# Symmetrical Fault Calculations Symmetrical Fault Calculations

Electronics - Devices

Oct 13, 2013 (4 years and 7 months ago)

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Symmetrical Fault Calculations
Symmetrical Fault Calculations
Example 1
Example 1
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
13.8 kV
F
Calculate the fault curr
ent at F
Example 1
Example 1
10/12.5 MVA
6%
F
13.8 kV
Calculate the fault curr
ent at F
A
55
.
2898
kV
5
.
34
MVA
100
kV
MVA
I
ohms
9
.
11
100
5
.
34
MVA
kV
Z
5
.
34
kV
100
MVA
base
base
base
2
base
2
base
base
base
base
=
=
=
=
=
=
=
=
Step 1: Calculate Base Values
34.5kV
SCC = 1200 MVA
Example 1
Example 1
10/12.5 MVA
6%
F
13.8 kV
Calculate the fault curr
ent at F
48
.
0
5
.
12
100
x
06
.
0
MVA
MVA
x
Z
Z
oldbase
base
t
Tpu
=
=
=
Step 2: Calculate p.u impedances
34.5kV
SCC = 1200 MVA
Example 1
Example 1
10/12.5 MVA
6%
F
13.8 kV
Calculate the fault curr
ent at F
48
.
0
5
.
12
100
x
06
.
0
MVA
MVA
x
Z
Z
oldbase
base
t
Tpu
=
=
=
Step 2: Calculate p.u impedances
0833
.
0
5
.
34
5
.
34
x
1200
100
kV
kV
x
MVA
MVA
Z
base
oldbase
oldbase
base
utility
=
=
=
34.5kV
SCC = 1200 MVA
Example 1
Example 1
10/12.5 MVA
6%
F
13.8 kV
Calculate the fault curr
ent at F
pu
775
.
1
0833
.
0
48
.
0
0
.
1
Z
V
I
total
pu
Fpu
=
+
=
=
Step 3: Calculate fault current
34.5kV
SCC = 1200 MVA
Example 1
Example 1
10/12.5 MVA
6%
F
13.8 kV
Calculate the fault curr
ent at F
pu
775
.
1
0833
.
0
48
.
0
0
.
1
Z
V
I
total
pu
Fpu
=
+
=
=
Step 3: Calculate fault current
A
7426
5
.
34
x
8
.
13
I
I
A
2970
3
55
.
2898
x
775
.
1
3
I
x
I
I
FHV
FLV
base
Fpu
FHV
=
=
=
=
=
34.5kV
SCC = 1200 MVA
Example 2
Example 2

34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
F
Calculate the fault curr
ent at F
Example 2
Example 2

0833
.
0
5
.
34
5
.
34
x
1200
100
kV
kV
x
MVA
MVA
Z
base
oldbase
oldbase
base
utility
=
=
=
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
F
Calculate the fault curr
ent at F
Example 2
Example 2

48
.
0
5
.
12
100
x
06
.
0
MVA
MVA
x
Z
Z
oldbase
base
t
Tpu
=
=
=
0833
.
0
5
.
34
5
.
34
x
1200
100
kV
kV
x
MVA
MVA
Z
base
oldbase
oldbase
base
utility
=
=
=
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
F
Calculate the fault curr
ent at F
Example 2
Example 2

48
.
0
5
.
12
100
x
06
.
0
MVA
MVA
x
Z
Z
oldbase
base
t
Tpu
=
=
=
0833
.
0
5
.
34
5
.
34
x
1200
100
kV
kV
x
MVA
MVA
Z
base
oldbase
oldbase
base
utility
=
=
=
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
4
.
2
5
100
x
12
.
0
MVA
MVA
x
Z
Z
oldbase
base
G
Gpu
=
=
=
F
Calculate the fault curr
ent at F
Example 2
Example 2

Step 2: Calculate equivalent impedances
34.5kV
SCC = 1200 MVA
1.0V
10/12.5 MVA
6%
F
13.8 kV
Calculate the fault curr
ent at F
5MVA
Xd”=0.12
0.0833
Zutility
ZGpu
2.4
ZTpu
0.48
Example 2
Example 2

Step 2: Calculate equivalent impedances
456
.
0
4
.
2
5633
.
0
4
.
2
*
5633
.
0
ZEq
=
+
=
1.0V
0.456
0.0833
Zutility
2.4
ZTpu
0.48
ZGpu
Example 2
Example 2

Step 3: Calculate fault current
456
.
0
4
.
2
5633
.
0
4
.
2
*
5633
.
0
ZEq
=
+
=
1.0V
0.456
pu
192
.
2
456
.
0
0
.
1
Z
V
I
Eq
pu
Fpu
=
=
=
0.0833
Zutility
2.4
ZTpu
0.48
ZGpu
Example 2
Example 2

