Dielectric Loss in the Cable

The following losses take place in the Cable.

Heating of cable

• The heating of cable depends upon dielectric loss, copper loss and inter sheath loss.

Copper Loss

• The copper loss depends upon current passing through conductor and resistance of the cable.

Inter sheath loss

• The inter sheath loss occurs due to circulating current flows in between the sheaths.

Dielectric loss

• The capacitor is formed between core and sheath. 
• There is no dielectric loss if the capacitor is pure but this is not possible. 
• The capacitor is represented by parallel combination of resistance and capacitor.  
• The Phasor diagram is shown in the Figure. 
• The current in the cable leads voltage by an angle less than 90 degree due to presence of resistance. 
• The losses occur in the capacitor because the cable is not perfect dielectric.

The capacitor current I_C flows

    I_C = V / X_C

         = ωVC

tan δ = I_R / I_C

        = ( V / R ) / ωVC

        = V / ωVC R

        = 1 / ωCR

    R = 1 / ωC tan δ

The dielectric loss P = V² / R

                                 = V² ωC tan δ

Where δ = Dielectric Loss angle

• As the dielectric loss angle is very small, it is considered as tan δ ≈ δ       The dielectric loss P = V² ωC  δ

Parameters affecting Dielectric Loss

• The dielectric loss is directly proportional to square of applied voltage and directly proportional to frequency.

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