Cigre test system description justifications and simulation results v3
cable ampacity calculations- IEC
1. F:Elementscable programscable ampacity calculation IEC.docx Page 1
1 SCOPE AND DEFINITIONS
The scope of the attached calculations is to determine the required cables sizes based on the
project standards and design criteria.
Design Criteria.
Following design criteria is used for the settings sheet.
Maximum Operating Conductor temperatures with Insulation:
1.1 Thermoplastic (PVC) = 75°C
1.2 Thermoset (XLPE or EPR) = 90°C
1.3 Cable Voltage Rating = 1 kV (Um = 1.2 kV)
3. F:Elementscable programscable ampacity calculation IEC.docx Page 3
Current-carrying capacities in amperes for methods of installation
PVC insulation, three loaded conductors/copper or aluminium –Conductor temperature: 70 °C, ambient
temperature: 30 °C in air, 20 °C in ground.
Current-carrying capacities in amperes for methods of installation
XLPE or EPR insulation, three loaded conductors/copper or aluminium – Conductor temperature: 90 °C,
ambient temperature: 30 °C in air, 20 °C in ground
MM2
DB
PVC- XLPE-
1-3/C-DB-COND
1-3/C -DB-
CABLE
1-3/C-DB-
COND
1-3/C -DB-
CABLE
2.5 24 24 28 30
4 30 33 36 39
6 38 41 44 49
10 50 54 58 65
16 64 70 75 84
25 82 92 96 107
35 98 110 115 129
50 116 130 135 153
70 143 162 167 188
95 169 193 197 226
120 192 220 223 257
150 217 246 251 287
185 243 278 281 324
240 280 320 324 375
300 316 359 365 419
400 400 400 400 500
4. F:Elementscable programscable ampacity calculation IEC.docx Page 4
2.2 Conductor Ampacity and Temperature de-rating factor (TDF)
Correction factor for ambient air temperatures other than 30 °C to be applied to the current-
carrying capacities for cables in the air.
AIR AMB TEMP
PVC-AIR-AMB-deg-C-10 1.22
PVC-AIR-AMB-deg-C-15 1.17
PVC-AIR-AMB-deg-C-20 1.12
PVC-AIR-AMB-deg-C-25 1.08
PVC-AIR-AMB-deg-C-30 1
PVC-AIR-AMB-deg-C-35 0.94
PVC-AIR-AMB-deg-C-40 0.87
PVC-AIR-AMB-deg-C-45 0.79
PVC-AIR-AMB-deg-C-50 0.71
PVC-AIR-AMB-deg-C-55 0.61
PVC-AIR-AMB-deg-C-60 0.5
XLPE-AIR-AMB-deg-C-10 1.15
XLPE-AIR-AMB-deg-C-15 1.12
XLPE-AIR-AMB-deg-C-20 1.08
XLPE-AIR-AMB-deg-C-25 1.04
XLPE-AIR-AMB-deg-C-30 1
XLPE-AIR-AMB-deg-C-35 0.96
XLPE-AIR-AMB-deg-C-40 0.91
XLPE-AIR-AMB-deg-C-45 0.87
XLPE-AIR-AMB-deg-C-50 0.82
XLPE-AIR-AMB-deg-C-55 0.76
XLPE-AIR-AMB-deg-C-60 0.71
5. F:Elementscable programscable ampacity calculation IEC.docx Page 5
Correction factors for ambient ground temperatures other than 20 °C to be applied to the current-
carrying capacities for cables in ducts in the ground.
