The clock representation is usually used to distinguish different connection groups, that is, the line voltage phasor of the primary side winding and the secondary side winding is used as a long needle and a short needle on the clock surface, and the long needle represents the primary side winding (high voltage) and fixed. Pointing to 12 o'clock, the short needle represents the secondary side winding (low voltage), and the hour point it refers to is the wiring group number. The clock is divided into 12 grids, each grid is 30°. The phase relationship between the long and short needles can be used to obtain the phase relationship of the voltage of the primary and secondary windings. If the long and short needles point to 12 points, it means that the voltage phase of the first and second side windings is the same, and the wiring group is 12, that is, Yy0; if the long needle points to 12 points and the short needle points to 11 points, it means one. The voltage difference between the secondary windings is 30°, and the wiring group is 11, which is Yd11.
There are 12 types of wiring groups for three-phase transformers, that is, there are 12 groups, which are represented by 0 to 11, respectively, with or without commas between the wiring symbols. Where the primary side winding is different from the secondary side winding connection, such as Y/â–³ or â–³/Y, it belongs to the odd array of 1, 3, 5, 7, 9, and 11, for a total of 6 groups; where the primary winding and the secondary side When the windings are connected in the same way, such as Y/Y or â–³/â–³, they belong to 0, 2, 4, 6, 8, 10 even arrays, and are also 6 groups.
The windings are mainly in the form of star, triangle and zigzag. The high voltage windings are indicated by uppercase letters Y, D and Z respectively; the low voltage or medium voltage windings are indicated by lowercase letters y, d and z, respectively. When there is a neutral line, the letter N or n is added instead of 0, such as YN, ZN and yn, zn.
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