2. For the power transformer in part (i), state the vector group symbol, sketch the vector diagram and explain the practical significance of this information.

The transformer we had discussed in our previous section has a vector transfiguration of YNd1. These vector groups are important because it helps us to determine the phase displacement between the primary and secondary side. They are also quite important to design a transformer system and deduce whether two or more transformers could be operated in parallel or not. Besides, when phasing

Transformer vector groups have been divided into 4 major groups as shown below:

Group1: 00 phase shift Yy0, Dd0, Dz0, Zd0

Group 2: 1800 phase shift Yy6, Dd6, Zd6, Dz1

Group 3: -300 phase shift Dy1, Yd1, Yz1, Zy1

Group 4: +300 phase shift Dy11, Yd1, YNd11, Yz11, Zy11

From the above group division table, it can be seen that YNd1 lies in group 4. Each term has its significance which is explained clearly below:

YNd1- High Voltage winding is Y connected with neutral terminal and Low Voltage winding is Delta connected. The phase angle of the LV winding lags the HV by 30 degrees.

Y written in capital signifies that the primary side is connected in star at high voltage.

N in the middle signifies that neutral is available and is connected to primary side.

d written in small letter means that the secondary side is delta connected with low voltage winding.

1 signifies that there is a phase shift of 300, where LV lags the HV.

Three phase transformers are allotted symbols giving the type of phase connection and the phase difference between the HV and LV terminal.

Figure below show s the YNd1 connection and its vector representation:

Fig: YNd1 group

http://books.google.com/books?id=uugjB9YAsnUC&pg=PA84&dq=Yd1+transformer&ei=CwYUStz6HY6WkQS0pKHtCQ#PPA83,M1

http://books.google.com/books?id=paPKsOXn5FMC&pg=PA482&dq=Yd1+transformer&ei=xlIVSpjZCI7UlQSs-9iIAg#PPA482,M1