1) The document discusses transformer vector groups, which indicate the winding configurations and phase angle differences between primary and secondary windings. 2) For a Yd1 transformer, the secondary voltage leads the primary voltage by 30 degrees. However, if the terminal markings are changed, the vector group can change (e.g. to Yd5). 3) For positive sequence currents in a Yd1 transformer, the secondary currents lead the primary currents by 30 degrees. But for negative sequence currents, the secondary currents lag the primary currents by 30 degrees.

1. Transformer Vector Group
& Its Effect on Phase Shift of
+Ve and –Ve phase
sequence current
component
between secondary and primary

2. Understanding Transformer
Vector Group
■
■
■
■
Transformer is magnetically coupled circuit
Its primary and secondary voltages either in
phase or out of phase
To say them in phase or out of phase will all
depend upon polarity considerations
Before to discussing polarity we will see
something about notational basics of
electricity

3. Transformer as magnetically
coupled device
This transformer is drawn such that whenever current enters from
top side of Primary, exits from top side of the secondary
Think about
emphasize
on the word
drawn

4. Transformer as magnetically
coupled device
This transformer is drawn such that whenever current enters from
top side of Primary, exits from Bottom side of the
secondary
Think about
emphasize
on the word
drawn

5. Polarity Marking on Transformer
A
B
a
b
A’
B’
a’
b’
The facts in previous slides can be represented in more
simplistic way by polarity marking as below in figure A
and Figure B respectively
Figure - A
Figure - B

6. Polarity Marking on Transformer
■ As for as one single phase transformer
considered polarity marking carries a
little meaning. Thus you will never see
such polarity marking on single phase
transformer. But if you want to connect
these single phase transformer for a
particular purpose. Then this polarity
marking are much use full

7. Vector diagram for single phase
transformer - 1
A
B
a
b
VAB
Vab
Voltage of a
wrt b is in
phase with
voltage of A
wrt B

8. Vector diagram for single phase
transformer - 2
VA’B’
A’
B’
a’
b’
Voltage of a’
wrt b’ is out
of phase
with voltage of
A’ wrt B’
Vb’a’
a’ at arrow tail and b’ at
arrow head Vb’a’ . arrow
direction is reverse to that
of physical arrow marking
near secondary coil and is
in phase with primary
voltage. To resolve such
confusion use consistent
Vcoa’nb’ventionand references
as in previous slide

9. Polarity marking on transformer
■ Consider a simple case of paralleling the
transformer in figure A and B.
A
B
a
b
A
’
B
’
a
’
b
’
Connect like
polarity

10. Kirchhoff's voltage law (KVL)
■ The directed sum of the electrical
potential differences (voltage) around
any closed circuit must be zero.
(http://en.wikipedia.org/wiki/Kirchhoff
%27s_circuit_laws) as on 11/09/10

11. Polarity marking on transformer
■ Consider another case of voltage doubling
by using both transformer as from figure A
B
A a
b
A
B
a
b
Connect dislike
polarity
X
Y
L

12. Apply KVL
Apply KVL starting from point L and traverse the
loop anti clockwise with convention that voltage
mentioned by double subscript notation with arrow
head wrt tail traversed in the direction of arrow is
+Ve else -Ve
VXY – Vab – Vab = 0
VXY = Vab + Vab
VAB
Vab Vab
VXY
w

13. ■ Consider yet another case of voltage
doubling by using one transformer as
figure A and other as figure B
A
B
a
b
A’
B’
a’
b’
Connect dislike
polarity
X
Y
L

14. Apply KVL
VXY - Vab – Vb’a’ = 0
VXY = Vab+ Vb’a’
Vab
Va’b’
Vb’a,’
VXY
w

15. Polarity of the transformer
If a transformer is considered as black box
this fact can be shown by a dot on
respective terminal of primary and
secondary. Here voltage Vab is considered
to be in phase with VAB

