Download - Transformer Construction
ECE 441 1
Transformer Construction
ECE 441 2
Three-Phase Transformer
ECE 441 3
Transformer Action -- DC
ECE 441 4
11
de N
dt
2 2
de N
dt
Opposes battery voltage Opposes flux buildup
ECE 441 5
Transformer Action -- AC
ECE 441 6
max4.44P PE N f max4.44S SE N f
Opposes VT Opposes ΦM
max
max
4.44
4.44PP P
S S S
N fE N
E N f N
ECE 441 7
“No-Load” Condition
ECE 441 8
“No load” condition continued
Io = Ife + IM
Io = exciting current
Io provides the “magnetizing flux” and the “core loss”
Ife = core-loss current Ife = VT / Rfe
IM = magnetizing current IM = VT / jXM
ECE 441 9
O fe M
P O P fe P M
I I I
N I N I N I
No-Load Excitation mmf
No-Load Core Loss mmf
Magnetizing mmf
P MM
core
N I
R
ECE 441 10
T P P P
T PP O
P
V I R E
V EI I
R
ECE 441 11
Close the load switch
Secondary current will set up an mmf in OPPOSITION to the primary mmf. The core flux will DECREASE to
P M S SM
core
N i N i
R
ECE 441 12
The decrease in flux causes a decrease in the counter-emf EP, and the primary current will increase by an amount known as IP,load, the load component of the primary current. Additional mmf due to this current adds to the magnetizing flux.
ECE 441 13
,P M P P load S SM
core
N i N i N i
RPrimary current increases until NPIP,load = NSIS. The flux ΦM and primary emf EP return to the same values as before the switch was closed.
ECE 441 14
Final steady – state primary current under loaded conditions is
,
0 ,
P fe M P load
P P load
I I I I
I I I
ECE 441 15
Component Fluxes – Loaded Transformer
ECE 441 16
ΦP = net flux in window of primary ΦS = net flux in window of secondary
Φlp = leakage flux of primary Φls = leakage flux of secondary
ΦM = mutual flux
ΦP = ΦM + Φlp
ΦS = ΦM – Φls