The problem of residual polarization can be overcome by :
- The terminals of the insulation shorted for a few minutes.
- The terminals are reversed after each measurement.
When a steady DC voltage is applied to an insulation, the observed behavior is a analogous to that of changing a leaky capacitance through a series high resistance. The resultant current comprises of these components.
- A charging current due to the natural capacitance. This is large in the beginning and becomes negligible in a few seconds.
- The absorption current flaws in the body of the dielectric and decays with time. The time may run to many minutes, this absorption current gives rise to polarization residue effect.
- The actual conduction current through the insulation. This is constant with time. But can vary with voltage & temperature.
- The surface leakage current depends much on Humidity contamination.
- Mechanical vibrations may rupture insulation.
- Temperature decreases thermal strength.
- Dust & moisture cause contamination & decay.
- Corrosive material & electrochemical reactions.
- Intrinsic breakdown.
- Thermal effects.
- High voltage bridge.
- Leakage current measurement method.
- Loss of charge method.
Pages 1, 2, 3 of DRT101 Insulation Tester and Tera Ohm Meter Operating Manual, A product that i used to make-n-sell. - delabs