16. Transformer redefined once again to avoid confusion between
HV/LV and Primary/ Secondary (useful while defining vector
group)
(From http://en.wikipedia.org/wiki/Transformer 13/09/10)
■
■ A transformer is a device that transfers electrical energy from one
circuit to another through inductively coupled conductors the
transformer's coils. A varying current in the first or primary winding
creates a varying magnetic flux in the transformer's core, and thus a
varying magnetic field through the secondary winding. This varying
magnetic field induces a varying electromotive force (EMF) or "voltage"
in the secondary winding. This effect is called mutual induction.
■ If a load is connected to the secondary, an electric current will flow in
the secondary winding and electrical energy will be transferred from the
primary circuit through the transformer to the load. In an ideal
transformer, the induced voltage in the secondary winding (VS) is in
proportion to the primary voltage (VP), and is given by the ratio of the
number of turns in the secondary (NS) to the number of turns in the
primary (NP) as follows:
(Power Flows From Primary To Secondary)
Vs Ns
---- = -----
Vp Np

17. (From http://en.wikipedia.org/wiki/Vector_group 13/09/10)
A Vector group is the International Electro
technical Commission (IEC) method of
categorizing the primary and secondary
winding configurations of three-phase
transformers. Within a polyphase
system power transformer it indicates
the windings configurations and the
difference in phase angle between
them.
Transformer Vector Group

18. The point of confusion is in how to use
this notation in a step-up transformer.
As the IEC60076-1 standard has
stated, the notation is HV-LV in
sequence. For example, a step-up
transformer with a delta-connected
primary (LV), and star-connected
secondary (HV), is not written as 'dY11‘,
but 'Yd1'. The 1 indicates the LV
winding lags the HV by 30 degrees.
Transformer Vector Group

19. Vector Group of Step-Up Transformer
Power
Flow
Secondary
HV
Primary
LV
dY11 LV Can’t be reference
Yd1 Select HV as reference

20. Transformer Vector Group
■ Depends upon Polarity as well as external
terminal marking
■
■
■
■ Because phase difference between two
magnetically coupled circuit is either 180 or 0
Hence whenever IEC specifies phase
difference it shall be treated as with respect
to line voltages
Hence terminal marking is affecting on vector
group and important
If external terminal marking changed Yd11
group may become Yd5

21. 3 Phase Supply Review
Vb Vy
Vry
Vr
Vyb
Vbr

22. With this back ground now we
are ready to understand
transformer connections for
Yd11 Transformer

23. Throughout this example instead of labels, colors are used purposely
Let the 3 ph. Transformer individual windings are connected as shown in
fig-A so as to form HV side Y and LV side delta.
This transformer is redrawn in fig-B so as to make it easy to account for
shift of 120 deg. between individual phases.
Note the associated limb colors in primary and secondary of fig-A and
Fig-B.
Associated limbs are kept parallel in Fig-B.
External leads of secondary are of Red, Yellow, Blue, different color than
that of limb
Color Red, Yellow, Blue carries normal meaning of Vr,Vy,Vb
Fig-A
Fig-B

24. By
resemblance
from previous
sheet
Transform to resemble with 3 Ph review
taken previously. Notice the changes in
vector diagram for color and direction
Dark Yellow limb voltage of
LV (Reversed) is line (R phase to
Y phase) voltage
Teal limb voltage of LV
(Reversed) is line (Y phase to B
phase) voltage
Brown limb voltage of LV
(Reversed) is line (B phase to R
phase) voltage
12 O'clock
11 O'clock

25. As stated previously transformer
vector group depends up on its
terminal marking.
How it happens we will see in
next 2 slides (This type of
connections are ANSI standard)
We may call it as Yd5
Transformer

26. Change the terminal marking in respect of secondary
such that in front of R Ph of primary there shall be
Yellow phase of secondary and so on. Revised
drawing is shown below
Fig-A
Fig-B

27. By
resemblance
from previous
sheet
Transform to resemble with 3 Ph review
taken previously. Notice the changes in
vector diagram for color and direction
Dark Yellow limb voltage of
LV (Reversed) is line (Y phase to
B phase) voltage
Teal limb voltage of LV
(Reversed) is line (B phase to R
phase) voltage
Brown limb voltage of LV
(Reversed) is line (R phase to Y
phase) voltage
12 O'clock
5 O'clock

