Cable_Design_Calculations_(Direct_Burial_&_Short_Circuit_Current).pdf

Earthfault Current 1Page

CALCULATION OF METALLIC SHIELD EARTH FAULT CURRENT I. CALCULATION CONDITION

1) Standard

IEC 949(1988)

2) Type of Cable

132kV 1Cx630sqmm XLPE Cable (CU/XLPE/CWS/LEAD/HDPE)

3) Operating Temperature

[

4) Maximum Short Circuit Temperature 5) Duration time of short circuit

]

70

[

]

250

[sec]

1.0

II. CALCULATION PROCEDURE

A. Lead Alloy 1. Permissible metallic shield earthfault current

I=

x Iad

2. Calculation of adiabatic earthfault current for metallic shield f + 2 Iad

2 2

x t = K S loge i +

Where, Iad ; Earthfault current calculated on an adiabatic

[Amp]

basis t ; Duration of earthfault

[sec]

1.0

K ; Constant depending on the material of the current 1/

[As /mm ]

carrying component c(

1/2

+20)

K=

= 20 x

10

41

1

S ; Geometrical cross sectional area of the current 2

carrying component ; Final temperature f

[mm ] [ C]

i ;

[ C]

70

[K]

230

Initial temperature

525.3 250

; Reciprocal of of temperature coefficient of of resistance o

of the current carrying component at 20 C c

; Volumetric specific heat of the current current carrying o

3

component at 20 C 20 ;

[J/K.m ]

1.45E+06

1.45E+06

[W.m]

2.14E-07

2.1400E-07

Electrical resistivity of the current carrying o

component at 20 C Therefore,

Iad =

14.8

[kA]

3. Calculation of non-adiabatic factor for conductor 2

= 1 + 0.61P - 0.069P + 0.0043P Where, P = M (t) = [

3

=

1.118

0.1984

( 2 / 2) + ( 3 / 3) ].F

M=

979.8 =

2

1

x 10

0.1984

[S

-1/2

]

-3

F : Factor to account for imperfect thermal contact between

0.7

828.08


Sheath(shield) material and non-metallic materials. 2, 3 ;

Volumetric specific heat of media either side of the shield [J/K.m ]

1 ;

1.45E+06

2:

2.40E+06

3:

2:

2.5

3:

:

2.20

3

Volumetric specific heat of shield(sheath)

[J/K.m ] 3

2,

1: 3

Thermal resistivity of the media either side of shield [J/K.m ]

3;

; Thickness of the shield(sheath)

[mm]

2.2

4. Results I =

x Iad =

16.5

[kA]

B. Copper Wire 1. Permissible metallic shield earthfault current

I=

x Iad


2 2

x t = K S loge i +


[Amp]


[sec]

1.0

K ; Constant depending on the material of the current 1/2

c(

2

[As /mm ]

carrying component 1/2

+20)

K=

=

226

1

20 x

S ; Geometrical cross sectional area of the current carrying component ; Final temperature f

[mm ] [ C]

i ;

[ C]

70

[K]

234.5

Initial temperature

163.4 250

; Reciprocal of temperature coefficient of resistance o


; Volumetric specific heat of the current carrying o


[J/K.m ]

3.45E+06

3.45E+06

[W.m]

1.72E-08

1.7241E-08



Iad =

25.2

[kA]

3. Calculation of non-adiabatic factor for conductor

= 1 + 0.61P - 0.069P + 0.0043P Where, P = M (t) =

=

1.070

0.1169

[ ( 2 / 2) +

( 3 / 3) ].F

M=

979.8 =

2

1

x 10

0.1169

979.8

]

-

F : Factor to account for imperfect thermal contact between Sheath(shield) material and non-metallic materials. 2, 3 ;

[S

-1/

0.7 1:

3.45E+06

2:

2.40E+06

3


3:


1 ; 2,


3

[J/K.m ] 3


3;


[mm]

1.70

4. Results I =

x Iad =

27.0

[kA]

