Cable Parameters: Insulation Resistance,Charging Current, Dielectric Losses

Cable Parameters: Insulation Resistance, Charging Current, Dielectric Losses

Before we formulated cable basic parameters resistance, inductance, and capacitance, now we will try to 3 more parameters like Insulation Resistance, Charging Current and Dielectric Losses.

Cable Insulation Resistance:

Using the following formula you can calculate insulation resistance in mega-ohm per kilometer of cable, to do this you consider the insulation material, diameter of cable including a semiconductor layer, and the diameter of the insulated core.

R =K In (D/d )  MΩ/km

Where

R = Insulation resistance in MΩ/km;

K = Constant depends on the insulation material;

d = Diameter of the conductor in mm including the semiconducting layer;

D = Diameter in mm of the insulated core;

MΩ- mega ohm, km- kilo meter, mm- mili meter.

Cable Charging Current:

The charging current is the capacitive current that flows when AC voltage is applied to the cables as a result of the capacitance between the conductor and earth, and for a multi-core cable in which cores are not screened, between conductors. The value can be calculated from the following equation.

IC = Uo ωC 10^-6   A/km

Where

IC = Charging current in Ampear/km;

Uo =Voltage in volt between phase and earth;

ω= 2 π f (π=22/7, f= frequency in hertz) Hz;

C= Capacitance in micro-farad per kilo-meter to neutral;

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Cable Dielectric Losses:

To calculate the dielectric losses of an AC cable are proportional to the Capacitance, the frequency, the phase voltage and the power factor. The value in watt per kilo-meter per phase can be calculated from the following equation.

WD = 2 π f C Uo² tanδ 10^-6   watt/km/phase

Where 

WD = Dielectric losses in watt/km/phase;

f = Frequency in hertz;

C = Capacitance in micro-farad per kilo-meter to neutral;

Uo = Voltage in volt between phase and earth;

tanδ=Dielectric power factor.