NDBU-95C Star connection branching unit ABB

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Overview

Essential details：NDBU-95C Star connection branching unit ABB

In the three-phase transformer, the three primary side coils and the three-phase AC power supply should be connected by two solutions, namely star connection and triangle 0 connection. As shown in Figure (a) and (b) below. When the star connection (Y-shape) is connected, when the first end 1U1, 1V1 and 1W1 are the leading end, the three phase ends 1U2, 1V2 and 1W2 are connected together to become the neutral point. If the neutral point is to be led out, it is marked with “N” and the connection mode is represented by YN. Similarly, the connection mode of the three secondary coils should also have these two connections.

The primary and secondary side windings of the three-phase transformer can be star connection and triangle connection. When the star connection is used, the neutral point can be drawn out or not, so that the primary and secondary side windings can have the following combination: Y/Y or Y/Yn; Y/△ or Yn/△; △/Y or △/Yn; △/△ and other connection modes.

However, these combined symbols are not enough to fully explain the connection relationship between primary and secondary windings, and the phase relationship of electromotive force between primary and secondary windings should be further illustrated by clockwise notation.

NDBU-95C

There are two hands on the clock dial, 12 characters, divided into 12 grids, each grid represents a clock, the Angle of a circle is 360 degrees, so each format is 30 degrees. In the clockwise direction of the short needle, for example, between 12 o ‘clock and 11 o ‘clock should be 30°*11=330°; If we turn the clock forward by 300 degrees, that must indicate that 300 degrees /30 degrees is equal to 10 points. The connection group of the transformer is the representation of the time meter indicating the phase relationship between the primary and secondary side voltages.

Because of the different wiring modes, there is a phase difference between the primary and secondary winding of the three-phase transformer. Take the primary line voltage as the long needle and fix it at 12 points, and the corresponding line voltage phasor at the secondary side as the short needle. If they are 330 degrees apart, the secondary line voltage phasor must fall at 330°/30=11 points, as shown in the figure on the right. If the difference is 180°, then the secondary voltage phasor must fall on 6 points, that is to say, this group of three-phase transformer wiring group belongs to 6 points.

As shown in the figure below, the primary and secondary side windings are not only Y connections, but also take the same polarity end as the first end of the primary and secondary sides. Therefore, it can be seen from the phasor diagram that the electromotive force of the primary and secondary sides is in the same phase, so it should be marked as “12”, that is, this connection is marked as Y/Y-12 connection group. The new standard uses (y, y0) to indicate that the polarity of the central side and the secondary side is different in Figure (b), so the 180° phase difference of the original secondary side can be seen in the same phasor diagram, so it should be marked as “6”, that is, this connection method becomes Y/Y-6 connection group (y, y6 in the new standard).

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