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Short Circuit Fault Calculations

The document discusses fault calculations for short circuit analysis using symmetrical components. It describes different fault types - single phase to ground, phase to phase, and three phase faults. It explains how symmetrical components decompose an unbalanced network into three balanced networks for the positive, negative, and zero sequences. Network equations and representations are provided for analyzing faults using symmetrical components. An example calculation is shown for a three phase and phase to ground fault.

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pulya123
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101 views17 pages

Short Circuit Fault Calculations

The document discusses fault calculations for short circuit analysis using symmetrical components. It describes different fault types - single phase to ground, phase to phase, and three phase faults. It explains how symmetrical components decompose an unbalanced network into three balanced networks for the positive, negative, and zero sequences. Network equations and representations are provided for analyzing faults using symmetrical components. An example calculation is shown for a three phase and phase to ground fault.

Uploaded by

pulya123
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Fault Calculations

Short Circuit Calculation


Fault Types – Single Phase to Ground

X
Z
A

G
X
C B

Z

Z

10
Fault Calculations

Short Circuit Calculations


Fault Types – Phase to Phase

A Z

G
C B

Z X


X
Z

11
Fault Calculations

Short Circuit Calculations


Fault Types – Three Phase

X
A Z

G
C B

X
Z

X
Z

12
Fault Calculations

Short Circuit Calculations – Unbalanced Faults


Symmetrical Components

Decomposes an unbalanced network into


three balanced network

1. Positive sequence network


2. Negative sequence network
3. Zero sequence network

26
Fault Calculations

Short Circuit Calculations


Symmetrical Components

lc1
lb2 la2 la0
lb0
la1 lc0

lb1 lc2

Positive Negative Zero

27
Fault Calculations

Short Circuit Calculations


Symmetrical Components
Network Equations

29
Fault Calculations

Symmetrical Components
Network Equations

Ia = I1+I2+I0 In three phase systems, the


neutral current is equal to
Ib = a 2 I1+aI2+I0
In = (Ia + Ib + Ic) and,
therefore, In = 3I0.
Ic = aI1+a2I2+I0

31
Fault Calculations

Symmetrical Components
Network Equations

The same equations apply to the voltages:

 V0 = 1/3(Va + Vb + Vc)

 V1 = 1/3(Va + a Vb + a2 Vc)

 V2 = 1/3(Va + a2Vb + aVc)

32
Fault Calculations
Short Circuit Calculations
Symmetrical Components
Network Representations

33
Fault Calculations

Short Circuit Calculations


Symmetrical Components
Three Phase Fault

Z1
X
1 pu I1

Positive Sequence

34
Fault Calculations

Short Circuit Calculations


Symmetrical Components
Phase to Phase Fault
Z1
X
1 pu I1

Positive Sequence

Z2
X
I2

Negative Sequence

35
Fault Calculations

Short Circuit Calculations


Symmetrical Components
Phase to Ground Fault
Z1
X
1 pu I1

Positive Sequence

Z2
X
I2

Negative Sequence

Z0
X
I0

Zero Sequence

36
Fault Calculations
Short Circuit Calculations
Symmetrical Components
Transformer Representations

H L
Z 1 or Z2

N1 or N2

Grounded Wye - Grounded Wye


H L
Z0

N0

37
Fault Calculations

Short Circuit Calculations


Symmetrical Components
Transformer Representations

38
Fault Calculations
Short Circuit Calculations
Symmetrical Components
Three Phase Fault

1 pu
0.08 pu 0.45 pu 0.25 pu I1

I 2 = I0 = 0
I a = I1 + I2 + I0 = I1 = 1.28 pu A
Ib = a2 I1 I c = a I1
I 25kV = 1.28 pu x 2309 A = 2960 A

40
Fault Calculations
Short Circuit Calculations
Symmetrical Components
Phase to Ground Fault
0.08 pu 0.45 pu 0.25 pu
X

1 pu

Positive Sequence
I1 = I 2 = I 0
I1 = 1.0 = 1pu = 0.35puA 0.08 pu 0.45 pu 0.25 pu
Z 2.86 pu
X

Ia = I 1 + I 2 + I 0 = 1.05puA
Negative Sequence
I25k V = 1.05 x 2309 = 2424 A

0.27 pu 0.45 pu 0.95 pu


X

Zero Sequence

41
Fault Calculations
Short Circuit Calculations
Symmetrical Components
Phase to Ground Fault

42

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