GR AMB TEMP
PVC-GR-AMB-deg-C-10 1.1
PVC-GR-AMB-deg-C-15 1.05
PVC-GR-AMB-deg-C-20 1
PVC-GR-AMB-deg-C-25 0.95
PVC-GR-AMB-deg-C-30 0.89
PVC-GR-AMB-deg-C-35 0.84
PVC-GR-AMB-deg-C-40 0.77
PVC-GR-AMB-deg-C-45 0.71
PVC-GR-AMB-deg-C-50 0.63
PVC-GR-AMB-deg-C-55 0.55
PVC-GR-AMB-deg-C-60 0.45
XLPE-GR-AMB-deg-C-10 1.07
XLPE-GR-AMB-deg-C-15 1.04
XLPE-GR-AMB-deg-C-20 1
XLPE-GR-AMB-deg-C-25 0.98
XLPE-GR-AMB-deg-C-30 0.93
XLPE-GR-AMB-deg-C-35 0.89
XLPE-GR-AMB-deg-C-40 0.85
XLPE-GR-AMB-deg-C-45 0.8
XLPE-GR-AMB-deg-C-50 0.76
XLPE-GR-AMB-deg-C-55 0.71
XLPE-GR-AMB-deg-C-60 0.65
XLPE-GR-AMB-deg-C-65 0.6
XLPE-GR-AMB-deg-C-70 0.53
XLPE-GR-AMB-deg-C-75 0.46
XLPE-GR-AMB-deg-C-80 0.38
6. F:Elementscable programscable ampacity calculation IEC.docx Page 6
Correction factors for cables buried direct in the ground or in buried ducts for soil thermal
resistivities other than 2,5 K·m/W to be applied to the current-carrying capacities
soil thermal resistivity
Thermal Resistivity-K*m/W-1(DB) 1.5
Thermal Resistivity-K*m/W-1.5(DB) 1.25
Thermal Resistivity-K*m/W-2(DB) 1.12
Thermal Resistivity-K*m/W-2.5(DB) 1
Thermal Resistivity-K*m/W-3(DB) 0.9
Thermal Resistivity-K*m/W-1(DUCT) 1.18
Thermal Resistivity-K*m/W-1.5(DUCT) 1.1
Thermal Resistivity-K*m/W-2(DUCT) 1.05
Thermal Resistivity-K*m/W-2.5(DUCT) 1
Thermal Resistivity-K*m/W-3(DUCT) 0.96
7. F:Elementscable programscable ampacity calculation IEC.docx Page 7
Reduction factors for more than one circuit, cables laid directly in the ground –
Installation method – Single-core or multi-core cables.
DB-1/C OR 3/C
DB-Touching-Circuit-1 1
DB-Touching-Circuit-2 0.75
DB-Touching-Circuit-3 0.65
DB-Touching-Circuit-4 0.6
DB-Touching-Circuit-5 0.55
DB-Touching-Circuit-6 0.5
DB-One Dia apart-Circuit-1 1
DB-One Dia apart-Circuit-2 0.8
DB-One Dia apart-Circuit-3 0.7
DB-One Dia apart-Circuit-4 0.6
DB-One Dia apart-Circuit-5 0.55
DB-One Dia apart-Circuit-6 0.55
DB-0.125-m - apart-Circuit-1 1
DB-0.125-m - apart-Circuit-2 0.85
DB-0.125-m - apart-Circuit-3 0.75
DB-0.125-m - apart-Circuit-4 0.7
DB-0.125-m - apart-Circuit-5 0.65
DB-0.125-m - apart-Circuit-6 0.6
DB-0.25-m - apart-Circuit-1 1
DB-0.25-m - apart-Circuit-2 0.9
DB-0.25-m - apart-Circuit-3 0.8
DB-0.25-m - apart-Circuit-4 0.75
DB-0.25-m - apart-Circuit-5 0.7
DB-0.25-m - apart-Circuit-6 0.7
DB-0.5-m - apart-Circuit-1 1
DB-0.5-m - apart-Circuit-2 0.9
DB-0.5-m - apart-Circuit-3 0.85
DB-0.5-m - apart-Circuit-4 0.8
DB-0.5-m - apart-Circuit-5 0.8
DB-0.5-m - apart-Circuit-6 0.8
8. F:Elementscable programscable ampacity calculation IEC.docx Page 8
Reduction factors for group of more than one multi-core cable to be applied to reference current-
carrying capacities for multi-core cables in free air –
Reduction factors for group of more than one
multi-core cable
to be applied to reference current-carrying
capacities for multi-core cables in free air –
Ladder Tary-multi-layer-Circuit-1 1
Ladder Tary-multi-layer-Circuit-2 0.8
Ladder Tary-multi-layer-Circuit-3 0.7
Ladder Tary-multi-layer-Circuit-4 0.65
Ladder Tary-multi-layer-Circuit-5 0.6
Ladder Tary-multi-layer-Circuit-6 0.57
Ladder Tary-multi-layer-Circuit-7 0.54
Ladder Tary-multi-layer-Circuit-8 0.52
Ladder Tary-multi-layer-Circuit-9 0.5
Ladder Tary-multi-layer-Circuit-12 0.45
Ladder Tary-multi-layer-Circuit-16 0.41
Ladder Tary-multi-layer-Circuit-20 0.38
Ladder Tary-Single-layer-Circuit-1 1
Ladder Tary-Single-layer-Circuit-2 0.87
Ladder Tary-Single-layer-Circuit-3 0.82
Ladder Tary-Single-layer-Circuit-4 0.8
Ladder Tary-Single-layer-Circuit-5 0.8
Ladder Tary-Single-layer-Circuit-6 0.79
Ladder Tary-Single-layer-Circuit-7 0.79
Ladder Tary-Single-layer-Circuit-8 0.78
Ladder Tary-Single-layer-Circuit-9 0.78
9. F:Elementscable programscable ampacity calculation IEC.docx Page 9
3 CABLE IMPEDANCE CALCULATIONS
3.1 Conductor Resistivity
The Resistivity is defined as the electrical resistance of a body of unit length, and
unit cross-sectional area or unit weight.
