Vector groups define the phase relationship between primary and secondary windings in transformers. There are 24 possible vector groups depending on whether the windings are star or delta connected. The vector group of transformers must be carefully selected to avoid circulating currents when transformers are connected in parallel, and to ensure the overall phase shift in a power system is zero at the distribution level. Vector groups are also chosen to allow proper grounding of generation, transmission and distribution networks.

1. Vector Group defines the relationship between the
Primary Voltage Vectors and the Secondary Voltage
Vectors. The Primary or Secondary Voltage Vectors may
Star or Delta.
 It is necessary to ensure that transformers to be
connected in parallel have the same vector group to
avoid circulating currents in the paralleled transformers
among other including same voltage level, same
percentage impedance and the same frequency.
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

2. The concept of vector groups was adopted for transformers in the Generation,
Transmission and Distribution Networks in a manner so as to avoid the transfer
of Zero Sequence Current from each of the networks into the other. Delta Blocks
the flow of Zero Sequence Current.
The vector groups was also chosen in manner so as to enable the Earthing or
grounding of the various networks to facilitate the control of earth fault current
by the use of Neutral Ground Resistor(NGR). Where the Network is solidly
earthed, the earthing system is designed based on the exact short circuit level of
the Network, be it Generation, Transmission and Distribution.
Resonant Grounding (Peterson Coil) is also used in countries like Germany,
where the Reactance of the Peterson coil is tuned to match the Fictitious
Capacitance of the network. This way the earth fault current is reduced to
approximately Zero at the instant of fault (Inductive Current minus (-) Capacitive
Current). By this means countries with these scheme do not normally trip on
earth fault.
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

3. The concept of vector groups was adopted for
transformers in the Generation, Transmission and
Distribution Networks in a manner so as to make
the overall phase shift Zero (0) at the Distribution
end close to the Customer.
The following slides analysis the various vector
group of the Generation, Transmission and
Distribution Network of the Ghana Power System.
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

4. Generation (Ynd1) Transmission (Ynd11)
Shifts Star ahead Delta Nullifies the Phase shift
by 30° by 30° by shifting Delta at 30 °
ahead Star
Distribution (MV) (Dyn1) Distribution (LV) (Dyn11)
Shifts Delta ahead Star Nullifies the Phase shift
by 30° by 30° by shifting Star at 30 °
ahead Delta
•RESULTANT PHASE SHIFT = ZERO (0)
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

5. It can be seen clearly that the Resultant Phase Shift in the
overall Vector Group of the Ghana Power System from
Generation through to the Distribution (LV) Network is
Zero (0). This way Customer end power is not affected by the
overall vector group of the power system.
The following slides show the various vector groups
available for Star-Delta, Star-Star, Delta-Star and Delta-Delta
Transformers.
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

6. Delta – Star
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
C B
A
Primary
Delta
Equi. Secondary
Star
Options of Naming Transformer Secondary
a
b
c
b
a
c
c
b
a
A AA
a
a a
11 3 7

7. Delta – Star
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
C B
A
Primary
Delta
Equi. Secondary
Star
Options of Naming Transformer Secondary
a
b
c
b
a
c
c
b
a
A AA
a
a a
5 9 1

8. As clearly shown above, there are six vector group options available for Delta –
Star Transformer Configuration. These are;
Dy1 Dy3 Dy5 Dyn1 Dyn3 Dyn5
Or
Dy7 Dy9 Dy11 Dyn7 Dyn9 Dyn11
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

9. Star – Delta
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
C B
A
Primary Star Equi. Secondary
Delta
Options of Naming Transformer Secondary
a
b
c
b
a
c
c
b
a
A AA
a
a a
1 9 5

10. Star – Delta
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
C B
A
Primary Star Equi. Secondary
Delta
Options of Naming Transformer Secondary
a
b
c
b
a
c
c
b
a
A AA
a a a
11 3 7

11. As clearly shown above, there are six vector group options available for Star –
Delta Transformer Configuration. These are;
Yd1 Yd3 Yd5 Ynd1 Ynd3 Ynd5
Or
Yd7 Yd9 Yd11 Ynd7 Ynd9 Ynd11
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
 Yd1 or Ynd1 is the same as Dy11 or Dyn11 as in both cases Star (Y) leads
Delta (D) by 30°.
 Yd11 or Ynd11 is the same as Dy1 or Dyn1 as in both cases Delta (D) leads
Star (Y) by 30°.
Note: By Inspection

12. Delta – Delta
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
C B
A
Primary
Delta
Equi. Secondary
Delta
Options of Naming Transformer Secondary
a
b
c
b
a
c
c
b
a
A AA
a
a a
0 8 4

13. Delta – Delta
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
C B
A
Primary
Delta
Equi. Secondary
Delta
Options of Naming Transformer Secondary
a
b
c
b
a
c
c
b
a
A AA
a
a a
6 2 10

14. As clearly shown above, there are six vector group options available for Delta –
Delta Transformer Configuration. These are;
Dd0 Dd2 Dd4
Dd6 Dd8 Dd10
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

15. Star – Star
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
C B
A
Primary Star Equi. Secondary
Star
Options of Naming Transformer Secondary
a
b
c
b
a
c
c
b
a
A AA
a
a a
0 8 4

16. Star – Star
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
C B
A
Primary Star Equi. Secondary
Star
Options of Naming Transformer Secondary
a
b
c
b
a
c
c
b
a
A AA
a
a a
6 2 10

17. As clearly shown above, there are six vector group options available for Star – Star
Transformer Configuration. These are;
Yy0 Yy2 Yy4 Yyn0 Yyn2 Yyn4
Or
Yy6 Yy8 Yy10 Yyn6 Yyn8 Yyn10
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

18. As clearly shown in the previous slides, there are Twenty-Four (24) vector groups
for Star Delta Transformers. Below is the reiteration of these vector groups;
Dy1 Dy3 Dy5 Or Dyn1 Dyn3 Dyn5
Dy7 Dy9 Dy11 Dyn7 Dyn9 Dyn11
Dd0 Dd2 Dd4
Dd6 Dd8 Dd10
Yd1 Yd3 Yd5 Or Ynd1 Ynd3 Ynd5
Yd7 Yd9 Yd11 Ynd7 Ynd9 Ynd11
Yy0 Yy2 Yy4 Or Ynyn0 Ynyn2 Ynyn4
Yy6 Yy8 Yy10 Ynyn6 Ynyn8 Ynyn10
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana

19. Dyn1
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
A
C B
c
b
a
30°
30°
30°
The Primary Voltage Vectors (Delta) leads the Secondary Voltage Vectors
(Star) by 30°. This is also known as lag in Aspen DistriView

20. Dyn11
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana
A
C B
c
b
a
30°
30°
30°
The Primary Voltage Vectors (Delta) lags the Secondary Voltage Vectors
(Star) by 30°. This is also known as lead in Aspen DistriView

21. Thank You Very Much For
Your Kind Attention
5/3/2016
Presentation By; Armstrong Okai Ababio
Electrical Engineer/ Electricity Company of
Ghana