Correlation between capacitance and dissipation factor used for assessment of stator insulation
Authors: Oslinger, J. L.; Castro, L. C. Journal: Waset, vol. 63, no. 72, pp. 365–371
Publication year: 2012
Keywords: Harmonics, Fourier,
Sequence Components, Distribution factor.
Abstract: Measurements of
capacitance C and dissipation factor tanδ of the stator insulation system
provide useful informationabout internal defects within the insulation. The
index k is defined asthe proportionality constant between the changes at high
voltage of capacitance ΔC and of the dissipation factor Δtanδ. ΔC and Δtanδ values
were highly correlated when small flat defects were within the insulation and
that correlation was lost in the presence oflarge narrow defects like
electrical treeing. The discrimination between small and large defects is made
resorting to partial discharge PD phase angle analysis. For the validation of
the results, C and tanδ measurements were carried out in a 15MVA 4160V steam
turbine turbogenerator placed in a sugar mill. In addition, laboratory
test results obtained by other authors were analyzed jointly. In such laboratory
tests, model coil bars subjected to thermal cycling resulted highly degraded and
DC and Δtanδ values were not correlated. Thus, the index k could not be
calculated.
