IEEE C57.12.70-2020 pdf free download – IEEE Standard for Standard Terminal Markings and Connections for Distribution and Power Transformers.
3. Definitions, acronyms, and abbreviations Standard transformer terminology available in IEEE Std C57.12.80 7 shall apply. For all other terms, consult the IEEE Standards Dictionary Online. 8 4. Marking of terminals and identification of windings
4.1 General The windings of a transformer shall be distinguished from one another as follows.
Two winding transformers shall have their windings designated as high voltage (HV or H) and low voltage (LV or X). Transformers with more than two windings shall have their windings designated as H, X, Y, and Z except where a specific IEEE C57 standard calls for a different designation e.g., IEEE Std C57.18.10-1998 (R2003) 6.9.3 b).
4.2 Sequence designation The highest voltage winding shall be designated as HV or H, except for transformers designed for three- phase to six-phase transformation (see Clause 8). The other windings, in order of decreasing voltage, are designated as X, Y, and Z. If two (or more) windings have the same voltage and different kilovolt ampere ratings, the higher kilovolt ampere winding receives the prior letter designation of the two (or more) letters available, according to the sequence by voltage as explained above. If two or more windings have the same kilovolt ampere and voltage rating, the designations of these windings are arbitrarily assigned.
4.3 External and Internal terminal designation In general, external terminals shall be distinguished from one another by marking each terminal with a capital letter, followed by a subscripted number. The terminals of the H winding are marked H 1 , H 2 , H 3 , etc. The terminals of the X winding are marked X 1 , X 2 , X 3 , etc. When two external terminals are connected to the same end of a winding, such as the terminals on loop feed transformers, they shall be identified by the same capital letter and subscripted numeral followed by an additional subscripted letter A or B, for example, H 1A and H 1B , H 2A and H 2B . The identification of external terminals shall be accomplished either by the use of the sketches on the nameplate showing locations of specific terminals, or by physically marking terminals. Internal winding termination shall be marked with numbers or letters in any manner that may permit convenient reference and that cannot be confused with the markings of the external transformer terminals.IEEE C57.12.70 pdf download.