The document discusses short-circuit analysis based on the IEC standard. It describes the purpose of short-circuit studies including verifying protective device ratings and settings. The types of short-circuit faults covered include three-phase, phase-to-phase, and phase-to-ground faults. The IEC method for calculating short-circuit currents is explained including initial, peak, and steady-state currents. Considerations for near-generator and far-from-generator faults are also covered.

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

2. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 2
Purpose of Short-Circuit
Studies
• A Short-Circuit Study can be used to determine
any or all of the following:
– 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

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

4. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 4
Types of SC Faults
•Three-Phase Ungrounded Fault
•Three-Phase Grounded Fault
•Phase to Phase Ungrounded Fault
•Phase to Phase Grounded Fault
•Phase to Ground Fault
Fault Current
•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 IL-G > I3-phase is rare.
Typically IL-G .87 * I3-phase
•In an industrial system, the three-phase fault condition
is frequently the only one considered, since this type of
fault generally results in Maximum current.
Types of Short-Circuit Faults

5. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 5
)tSin(Vmv(t)
i(t)v(t)
Short-Circuit Phenomenon

6. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 6
    
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expressionfollowingtheyields1equationSolving
i(t)v(t)

7. DC Current
AC Current (Symmetrical) with
No AC Decay
©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. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 9
Machine Reactance ( λ = L I )
AC Decay Current

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

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

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

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

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

15. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 15
Types of Short-Circuits
• 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) without motors.

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

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

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

19. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 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
• λmin & λmax – calc ik

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

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

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

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

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

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

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

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

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

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

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

31. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 31
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L-G Fault Sequence
Network Connections

32. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 32
21
efaultPr
f
aa
ZZ
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I
II 12
L-L Fault Sequence Network
Connections

33. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 33
0
ZZ
ZZ
Z
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L-L-G Fault Sequence
Network Connections

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

35. ©1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC Slide 35
grounded.
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Solid Grounded Devices
and L-G Faults

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

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

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

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

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

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

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

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

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

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