Dynamic Polarization Depolarization Losses under Non Equilibrium Radial Heat Diffusion Conditions
Dynamic radial thermal gradients shift peak electric field stress outward and double dielectric depolarization losses compared to isothermal estimates.
Stress Migration
Meaning
Gradual shift in the location of the maximum mechanical or electrical stress within an insulating layer due to changing operational conditions. The occurrence of stress migration under high-voltage direct current conditions is driven by the temperature gradient and the electrical field.
Physical Process
During continuous operation, the temperature of the cable conductor rises, creating a hot zone near the center and a cold zone near the outer sheath. Because the conductivity of the polymer increases with temperature, the electrical stress slowly migrates from the hot inner conductor to the colder outer regions. This displacement means that the sheath must withstand higher electrical gradients than those present under isothermal conditions, posing a significant challenge to the long-term integrity of the cable.
Process Verification
High-voltage prototype testing involves monitoring this stress shift using non-destructive measurements and computer simulations. The cable undergoes continuous heating and cooling cycles while subjected to high voltages to track the movement of the stress front. Conducting these trials during the qualification stage ensures that the material formulation can withstand the dynamic shifts.
System Failure
If the material does not accommodate this stress shift, localized breakdown will occur at the insulation boundaries during load changes. Developing a resilient formulation that limits this stress movement is essential to prevent costly field failures after the cable is deployed. A fully verified design ensures that the stress profile remains within safe operational limits throughout the entire service life of the transmission system.