IEC 60137:2008 gives the characteristics and tests for insulated bushings intended for use in electrical apparatus, machinery, transformers, switchgear and installations for three-phase alternating current systems, having highest voltage for equipment above 1 000 V and power frequencies of 15 Hz up to and including 60 Hz. Special requirements and tests for transformer bushings in this standard apply also to reactor bushings. This edition includes the following significant technical changes with respect to the previous edition: - Long duration power-frequency for transformer bushings; - Special requirements for type and acceptance tests applicable to transformer and GIS bushings; - Specific insulation levels for bushings fitted to transformers and GIS; - According to IEC Guide 111, clauses relating to safety and the environment have been added; and - The altitude correctino procedure has been revised (> 1 000 m).