Real-time electric field estimation for HVDC cable dielectrics

For HVDC cables, dielectric field inversion normally occurs due to the temperature drop across the insulation. Unlike AC applications where the field distribution is primarily determined by the cable geometry, the DC field can be significantly affected by the load current and hence the dielectric temperature profile. Higher temperature drops lead to higher electrical stress at the insulation screen, increasing the risk of breakdown. Thus, a real-time dielectric DC field estimator would be very useful to prevent over-stressing the cable. Theoretically, the electrical field can be calculated from the overall dielectric temperature drop. Therefore, by monitoring the temperature profile and integrating with mathematical algorithms, the DC field distribution might be assessed in real time. In this paper, a mathematical algorithm for calculation of the DC field is demonstrated, using standard online temperature monitoring techniques.