The document outlines the purpose and methodology of short-circuit studies as per IEC standards, detailing the analysis of various short-circuit fault types and their impact on system reliability. It covers calculations for symmetrical and asymmetrical fault currents, including adjustments for different electrical components and settings for relay coordination. Emphasis is placed on the complexities of machine reactance and the importance of understanding fault characteristics in industrial settings.

1. Short-Circuit Analysis
IEC Standard
IEC Standard
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

2. Purpose of Short-Circuit
St di
Studies
• A Short-Circuit Study can be used to determine
A Short Circuit Study can be used to determine
any or all of the following:
V if t ti d i l d l t h bilit
– Verify protective device close and latch capability
– Verify protective device interrupting capability
– Protect equipment from large mechanical forces
(maximum fault kA)
– I2t protection for equipment (thermal stress)
Selecting ratings or settings for relay coordination
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 2
– Selecting ratings or settings for relay coordination

3. Types of Short-Circuit Faults
©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 3

4. Types of Short-Circuit Faults
Types of SC Faults
•Three-Phase Ungrounded Fault
Th Ph G d d F lt
•Three-Phase Grounded Fault
•Phase to Phase Ungrounded Fault
•Phase to Phase Grounded Fault
•Phase to Ground Fault
•Phase to Ground Fault
Fault Current
•IL G can range in utility systems from a few percent to
IL-G can range in utility systems from a few percent to
possibly 115 % ( if Xo < X1 ) of I3-phase (85% of all
faults).
•In industrial systems the situation I > I is rare
•In industrial systems the situation IL-G > I3-phase is rare.
Typically IL-G ≅ .87 * I3-phase
•In an industrial system, the three-phase fault condition
f f
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 4
is frequently the only one considered, since this type of
fault generally results in Maximum current.

5. Short-Circuit Phenomenon
)
t
Sin(
Vm
v(t) θ
ω +
∗
=
i(t)
v(t)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 5

6. i(t)
v(t)
i(t)
( )
(1)
)
t
Sin(
Vm
dt
di
L
Ri
v(t) +
×
=
+
= θ
ω
t
Vm
Vm
dt
R
-
expression
following
the
yields
1
equation
Solving
4
4
4
4 3
4
4
4
4 2
1
4
4
4 3
4
4
4 2
1
Off t)
(DC
Transient
State
Steady
t
)
-
sin(
Z
Vm
)
-
t
sin(
Z
Vm
i(t)
L
e
×
×
+
+
×
= φ
θ
φ
θ
ω
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 6
Offset)
(DC

7. AC Current (Symmetrical) with
No AC Decay
No AC Decay
DC Current
DC Current
©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 7

8. AC Fault Current Including the
DC Offset (No AC Decay)
©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 8

9. Machine Reactance ( λ = L I )
AC Decay Current
AC Decay Current
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 9

10. Fault Current Including AC & DC Decay
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 10

11. IEC Short-Circuit
C l l ti (IEC 909)
Calculation (IEC 909)
• Initial Symmetrical Short Circuit Current (I"k)
• Initial Symmetrical Short-Circuit Current (I k)
• Peak Short Circuit Current (ip)
• Peak Short-Circuit Current (ip)
• Symmetrical Short Circuit Breaking Current
• Symmetrical Short-Circuit Breaking Current
(Ib)
• Steady-State Short-Circuit Current (Ik)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 11

12. IEC Short-Circuit
C l l ti M th d
Calculation Method
• Ik” = Equivalent V @ fault location divided by
• Ik = Equivalent V @ fault location divided by
equivalent Z
• Equivalent V is based bus nominal kV and c
factor
factor
• XFMR and machine Z adjusted based on
• XFMR and machine Z adjusted based on
cmax, component Z & operating conditions
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 12

13. Transformer Z Adjustment
• KT -- Network XFMR
• KS,KSO – Unit XFMR for faults on system
side
side
• K K Unit XFMR for faults in auxiliary
• KT,S,KT,SO – Unit XFMR for faults in auxiliary
system, not between Gen & XFMR
• K=1 – Unit XFMR for faults between Gen &
XFMR
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 13
XFMR

14. Syn Machine Z Adjustment
• KG – Synchronous machine w/o unit XFMR
• KS,KSO – With unit XFMR for faults on
system side
system side
• K K With unit XFMR for faults in
• KG,S,KG,SO – With unit XFMR for faults in
auxiliary system, including points between
Gen & XFMR
Gen & XFMR
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 14

15. Types of Short-Circuits
• Near To Generator Short Circuit
• Near-To-Generator Short-Circuit
– This is a short-circuit condition to which at least
one synchronous machine contributes a
prospective initial short-circuit current which is
more than twice the generator’s rated current, or
a short-circuit condition to which synchronous
and asynchronous motors contribute more than
5% of the initial symmetrical short-circuit current
( I"k) ith t t
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 15
( I"k) without motors.

