NATIONAL FOREWORD

This Indian Standard which is identical with IEC 60422 : 2013 ‘Mineral insulating oils in electrical equipment - Supervision and maintenance guidance’ issued by the International Electrotechnical Commission (IEC) was adopted by the Bureau of Indian Standards on the recommendation of the Fluids for Electrotechnical Applications Sectional Committee and approval of the Electrotechnical Division Council.

This standard was first published in 1961 to cover the maintenance of insulating oil complying with IS 335 : 1953 ‘Insulating oils for transformers and switchgear’. The first revision was undertaken in 1978 to bring in line with the new oil requirements given in IS 335 : 1972 ‘Specification for new transformers and switchgear’. The second revision was carried out to align with the corresponding IEC 60422 (1973). The third revision has been aligned with IEC 60422 (1989) ‘Supervision and maintenance guide for mineral insulating oils in electrical equipment’ issued by International Electrotechnical Commission. Values of permissible limits, relating to resistivity, dielectric dissipation factor (Tan delta) and neutralization value of oil have been aligned with those in IEC 60422 (1989). This revision has been undertaken to align the standard with the latest edition of IEC 60422 to harmonize it with the latest developments that have taken place at the international level.

The text of IEC Standard has been approved as suitable for publication as an Indian Standard without deviations. Certain terminology and conventions are, however, not identical to those used in Indian Standards. Attention is particularly drawn to the following:

a) Wherever the words ‘International Standard’ appear referring to this standard, they should be read as ‘Indian Standard’.

b) Comma (,) has been used as a decimal marker, while in Indian Standards the current practice is to use a point (.) as the decimal marker.