20 January 2020

Dielectric Loss in the Cable

The following losses take place in the Cable.
Heating of cable
Copper Loss
Inter sheath loss
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 IC flows
    IC = V / XC
         = ωVC
tan δ = IR / IC
        = ( 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
  • The dielectric loss is directly proportional to square of applied voltage and directly proportional to frequency.
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