III. CALCULATION RESULTS

Components Matallic Sheath

Earthfault Current (kA) 16.5

kA/1sec

27.0

kA/1sec

43.5

kA/1sec

(Lead Alloy) Matallic Shield (Copper Wires) Total

Remarks

2:

2.5

:

1.7

3:



2.40E+06 3.5

2.40E+06


2.5


CALCULATION OF METALLIC SHIELD EARTH FAULT CURRENT I. CALCULATION CONDITION

1) Standard

IEC 949(1988)

2) Type of Cable

132kV 1Cx630sqmm XLPE Cable (CU/XLPE/CWS/LEAD/HDPE)

3) Operating Temperature

[

4) Maximum Short Circuit Temperature 5) Duration time of short circuit

]

70

[

]

250

[sec]

1.0

II. CALCULATION PROCEDURE

A. Lead Alloy 1. Permissible metallic shield earthfault current

I=

x Iad


2 2

x t = K S loge i +


[Amp]


[sec]

1.0

K ; Constant depending on the material of the current 1/

[As /mm ]

carrying component c(

1/2

+20)

K=

= 20 x

10

41

1

S ; Geometrical cross sectional area of the current 2

carrying component ; Final temperature f

[mm ] [ C]

i ;

[ C]

70

[K]

230

Initial temperature

525.3 250




3


[J/K.m ]

1.45E+06

1.45E+06

[W.m]

2.14E-07

2.1400E-07



Iad =

14.8

[kA]

3. Calculation of non-adiabatic factor for conductor 2

= 1 + 0.61P - 0.069P + 0.0043P Where, P = M (t) = [

3

=

1.118

0.1984

( 2 / 2) + ( 3 / 3) ].F

M=

979.8 =

2

1

x 10

0.1984

[S

-1/2

]

-3

F : Factor to account for imperfect thermal contact between

0.7

828.08


Sheath(shield) material and non-metallic materials. 2, 3 ;


1 ;

1.45E+06

2:

2.40E+06

3:

2:

2.5

3:

:

2.20

3


[J/K.m ] 3

2,

1: 3


3;


[mm]

2.2

4. Results I =

x Iad =

16.5

[kA]

B. Copper Wire 1. Permissible metallic shield earthfault current

I=

x Iad


2 2

x t = K S loge i +


[Amp]


[sec]

1.0

K ; Constant depending on the material of the current 1/2

c(

2

[As /mm ]

carrying component 1/2

+20)

K=

=

226

1

20 x

S ; Geometrical cross sectional area of the current carrying component ; Final temperature f

[mm ] [ C]

i ;

[ C]

70

[K]

234.5

Initial temperature

163.4 250





[J/K.m ]

3.45E+06

3.45E+06

[W.m]

1.72E-08

1.7241E-08



Iad =

25.2

[kA]

3. Calculation of non-adiabatic factor for conductor

= 1 + 0.61P - 0.069P + 0.0043P Where, P = M (t) =

=

1.070

0.1169

[ ( 2 / 2) +

( 3 / 3) ].F

M=

979.8 =

2

1

x 10

0.1169

979.8

]

-

F : Factor to account for imperfect thermal contact between Sheath(shield) material and non-metallic materials. 2, 3 ;

[S

-1/

0.7 1:

3.45E+06

2:

2.40E+06

3


3:


1 ; 2,


3

[J/K.m ] 3


3;


[mm]

1.70

4. Results I =

x Iad =

27.0

[kA]

III. CALCULATION RESULTS

Components Matallic Sheath

Earthfault Current (kA) 16.5

kA/1sec

27.0

kA/1sec

43.5

kA/1sec

(Lead Alloy) Matallic Shield (Copper Wires) Total

Remarks

2:

2.5

:

1.7

3:



2.40E+06 3.5

2.40E+06


2.5

Cable_Design_Calculations_(Direct_Burial_&_Short_Circuit_Current).pdf

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