ECE 524:
Transients in Power Systems
Session 7; Page 1/9
Spring 2012
Transient R-L Circuit Example
Given a 230kV:34kV,
-Ygrounded, 100MVA transformer supplied supplied by a source
with a short circuit MVA of 2000. The transformer has a per unit reactance of 0.1pu on its
ratings base. Both the transformer and the source impedance have an X/R ratio of 12.
Calculate the complete phase A fault current if a fault occurs on the LV side
of the transformer at 70 degrees past the voltage peak.
Define Units:
MVA
1000kW
S
BASE
100MVA
pu
1
Transformer parameters:
S
rated
100MVA
XoverR
12
V
hv
230kV
V
lv
34.5kV
X
trans
0.1pu
R
trans
X
trans
XoverR
R
trans
0.01 pu
Find the transformer impedances referred to the LV side since the
fault occurs on that side.
Z
BLV
V
lv
2
S
rated
Z
BLV
11.9
Ω
R
transLV
R
trans
Z
BLV
R
transLV
0.0992
Ω
X
transLV
X
trans
Z
BLV
X
transLV
1.19
Ω
L
transLV
X
transLV
2
π
60
Hz
L
transLV
3.157 mH
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