Al-Owied

Report
EE 306
TRANSFORMERS
Instructor:
Dr. Mahamed Shwehdi
Done By:
Ahmad Saleh Al-Owied
1
Transformers
Very large three-phase network transformer.
2
Transformer
electromagnetic device (mutual induction)
1. components:
-- 2 adjacent coils
-- coils not physically connected to each other
3
Transformer (cont.)
2. operation:
a) AC in primary coil produces D B
b) Secondary coil receives a D in I & V
S
N
S
N
4
Transformers
Wye / Wye connection
IA
Ia
A
a
V AB
B
C
V BN
V an
V AN
N
V CN
V bn
n
V cn
V ab
b
c
5
Transformers
Three-phase network supplies a
load through a transformer.
Transform er
S upply
N etw ork
Load
Y -Y
V net_ A N
X n et
V AN
V an
X tr_ s
A
a
Ia
IA
V lo ad _a n
Equivalent circuit of the wye-wye
n
N
S upply N etw ork
T ra nsform er
X tr_s
X net
V n et_A N
IA
L oad
V AN
V an
Ia
V load _an
Single-phase equivalent circuit for phase
A of the three-phase wye-wye
transformer system
6
Wye / Delta connection
Ia
IA
A
a
a
V AB
V CA
V AN
VBN
B
V CN
N
V BC
C
I ac
c
I ba
b
Ib
V ab
b
Icb
Ic
V ca
V bc
c
7
Transformers
V AN
T ran sfo rm er
A
IA
I ba
AC
V BN
V AN
V AB
V CA
B
IB
a
V ab
Ia
V ab
V ca
I cb
b
Ib
I ca
I ac
AC
V CN
C
AC
S u p p ly
V BN
V BC
IC
V bc
I ac
V CN
V bc
c
I ab
I bc
Ic
V ca
L oad
N
Wye-delta connected transformer
8
Transformers
R tr_ p
X tr_p
T
IA
V p_ A N
Rc
Xm
spe
X tr_ s
V an
V AN
R tr _s
Ia
V s_a n
Y -D
Single-phase equivalent circuit of a wye-delta transformer.
9
Delta / Wye connection
IA
A
V AB
V CA
B
a
IAB
n
IB
IC A
V BC
C
Ia
V bn
IC
IB C
V an
Ib
V cn
Ic
V ab
b
V ca
V bc
c
10
Delta / Delta connection
IA
A
Ia
a
Ib a
IAB
V AB
B
V ab
ICA
I ac
b
c
C
11
Transformers
Three-phase Transformer Relations
Transformer
Connection
Primary and Secondary Voltage Phase
Relation
Wye-Wye
VAN is in phase with Van
Zero
A and a
Wye-Delta
VAN is in phase with Vab
30°
A and ab
Delta-Wye
VAB is in phase with Van
–30°
AB and a
Delta-Delta
VAB is in phase with Vab
Zero
AB and ab
Phase Shift*
Windings Placed on the Same
Leg
* Note:
Phase shift lead between line-to-line voltages, VAB and Vab, and line-to-neutral voltages, VAN and Van, and line
currents, IA and Ia.
12
Transformer Turns Ratio


ratio of the # of turns in the
secondary coil to the # of turns in
the primary coil
TR 
NS
NP
numerical factor indicating relative change in
PD across a transformer
TR > 1 = V (step up)
TR < 1 = V (step down)
13
Transformer Law
(change in voltage in a transformer)

D in V is directly proportional to the ratio of the
# of turns in the secondary to the # of turns in
the primary

Formula:
NS
NP
=
VS
VP
NS secondary coil turns
NP primary coil turns
VS secondary voltage
VP primary voltage
direct relationship
14
Transformer Current


Current in a transformer will be inversely
proportional to the TR of the transformer
IP primary coil current
formula: N S IP
NP

=
IS
IS secondary coil current
I vs. V = inverse relationship
VS
VP
=
IP
IS
15
Types of Transformers

Based on TURNS RATIO
1. step-up
turns ratio > 1
VS > VP
IS < IP
2. step-down
turns ratio < 1
VS < VP
IS > IP
16
Transformer Types (cont.)
Based on STRUCTURE OF COILS
1. air core
-- inside area of coil is
empty
-- inefficient induction
2. open core
-- ferromagnetic
material inside coils
-- B = induction
17
Transformer Types (cont.)
3. closed core
-- ferromagnetic ends
connected
-- B  induction
4. shell
-- lazy square eight
-- overlap of coils on
same ferromagnetic
core
18

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