A brief description of transformer

1. ECE 441 1

2. ECE 441 2

3. ECE 441 3

4. ECE 441 4
11
d
e N
dt
φ
= 2 2
d
e N
dt
φ
=
Opposes battery voltage Opposes flux buildup

5. ECE 441 5

6. ECE 441 6
max4.44P PE N f= Φ max4.44S SE N f= Φ
Opposes VT Opposes ΦM
max
max
4.44
4.44
PP P
S S S
N fE N
E N f N
Φ
= =
Φ

7. ECE 441 7
“No-Load” Condition

8. “No load” condition continued
ECE 441 8
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

9. 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 M
M
core
N I
Φ =
R

10. ECE 441 10
T P P P
T P
P O
P
V I R E
V E
I I
R
= +
−
= =

11. Close the load switch
P M S S
M
core
N i N i−
Φ =
R
ECE 441 11
Secondary current will set up an mmf in OPPOSITION
to the primary mmf. The core flux will DECREASE to

12. 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.

13. ECE 441 13
,P M P P load S S
M
core
N i N i N i+ −
Φ =
R
Primary current increases until NPIP,load = NSIS.
The flux ΦM and primary emf EP return to the
same values as before the switch was closed.

14. 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
= + +
= +

15. ECE 441 15

16. 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