Application of low frequency dielectric spectroscopy to estimate condition of mineral oil

Conventional loss factor and capacitance measurements are used to determine condition of insulating liquid. In the new IEC 61620 standard capacitance and conductance are measured at low voltage and low frequency with square wave method to over come some difficulties of the conventional method. Nowadays low frequency dielectric spectroscopy becomes a powerful diagnostics tools for high voltage apparatus and utilities provide spectroscopy measurement system for diagnosis of their power apparatus. In this paper is shown that the space charge polarization can be observed with low frequency spectroscopy for insulating liquids. Increase of capacitance at low frequency can be defined as a new parameter and help to accurate determination of state of insulating liquid. Space charge polarization of insulating liquids can influence the result of dielectric spectroscopy of liquid impregnated insulation system too and must be considered for better interpretation of spectroscopy results.