There are a total of 12 types of outdoor three-phase power transformers, but in order to avoid confusion in manufacturing and use, China has only 5 types of three-phase dual-winding power transformers: Yyn0, Yd11, YNd11, YNy0 and Yy0.
Standard group application
The outdoor power transformer of the Yyn0 group is used in a three-phase four-wire power distribution system to supply power to the hybrid load of power and lighting;
The three-phase transformer of the Yd11 group is used in the line with a low voltage higher than 0.4kV;
The power transformer of the YNd11 group is used in a high voltage line to be grounded at a neutral point above 110kV;
The three-phase power transformer of the YNy0 group is used in the system where the primary side needs to be grounded;
The outdoor three-phase power transformer of the Yy0 group is used to supply power to the line of the three-phase power load.
In the connection group of the power transformer, “Yn” indicates that the primary side is a star-belt neutral line, Y represents a star, n represents a neutral line, and “d” indicates that the secondary side is a delta connection. “11” indicates that the line voltage Uab on the secondary side of the three-phase transformer lags the primary side line voltage UAB by 330 degrees (or 30 degrees ahead).
The representation of the connection group of the outdoor transformer is: uppercase letters indicate the primary side (or primary side) wiring, and lowercase letters indicate the secondary side (or secondary side) wiring. Y (or y) is a star connection and D (or d) is a delta connection. The number uses the clock notation to indicate the phase relationship of the primary and secondary side line voltages. The primary side line voltage phasor is used as the minute hand, the fixed finger is at the 12 o’clock position, and the secondary side line voltage phasor is used as the hour hand.
“Yn, d11”, where 11 means that when the primary side line voltage phasor is used as the minute hand at the position of the clock 12 o’clock, the line voltage phasor of the secondary side is at the 11 o’clock position of the clock. That is, the line voltage Uab of the secondary side lags the primary side line voltage UAB by 330 degrees (or 30 degrees ahead).
There are four basic connection forms for the three-phase transformer wiring: “Y, y”, “D, y”, “Y, d” and “D, d”. China only uses “Y, y” and “Y, d”. Since the Y connection is also provided with a neutral line and no neutral line, without the neutral line, no symbolic representation is added, and the neutral line is indicated by the letter n after the letter Y.
Three-phase transformers in the power system and three-phase controllable rectifier trigger circuit, will encounter the polarity of the transformer and the wiring problem of the connection group. The connection group of the transformer winding is different from the original and secondary three-phase windings of the power transformer, so that the phase relationship of the corresponding line voltages between the primary and secondary sides is different to divide the connection group.
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