On the Feasibility of Using Poles Computed from Frequency Domain Spectroscopy to Assess Oil Impregnated Paper Insulation Conditions

Abstract

Frequency Domain Spectroscopy (FDS) is an effective tool allowing assessing the condition of oil-paper insulation system in power equipment. However, results from these measurements are known to be greatly influenced by various parameters, including insulation aging, moisture content, and insulation geometry/volume, together with environmental condition such as temperature. In this contribution, a series of experiments have been performed under controlled laboratory conditions. The dielectric response of the oil impregnated paper, along with the degree of polymerization and moisture content, were monitored. Since dielectric parameters are geometry dependent, poles (independent of the geometry) which depends on resistivity and permittivity, were considered to assess the condition of the insulation. From the investigations performed on new and aged samples, it is shown that poles (P) can be regarded as insulation aging indicator. It is also shown that a per unit value based on the Dielectric Dissipation Factor (DDF), measured in the frequency range from 1 to 1000 Hz can be correlated to moisture content in the insulation paper.

Study on Quantitative Correlations between the Ageing Condition of Transformer Cellulose Insulation and the Large Time Constant Obtained from the Extended Debye Model

“…So far, many of the research findings in relation to PDC behavior have been commonly reported for diagnosing water content and ageing condition in transformer cellulose insulation [16][17][18]. However, it is somewhat difficult for power utilities to reliably and accurately predict the water content and ageing condition using the PDC technique due to the different insulation size and geometry in transformers [22][23][24][25]. Fofana et al [22] and Hadjadj et al [23] investigated whether the poles could be utilized for predicting the ageing condition of the whole transformer insulation.…”

“…However, it is somewhat difficult for power utilities to reliably and accurately predict the water content and ageing condition using the PDC technique due to the different insulation size and geometry in transformers [22][23][24][25]. Fofana et al [22] and Hadjadj et al [23] investigated whether the poles could be utilized for predicting the ageing condition of the whole transformer insulation. This new idea represented a major contribution because the poles are geometry independent.…”

Study of the Impact of Initial Moisture Content in Oil Impregnated Insulation Paper on Thermal Aging Rate of Condenser Bushing

“…The results researched by Issouf Fofana et al indicate that capacitance ratio and direct current conductivity deduced from the spectroscopic measurements can be used to accurately monitor insulation condition, and both parameters were found to increase with moisture or aging duration [8]. In addition, the poles computed from frequency domain spectroscopy also can assess oil-paper insulation condition [11]. It is mentioned in [12,13] that the dielectric spectroscopy of oil-paper condenser bushing is different from that of oil-paper in transformers at low frequency interval and the characteristics of dielectric spectroscopy at frequency interval 10´2-10 3 Hz can sensitively reflect the variation of moisture content in condenser bushing.…”

“…From another perspective, the frequency domain dielectric spectroscopy (FDS) results of oil-impregnated paper may be impacted by the moisture content and the aging time, simultaneously. Some separation attempts of moisture content and aging time have been reported recently, but it must be emphasized that moisture and aging separation still constitute a challenging point in this domain [11,30,31].…”

“…At present, dielectric spectroscopy in time or frequency domain offers new opportunities for an off-line, insulation condition assessment of high voltage (HV) electric power equipment and its predictive maintenance nondestructively and reliably in the field [8][9][10][11]. Dielectric spectroscopy techniques in time and frequency domain can be applied to monitor the condition of oil-impregnated paper condenser bushings [9].…”