BS 171-4:1978

National foreword
Cooperating organizations
Section one - Tappings
Clause
1 Scope
2 Requirements valid for all categories of voltage
     variation
2.1 General
2.2 Principal tapping
2.3 Specification of the tapping range
2.4 Short-circuit impedance specification
2.5 Load loss requirements
2.6 Requirements related to temperature rise
     (guarantees and tests)
2.7 Requirements related to operation at a voltage
     higher than the tapping voltage
3 Definition and additional requirements for constant
     flux voltage variation
3.1 Definition of constant flux voltage variation
     (C.F.V.V.)
3.2 Additional requirements for constant flux voltage
     variation (C.F.V.V.)
3.3 Separate winding transformers of rated power up to
     and including 3 150 kVA and a tapping range up to
     and including + or - 5%
4 Definition and additional requirements for variable
     flux voltage variation
4.1 Definition of variable flux voltage variation
     (V.F.V.V.)
4.2 Additional requirements for variable flux voltage
     variation (V.F.V.V.)
5 Definition and additional requirements for combined
     voltage variation
5.1 Definition of combined voltage variation (Cb.V.V.)
5.2 Additional requirements for combined voltage
     variation (Cb.V.V.)
Section two - Connections
6 Connections of phase windings
7 Phase displacement between windings
Appendix A Examples of specifications for transformers
            with tappings
Appendix B Transformer connections in general use
Figures

Requirements valid for all categories of voltage variation, additional requirements for particular types of voltage variation, connections of phase windings and phase displacement between windings.