16. Near-To-Generator Short-Circuit
©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 16

17. Types of Short-Circuits
F F G t Sh t Ci it
• Far-From-Generator Short-Circuit
– This is a short-circuit condition during which the
This is a short circuit condition during which the
magnitude of the symmetrical ac component of
available short-circuit current remains essentially
available short-circuit current remains essentially
constant.
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 17

18. Far-From-Generator Short-Circuit
©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 18

19. Factors Used in If Calc
• κ – calc ip based on Ik”
• μ – calc ib for near-to-gen & not meshed network
• q – calc induction machine ib for near-to-gen & not
meshed network
• Equation (75) of Std 60909-0, adjusting Ik for
near to gen & meshed network
near-to-gen & meshed network
• λmin & λmax – calc ik
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 19
λmin & λmax calc ik

20. IEC Short-Circuit Study Case
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 20

21. Types of Short-Circuits
When these options
are selected
• Maximum voltage factor is used
• Minimum impedance is used (all negative
tolerances are applied and minimum
tolerances are applied and minimum
resistance temperature is considered)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 21

22. Types of Short-Circuits
When this option is
selected
• Minimum voltage factor is used
• Maximum impedance is used (all positive
tolerances are applied and maximum
tolerances are applied and maximum
resistance temperature is considered)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 22

23. Voltage Factor (c)
• Ratio between equivalent voltage &
nominal voltage
nominal voltage
• Required to account for:
q
• Variations due to time & place
• Transformer taps
• Static loads & capacitances
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 23
• Generator & motor subtransient behavior

24. Calculation Method
• Breaking kA is more
• Breaking kA is more
conservative if the option
No Motor Decay is
No Motor Decay is
selected
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 24

25. IEC SC 909 Calculation
©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 25

26. Device Duty Comparison
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 26

27. Mesh & Non-Mesh If
• ETAP automatically determines mesh & non-
meshed contributions according to individual
meshed contributions according to individual
contributions
• IEC Short Circuit Mesh Determination
Method 0 1 or 2 (default)
Method – 0, 1, or 2 (default)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 27

28. L
L-
-G Faults
G Faults
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 28

29. L-G Faults
Symmetrical Components
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 29

30. Sequence Networks
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 30

31. L-G Fault Sequence
N t k C ti
Network Connections
I
3
I ×
=
V
3
I
I
3
I
efault
Pr
a
f 0
×
=
×
=
0
Z
Z
Z
I
0
2
1
f
=
+
+
=
Z
if 0
g
Z
if
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 31

32. L-L Fault Sequence Network
C ti
Connections
a
a
V
3
I
I 1
2
×
−
=
2
1
efault
Pr
f
Z
Z
V
3
I
+
×
=
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 32

33. L-L-G Fault Sequence
N t k C ti
Network Connections
I
0
I
I
I a
a
a
a 0
1
2
=
=
+
+
Z
Z
Z
V
I
2
0
efault
Pr
f
⎟
⎞
⎜
⎛
=
0
Z
Z
Z
2
0
2
0
1 ⎟
⎟
⎠
⎜
⎜
⎝ +
+
Z
if 0
=
g
Z
if
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 33

34. Transformer Zero Sequence Connections
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 34

35. Solid Grounded Devices
d L G F lt
the
is
fault
phase
-
3
a
Generally
and L-G Faults
:
if
greater
be
can
faults
G
-
L
case.
severe
most
I
:
then
true
are
conditions
this
If
& 1
0
2
1 <
=
I
Z
Z
Z
Z
solidl
are
er
transform
Connected
Y/
or
Generators
if
case
the
be
may
This
I 1
f3
Δ
< φ
φ f
I
grounded.
solidly
are
er
transform
Connected
Y/Δ
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 35

36. Zero Sequence Model
• Branch susceptances and static
loads including capacitors will be
loads including capacitors will be
considered when this option is
checked
• Recommended by IEC for
systems with isolated neutral
systems with isolated neutral,
resonant earthed neutrals &
earthed neutrals with earth fault
factor > 1.4
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 36

37. Unbalanced Faults Display
& R t
Complete reports that include individual
branch contributions for:
& Reports
•L-G Faults
•L-L-G Faults
•L-L Faults
L L Faults
One-line diagram displayed results that
include:
include:
•L-G/L-L-G/L-L fault current
contributions
•Sequence voltage and currents
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 37
•Sequence voltage and currents
•Phase Voltages

38. Transient Fault Current
C l l ti (IEC 61363)
Total Fault Current Waveform
Calculation (IEC 61363)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 38

39. Transient Fault Current
C l l ti (IEC 61363)
Percent DC Current Waveform
Calculation (IEC 61363)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 39

40. Transient Fault Current
C l l ti (IEC 61363)
AC Component of Fault Current Waveform
Calculation (IEC 61363)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 40

41. Transient Fault Current
C l l ti (IEC 61363)
Top Envelope of Fault Current Waveform
Calculation (IEC 61363)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 41

42. Transient Fault Current
C l l ti (IEC 61363)
Top Envelope of Fault Current Waveform
Calculation (IEC 61363)
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 42

43. IEC Transient Fault Current
C l l ti
Calculation
©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 43

44. Unbalanced Faults Display
& R t
Complete reports that include individual
branch contributions for:
& Reports
•L-G Faults
•L-L-G Faults
•L L Faults
•L-L Faults
One-line diagram displayed results that
include:
include:
•L-G/L-L-G/L-L fault current
contributions
•Sequence voltage and currents
©1996-2010 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 44
Sequence voltage and currents
•Phase Voltages

45. ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 45

46. ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 46