1 ee 306 transformers instructor: dr. mahamed shwehdi done by: ahmad saleh al-owied
Post on 21-Dec-2015
218 Views
Preview:
TRANSCRIPT
1
EE 306
TRANSFORMERS
Instructor:
Dr. Mahamed Shwehdi
Done By:
Ahmad Saleh Al-Owied
2
Transformers
Very large three-phase network transformer.
3
Transformer electromagnetic device (mutual induction)electromagnetic device (mutual induction)
1. components:-- 2 adjacent coils
-- coils not physically connected to each other
4
Transformer (cont.)
2. operation:a) AC in primary coil produces B
b) Secondary coil receives a in I & V
N
SN
SN
SN
SN
SN
S
5
Transformers
N n
A
B
C
a
b
c
IA Ia
VANVAB
VCN
VBN Vbn
Van
Vcn
Vab
Wye / Wye connection
6
Transformers
LoadSupplyNetwork
Transformer
Y-Y
Three-phase network supplies a load through a transformer.
Transformer LoadSupply Network
Xtr_s
Van Vload_anVAN
Vnet_ANXnet
IAIa
N
n
A
a
Xtr_s
Van Vload_anVAN
IAIaVnet_AN
Xnet
Equivalent circuit of the wye-wye
Single-phase equivalent circuit for phase A of the three-phase wye-wye transformer system
7
Wye / Delta connection
A
B
C
N
VANVAB
VBN
VBC
VCN
IA
Iba
Icb
VCA
a
b
c
a
b
c
Ia
Ic
IbVab
Vbc
Vca
Iac
8
Transformers
Ia
Ib
Ic
Vab
Vbc
VcaVCN
VBN
VAN
A
B
C
a
b
c
Icb
Iba
Iac
Transformer
AC
AC
AC
IC
IB
IA
VAN
VBN
VCN
Supply
Iab
Ibc
Ica
Load
VAB
VBC
VCA
Iac
Vca
Vbc
Vab
N
Wye-delta connected transformer
9
Transformers
Single-phase equivalent circuit of a wye-delta transformer.
Xtr_s
Van Vs_anVAN
IA Ia
Vp_AN
Xtr_pRtr_p Rtr_s
XmRc
Tspe
Y-
10
Delta / Wye connection
A
B
C
n
a
b
cVBC
IaIA
Ib
Ic
VAB
VCA Vca
Vab
Vbc
Van
Vbn
Vcn
IC
IBICA
IAB
IBC
11
Delta / Delta connection
A
B
C
a
b
c
VAB
Ia
Iba
Iac
IA
IAB
ICA
Vab
12
Transformers
Transformer Connection
Primary and Secondary Voltage Phase Relation
Phase Shift*Windings Placed on the Same
Leg
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
* 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.
Three-phase Transformer Relations
13
Transformer Turns Ratio ratio of the # of turns in the
secondary coil to the # of turns in the primary coil P
S
N
NTR
numerical factor indicating relative change in PD across a transformer
TR > 1 = V (step up)TR < 1 = V (step down)
14
Transformer Law (change in voltage in a transformer) in V is directly proportional to the ratio of the
# of turns in the secondary to the # of turns in the primary
Formula: NN
VV
S
P
S
P
=NS secondary coil turnsNP primary coil turns
VS secondary voltageVP primary voltage
direct relationship
15
Transformer Current
Current in a transformer will be inversely proportional to the TR of the transformer
formula: NN
II
S
P
P
S
=
VV
II
S
P
P
S
=
IP primary coil currentIS secondary coil current
I vs. V = inverse relationship
16
Types of Transformers Based on TURNS RATIO
2. step-down turns ratio < 1VS < VP
IS > IP
1. step-up turns ratio > 1VS > VP
IS < IP
17
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
18
Transformer Types (cont.)
3. closed core-- ferromagnetic ends
connected-- induction
4. shell -- lazy square eight-- overlap of coils on
same ferromagnetic core
top related