Cable Sizing Calculation
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CABLE SIZING CALCULATION A. EQUIPMENT - GENERATOR (1800 kW) 1. INPUT DATA Voltage rating of Generator (V)
=
3.3
KV
Rating of Generator
=
1800
KW
Power Factor
=
0.9
Over Loading in percentage
=
0.1
2. DERATING FACTOR a. Derating for Ambient temperature Considering maximum ambient temperature 450 C Derating Factor for ambient temperature
=
0.95
b. Derating for Grouping 0
Considering maximum ambient temperature 45 C 1. Derating factors for single core cables laid on racks with removable covers where air circulation is restricted, Trefoils are separated by two cable diameter horizontally & the trays are in tiers having 300 mm distance No. of trefoils in horizontal formation
=
2
No. of racks/trays in tiers
=
3
Cable De-rating factor for grouping
=
0.83
c. Overall derating factor, Df
=
0.79
=
384.90
From POLYCAB cables catalogue Table No.'B'
3. CALCULATIONS Full load current ( I )
A
a. Checknig for short circuit current withstand capacity of cable Fault with standing time (t) = 1 sec Fault current (Isc)
=
Cable cross-sectional area
= =
25
KA
6.99 x Isc x Sqrt (t) 175 Sq.mm
RESULT From the above, it is seen that 3 No. 1C x 185 sq.mm CU. Cable can safely withstand the fault current. b. Cable selection based on continuous current carrying capacity of cable The size of cable selected shall ensure that the de-rated current carrying capacity of cable is greater than or equal to the maximum permanent current in the feeder. Proposed cable size
=
3R. 1C x 185 Sq.mm Cu
Type & Voltage rating of cable
=
XLPE, 3.3 KV
=
510
Nominal current carrying capacity of cable in air -Ic Derated current carrying capacity of cable in air -Icd Therefore, No. of runs required Say
=
Ic x Df
=
402.135
=
I / Icd
=
0.96
=
1
A
(From POLYCAB cables Table No. 8)
A
Run
RESULT From the above, it is seen that the thermal current carrying capacity of 3R. 1C x 185 Sq.mm CU cable is sufficient to carry rated current of Generator. Hence the proposed cable is safe. 4. CONCLUSION Comparing the above results, the following cable has been chosen. Cable for 1.8 MW 3.3 KV Generator : 3 R. 1C x 185 sq.mm Copper conductor, XLPE insulated, Armoured
CABLE SIZING CALCULATION B. EQUIPMENT - 2500 KVA POWER TRANSFORMER (3.3KV side) 1. INPUT DATA Voltage rating of Transformer (V) Rating of Transformer
= =
3.3 2500
KV KVA
2. DERATING FACTOR a. Derating for Ambient temperature 0
Considering maximum ambient temperature 45 C Derating Factor for ambient temperature
=
0.95
b. Derating for Grouping Considering maximum ambient temperature 450 C 1. Derating factors for single core cables laid on racks with removable covers where air circulation is restricted, Trefoils are separated by two cable diameter horizontally & the trays are in tiers having 300 mm distance No. of trefoils in horizontal formation
=
2
No. of racks/trays in tiers
=
3
Cable De-rating factor for grouping
=
0.95
c. Overall derating factor, Df
=
0.90
=
437.4
From POLYCAB cables catalogue Table No.'B'
3. CALCULATIONS Full load current ( I )
A
a. Checknig for short circuit current withstand capacity of cable Fault withstanding time (t) = 1 sec Fault current (Isc) Cable cross-sectional area
= = =
25 KA 6.99 x Isc x Sqrt (t) 175
Sq.mm
RESULT From the above, it is seen that 3R. 1C x 240 sq.mm CU. Cable can safely withstand the fault current. b. Cable selection based on continuous current carrying capacity of cable The size of cable selected shall ensure that the de-rated current carrying capacity of cable is greater than or equal to the maximum permanent current in the feeder i.e. I/Icd < 1. Proposed cable size Type & Voltage rating of cable Nominal current carrying capacity of cable in air -Ic Derated current carrying capacity of cable in air -Icd Therefore, No. of runs required Say
=
3R. 1C x 185 Sq.mm Cu
=
XLPE, 3.3 KV
=
510
=
Ic x Df
=
460.275
=
I / Icd
=
0.95
=
1
A
(From POLYCAB cables Table No. 7)
A
Runs
RESULT From the above, it is seen that the thermal current carrying capacity of 3R. 1C x 185 Sq.mm CU cable is sufficient to carry rated current of Transformer. Hence the proposed cable is safe. 4.CONCLUSION Comparing the above results, the following cable has been chosen. Cable for 2.5 MVA 3.3 KV Power Transformer : 3R. 1C x 185 sq.mm Copper conductor, XLPE insulated, Armoured. However as per the actual current flow through tranformer, cable size of 3R. 1C x 185 sq.mm Copper conductor, XLPE insulated, Armoured is considered as per discussion with Client's consultant.
