A method for determining the state of a cable insulation parameter of a cable in an electrical system, the method comprising the steps of: providing, by an AC voltage source, a plurality of alternating current signals between a conductor of the cable and an electrical ground, wherein the plurality of alternating current signals comprise a plurality of frequencies, in which each alternating current signal comprises a different frequency greater than zero; measuring a frequency response for each of the plurality of alternating current signals; determining a plurality of phase shifts, each of the plurality of phase shifts being between each injected alternating current signal and the corresponding measured frequency response, characterized by: If each of the phase shifts being represented as a phasor vector having a magnitude and a phase angle and including a resistive component and a capacitive component, the method further comprising the step of: extrapolating the phasor vectors to: i) estimate the cable insulation parameter being an insulation resistance leakage current corresponding to the resistive component when the capacitive component is zero to provide a DC insulation resistance value, or ii) estimate the cable insulation parameter being the insulation capacitance by extrapolating the plurality of phase shifts to a point that is asymptotic and determining the capacitive component at the asymptotic point. providing, by an AC voltage source, a plurality of alternating current signals between a conductor of the cable and an electrical ground, wherein the plurality of alternating current signals comprise a plurality of frequencies, in which each alternating current signal comprises a different frequency greater than zero; measuring a frequency response for each of the plurality of alternating current signals; determining a plurality of phase shifts, each of the plurality of phase shifts being between each injected alternating current signal and the corresponding measured frequency response, characterized by: If each of the phase shifts being represented as a phasor vector having a magnitude and a phase angle and including a resistive component and a capacitive component, the method further comprising the step of: extrapolating the phasor vectors to: i) estimate the cable insulation parameter being an insulation resistance leakage current corresponding to the resistive component when the capacitive component is zero to provide a DC insulation resistance value, or ii) estimate the cable insulation parameter being the insulation capacitance by extrapolating the plurality of phase shifts to a point that is asymptotic and determining the capacitive component at the asymptotic point. each of the phase shifts being represented as a phasor vector having a magnitude and a phase angle and including a resistive component and a capacitive component, the method further comprising the step of: extrapolating the phasor vectors to: i) estimate the cable insulation parameter being an insulation resistance leakage current corresponding to the resistive component when the capacitive component is zero to provide a DC insulation resistance value, or ii) estimate the cable insulation parameter being the insulation capacitance by extrapolating the plurality of phase shifts to a point that is asymptotic and determining the capacitive component at the asymptotic point. i) estimate the cable insulation parameter being an insulation resistance leakage current corresponding to the resistive component when the capacitive component is zero to provide a DC insulation resistance value, or ii) estimate the cable insulation parameter being the insulation capacitance by extrapolating the plurality of phase shifts to a point that is asymptotic and determining the capacitive component at the asymptotic point.