Step 3: Calculate fault current
456
.
0
4
.
2
5633
.
0
4
.
2
*
5633
.
0
ZEq
=
+
=
1.0V
0.456
pu
192
.
2
456
.
0
0
.
1
Z
V
I
Eq
pu
Fpu
=
=
=
0.0833
Zutility
2.4
ZTpu
0.48
ZGpu
A
9170
5
.
34
x
8
.
13
I
I
A
3668
3
55
.
2898
x
192
.
2
3
I
x
I
I
FHV
FLV
base
Fpu
FHV
=
=
=
=
=
Example 1 & 2 Comparison
Example 1 & 2 Comparison
34.5kV
SCC = 1200 MVA
34.5kV
10/12.5 MVA
6%
F
13.8 kV
5MVA
Xd”=0.12
IF
=9170 Amps
SCC = 1200 MVA
10/12.5 MVA
6%
13.8 kV
F
IF
=7426 Amps
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
F
3 MVA
5%
2.4 kV
M
2500 HP
Xd”=0.17
Calculate the fault current at F
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
0833
.
0
5
.
34
5
.
34
x
1200
100
kV
kV
x
MVA
MVA
Z
base
oldbase
oldbase
base
utility
=
=
=
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
F
3 MVA
5%
2.4 kV
M
2500 HP
Xd”=0.17
Calculate the fault current at F
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
0833
.
0
5
.
34
5
.
34
x
1200
100
kV
kV
x
MVA
MVA
Z
base
oldbase
oldbase
base
utility
=
=
=
48
.
0
5
.
12
100
x
06
.
0
MVA
MVA
x
Z
Z
oldbase
base
t
1
Tpu
=
=
=
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
F
3 MVA
5%
2.4 kV
M
2500 HP
Xd”=0.17
Calculate the fault current at F
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
0833
.
0
5
.
34
5
.
34
x
1200
100
kV
kV
x
MVA
MVA
Z
base
oldbase
oldbase
base
utility
=
=
=
48
.
0
5
.
12
100
x
06
.
0
MVA
MVA
x
Z
Z
oldbase
base
t
1
Tpu
=
=
=
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
F
3 MVA
5%
2.4 kV
4
.
2
5
100
x
12
.
0
MVA
MVA
x
Z
Z
oldbase
base
G
Gpu
=
=
=
M
2500 HP
Xd”=0.17
Calculate the fault current at F
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
pu
4
.
2
Z
pu
48
.
0
Z
pu
0833
.
0
Z Gpu
1
Tpu
utility
=
=
=
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
F
13.8 kV
Calculate the fault current at F
667
.
1
3
100
x
05
.
0
MVA
MVA
x
Z
Z
oldbase
base
t
2
Tpu
=
=
=
3 MVA
5%
2.4 kV
M
2500 HP
Xd”=0.17
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
pu
667
.
1
Z
pu
4
.
2
Z
pu
48
.
0
Z
pu
0833
.
0
Z
2
Tpu
Gpu
1
Tpu
utility
=
=
=
=
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
10/12.5 MVA
6%
5MVA
Xd”=0.12
89
.
7
154
.
2
100
x
17
.
0
MVA
MVA
x
Z
Z
2154
866
.
0
1865
pf
746
.
0
*
2500
rating
Motor
oldbase
base
m
Mpu
=
=
=
=
=
=
13.8 kV
F
3 MVA
5%
2.4 kV
M
2500 HP
Xd”=0.17
Calculate the fault current at F
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
Step 1: Calculate impedances
34.5kV
SCC = 1200 MVA
pu
89
.
7
Z
pu
667
.
1
Z
pu
4
.
2
Z
pu
48
.
0
Z
pu
0833
.
0
Z
Mpu
2
Tpu
Gpu
1
Tpu
utility
=
=
=
=
=
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
F
3 MVA
5%
2.4 kV
M
2500 HP
Xd”=0.17
Calculate the fault current at F
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
Step 2: Calculate Equivalent impedances
34.5kV
SCC = 1200 MVA
1.0V
10/12.5 MVA
6%
5MVA
Xd”=0.12
F
13.8 kV
Calculate the fault current at F
3 MVA
5%
2.4 kV
M
2500 HP
Xd”=0.17
ZTpu1
0.0833
Zutility
0.48
ZGpu
2.4
7.89
1.667
Z
Mpu
ZTpu2
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
Step 2: Calculate Equivalent impedances
1.0V
1.0V
ZTpu1
0.0833
Zutility
0.48
ZGpu
2.4
7.89
1.667
ZMpu
0.4354
ZTpu2
Example 3
Example 3

Presence of transformer & motor
Presence of transformer & motor
Step 3: Calculate fault current
pu
297
.
2
4354
.
0
0
.
1
Z
V
I
Eq
pu
Fpu
=
=
=
1.0V
A
9609
5
.
34
x
8
.
13
I
I
A
3844
3
55
.
2898
x
297
.
2
3
I
x
I
I
FHV
FLV
base
Fpu
FHV
=
=
=
=
=
0.4354
Symmetrical Fault
Symmetrical Fault
34.5kV
34.5kV
34.5kV
SCC = 1200 MVA
SCC = 1200 MVA
SCC = 1200 MVA
10/12.5 MVA
6%
10/12.5 MVA
6%
10/12.5 MVA
6%
5MVA
Xd”=0.12
13.8 kV
5MVA
Xd”=0.12
F
IF
=7426 Amps
F
13.8 kV
F
13.8 kV
3 MVA
5%
2.4 kV
M
2500 HP
Xd”=0.17
IF
=9170 Amps
IF
=9609 Amps