vector group

Why is vector group important?

• Because it determines the phase angle displacement between the primary (HV) and secondary (LV) windings.

If the vector-group is changed from Yd11 to Yd1, how will it affect generator synchronization?

  

• The Yd11 has an HV to LV phase angle displacement of plus 30°, while that of the Yd1 is minus 30°. Synchronization could be done if the HV and LV configurations were reversed, i.e., Yd11 and Dy1 in parallel. But, it is not possible if the Yd1 were to be paralleled with a Yd11 if the primary of both transformers were supplied from the same source.

Phase displacement:

• Phase rotation is always anti-clockwise. (international adopted convention) 
• Use the hour indicator as the indicating phase displacement angle. Because there are 12 hours on a clock, and a circle consists out of 360°, each hour represents 30°. 
• Thus 1 = 30°, 2 = 60°, 3 = 90°, 6 = 180° and 12 = 0° or 360°. 
• The minute hand is set on 12 o'clock and replaces the line to neutral voltage (sometimes imaginary) of the HV winding. This position is always the reference point. 
• Because rotation is anti-clockwise, 1 = 30° lagging (LV lags HV with 30°)and 11 = 330° lagging or 30° leading (LV leads HV with 30°)