A Novel Universal Approach for Temperature Correction on Frequency Domain Spectroscopy Curve of Transformer Polymer Insulation

Abstract

It is a fact that the frequency domain spectroscopy (FDS) curve at different temperatures can be corrected by the shift factor (αT) extracted from the master curve. However, the αT and master curve reported by previous works are distinctive due to the difference in the construction algorithm. Therefore, it is of great significance to report a universal approach for extracting αT. In this work, the unaged oil-immersed pressboards with different moisture content (mc%) are firstly prepared and selected as the research specimen. Then, the αT of FDS curves on the above pressboard is extracted based upon the master curve technique. The influence mechanism under the various test temperature (T) and mc% is therefore analyzed so as to establish a universal model for predicting the αT. The present findings reveal that the αT value extracted from FDS curves is both temperature-dependent and moisture-dependent. In addition, the predicted αT is not only suitable for temperature correction on FDS curve of same type pressboard with different insulation conditions (moisture contents and aging degrees), but also maintains considerable accuracy when applied to different types of pressboard. Therefore, the obtained conclusions will provide a universal method for temperature correction on FDS curve of transformer polymer insulation.

Correction for Polarization Current Curve of Polymer Insulation Materials in Transformers Considering the Temperature and Moisture Effects

“…addition, the balance of moisture between the insulating oil and pressboards is also affected by temperature changes, which influences the relaxation behavior to some extent. In fact, studies have shown that the test temperature only shifts the PDC curve without changing its shape [16][17][18]. The PDC curves of the oil-immersed polymer pressboards tested at different temperatures can be shifted to coincidence by a series of the movement (horizontal and vertical).…”

“…where T is the test temperature, Tref is the reference temperature, τT is the time-shift factor at temperature T, while tT and tTref are the time corresponding to a certain point in the polarization current curve at T and Tref, respectively. Similarly, αT is the amplitude-shift factor, while hT and hTref In fact, studies have shown that the test temperature only shifts the PDC curve without changing its shape [16][17][18]. The PDC curves of the oil-immersed polymer pressboards tested at different temperatures can be shifted to coincidence by a series of the movement (horizontal and vertical).…”

“…Saha and Purkait [14] investigated the PDC curves at different temperatures to indicate that the polarization time will be shortened as the temperature increase. In response to the above research results, the master curve technique based on the time-temperature superposition theory is used as an available model to correct the temperature effect of the transformer polymer insulation materials, which provides a novel idea for related research [15][16][17][18][19][20]. However, the temperature effect is considered as the single factor affecting the PDC test results in the existing research, which ignores the fact that moisture content is also an important factor affecting the polarization data of polymer material.…”

Physical Model for Frequency Domain Spectroscopy of Oil–Paper Insulation in a Wide Temperature Range by a Novel Analysis Approach

“…Jonscher's research emphasizes that a special non-Debye process, called low-frequency dispersion (LFD), will also lead to a linearly decreasing trend in ε"(ω), but its mechanism and frequency response characteristics are significantly different from the charge conduction [18]. Moreover, power equipment may be tested by FDS in a wide temperature range due to factors such as location, season or cooling time after ceasing operation; in this case, temperature will play an important role in determining the charge's trap-hopping motions [19]. Thus, there is no doubt that the dominant microscopic processes of a certain dielectric material's corresponding FDS curves will change if the testing temperatures are considerably different.…”

A Modified Aging Kinetics Model for Aging Condition Prediction of Transformer Polymer Insulation by Employing the Frequency Domain Spectroscopy

“…Existing researches show that the degree of polymerization (DP) can be serviced as the most direct and effective indicator for reflecting the aging condition (mechanical strength) of polymer insulation [1][2][3]. Reviewing the published researches, we found out that the method for predicting (or measuring) the DP value of transformer polymer insulation consists of several prevailing approaches, such as the direct method (viscosity testing) [4] and indirect methods (including the Frequency Dielectric Spectroscopy (FDS) [5][6][7][8][9] technique, aging kinetics model [10][11][12], etc.). Although the viscosity test method is accurate enough, it is not appropriate for analyzing the field equipment due to its destructiveness.…”