155 / 2018-08-25 16:47:51

Variation of loss angle with frequency as a diagnostic tool for insulation condition assessment

insulation condition,loss angle,fault diagnosis

Insulation quality plays a significant role in the performance of high voltage systems. The condition assessment of the insulation is essential for secure and reliable operation of any HV equipment. Aging and degradation of the insulation, coupled with the ingress of water, increases the amount of energy that is converted to heat in the insulation. Therefore, if degradation of the insulation can be detected/diagnosed earlier, then corrective action such as repair, oil treatment or drying can be initiated.

Diagnosis of insulation systems requires certain destructive and non-destructive tests. There are many methods such as RVM (Recovery Voltage Measurement), PDC (Polarization and Depolarization Currents), FDS (Frequency Domain Spectroscopy) and measurements of capacitance C and loss tangent (tan δ). Thus Tan Delta (tan δ) is a diagnostic method used to determine the general quality of the insulation and dielectrics. With tan δ or dissipation factor testing systems, we can determine the insulation quality as a function of Voltage (V), Temperature (T) and frequency (f). If the power system parameters such as frequency and voltage level are not steady, then measured tan δ values will also change. Therefore, tan δ measurements should be realized in case of unsteady power system conditions to get more exact diagnostic results.

Measurements of loss angle (tan δ) is a classical method and more attention is being paid to such measurements over a wide frequency range. Particularly at low frequency measurements of tan δ seem to yield much information about the state of the insulation. The values of tan δ, as well as other parameters of dielectrics, for a given specimens of material, are not strictly constant and depend on various factors as frequency, temperature, humidity and voltage. Thus it is important to understand such relationships by experimental investigations.

In this study measurement of tan δ at different frequencies (such as 60 Hz, 0.1 Hz, 0.01 Hz etc.) for HV cables, cable joints and insulators will be evaluated. The measurements are taken under normal environmental conditions and different aging conditions in the laboratory. Finally, the obtained values of tan δ from the measurements will be analyzed in order to determine if there is a co-relation between tan δ as a function of frequencies (f) with the insulation condition.