Three phase transformer in Yd connection
by Jakub Olichwier (2005)
The problem
The transformer is connected in Yd, input voltage is 400V. The task is to calculate the
output voltage and draw voltages. The ratio of transformer is equal 1.
Solution:
Interfacial voltage is 400V. In Y phase voltage is 3 smaller and equals 230V. The
turn ratio equals 1 so phase voltages in D are same as the ones in Y and equal 230V.
Interfacial voltages are the same as phase voltages and equal 230V.
To make vectors’ diagram, for Y connection, first we draw phase voltages’ vectors.
Their beginnings are in the same point (red vectors on graph a) and the angle between them is
120°. To draw interfacial voltages’ vectors we must sum phase voltages’ vectors. We ought to
get equilateral triangle based on interfacial voltages’ vectors.
To make vectors’ diagram, for D connection we must know that phase voltages in that
connection are the same as phase voltages id Y connection and they are parallel (compare
graph a and b to see that). In D connection phase and interfacial voltages are the same. That’s
why we draw only 3 vectors, but we must mark on the graph that they are equal (graph b).
Transformer’s scheme:
UCA
A
UAB
B
UA
UBC
C
UB
UC
Uca
Ua
Uc
Ub
a
Uab
b
Ubc
c
Graphs:
a)
b)
UCA
B
UC
UBC
UA
Ub=Uab
Uc=Ubc
UB
UAB
A
Ua=Uca
C