28. Most commonly used vector
groups
■ Dy1
■ Yd1
■ Dy5
■ Yd5
■ Dy11
■ Yd11

29. Connections for Yd1 T/F
Here connections of Yd1
transformer are described to
demonstrate effect of polarity of
delta connections on
transformer vector group

30. Change the connections of delta
with respect to it’s polarity
Fig-A
Fig-B

31. By
resemblance
from previous
sheet
Transform to resemble with 3 Ph review
taken previously. Notice the changes in
vector diagram for color only shown doted to
indicate it out of phase wrt HV
Dark Yellow limb voltage of
LV is line (Y phase to B phase)
voltage
Teal limb voltage of LV is
line (B phase to R phase) voltage
Brown limb voltage of LV
is line (R phase to Y phase)
voltage
5 O'clock
Final Results
1800 to
compensate for
out of phase
primary and
secondary
12 O'clock

32. Or instead of shifting R Ph
secondary voltage at last stage,
we will redraw the same by
different way so that primary and
secondary windings shall have
similar arrow markings ( may call
as a tricky way)

33. Change the connections of delta
with respect to it’s polarity
Fig-A
Fig-B

34. By
resemblance
from previous
sheet
Transform to resemble with 3 Ph review
taken previously. Notice the changes in
vector diagram for color only
Dark Yellow limb voltage of
LV is line (Y phase to B phase)
voltage
Teal limb voltage of LV is
line (B phase to R phase) voltage
Brown limb voltage of LV
is line (R phase to Y phase)
voltage
12 O'clock
1 O'clock

35. For the standard Yd1 transformer
discussed previously now we will
check relationship between +Ve
and –Ve sequence currents
reflected on primary with respect
to that of on secondary

36. Let the power flows from Y side to D
side. Show the currents instead of
voltages
Fig-A
Fig-B

37. Note : Primary Y Winding currents shown out of phase wrt
secondary. However source currents follows secondary
limb current.
C
Apply KCL at point C
Secondary R Ph Line Current + Teal Limb Current =
Brown Limb Current
Secondary R Ph Line Current = Brown Limb Current
- Teal Limb Current
& Brown limb current is primary current
IS
`
Di
IP Yi
For Yd1 Transformer with
Y as primary and D as
secondary Y Side Line
Currents Leads D side
Line Current by 300

38. Let the power flows from D side to Y
side. Show the currents instead of
voltages
Fig-A
Fig-B

39. Note: Secondary load current follows secondary winding
current
C
Apply KCL at point C
Primary R Ph Line Current + Teal Limb Current =
Brown Limb Current
Primary R Ph Line Current = Brown Limb Current -
Teal Limb Current
& Brown limb current is primary current
IP
For Yd1 Transformer with
D as primary and Y as
secondary Y Side Line
Currents Leads D side
Line Current by 300
`
Di
IS Yi

40. To check the situation for –Ve
sequence currents of Yd1
transformer let its source is
replaced by RBY source hence
new circuit will be

41. Let the power flows from Y side to D
side. Show the currents instead of
voltages and interchange Y and B
limb in primary. Redraw secondary
Fig-A
Fig-B

42. Note : Primary Y Winding currents shown out of phase wrt
secondary. However source currents follows secondary
limb current.
Apply KCL at point C
Secondary R Ph Line Current + Teal Limb Current =
Brown Limb Current
Secondary R Ph Line Current = Brown Limb Current
- Teal Limb Current
& Brown limb current is primary current
IP2
`
IS2 Di
Yi
For Yd1 Transformer with
Y as primary and D as
secondary For –Ve
Sequence Y Side Line
Currents lags D side Line
Current by 300
Fig-B

43. Results of Yd11 and Yd1 for +Ve
sequence and –Ve sequence are
tabulated as below
For Yd1
transformer
Y side current leads
D side current by 300
For Yd11
transformer
Y side current lags D
side current by 300
For +Ve
sequence
current
component
For -Ve
sequence
current
component
Y side current lags D
side current by 300
Y side current leads
D side current by 300

44. a
b
c
A
B
C
N
A shortcut to identify vector
group
12 O’Clock
1 O’Clock
Yd1

45. Yd1 and Dy11 are duels
A
B
C
a
b
c
a
b
c
n
N
A
B
C
D
Yy
d1
11