Short-Circuit Analysis IEC Standard Operation Technology, Inc. Workshop Notes: Short-Circuit IEC

Transcription

1 Short-Circuit Analysis IEC Standard Operation Technology, Inc. Workshop Notes: Short-Circuit IEC

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) I 2 t protection for equipment (thermal stress) Selecting ratings or settings for relay coordination Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 2

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

4 Types of Short-Circuit Faults 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 I L-G can range in utility systems from a few percent to possibly 115 % ( if X o < X 1 ) of I 3-phase (85% of all faults). In industrial systems the situation I L-G > I 3-phase is rare. Typically I L-G.87 * I 3-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 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 4

5 Short-Circuit Phenomenon v(t) i(t) v(t) Vm Sin( t ) Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 5

6 v(t) i(t) di v(t) Ri L dt Solving equation i(t) Vm sin( t - ) Z Steady State Vm 1 yields Sin( the t ) following (1) expression R Vm t sin( - ) e - L Z Transient (DC Offset) Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 6

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

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

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

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

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) Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 11

12 IEC Short-Circuit Calculation Method Ik = Equivalent fault location divided by equivalent Z Equivalent V is based bus nominal kv and c factor XFMR and machine Z adjusted based on c max, component Z & operating conditions Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 12

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

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

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 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 15

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

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 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 17

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

19 Factors Used in I f Calc κ calc i p based on I k μ calc i b for near-to-gen & not meshed network q calc induction machine i b for near-to-gen & not meshed network Equation (75) of Std , adjusting Ik for near-to-gen & meshed network λ min & λ max calc i k Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 19

20 IEC Short-Circuit Study Case 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 resistance temperature is considered) 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 resistance temperature is considered) Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 22

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 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 23

24 Calculation Method Breaking ka is more conservative if the option No Motor Decay is selected Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 24

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

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

27 Mesh & Non-Mesh I f ETAP automatically determines mesh & nonmeshed contributions according to individual contributions IEC Short Circuit Mesh Determination Method 0, 1, or 2 (default) Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 27

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

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

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

31 L-G Fault Sequence Network Connections I I f if 3 3 Z I f a 0 Z g 1 0 V Z Prefault 2 Z Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 31

32 L-L Fault Sequence Network Connections Ia I 2 a1 I f 3 Z 1 V Z Prefault Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 32

33 L-L-G Fault Sequence Network Connections I I f if I Z 0 I a 2 a1 a 0 Z g 1 V Prefault Z Z Z2 Z 2 I a Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 33

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

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

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 > Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 36

37 Unbalanced Faults Display & Reports 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 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 37

38 Transient Fault Current Calculation (IEC 61363) Total Fault Current Waveform Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 38

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

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

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

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

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

44 Unbalanced Faults Display & Reports 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 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 44

45 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 45

46 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 46