The aim will be to investigate the effect of thermal and mechanical stresses on the electric field intensity that could subsequently lead to stress enhancement or partial discharge. The project can be divided into three main stages. Firstly, thermal mechanical deformation, gaps and the possibility of void under multi-stresses in joints (at the interface of insulation materials) will be verified. Then, the electric field will be examined in the faulty regions if any is formed. Then, a numerical model will be established to estimate the pressure at the interface. The second stage, will examine the effect of mechanical stresses at interfaces in three core cables by coupled thermal mechanical electrical model.