1 Department of Energy Engineering, Technical University of Denmark2 Department of Mechanical Engineering, Technical University of Denmark
A phenomenological unsteady, one-dimensional model is presented for the description of the hysteresis phenomenon of accommodated oil volume versus pressure observed when a cable is pressurized with oil and subsequently depressurized. The model includes the elastic deformation of oil channels, giving no hysteresis, and the elastic deformation of the solid structure in the porous paper insulation due to changes in pressure. The latter process give rise to hysteresis. The high pressure in inflow areas near oil channels during filling opens the pores, hence facilitates inflow, while the low pressure in the same areas during emptying makes the pores contract, hence hinders outflow. Numerical results illustrate the effect waiting time between step changes in pressure. It remains to relate model parameters to physical properties of cables. The model may be approximated by a zero-dimensional version with two time constants.