“Real” Transformer
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Transcript “Real” Transformer
“Real” Transformer
EP = 4.44NPfΦP
ES = 4.44NSfΦS
ΦP = ΦM + Φlp
ΦS = ΦM – Φls
EP = E’P + Elp
ES = E’S - Els
“Real” Transformer (continued)
KVL @ primary
VT = EP + IPRP = E’P+ Elp +IPRP
IP = Ife + IM + IP LOAD
Equivalent Circuit of a Real Transformer
VT = EP + IPRP = E’P+ Elp +IPRP
“Real” Transformer (continued)
KVL @ secondary ES = ISRS + VLOAD = E’S – Els
E’S = Els + ISRS + VLOAD
Equivalent Circuit of a Real Transformer
VT = EP + IPRP = E’P+ Elp +IPRP
E’S = Els + ISRS + VLOAD
Flux in the “Leakage coils”
ls
lp
N pI p
Rlp
Ns Is
Rls
Ns Is
ls
Rls
Voltage generated by flux through the
window of a coil
e 2 fN max cos(2 ft )
Emax 2 fN max
N p I p max
Elp ,max 2 fN p
R
lp
N p2
Elp ,max 2 f
I
R p max
lp
N p2
Elp ,rms 2 f
I
R p ,rms
lp
N2
L
R
Elp (2 fLlp )( I p )
Elp I p X lp
Similar expression for the secondary
Equivalent Circuit using Leakage Reactance
Equivalent Impedance of a Transformer
'
E
Zin' a 2 S
IS
ES'
IS
RS jX ls Z load
ES'
RS jX ls Z load
IS
Z in' a 2 ( RS jX ls Z load )
Z in' a 2 RS ja 2 X ls a 2 Z load
Equivalent Circuit
Parameters Referred to the Primary
Z eq , P RP a 2 RS j ( X lp a 2 X ls )
Z eq , P Req , P jX eq , P
Define ZeqP = The “equivalent impedance” with all
parameters referred to the primary
Z eq , P RP a 2 RS j ( X lp a 2 X ls )
Z eq , P Req , P jX eq , P
Equivalent Circuit
Parameters Referred to Secondary
Z eq , S
Z eq , S
X lp
RP
RS 2 j ( X ls 2 )
a
a
Req , S jX eq ,S
Note that the excitation branch has been moved to the left!
It’s OK as long as the transformer is operated near rated
conditions!
Equivalent Circuit for Step-Down Operation
Using High-Side Values
Use this equivalent circuit to determine the input
impedance of the transformer and load.
Equivalent Circuit for Step-Down Operation
Using Low-Side Values
Use this equivalent circuit to determine the no-load
voltage and the voltage regulation.
Equivalent Circuit for Step-Up Operation
Using Low-Side Values
Use this equivalent circuit to determine the input
impedance of the transformer and load.
Equivalent Circuit for Step-Up
High-Side Values
Use this equivalent circuit to determine the no-load
voltage and the voltage regulation.