1 Contemporary Diagnostic Methods of HV Rotating Machine and Transformer Insulation

Dielectric polarization of insulating materials is analyzed to assess the condition of HV motor insulation. Ramp application of the test voltage, measurement of the dielectric loss factor (tgδ), and capacitance at very low frequency (Frequency Domain Spectroscopy) are used to evaluate the condition of composite solid insulation. Examples of large HV rotating machines are presented that experienced different operating conditions. It has been concluded that FDS can be used to assess the condition of “epoxy-mica-glass ” insulation in service and during production, as well as acceptance tests. Measurements of Polarization and Depolarization Current (PDC), as well as FDS are employed to evaluate the condition of paper-oil insulation of HV transformers. A co-relation between cellulose conductivity and certain parameters of PDC can be used to assess the condition of paper-oil insulation, and specifically its water content. Measurements have confirmed an agreement between the water content determined using FDS and the Recover