CABLE SIZING CALCULATION C. EQUIPMENT - 2500 KVA POWER TRANSFORMER (33KV side) 1. INPUT DATA Voltage rating of Transformer (V) Rating of Transformer
= =
33 2500
KV KVA
2. DERATING FACTOR a. Derating for Ambient temperature 0
Considering maximum ambient temperature 45 C Derating Factor for ambient temperature
=
0.95
b. Derating for Grouping Considering maximum ambient temperature 450 C 1. Derating factors for single core cables laid on racks with removable covers where air circulation is restricted, Trefoils are separated by two cable diameter horizontally & the trays are in tiers having 300 mm distance No. of trefoils in horizontal formation
=
2
No. of racks/trays in tiers
=
3
Cable De-rating factor for grouping
=
0.95
c. Overall derating factor, Df
=
0.90
=
43.7
From POLYCAB cables catalogue Table No.'B'
3. CALCULATIONS Full load current ( I )
A
a. Checknig for short circuit current withstand capacity of cable Fault withstanding time (t) = 0.3 sec Fault current (Isc) Cable cross-sectional area
= = =
25 KA 6.99 x Isc x Sqrt (t) 96
Sq.mm
RESULT From the above, it is seen that 3R. 1C x 185 sq.mm CU. Cable can safely withstand the fault current. b. Cable selection based on continuous current carrying capacity of cable The size of cable selected shall ensure that the de-rated current carrying capacity of cable is greater than or equal to the maximum permanent current in the feeder i.e. I/Icd < 1. Proposed cable size Type & Voltage rating of cable Nominal current carrying capacity of cable in air -Ic Derated current carrying capacity of cable in air -Icd Therefore, No. of runs required Say
=
1C x 185 Sq.mm Cu
=
XLPE, 33 KV
=
400
=
Ic x Df
=
361
=
I / Icd
=
0.12
=
1
A
(From POLYCAB cables Table No. 16)
A
Runs
RESULT From the above, it is seen that the thermal current carrying capacity of 3R. 1C x 185 Sq.mm CU cable is sufficient to carry rated current of Transformer. Hence the proposed cable is safe. 4.CONCLUSION Comparing the above results, the following cable has been chosen. Cable for 2.5 MVA 33 KV (E) Power Transformer : 3R. 1C x 185 sq.mm Copper conductor, XLPE insulated, Armoured.
CABLE SIZING CALCULATION D. EQUIPMENT - 100 KVA UNIT AUXILIARY TRANSFORMER (HT SIDE) 1. INPUT DATA Voltage rating of Transformer (V) Rating of Transformer
= =
33 100
KV KVA
2. DERATING FACTOR a. Derating for Ambient temperature 0
Considering maximum ambient temperature 45 C Derating Factor for ambient temperature
=
0.95
b. Derating for Grouping Considering maximum ambient temperature 450 C 1. Derating factors for single core cables laid on racks with removable covers where air circulation is restricted, Trefoils are separated by two cable diameter horizontally & the trays are in tiers having 300 mm distance No. of trefoils in horizontal formation
=
2
No. of racks/trays in tiers
=
3
Cable De-rating factor for grouping
=
0.81
c. Overall derating factor, Df
=
0.77
=
1.7
From POLYCAB cables catalogue Table No.'B'
3. CALCULATIONS Full load current ( I )
A
a. Checknig for short circuit current withstand capacity of cable Fault withstanding time (t) = 1 sec Fault current (Isc) Cable cross-sectional area
= = =
25 KA 6.99 x Isc x Sqrt (t) 175
Sq.mm
RESULT From the above, it is seen that 3R. 1C x 185 sq.mm AL. Cable can safely withstand the fault current. b. Cable selection based on continuous current carrying capacity of cable The size of cable selected shall ensure that the de-rated current carrying capacity of cable is greater than or equal to the maximum permanent current in the feeder i.e. I/Icd < 1. Proposed cable size Type & Voltage rating of cable Nominal current carrying capacity of cable in air -Ic Derated current carrying capacity of cable in air -Icd Therefore, No. of runs required Say
=
3R. 1C x 185 Sq.mm Cu
=
XLPE, 33 KV
=
510
=
Ic x Df
=
392.445
=
I / Icd
=
0.0045
=
1
A
(From POLYCAB cables Table No. 16)
A
Runs
RESULT From the above, it is seen that the thermal current carrying capacity of 3R. 1C x 185 Sq.mm Cu cable is sufficient to carry rated current of Transformer. Hence the proposed cable is safe. 4.CONCLUSION Comparing the above results, the following cable has been chosen. Cable for 100 KVA 33/0.415 kV Aux.Transformer: 3 R. 1C x 185 sq.mm Copper conductor (E), XLPE insulated, Armoured
=
3.3
KV
Rating of Generator
=
1800
KW
