On the computation of electric field and temperature distribution in HVDC cable insulation

Abstract

The paper presents certain aspects of electrical / thermal failure of dc power cables. Closed form theoretical formulations for computing the critical stress and temperature due to an external heat source in the form of a steady current through the conductor is presented. The criticality here implies an unstable state of the dielectric and is shown, more often than not, to be different, from that corresponding to thermal decomposition limits. Formulation and solution of continuity equations under first and second kind boundary conditions taking account of electric stress and temperature-dependent dc conductivity is covered. Using the suggested model, stress and temperature distribution in the body of the insulation can be obtained to a reasonable degree of accuracy.Index Termsdc cable, thermal breakdown, critical stress, critical temperature, stress distribution, temperature distribution, thermal instability.

Numerical investigation of temperature and electric field dynamics in polymer insulation at HVDC

“…Such effects can be incorporated in the numerical model by allowing the conductivity model (8) to include other terms than the temperature and field dependence terms. IV.…”

“…The conductivity models were derived from experimental data presented in [7]. The mathematical model is based on analytical solutions to the steady-state temperature field and the electric field assuming constant thermal conductivity and an exponential field dependence of the electrical conductivity, see also [8]. The thickness dependence of the thermal breakdown strength was shown, and the thermal breakdown strength for a 0.2 mm thick sample was almost twice as high as for a 20 mm sample.…”

On the thermal breakdown of AC cables and transformer bushings

“…Theory of thermal breakdown is based on two continuity equations, namely, thermal continuity equation and current continuity equation [1][2][3][4][5][6][7]. While Fourier's thermal continuity equation is well accepted, recently, there have been certain concerns or misunderstandings on the legitimacy of using current continuity equation instead of Poisson's or Maxwell's equations for electric field or thermal maximum voltage.…”

“…Although the use of current continuity equation for such purpose is not new [1][2][3][4][5][6][7], considering the importance of the concerns the author wishes to put forth some developments on Maxwell's equations.…”

“…It has been recently reported that the thermal maximum voltage under dc conditions gets decreased due to external heat injection that causes some difference in boundary temperatures and unidirectional temperature gradient [6][7][8][9][10].…”