45 5655 EE422 2016 1 1 1 Open Delta Transformers Connection
45 5655 EE422 2016 1 1 1 Open Delta Transformers Connection
45 5655 EE422 2016 1 1 1 Open Delta Transformers Connection
A1
A2
B1
B2
C1
C2
Opendelta
c1
a2
A1
B1
A2
b1
b2
B2
c2
Opendelta
c1
a2
A1
B1
A2
b1
b2
B2
c2
Opendelta
a1
b1
a2
b2
c1
c2
Opendelta
a2
a1
A1
A2
b2
b1
B1
B2
c1
c2
Vab = V0
Vbc = V 120
a1
b1
a2
b2
c1
c2
Opendelta
a2
a1
A1
A2
b2
b1
B1
B2
c1
c2
Vab = V0
Vbc = V 120
a1
b1
a2
b2
c1
c2
= V0 V 120
= V + 0.5V + j 0.866V
= (0.5 + j 0.866)V
= V120
Opendelta
a2
a1
A1
A2
b2
b1
B1
B2
c1
c2
Vab = V0
Vbc = V 120
a1
b1
a2
b2
c1
c2
= V0 V 120
= V + 0.5V + j 0.866V
= (0.5 + j 0.866)V
= V120
Vca = V120
a1
b1
I c2 a2 = I120
a2
Va2b2 = V0
I a2b2 = I0
I b2c2 = I 120
Vbc = V 120
b2
c1
c2
Vca = V120
a1
b1
I c2 a2 = I120
a2
Va2b2 = V0
I a2b2 = I0
I b2c2 = I 120
b2
c1
Vbc = V 120
I a2 = I a2b2 I c2 a2 = I0 I120 = I 30
c2
Vca = V120
a1
b1
a2
Va2b2 = V0
I c2 a2 = I120
I a2b2 = I0
I b2c2 = I 120
b2
c1
Vb2c2 = V 120
c2
I a2 = I a2b2 I c2 a2 = I0 I120 = I 30
I c2 = I c2 a2 I b2c2 = I120 I 120 = I90
a2
b2
N.B.: Line currents have the same values and angles even if the load was
star connected
c2
st
1 Transformer :
2 nd Transformer :
Vbc = V 120
I c2 = I90
I a2
Va2b2 = V0
I a2 = I 30
Va2b2 = V0
I c2
Vb2c2 = V 120
I c2 = I 90
S T1
ST 1 = Va2b2 I
= (V0 )(I30 )
= VI30
S VV
*
a2
S VV = S T 1 + S T 2 = 3 VLine I Line
ST 2 = Vb2c2 ( I c2 )*
= (V 120 )(I90 )
S T2
= VI 30
Q T1 = Q T 2
1
= (VLine I Line )
2
I Line = I Phase
A1
B1
A2
B2
Deratingofopendelta
S = 3 V phase I Phase
S VV = S T 1 + S T 2 3 VLine I Line
= 3 VLine ( I Phase )
= 3 VLine I Phase
SVV
1
57.7%
S
3
I Line = I Phase
A1
B1
A2
B2
Deratingofopendelta
S = 3 V phase I Phase
S VV = S T 1 + S T 2 = 3 VLine I Line
= 3 VLine ( I Phase )
= 3 VLine I Phase
SVV
1
57.7%
S
3
I Line = I Phase
A1
B1
A2
B2
Deratingofopendelta
S = 3 V phase I Phase
S VV = S T 1 + S T 2 = 3 VLine I Line
= 3 VLine ( I Phase )
= 3 VLine I Phase
SVV
1
57.7%
S
3
I Line = I Phase
A1
A2
B1
B2
IAB
IB
IBC
Opendelta
Disadvantages:
- De-rated operation, 57.7% of
bank; (3/2) = 86.6% of the capacity
of the remaining two transformers
-Average P.F. of V bank < Load P.F.
( 86.6% of balanced load P.F.);
The two transformers operate at
different power factors; for a
balanced load P.F. of cos, one
transformer has a P.F. of cos(30-)
while the other has a P.F. of
cos(30+),
accordingly
voltage
regulation differs.
- Accordingly, increasing load (even
if perfectly balanced), causes
terminal secondary voltages to be
unbalanced
Two single phase 150 kVA, 7200/600 V transformers are connected in open
delta configuration. Find the maximum three phase load supplied.
Rated Secondary current of either transformer = 150 000 / 600 = 250 A
This current should not be exceeded whatever was the type of connection,
Accordingly:
(S Load )maximum =
B1
B2
C1
C2
OpenYOpenDelta
A1
B1
n
A2
B2
OpenYOpenDelta
Disadvantages:
- Very large return current flow
in neutral of primary