Dielectric loss in cable - QuickField simulation example
IEC 60287* suggests that for unfilled XLPE cables rated above the 127 kV level dielectric losses should be calculated.
How to calculate the capacitance and dielectric losses in the cable?
Answer Typical applications Geometry
Given
Task
Solution
Capacitance = charge / potential difference.
Results
References:
Engineering question
Use an AC-conduction model with the peak voltage; represent dielectric loss by the equivalent conductivity derived from loss tangent, then obtain capacitance from charge-to-voltage ratio and dielectric loss from active power.
XLPE power cables, HV cable insulation systems, underground cable insulation
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Simulation problem
Problem Type
Plane-parallel problem of AC conduction.
Cable length is 1 km
Voltage U = 132 kV (r.m.s.), frequency f = 50 Hz.
XLPE permittivity 2.5, loss tangent tan(δ) = 0.001
Calculate the capacitance and dielectric losses in the cable.
In AC conduction problem we should specify the electric potential amplitude, which is U * √2.
Electrical conductivity of materials should be set in AC conduction problems. We can take into account dielectric losses by specifying the apparent value of the conductivity**:
σ = 2πf·εε0·tan(δ) = 2*3.142*50*2.5*8.854e-12*0.001 = 6.95 pS/m.
Cable dielectric losses are 809 W per 1 km of the cable length.
Conductor-to-screen capacitance is C = 0.02758 / (132000* √2) = 0.148 μF per 1 km of the cable length. Reference*** value is 0.147 μF/km.
*IEC 60287-1-1. Electric Cables - Calculation of the current rating.
** Wikipedia, Dielectric loss.
*** XLPE Al single core 76/132 kV cable datasheet.
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