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Symmetrical Fault CalculationsSymmetrical Fault Calculations

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Example 1Example 1

34.5kV

SCC = 1200 MVA

10/12.5 MVA

6%

13.8 kV

F

Calculate the fault current at F

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Example 1Example 1

10/12.5 MVA

6%

F

13.8 kV

Calculate the fault current at F

A55.2898

kV5.34MVA100

kVMVAI

ohms9.11100

5.34MVA

kVZ

5.34kV100MVA

base

basebase

2

base

2base

base

base

base

=

==

==

=

=

=

Step 1: Calculate Base Values34.5kV

SCC = 1200 MVA

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Example 1Example 1

10/12.5 MVA

6%

F

13.8 kV

Calculate the fault current at F

48.05.12

100x06.0

MVA

MVAxZZ

oldbase

basetTpu

==

=

Step 2: Calculate p.u impedances34.5kV

SCC = 1200 MVA

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Example 1Example 1

10/12.5 MVA

6%

F

13.8 kV

Calculate the fault current at F

48.05.12

100x06.0

MVA

MVAxZZ

oldbase

basetTpu

==

=

Step 2: Calculate p.u impedances

0833.0

5.34

5.34x

1200

100kV

kVx

MVA

MVAZ

base

oldbase

oldbase

baseutility

=

=

=

34.5kV

SCC = 1200 MVA

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Example 1Example 1

10/12.5 MVA

6%

F

13.8 kV

Calculate the fault current at F

pu775.10833.048.0

0.1

Z

V

Itotal

puFpu

=

+

=

=

Step 3: Calculate fault current34.5kV

SCC = 1200 MVA

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Example 1Example 1

10/12.5 MVA

6%

F

13.8 kV

Calculate the fault current at F

pu775.10833.048.0

0.1

Z

V

Itotal

puFpu

=

+

=

=

Step 3: Calculate fault current

A7426

5.34x

8.13

II

A29703

55.2898x775.1

3

IxII

FHVFLV

baseFpuFHV

=

=

==

=

34.5kV

SCC = 1200 MVA

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Example 2Example 2 –– Addition of a GeneratorAddition of a Generator

34.5kV

SCC = 1200 MVA

10/12.5 MVA

6%

5MVAXd

”=0.12

13.8 kV

F

Calculate the fault current at F

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Example 2Example 2 –– Addition of a GeneratorAddition of a Generator

0833.0

5.345.34x

1200100

kV

kVx

MVA

MVAZ

base

oldbase

oldbase

baseutility

=

=

=

Step 1: Calculate impedances

34.5kV

SCC = 1200 MVA

10/12.5 MVA

6%

5MVAXd

”=0.12

13.8 kV

F

Calculate the fault current at F

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Example 2Example 2 –– Addition of a GeneratorAddition of a Generator

48.05.12

100x06.0

MVA

MVAxZZ

oldbase

basetTpu

==

=

0833.0

5.345.34x

1200100

kV

kVx

MVA

MVAZ

base

oldbase

oldbase

baseutility

=

=

=

Step 1: Calculate impedances

34.5kV

SCC = 1200 MVA

10/12.5 MVA

6%

5MVAXd

”=0.12

13.8 kV

F

Calculate the fault current at F

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Example 2Example 2 –– Addition of a GeneratorAddition of a Generator

48.05.12

100x06.0

MVA

MVAxZZ

oldbase

basetTpu

==

=

0833.0

5.34

5.34x

1200

100

kV

kVx

MVA

MVAZ

base

oldbase

oldbase

baseutility

=

=

=

Step 1: Calculate impedances

34.5kV

SCC = 1200 MVA

10/12.5 MVA

6%

5MVAXd

”=0.12

13.8 kV

4.25

100x12.0

MVA

MVAxZZ

oldbase

baseGGpu

==

=

F

Calculate the fault current at F

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Example 2Example 2 –– Addition of a GeneratorAddition of a Generator

Step 2: Calculate equivalent impedances

34.5kV

SCC = 1200 MVA 1.0V

10/12.5 MVA

6%

F

13.8 kV

Calculate the fault current at F

5MVAXd

”=0.12

0.0833

Zutility ZGpu2.4

ZTpu 0.48

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Example 2Example 2 –– Addition of a GeneratorAddition of a Generator

Step 2: Calculate equivalent impedances

456.04.25633.0

4.2*5633.0Z

Eq  =

+

=

1.0V

0.456

0.0833

Zutility2.4

ZTpu 0.48

ZGpu

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Example 2Example 2 –– Addition of a GeneratorAddition of a Generator

Step 3: Calculate fault current

456.04.25633.0

4.2*5633.0Z

Eq  =

+

=

1.0V

0.456

pu192.2

456.0

0.1

Z

VI

Eq

puFpu   ===

0.0833

Zutility

2.4

ZTpu 0.48

ZGpu

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Example 2Example 2 –– Addition of a GeneratorAddition of a Generator

