China’s revised national standard for transformer oil, GB 2536-2025, Unused Mineral Insulating Oil for Electrical Fluids, Transformers, and Switchgear, took effect July 1, introducing stricter technical requirements for mineral insulating oils used in electrical equipment. The updated standard replaces the 2011 edition and strengthens controls on additives, base oil quality and performance characteristics, reflecting higher technical requirements for transformer and switchgear applications.
The revised specification comes as electrical infrastructure continues to demand higher reliability and performance from insulating fluids. By tightening quality and testing requirements, the standard establishes more rigorous criteria for oils used in increasingly demanding power transmission and distribution systems, including ultra-high-voltage and extra-high-voltage equipment.
GB 2536-2025 requires tighter control over the use of metal passivators and mandates reporting of additive types and concentrations. It also introduces requirements covering the degree of base oil refining and natural corrosion resistance. New performance indicators include color limits of less than 1.5 for general oils and less than 0.5 for specialty oils, along with limits for potentially corrosive sulfur and dibenzyl disulfide. Additional requirements covering surface tension and gas-generating properties are intended to improve performance in high-voltage applications.
The new standard “imposes substantially stricter requirements in three key areas,” strengthening controls over formulation, quality and performance for transformer oils used in China’s electrical sector.