Combinations of transformer winding connections
Primary Secondary Common Uses
Industrial applications
Star (Y) Star (Y)
Commercial and industrial
Star (Y) Delta (∆)
(most common method)
High voltage transmissions
Delta (∆) Star (Y)
Rarely used - causes harmonics
Delta (∆) Delta (∆)
and balancing problems

120 V ! 0 o
+ -
+
winding 120 V
failed open! ! 120o
-

!

!

m a three-phase transformer bank is paying attention
ed to denote “polarity” of windings). Remember the prop
hase windings of ∆ and Y: (Figure 10.41)
+ !0 -
o
+ +
!0 o
! 120 o
- -
- - +
! 240 o ! 240o ! 120 o
+ -
+
(Y) ( ")
he center point of the “Y” must tie either all the “-” or a
The winding polarities must stack together in a comple

STAR and DELTA connection of
Three-phase Squirrel-cage Electric Motors
STAR DELTA
L1 L2 L3 E L1 L2 L3 E
To change direction of rotation swap any two Life (L1, L2, L3) inlet leads.