Transformer Dyn11 connection: high voltage side triangle, low voltage side star and neutral line, high voltage and low voltage have a 30℃ phase difference
Transformer Yyn0 connection: high voltage side star, low voltage side star and neutral line, high voltage and low voltage no phase difference
Yyn0: means high pressure Y connection, that is, star connection, low pressure is also Y connection, low pressure neutral point leads out, high and low pressure side phase Angle is 0 on the clock.
Dy11: means high voltage D connection, that is, triangle connection, low voltage is Y connection, high and low voltage side phase Angle is the 11 o 'clock Angle of the clock, "11" means that the line voltage of the secondary side of the transformer lags behind the primary side voltage 330℃ (or 30 ℃ ahead).
There are three kinds of connections: star, triangle and zigzag. The high voltage windings are respectively represented by symbols Y, D, Z (capital letters); The medium-voltage and low-voltage windings are represented by Y, D and Z (lowercase) respectively. YN, ZN (high pressure neutral point) and YN, ZN (low pressure neutral point) respectively when the neutral point is extracted.
Different characteristics of the three commonly used binding groups:
Y connection: the characteristic of star connection is that the high voltage winding is the most economical. Star wiring allows for reduced insulation at the midpoint, allowing the transformer high-voltage windings to be classed insulated, thus reducing costs. The winding voltage of the star connection is equal to 1/√3 of the line voltage, and the winding current is equal to the line current. Star connection of the neutral lead can also be used for direct grounding, or through the arc suppression coil grounding, if not grounding can also be connected to the arrester, to prevent operating overvoltage and lightning overvoltage. In addition, the neutral point leads to ground, can also be used to achieve four - wire power supply. The main disadvantage of this connection is that there is no third harmonic current loop.
2. D connection: triangle connection is the most economical for the low-voltage winding of transformer with low voltage and large current. Because the triangle connection must be made equal insulation, not graded insulation, for the low-voltage winding, because the voltage is lower, this will not matter. The current in each phase winding of the triangle connection is only 1/√3 of the outgoing current. Triangle connection in the winding can flow zero sequence current and third harmonic current, produce flat zero sequence flux and third harmonic flux, so that the transformer induced electromotive force to avoid distortion.
3. Z connection: Z connection has the advantage of Y connection, the number of turns is 15.5% more than Y connection, and the cost is higher. Its zero sequence impedance is small, suitable for manufacturing grounding transformer. Because it can reduce the neutral point displacement, it is suitable for manufacturing low-voltage windings of medium and small-capacity transformers requiring unbalanced three-phase loads. In addition, to prevent lightning overvoltage also has a certain role.
The difference between Dyn11 and Yyn0:
Dyn11
Because the high voltage side is triangular wiring, when there is zero sequence flux or third harmonic flux in the transformer core, zero sequence electromotive force or third harmonic electromotive force is induced in the triangular winding. Because the induced electromotive force is three same phase, it is superposed in series in the triangular winding and produces the corresponding current. This zero-sequence (third harmonic) cycle current generates an antiflux that minimizes the zero-sequence (third harmonic) flux in the core, thus reducing the voltage shift at the neutral point of the star wiring windings on the low-voltage side. At the same time, the zero-sequence (third harmonic) induced electromotive force in the
high-voltage side winding is reduced to the minimum, so as to avoid the voltage waveform pollution in the high-voltage side power grid caused by the distortion of the low-voltage
side load current waveform. Therefore, the transformer with triangular wiring can prevent the influence of third harmonic or zero sequence flux on the voltage waveform of the high voltage side power supply. In addition, this coupling method also has a good effect on preventing the overvoltage of lightning intrusion wave. Because the three-phase lightning intrusion wave is also in the same direction, this situation is similar to the zero-sequence current. The circulating current generated in the triangular winding also has an inhibitory effect on the magnetic flux generated by the lightning current in the three-phase iron core of the transformer.
Yyn0
Y= Primary star connection
N=Primary Neutral
y=secondary star connection
n=secondary neutral
and
0=No phase shift between primary and secondary.
In this connection combination, there is a neutral line on the low-voltage side, and the third-harmonic current in the low-voltage load and the zero-sequence current in the three-phase unbalanced load can flow through the neutral line in the transformer windings. If iron core for three phase three columns, three times with zero sequence current and harmonic current in the winding cannot be formed in the core of toroidal flux produced by the closed loop (three times because the three-phase core column of harmonic magnetic flux and the zero sequence current magnetic flux is same direction), only the more the core by the transformer insulating medium (transformer oil) and body iron metal core again. Because the magnetic resistance of the insulating medium outside the core is large, the zero-order flux and third-harmonic flux are small. But by its induction generation of zero sequence electromotive force and three harmonic electromotive force, superimposed on the phase voltage, so that three-phase voltage asymmetry, cause the neutral point displacement, some phase voltage, some phase voltage reduced. In order to prevent serious asymmetric three-phase voltage from affecting normal power consumption, the industry standard SD-292-1988 "Overhead Distribution Lines and Equipment Operation Regulations (Trial)" stipulates that the unbalanced degree of three-phase load should not exceed 15%. A small amount of single-phase load is allowed in the three-phase transformer, but the neutral line current should not exceed 25% of the rated current. Therefore, this provision is made in order to limit the neutral point displacement voltage to about 5%.
