Very high voltage can generally be measured with a capacitor divider. In order to design such a sensor on one hand and to standardize it on the other, a calculation of the field distribution is necessary to determine the different capacitances of the system. A large number of numerical methods are very efficient for this. However, the constant improvement of dielectric materials allows us to use thinner and thinner insulations to the point where traditional methods seem inadequate. This is why the authors propose and analyse the different approaches that they have used to treat this problem. This is how first an extended finite elements method with the calculation of floating potential and of analytical elements to simulate thin layers, then a method of two potentials Boundary Integral Equation; on one hand using a direct approach, on the other introducing external global value like capacitances. In conclusion, we shall analyse the efficiency of these methods.