Step 3: Calculate fault current

456.04.25633.0

4.2*5633.0Z

Eq  =

+

=

1.0V

0.456

pu192.2

456.0

0.1

Z

VI

Eq

puFpu   ===

0.0833

Zutility

2.4

ZTpu 0.48

ZGpu

A91705.34x8.13

I

I

A36683

55.2898x192.2

3

IxII

FHV

FLV

baseFpuFHV

=

=

==

=

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Example 1 & 2 ComparisonExample 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

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Example 3Example 3 ––Presence of transformer & motorPresence 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 HPXd

”=0.17

Calculate the fault current at F

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Example 3Example 3 ––Presence of transformer & motorPresence of transformer & motor

0833.0

5.34

5.34x1200

100

kV

kVx

MVA

MVAZ

base

oldbase

oldbase

baseutility

=

=

=

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 HPXd

”=0.17

Calculate the fault current at F

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Example 3Example 3 ––Presence of transformer & motorPresence of transformer & motor

0833.0

5.34

5.34x1200

100

kV

kVx

MVA

MVAZ

base

oldbase

oldbase

baseutility

=

=

=

48.05.12

100x06.0

MVA

MVAxZZ

oldbasebaset1Tpu

==

=

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 HPXd

”=0.17

Calculate the fault current at F

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Example 3Example 3 ––Presence of transformer & motorPresence of transformer & motor

0833.0

5.34

5.34x1200

100

kV

kVx

MVA

MVAZ

base

oldbase

oldbase

baseutility

=

=

=

48.05.12

100x06.0

MVA

MVAxZZ

oldbasebaset1Tpu

==

=

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

4.25

100x12.0

MVA

MVAxZZ

oldbase

baseGGpu

==

=

M 2500 HPXd

”=0.17

Calculate the fault current at F

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Example 3Example 3 ––Presence of transformer & motorPresence of transformer & motor

pu4.2Z

pu48.0Z

pu0833.0Z

Gpu

1Tpu

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

667.13

100x05.0

MVA

MVAxZZ

oldbase

baset2Tpu

==

=

3 MVA

5%

2.4 kV

M 2500 HPXd

”=0.17

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Example 3Example 3 ––Presence of transformer & motorPresence of transformer & motor

pu667.1Z

pu4.2Z

pu48.0Z

pu0833.0Z

2Tpu

Gpu

1Tpu

utility

=

=

=

=Step 1: Calculate impedances

34.5kV

SCC = 1200 MVA

10/12.5 MVA

6%5MVA

Xd”=0.12

89.7154.2

100x17.0

MVAMVAxZZ

2154866.0

1865

pf 

746.0*2500ratingMotor

oldbase

basemMpu

==

=

==

=13.8 kV

F 3 MVA

5%

2.4 kV

M 2500 HPXd

”=0.17

Calculate the fault current at F

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Example 3Example 3 ––Presence of transformer & motorPresence of transformer & motor

Step 1: Calculate impedances

34.5kV

SCC = 1200 MVA

pu89.7Z

pu667.1Z

pu4.2Z

pu48.0Z

pu0833.0Z

Mpu

2Tpu

Gpu

1Tpu

utility

=

=

=

=

=10/12.5 MVA

6%5MVA

Xd”=0.12

13.8 kV

F 3 MVA

5%

2.4 kV

M 2500 HPXd

”=0.17

Calculate the fault current at F

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Example 3Example 3 ––Presence of transformer & motorPresence 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 HPXd

”=0.17

ZTpu1

0.0833

Zutility

0.48

ZGpu

2.4

7.89

1.667

ZMpu

ZTpu2

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Example 3Example 3 ––Presence of transformer & motorPresence 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

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Example 3Example 3 ––Presence of transformer & motorPresence of transformer & motor

Step 3: Calculate fault current

pu297.24354.0

0.1

Z

V

IEq

pu

Fpu   ===1.0V

A9609

5.34x8.13

II

A38443

55.2898x297.2

3

IxII

FHVFLV

base

FpuFHV

=

=

==

=

0.4354

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Symmetrical FaultSymmetrical Fault

34.5kV34.5kV34.5kV

SCC = 1200 MVASCC = 1200 MVASCC = 1200 MVA

10/12.5 MVA

6%

10/12.5 MVA

6%

10/12.5 MVA

6%

5MVA

Xd”

=0.12

13.8 kV5MVA

Xd”=0.12

F

IF =7426 Amps

F

13.8 kV

F

13.8 kV

3 MVA

5%

2.4 kV

M 2500 HPXd

”=0.17

IF =9170 Amps IF =9609 Amps