Table 2 Proposed features.

x₁

Flashover voltage

U_F

Extracted by measuring voltage at breakdown insulator)

x₂

Harmonics factor

I₅/I₃

Extracted from measured fifth and third harmonics component of LC

x₃

Electric Field

\(E= - \nabla V\)

Extracted by simulation insulators using FEM

x₄

Total harmonics index

\({\text{THD}}=\frac{1}{{{I_1}}}\sqrt {\sum\limits_{{n=1}}^{m} {{{\left( {{I_n}} \right)}^2}} } \times 100\%\)

Extracted by analyze leakage current signal

x₅

Insulation resistance

R = Us/LC

Extracted according to Ohm’s law from applied voltage and LC

x₆

Dielectric loss

tan = (90 − φ)

Extracted by measure phase shift between applied voltage and LC using MATLAB software.