This paper investigates the influence of insulations’ physical and geometrical parameters on cable sheath transients and insulation losses considering power cables for high voltage alternating current (HVAC) applications. The study is based on theoretical analysis, Electromagnetic Transient Program (EMTP) simulations, and finite element (FE) simulations. Special attention is paid to the effects of the insulations’ relative permittivities and the protective jacket thickness on cable capacitance, transient voltages, and dielectric losses for different possible conditions including the variations in insulation permittivity and ground resistivity. The cable model used in this work is a single core (SC) underground coaxial cable with an AC voltage supply of 220 kV and 60 Hz frequency. A method for calculating the dielectric losses in cable insulations due to transient voltages was developed. The proposed method is based on the numerical calculations of the flowing electric currents through insulations using FE model. In addition, the relation of the dielectric loss and the maximum sheath overvoltage as a function of permittivites and as a function of protective jacket thickness was explored to obtain an optimum protective jacket relative permittivity from the viewpoint of both the overvoltage and the loss. For given cable system parameters, the transient voltage waveforms within a time period of t = 0–2 ms obtained on the core and the sheath produced dielectric losses 34.362 [W/m] and 3.365 [W/m] at insulation and protective jacket, respectively.Results and conclusion provide a useful background for the ongoing power cable design process and application studies.