BS 171-3:1987

Foreword
Committees responsible
Clause
1 Definitions
2 General
3 Highest voltage for equipment and insulation level
4 Rules for some special classes of transformers
5 Insulation requirements and dielectric tests - Basic
    rules
6 Tests on a transformer having a tapped winding
7 Insulation requirements and test conditions for
    dry-type transformers
8 Repeated dielectric tests
9 Insulation of auxiliary wiring
10 Separate-source voltage withstand test
11 Induced overvoltage withstand test
12 Lightning impulse test
13 Test with lightning impulse chopped on the tail
14 Switching impulse test
Appendix A Application guide for partial discharge
            measurements during induced overvoltage
            withstand test on transformers according
            to Sub-clause 11.4
Appendix B Overvoltage transferred from the high-
            voltage winding to a low-voltage winding
Appendix C Information on transformer insulation and
            dielectric tests to be supplied with an
            enquiry and with an order

Applicable to power transformers (including auto-transformers) with the exception of small and special transformers listed in the scope of BS 171:Part 1.