Rp resistance (IR)
The insulation resistance Rins of a capacitor is a measure of its resistivity in DC. Under a stationary DC voltage, a leakage current flows through the dielectric and over the capacitor surfaces. Rins is measured by determining the ratio of the applied DC voltage to the resulting leakage current flowing through the capacitor, once the initial charging current has ceased (typically after a period of 1 min ± 5 s). The measuring voltage depends on the rated voltage. It is specified in IEC 60384-1, section 4.5.2:
The specified measuring temperature is 20 °C. At other temperatures, a correction shall be made to the measured value to obtain the equivalent value for 20 °C by multiplying the measured result by the appropriate correction factor.
In case of doubt a reference measurement at 20 °C and (50 ± 2)% relative humidity is decisive. In the data sheets for the individual types, the insulation resistance Rins is given as a minimum asdelivered value and as a limit value attained after the "damp heat, steady-state" test. For capacitors with capacitance ratings >0.33 microF the insulation is given in terms of a time constant. tau = Rins CR (in s)(conversion tip: 1 MΩ μF = 1 s)
The insulation resistance is affected by temperature.