Power Factor
=
0.9
Over Loading in percentage
=
0.1
2. DERATING FACTOR a. Derating for Ambient temperature Considering maximum ambient temperature 450 C Derating Factor for ambient temperature
=
0.95
b. Derating for Grouping 0
Considering maximum ambient temperature 45 C 1. Derating factors for single core cables laid on racks with removable covers where air circulation is restricted, Trefoils are separated by two cable diameter horizontally & the trays are in tiers having 300 mm distance No. of trefoils in horizontal formation
=
2
No. of racks/trays in tiers
=
3
Cable De-rating factor for grouping
=
0.83
c. Overall derating factor, Df
=
0.79
=
384.90
From POLYCAB cables catalogue Table No.'B'
3. CALCULATIONS Full load current ( I )
A
a. Checknig for short circuit current withstand capacity of cable Fault with standing time (t) = 1 sec Fault current (Isc)
=
Cable cross-sectional area
= =
25
KA
6.99 x Isc x Sqrt (t) 175 Sq.mm
RESULT From the above, it is seen that 3 No. 1C x 185 sq.mm CU. Cable can safely withstand the fault current. b. Cable selection based on continuous current carrying capacity of cable The size of cable selected shall ensure that the de-rated current carrying capacity of cable is greater than or equal to the maximum permanent current in the feeder. Proposed cable size
=
3R. 1C x 185 Sq.mm Cu
Type & Voltage rating of cable
=
XLPE, 3.3 KV
=
510
Nominal current carrying capacity of cable in air -Ic Derated current carrying capacity of cable in air -Icd Therefore, No. of runs required Say
=
Ic x Df
=
402.135
=
I / Icd
=
0.96
=
1
A
(From POLYCAB cables Table No. 8)
A
Run
RESULT From the above, it is seen that the thermal current carrying capacity of 3R. 1C x 185 Sq.mm CU cable is sufficient to carry rated current of Generator. Hence the proposed cable is safe. 4. CONCLUSION Comparing the above results, the following cable has been chosen. Cable for 1.8 MW 3.3 KV Generator : 3 R. 1C x 185 sq.mm Copper conductor, XLPE insulated, Armoured
CABLE SIZING CALCULATION B. EQUIPMENT - 2500 KVA POWER TRANSFORMER (3.3KV side) 1. INPUT DATA Voltage rating of Transformer (V) Rating of Transformer
= =
3.3 2500
KV KVA
2. DERATING FACTOR a. Derating for Ambient temperature 0
Considering maximum ambient temperature 45 C Derating Factor for ambient temperature
=
0.95
b. Derating for Grouping Considering maximum ambient temperature 450 C 1. Derating factors for single core cables laid on racks with removable covers where air circulation is restricted, Trefoils are separated by two cable diameter horizontally & the trays are in tiers having 300 mm distance No. of trefoils in horizontal formation
=
2
No. of racks/trays in tiers
=
3
Cable De-rating factor for grouping
=
0.95
c. Overall derating factor, Df
=
0.90
=
437.4
From POLYCAB cables catalogue Table No.'B'
3. CALCULATIONS Full load current ( I )
A
a. Checknig for short circuit current withstand capacity of cable Fault withstanding time (t) = 1 sec Fault current (Isc) Cable cross-sectional area
= = =
25 KA 6.99 x Isc x Sqrt (t) 175
Sq.mm
RESULT From the above, it is seen that 3R. 1C x 240 sq.mm CU. Cable can safely withstand the fault current. b. Cable selection based on continuous current carrying capacity of cable The size of cable selected shall ensure that the de-rated current carrying capacity of cable is greater than or equal to the maximum permanent current in the feeder i.e. I/Icd < 1. Proposed cable size Type & Voltage rating of cable Nominal current carrying capacity of cable in air -Ic Derated current carrying capacity of cable in air -Icd Therefore, No. of runs required Say
=
3R. 1C x 185 Sq.mm Cu
=
XLPE, 3.3 KV
=
510
=
Ic x Df
=
460.275
=
I / Icd
=
0.95
=
1
A
(From POLYCAB cables Table No. 7)
A
Runs
RESULT From the above, it is seen that the thermal current carrying capacity of 3R. 1C x 185 Sq.mm CU cable is sufficient to carry rated current of Transformer. Hence the proposed cable is safe. 4.CONCLUSION Comparing the above results, the following cable has been chosen. Cable for 2.5 MVA 3.3 KV Power Transformer : 3R. 1C x 185 sq.mm Copper conductor, XLPE insulated, Armoured. However as per the actual current flow through tranformer, cable size of 3R. 1C x 185 sq.mm Copper conductor, XLPE insulated, Armoured is considered as per discussion with Client's consultant.
