In fact, this problem is very simple! The wiring group of transformer is a representation of the combined wiring form of primary winding and secondary winding.
We usually have two common transformer windings, one is "triangular connection" and "star connection"; In the connection group, "d" refers to triangular connection, "yn" refers to star connection with neutral line, y refers to star, and N refers to neutral line; "11" refers to the line voltage UAB on the secondary side lagging behind the line voltage uab330 on the primary side (or leading 30 degrees).
Then the connection group is represented as follows: capital letters represent the wiring mode of the primary side (or primary side), and small letters represent the wiring mode of the secondary side (or secondary side). Y (or y) is star wiring, and D (or D) The number adopts clock representation to represent the phase relationship between the primary and secondary side line voltage. The primary side line voltage phasor is used as the minute hand, fixed at the position of 12 o'clock, and the secondary side line voltage phasor is used as the hour hand.
"YN, D11", where 11 means that when the line voltage phasor on the primary side is indicated as the minute hand at 12 o'clock, the line voltage phasor on the secondary side is at 11 o'clock. That is, the line voltage UAB on the secondary side lags behind the line voltage uab330 on the primary side (or 30 degrees ahead).
The two windings of transformer are combined to form four wiring groups: "Y, Y", "D, Y", "Y, D" and "D, D". Only "Y, Y" and "Y, D" are used in China . since there are two types of Y connection: with neutral wire and without neutral wire, without neutral wire, no symbol is added, and with neutral wire, the letter Y is followed by the letter n. n indicates that the neutral point has outgoing line. Yn0 wiring group, UAB coincides with UAB, and the hour and minute hands refer to 12. "12" is represented by "0" in the new wiring group.
The above knowledge, I hope to help you!