is classified into three testing techniques. - Resistance test: sometimes called Polarization Index, PI, is the relationship between the measured resistance at tenth minute, R10, and at first minute, R1.
- Insulation power factor Test: detects the insulation integrity of windings and also determines a power factor of overall insulation including bushings, oil and windings.
- Capacitance test: inspects winding deformation and structure problems such as displaced wedging and supports of winding and core. Its value will be compared to previous ones or factory tests.