CABLE SIZING CALCULATION C. EQUIPMENT - 2500 KVA POWER TRANSFORMER (33KV side) 1. INPUT DATA Voltage rating of Transformer (V) Rating of Transformer
= =
33 2500
KV KVA
2. DERATING FACTOR a. Derating for Ambient temperature 0
Considering maximum ambient temperature 45 C Derating Factor for ambient temperature
=
0.95
b. Derating for Grouping Considering maximum ambient temperature 450 C 1. Derating factors for single core cables laid on racks with removable covers where air circulation is restricted, Trefoils are separated by two cable diameter horizontally & the trays are in tiers having 300 mm distance No. of trefoils in horizontal formation
=
2
No. of racks/trays in tiers
=
3
Cable De-rating factor for grouping
=
0.95
c. Overall derating factor, Df
=
0.90
=
43.7
From POLYCAB cables catalogue Table No.'B'
3. CALCULATIONS Full load current ( I )
A
a. Checknig for short circuit current withstand capacity of cable Fault withstanding time (t) = 0.3 sec Fault current (Isc) Cable cross-sectional area
= = =
25 KA 6.99 x Isc x Sqrt (t) 96
Sq.mm
RESULT From the above, it is seen that 3R. 1C x 185 sq.mm CU. Cable can safely withstand the fault current. b. Cable selection based on continuous current carrying capacity of cable The size of cable selected shall ensure that the de-rated current carrying capacity of cable is greater than or equal to the maximum permanent current in the feeder i.e. I/Icd < 1. Proposed cable size Type & Voltage rating of cable Nominal current carrying capacity of cable in air -Ic Derated current carrying capacity of cable in air -Icd Therefore, No. of runs required Say
=
1C x 185 Sq.mm Cu
=
XLPE, 33 KV
=
400
=
Ic x Df
=
361
=
I / Icd
=
0.12
=
1
A
(From POLYCAB cables Table No. 16)
A
Runs
RESULT From the above, it is seen that the thermal current carrying capacity of 3R. 1C x 185 Sq.mm CU cable is sufficient to carry rated current of Transformer. Hence the proposed cable is safe. 4.CONCLUSION Comparing the above results, the following cable has been chosen. Cable for 2.5 MVA 33 KV (E) Power Transformer : 3R. 1C x 185 sq.mm Copper conductor, XLPE insulated, Armoured.
CABLE SIZING CALCULATION D. EQUIPMENT - 100 KVA UNIT AUXILIARY TRANSFORMER (HT SIDE) 1. INPUT DATA Voltage rating of Transformer (V) Rating of Transformer
= =
33 100
KV KVA
2. DERATING FACTOR a. Derating for Ambient temperature 0
Considering maximum ambient temperature 45 C Derating Factor for ambient temperature
=
0.95
b. Derating for Grouping Considering maximum ambient temperature 450 C 1. Derating factors for single core cables laid on racks with removable covers where air circulation is restricted, Trefoils are separated by two cable diameter horizontally & the trays are in tiers having 300 mm distance No. of trefoils in horizontal formation
=
2
No. of racks/trays in tiers
=
3
Cable De-rating factor for grouping
=
0.81
c. Overall derating factor, Df
=
0.77
=
1.7
From POLYCAB cables catalogue Table No.'B'
3. CALCULATIONS Full load current ( I )
A
a. Checknig for short circuit current withstand capacity of cable Fault withstanding time (t) = 1 sec Fault current (Isc) Cable cross-sectional area
= = =
25 KA 6.99 x Isc x Sqrt (t) 175
Sq.mm
RESULT From the above, it is seen that 3R. 1C x 185 sq.mm AL. Cable can safely withstand the fault current. b. Cable selection based on continuous current carrying capacity of cable The size of cable selected shall ensure that the de-rated current carrying capacity of cable is greater than or equal to the maximum permanent current in the feeder i.e. I/Icd < 1. Proposed cable size Type & Voltage rating of cable Nominal current carrying capacity of cable in air -Ic Derated current carrying capacity of cable in air -Icd Therefore, No. of runs required Say
=
3R. 1C x 185 Sq.mm Cu
=
XLPE, 33 KV
=
510
=
Ic x Df
=
392.445
=
I / Icd
=
0.0045
=
1
A
(From POLYCAB cables Table No. 16)
A
Runs
RESULT From the above, it is seen that the thermal current carrying capacity of 3R. 1C x 185 Sq.mm Cu cable is sufficient to carry rated current of Transformer. Hence the proposed cable is safe. 4.CONCLUSION Comparing the above results, the following cable has been chosen. Cable for 100 KVA 33/0.415 kV Aux.Transformer: 3 R. 1C x 185 sq.mm Copper conductor (E), XLPE insulated, Armoured
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