Single-phase transformers have two adjacent coils that are not physically connected. An alternating current in the primary coil produces a changing magnetic field that induces a voltage in the secondary coil. Transformers can be connected in various configurations including wye-wye, wye-delta, delta-wye, and delta-delta to step up or step down voltages depending on the ratio of turns in the secondary coil to the primary coil.
5. Load
Supply
Network
Transformer
Y-Y
Transformer LoadSupply Network
Xtr_s
Van Vload_an
VAN
Vnet_AN
Xnet
IA
Ia
N
n
A
a
5
Three-phase network supplies a
load through a transformer.
Xtr_s
Van
Vload_an
VAN
IA
IaVnet_AN
Xnet
Equivalent circuit of the wye-wye
Single-phase equivalent circuit for phase
A of the three-phase wye-wye
transformer system
6. Wye / Delta connection
6
A
B
C
N
VAN
VAB
VBN
VBC
VCN
IA
Iba
Icb
VCA
a
b
c
a
b
c
Ia
Ic
Ib
Vab
Vbc
Vca
Iac
9. Delta / Wye connection
9
A
B
C
n
a
b
c
VBC
IaIA
Ib
Ic
VAB
VCA
Vca
Vab
Vbc
Van
Vbn
Vcn
IC
IB
ICA
IAB
IBC
10. Delta / Delta connection
10
A
B
C
a
b
c
VAB
Ia
Iba
Iac
IA
IAB
ICA
Vab
11. ratio of the # of turns in the
secondary coil to the # of turns in
the primary coil
11
P
S
N
N
TR =
numerical factor indicating relative change in
PD across a transformer
TR > 1 = V (step up)
TR < 1 = V (step down)
12. ∆ in V is directly proportional to the ratio of
the # of turns in the secondary to the # of turns
in the primary
Formula:
12
N
N
V
V
S
P
S
P
=
NS secondary coil turns
NP primary coil turns
VS secondary voltage
VP primary voltage
direct relationship
13. Current in a transformer will be inversely
proportional to the TR of the transformer
formula:
13
N
N
I
I
S
P
P
S
=
V
V
I
I
S
P
P
S
=
IP primary coil current
IS secondary coil current
I vs. V = inverse relationship
14. Based on TURNS RATIO
14
2. step-down
turns ratio < 1
VS < VP
IS > IP
1. step-up
turns ratio > 1
VS > VP
IS < IP
15. 1. air core
--inside area of coil is
empty
-- inefficient induction
15
2. open core
-- ferromagnetic
material inside coils
-- ↑B = ↑induction
16. 3. closed core
-- ferromagnetic ends
connected
-- ↑Β = ↑ induction
16
4. shell
-- lazy square eight
-- overlap of coils on
same ferromagnetic
core