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# Two methods for judging transformer connection group

For technicians engaged in the operation, maintenance and management of high and low voltage power grids, it is necessary to be able to quickly and accurately determine the transformer connection group number.

1 transformer connection group label common determination method
Determine the transformer connection group number usually adopts the international clock representation, that is to say the original winding wire electromotive force vector EAB as the clock pointer fixed finger "12" position, the secondary winding electromotive force vector Eab as the hour hand to the clock that figure, The figure is the three-phase transformer connection group label. The following Yy0 as an example, set out to determine the specific steps of the connection group label. Draw the original winding and secondary winding wiring diagram (see Figure 1 (a)). Note drawing the same column winding up and down alignment, to find the same core winding induced electromotive force with the same polarity.
The connection group of three-phase transformer is determined by the phase difference between the potential of the secondary side line and the line potential corresponding to the primary side. It is not only related to the winding method of the winding and the connection method of the three-phase coil, but also to the leading and end marks of the winding . The simple method of distinguishing is similar to converting different quantities into digital quantities, that is, the three are respectively represented by three simple Arabic numerals, and the algebraic sum of the three numbers determines the connection group of the three-phase transformer. The  application, the connection group to determine the three-phase transformer connection group diagram. Specific operations are as follows:
(1) According to the connection group diagram to determine the original, secondary winding wiring.
(2) When the same core column on the original, secondary windings of the same name at the same end, take the number "12" or "0"; otherwise, take the number "6". That is the same name at the same end, the same core column on the original, the winding voltage in phase, the short needle clock and long needle coincidence; the contrary, the clock short needle and long needle in the opposite direction.
(3) The deputy phase voltage terminal symbol shift is based on the three-phase power supply voltage three-phase symmetry, each adjacent two-phase mutual difference of 120 ° between the phase sequence connection, each move backward 1 (ie a core column) (120 ° / 30 ° = 4), that is, the auxiliary phase voltage terminal symbol is shifted backward by 1 "4" (4x30 ° = 120 °) Move back the two core columns with "8" (8x30 ° = 240 °).
(4) When the phase sequence is connected to the primary stage, it means that the secondary stage corresponds to the line voltage hysteresis of 30 ', or the primary line voltage leads the auxiliary line voltage by 30 °. Therefore, "-1", while the number of vice-level take the opposite of the original level.With the phase sequence connection refers to the three-phase winding arranged by UVW phase sequence,  phase sequence connection refers to the three-phase winding arranged by UWV phase sequence.
(5) Algebraic sum of the above three determines the connection group of the three-phase transformer. When its algebra and greater than 12 and less than 24, the algebra and minus 12, the result is the connection group number.
(6) Inverse application of the method: ① The primary phase voltage terminals are arranged from left to right according to the U-V-W phase sequence. ② determine the original, vice-level windings of the same name. Only in-phase and anti-phase two possibilities, namely, "12" and "6" two figures. ③ determine the deputy phase voltage terminal symbol is shifted, every right shift by 1 "4", so there are numbers "0", "4", "8" three cases. ④ determine the phase sequence △ winding. The primary △ connection to take "-1" when the sequence connection, take the "+1" for the  phase sequence connection, the secondary winding is the opposite. If the original, vice-level wiring in the same form, the first three figures to take "0". ⑤ so that the three algebra and just know the number of clocks. For even connection group, if can not meet the known number of clocks, the first number ② take another possible number. For odd-numbered connection groups, two connection methods may appear, but the correctness of the connection is not affected and can be  according to the actual situation.
2, the line voltage focus on legitimate working principle
For a long time, the line voltage method has been used. Due to the International Electrotechnical Commission (IEC) recommended a new method, that is, the center line of the line voltage triangle overlap using phase diagram to determine the winding junction group method, referred to as line center of gravity coincidence. This method compared with the traditional line voltage method, that is simple and . China's standard "GB1094-85" also used this method. Now introduced as follows, whether it is shaped, shaped or shaped connection of the winding, the phasor diagram of the three vertices line, you can form a triangle, known as the line voltage triangle. The centers of gravity of the high and low voltage winding wire voltage triangles are superposed together, and the center of gravity is respectively connected to the corresponding wire ends of the same phase of the high voltage and the low voltage, for example, by the center of gravity, and the longer wire segment Of the minute hand, and the shorter line (ie, low pressure side) that the clock's hour hand, then the hour hand shows the number of hours is the group.
Three-phase transformer is an important electrical equipment in the power system. Since the three-phase windings of the three-phase transformer are co-located on a core connected to a magnetic circuit, the connection mode is directly related to the circuit system. If the transformer is not connected in the installation process Correct, not only can not normally supply power to the device, there may be harm to the equipment and even the power grid. Therefore, the three-phase transformer connection label for its normal operation is extremely important, we must correctly judge. The three-phase transformer connected to the desired connection group or the three-phase transformer has been connected to determine the group, is the electrical installation of a very important issue.
The above method is used to determine the coupling group is consistent with the results obtained by the traditional line voltage method. Because the center of gravity of the two equilateral triangles coincide, the angle between the corresponding neutral line and the corresponding edge is always equal, so the phase relationship between the phasor represented by the corresponding neutral line is exactly the same as that of the line voltage represented by the corresponding edge The same phase relationship between. Traditional clock time series and the national standard GB1094-85 clock timing is basically the same, but the traditional clock time series, the standard GB1094-85 provisions "" said. 