Volume Resistivity is commonly expressed in ohms for a theoretical conductor of
unit length and cross-sectional area, in inch-pound units in Ω ·cmil / ft and in
acceptable metric units in Ω·mm2/m. It may be calculated by the following equation:
Where: = ρ = Volume resistivity, Ω·cmil / ft,
A = cross-sectional area, cmil,
L = gauge length, used to determine R, ft
R = measured resistance.
In Accordance with ASTM- B-193, Table 2
Volume resistivity for Copper, Ω·cmil/ft or Ω·mm2/m = 10.371
A
L
R
10. F:Elementscable programscable ampacity calculation IEC.docx Page 10
3.2 Temperature Correction
The measurement is made at any other than a reference temperature; the
resistance may be corrected for moderate temperature differences to what it would
be at the reference temperature, as follows:
Where:
Rt = resistance at reference temperature T2,
R = resistance as measured at temperature T1,
Alpha T = known or given temperature coefficient of
resistance
of the specimen being measured at reference temperature T,
T2 = reference temperature, and
T1 = temperature at which measurement is made.
NOTE 1—The parameter AlphaT, in the above equation, varies with
conductivity and temperature. For copper of 100 % conductivity and a reference
temperature of 20°C, its value is 0.00393.
Rt R 1 T2 T1
18. F:Elementscable programscable ampacity calculation IEC.docx Page 18
3.4 Conductor Reactance
D= Spacing between conductors
D= diameter of wire (2 x radius) + 2 x insulation thickness
r = Radius of conductors.
, the insulation thickness for multiconductor cables with outer coverings is as
follows,
XL 2 f L
L
8
1 4 ln
D
r
4 10
7
H
m
20. F:Elementscable programscable ampacity calculation IEC.docx Page 20
4 CABLE VOLTAGE DROP CALCULATIONS.
Permissible Voltage Drop, with respect to Load Power Factor.
Volt drop can be defined as the difference in magnitude of the voltage at the supply
compared to the voltage at the load. This voltage drop is based on the loads power
factor, the cable's internal resistance and reactance, and the cable length.
The three phase voltage drop permitted on the circuit run is calculated using the
following equation.
Vd.3 I L R cos ( ) X sin ( )( 3
Where:
Vd3p = three phase voltage drop, volts (V)
ө = Power factor Angle
I = current flowing in cable, amperes (A)
L = route length of circuit, meters (m)
R = AC resistance of cable, ohm/kilometer (W/km)
X = reactance of cable, ohm/kilometer (W/km)
21. F:Elementscable programscable ampacity calculation IEC.docx Page 21
5 CABLE SIZING & CURRENT-CARRYING CAPACITY
CALCULATION STEPS
To calculate the current-carrying capacity requirements of a circuit:
STEP-1 Determine the current requirements, based on 1.25 times the FLA
continuous current, of the Loads.
STEP-2 Select the Cable Size based on the De-Rated Ampacity of the
Cable.
STEP-3 Calculate Length x Amp factor for each size of the cable based on
% voltage drop and the circuit power factor, as per the following formula.
STEP-4 Calculate the length of the selected cable based on the FLA of the
circuit.
STEP-4 If the calculated length L is < than the circuit length D, then
calculate Length x Amp FLA x D of the circuit.
STEP-5 Select the cable FLA x D with the matching Length x Amp L X I
factor.
STEP-6 Calculate Length x Amp factor for each size of the cable based on
% voltage drop and the circuit power factor, as per the above formula.
STEP-7 Calculate the Circuit Voltage drop for the length of the circuit.
STEP-8 if the voltage drop exceeds the design criteria then increases the
Cable size to meet the voltage drop.
STEP-9 SELECTS THE CALCULATED CABLE SIZE.
IL
Vd3
R cos ( ) X sin ( )(
L
Vd3
R cos ( ) X sin ( )( )( I