ICS 17.220.01; 29.240.20                         ETD 20

NATIONAL FOREWORD

This Indian Standard (Part 3) which is identical with IEC 60909-3 : 2009 ‘Short-circuit currents in three-phase a.c. systems - Part 3: Currents during two separate simultaneous line-to-earth short circuits and partial short-circuit currents flowing through earth’ issued by the International Electrotechnical Commission (IEC) was adopted by the Bureau of Indian Standards on the recommendation of Electrical Installations Sectional Committee and approval of the Electrotechnical Division Council.

This standard was first published as IS 5728 : 1970 ‘Guide for short-circuit calculations’, which was superseded by IS 13234 : 1992 ‘Guide for short-circuit current calculation in three-phase ac systems’.

IS 13234 : 1992 and was identical to IEC 60909 : 1998, which has been superseded by IEC 60909 series of standards. This standard is one of the IS 13234 series of standards which are identical with

IEC 60909 series of standards. Other parts of IS 13234 series are:

Part 0 Calculation of currents

Part 1 Factors for the calculation of short-circuit currents in three-phase a.c. systems according to IEC 60909-0

Part 2 Data of electrical equipment for short-circuit current calculations

Part 4 Examples for the calculation of short-circuit currents

The text of IEC Standard has been approved as suitable for publication as an Indian Standard without deviations. Certain 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.