Pre-Construction Carbon Accounting of Transmission and Substation Equipment: Methodology and Application

Accurate pre-construction carbon accounting for power equipment is critical for grid decarbonization, yet a standardized methodology applicable to transmission and substation projects remains lacking. This study develops a pre-construction carbon accounting methodology for transmission and substation equipment and applies it to a 220 kV project in China, employing localized emission factors and investment-based screening to identify nine key equipment categories. The analysis quantifies carbon emissions in raw material extraction and manufacturing stages, yielding 23 154 tCO2. Results show that substation equipment, despite its compact footprint, accounts for 35% (8087 tCO2) of total emissions—disproportionately high relative to the 30 km transmission line. Emissions are highly concentrated: aluminum conductor steel-reinforced (ACSR), gas-insulated switchgear (GIS), and steel towers collectively contribute nearly 90%, with aluminum dominating ACSR and GIS emissions due to its high emission intensity (28.5 tCO2/t). Sensitivity and scenario analyses identify aluminum and steel emission factors and GIS aluminum mass as the dominant uncertainty sources. The low-carbon scenario demonstrates a 34.7% abatement potential (8024 tCO2) through hydropower-based aluminum, direct-reduced iron–electric arc furnace (DRI–EAF) steel, and compact GIS design, while the equipment-level emission hierarchy remains stable across all scenarios. These findings underscore that material decarbonization and compact design, pursued synergistically, offer high-impact pathways for pre-construction emission reduction.