreover, government intervention and infrastructure development further amplify the agglomeration effect. Furthermore, the manufacturing agglomeration induced by UHV projects promotes economic growth, green development, and urban sustainability. These findings provide system-level insights into the role of power transmission infrastructure in energy–industrial integration and offer implications for the design and optimization of sustainable energy systems.