Connection section labels:
The connection section label represents the connection method of transformer windings and the symbol indicates the phase relationship of line potentials between the primary and secondary sides. The connection section label consists of two parts: characters and numbers. The characters on the left indicate the connection methods of the high-voltage and low-voltage windings, while the numbers on the right can be integers from 0 to 11. The number represents the magnitude of the phase shift of the low-voltage winding line potential concerning the high-voltage winding line potential, and multiplying this number by 30° gives the angle by which the low-voltage side lags behind the high-voltage side in terms of phase shift. This phase relationship is typically illustrated using the "clock representation method," where the primary side line potential vector serves as the minute hand of a clock fixed at the noon position, and the corresponding secondary sideline potential vector serves as the hour hand, pointing to the hour corresponding to the number in the connection section label.
Representation method:
In transformer connection sections, "Yn" indicates a connection with a star (Y) on the primary side and a neutral wire (n). "d" represents a delta (triangle) connection on the secondary side. "11" signifies that the line voltage UAB on the secondary side lags behind the line voltage UAB on the primary side by 330 degrees (or leads by 30 degrees).
The representation of transformer connection sections is as follows: uppercase letters indicate the connection method of the primary (or original) side, and lowercase letters indicate the connection method of the secondary (or secondary) side. Y (or y) denotes a star (Y) connection, and D (or d) denotes a delta (triangle) connection. Numbers use the clock representation method to indicate the phase relationship of line voltages on the primary and secondary sides, where the primary side line voltage vector acts as the minute hand, fixed at the noon position, and the secondary side line voltage vector acts as the hour hand.
"Yn, d11," where 11 indicates that when the primary side line voltage vector points to the clock's noon position, the secondary side line voltage vector is at the 11 o'clock position. In other words, the line voltage UAB on the secondary side lags behind the line voltage UAB on the primary side by 330 degrees (or leads by 30 degrees).
There are four basic connection forms for transformer connections: "Y, y," "D, y," "Y, d," and "D, d." In the case of the Y connection, there are two variations: with neutral wire and without neutral wire. The absence of a neutral wire is not represented with any additional symbols. In contrast, a neutral wire is indicated by adding the letter 'n' after the letter 'Y.'
Clock representation method: The high-voltage winding line potential is treated as the long hand of a clock, always pointing to the "12" position on the clock and the low-voltage winding line potential is treated as the shorthand, pointing to different hours based on the phase relationship between high and low-voltage winding line potentials.
Application of standard sections:
Yyn0 is used for three-phase power transformers in three-phase four-wire distribution systems, supplying mixed loads for power and lighting.
Yd11 is used for three-phase power transformers in low-voltage lines above 0.4 kV.
YNd1 is used for three-phase power transformers in high-voltage lines above 110 kV where the neutral point needs to be grounded.
YNy0 is used for three-phase power transformers in systems where the primary side needs to be grounded.
Yy0 is used for three-phase power transformers supplying three-phase power loads.