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Ahmedabad Institute of Technology
Branch
:
Electrical
Subject
:
DC Machine & Transformer (2130904)
Semester
:
3rd
Enrollment no
Name
130020109014
130020109015
130020109016
130020109017
130020109018
130020109019
130020109020
130020109021
130020109022
Halpati Brijal
Hedau Nikita
Jadav Yash
Jadia Sachin
Kamaliya Dipak
Koladiya Prakash
Kothadiya Umang
Kumawat Nirav
Ladumor Mayur
Three Phase
Transformer
Connection
Introduction

There are different method for connecting 3-phase transformers 3phase voltage to higher or lower value.

The HV &LV winding of a 3-phase transformer can be connected
in star or delta.

The choice of a particular connection depends upon the condition
under which the transformer is to be operated.

The most common & widely used transformer connection are
(1) Star/Star
(2) Delta/Delta
(3) Delta/Star or Star/Delta
(4) Zig Zag
Star/Star
 This is the most economical
connection for small, high voltage
transformer.
 As the phase voltage Vph = VL /
31/2, it needs lesser turns per phase
& insulation required is minimum.
 Possibility to provide neutral
connection. The star point can be
used in case of 3-phase, four wire
system.
 This connection is more suitable
for core type transformers.
Delta/Delta
 This connection is more suitable for
large, low voltage transformers.
 It increases the number of turns per
phase & reduces the necessary cross
section area of conductors, thus
insulation problem is not present
 It gives satisfactory performance
even if there is large unbalanced in
load.
 The third harmonic voltages are
absent due to closed delta.
 The absence of star or neutral point
is the disadvantages of this
connection.
Delta/Star or Star/Delta
 This connection is most commonly
used for power supply transformer.
 The neutral point allows both types
of loads to be met.
 The delta connected winding carries
third harmonic current due to which
potential of neutral point is
stabilized.
 The HV side is normally connected
in delta so that the three phase loads
& single phase loads can be supplied
by LV side using three phase, four
wire system.
Zig Zag connection
 This connection reduces the third harmonic voltages.
 It allows unbalance loading.
 This connection is mainly employed for LV winding.
 For a given total voltage per phase, the Zig Zag side requires 15% more
turns as compared to normal phase connection.
 Zig Zag connection is used where delta connections are mechanically
weak due to large number of turns & small cross section of conductor
in case of delta in high voltage transformers. It also used for rectifiers.
Terminal marking
 According to standards, the terminals of transformer are brought out in
rows with HV winding on one side while LV winding on the other side.
 The HV terminals are represented with capital letters. Generally A, B & C
are used for three phases. The LV terminals are represented with small
letters. Generally a, b & c are used for three phases.
 The neutral terminal are represented after line terminals. The capital letter
N is used to represent the HV side neutral terminal & small letter n is used
for representing the LV side neutral.
 The two ends of each winding are designated by subscript numbers 1,2.
 The phase displacement between HV & LV winding id indicated by the
angle in terms of clock face.
 The vector for the HV winding is taken as reference phasor. The phase
displacement of the phasor of LV winding from the reference phasor is
represented by the use of clock hour method. The HV vector being at 12
o’clock & the corresponding LV vector at hour hand number.
 For example, if the connection is written as ‘Dy11’ then it represent ,HV side
delta, LV side star connected transformer & LV emf vector is at 11o’clock
position i.e. =30o in advance of the 12 o'clock position of HV emf. It
represented by clock face method as shown in fig
Phase Groups &Vector diagrams
For transformer Connection
 In three phase transformer, the polarity alone is insufficient to
represent the relation between HV & LV windings. In addition to the
terminal markings on HV & LV windings, the vector diagram of
induced voltages are required to show the angular displacement
between HV & LV windings.
 According to Indian Standards, there are four vector or phase groups of
standard connection.
Group(1) : Zero phase displacement (Yy0, Dd0, Dz0)
Group(2) : 180o phase displacement ( Yy6, Dd6, Dz6)
Group(3) : 30o lag phase displacement (Dy1, Yd1, Yz1)
Group(4) : 30o lead phase displacement (Dy11, Yd11, Yz11)
Group 1 : Zero phase displacement
Group 2 : 180o phase displacement
Group 3 : 30o lag phase
displacement
Group 4 : 30o lead phase
displacement
Thank
You