| Charging current |
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The charging current is the capacitive current which flows when A.C voltage is applied to the cable as a result of the capacitance between the conductors and earth and, for a multicore cable in which the individual cores are not screened ,between conductors. The value can be derived from the equation. |
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Ic = Uo co C 10-6 (A/km)
Where:
Uo = Voltage between phase and arth.(V)
ω = 2πf
F = Frequency HZ
C = capacitance to neutral (μf/km) |
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Dielectric losses
Losses The dielectric losses of an A.C cable are proportional to the capacitance, the frequency, the phase voltage and the power factor. They are given by:
D =2π f c Uo'tan δ 10-6(watt/km/phase) |
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Where:
f = Frequency HZ
C = capacitance to neutral (μf/km)
Uo = voltage between phase and earth.(V )
tan δ = Dielectric pwoer factor |
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Voltage Drop When current flows in a cable conductor there
is a voltage drop between the ends of the conductor which is the product of the current and the impedance .The following equations should be used to calculate the voltage drop:
1- Single phase system
Vd = 2 ( R cos Φ + x sin Φ) (Volt/amp/meter)
2- Three phase system
Vd =√3(R cosΦ + x sinΦ) (Volt/amp/meter)
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Where:
Vd = voltage drop mV/amp/m
R = a.c resistance of conductor at a maximum conductor temperature
X = Inductive reactance of cable (Ω/km)
cos Φ = power factor of load (Ω/km)
* Data voltage drop for LV Cagles are tabulated in tables 17 to 24. |
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