On-site non-destructive dielectric response diagnosis of rotating machines

An on-site off-line non-destructive diagnostic tool for insulation assessment of rotating machines by means of the dielectric spectroscopy is introduced. The technique is based on time-domain measurement of both Polarization and Depolarization Current (PDC) in addition to frequency-domain processing of the measurement results in terms of the Dielectric Dissipation Factor (DDF) and Capacitance (C). The article emphasizes the importance of depolarization current, or equivalently the absorption current, which shall be measured in conjunction with polarization current for equal length of time, in order to identify the aging type of insulating materials. Factors affecting the measurement are discussed. The proposed interpretation of the dielectric response results demonstrates a need for using both time-domain and frequency-domain analyses as well as provides a decisive measure for safe operation of rotating machine.