EE 4420: Homework #2
Name: ……………………
1. A singlephase transformer has the following data: 10 kVA, 2200/220 V, 60 Hz and its
circuit parameters are as follows: L
1
= 23.75 H, L
2
= 0.2375 H, R
1
= 5.2
Ω
, R
2
= 0.052
Ω
,
M = 2.37 H.
The transformer was connected to the supply of rated voltage. Write the voltage
equations, draw the block diagram and simulate transient currents, applying SIMULING
if:
1) the transformer has the open secondary winding and the supply voltage

has the maximum value,

has zero value
at the moment of switching on. In both cases find the maximum primary
current and current at steady state.
2) the transformer has the shorted secondary winding. Determine the maximum
and steady state primary current for switching on at zero supply voltage.
Solution:
The voltage equations in the Laplace form:
()
111
1
vR
s
L
i
s
M
=+
+
2
i
1
i
(1)
222
2
s
L
i
s
M
+
(2)
The current equations:
11
2
1
iv
s
M
i
R
sL
=−
+
(3)
22
1
1
s
M
i
R
sL
+
(4)
where:
sin
m
vV
t
ω
ϕ
1) Switching on at open secondary circuit
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 Fall '10
 Wu
 Alternating Current, Laplace, Inductor, 20 sec, Mains electricity

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