This standard applies to on-load tap-changers* for power transformers and their motor-drive mechanisms. It relates mainly to tap-changers immersed in transformer oil according to IEC Publication 296, but may also be used for gas-insulated tap-changers in so far as conditions are applicable.Note.- For the purpose of this standard, a synthetic insulating liquid is regarded as an oil. A synthetic insulating liquid can be used for a tap-changer only if it is compatible with the tap-changer design.Tap-changers for transformers for railway rolling stock are excluded from this standard.In selecting a tap-changer for a particular application, reference should be made to IEC Publication 542.