Investigations of Temperature Effects on the Dielectric Response Measurements of Transformer Oil-Paper Insulation System

Queensland Univ., Brisbane
IEEE Transactions on Power Delivery (Impact Factor: 1.73). 02/2008; 23(1):252 - 260. DOI: 10.1109/TPWRD.2007.911123
Source: IEEE Xplore


Dielectric testing techniques, in both time and frequency domains, are currently widely used by power utilities for assessment of the condition of transformer oil-paper insulation systems. However, it has been reported that results of these tests are highly influenced by the operating temperature during measurements. The distribution, migration and equilibrium of moisture between oil and paper in a complicated insulation system is highly temperature dependent. It requires adequate experience and proper understanding to interpret the dielectric response results in the presence of temperature variations and thermal instability. Proper analysis of the dielectric test result is only possible with an understanding of the physical behavior of the insulation system in response to temperature. A circuit model, which describes the dielectric behavior of the transformers main insulation system, has been investigated in this paper. The values of the parameters of the model have been identified from the dielectric tests. A correlation has been observed between the operating temperature and the equivalent model parameters that can be used as additional information for better interpretation of the dielectric test results. This paper thus reports a detailed study on the effects of temperature on dielectric measurements of a transformer under controlled laboratory conditions. Some results of practical on-site testing are also presented to demonstrate the possibility of errors that may be introduced in dielectric test results analysis unless temperature effects are taken into consideration.

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Available from: Prithwiraj Purkait, Jan 14, 2016
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    • "As a consequence, the deterioration of paper can lead to short circuits resulting in the transformer failure. Degradation and aging of insulation is, consequently, recognized as one of the major causes of transformer breakdown [2] [3] [4] [5] [6] [7] [8] [9] [10]. In order to ensure the proper functioning of these transformers, several diagnostic techniques are used with the aim of knowing the condition of the transformer insulation system and taking the necessary measures for its care and its maintenance. "
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    ABSTRACT: This paper presents a study of the impact of two important parameters, moisture and aging of the oil/paper dielectric used as insulation in power transformers.The way in which these two parameters influence different parameters of the Frequency Domain Spectroscopy (FDS) measurements, is emphasized.Different FDS parameters were measured by varying the moisturecontent and the aging degree of the oil impregnated paper.The use of two types of neural networks for analysis of the results was necessary in order to help discriminating the impact of moisture and aging on the FDS measurements and, in some cases, to estimate the aging duration of the paper impregnated with oil.
    Full-text · Article · Aug 2015 · IEEE Transactions on Dielectrics and Electrical Insulation
    • "The solubility of water in oil changes as it degrades[4], and thus, the accuracy of measurements involving adsorption isotherms decreases over time. A notable improvement in the measurement of water concentration has been the use of dielectric response methods (in the time or frequency domain)[5]. These methods indirectly measure the concentration of water adsorbed by the insulation paper and the pressboard between the windings of a transformer. "
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    ABSTRACT: It is necessary to monitor the water content of the paper insulation (WCP) within a power transformer because, if it becomes too large, the paper insulation may age prematurely or the transformer may fail on overload. It is nearly always unfeasible to extract a paper insulation sample from a transformer for a laboratory measurement of its water content because it involves removing part of the insulation.
    No preview · Article · Jun 2015 · IEEE Electrical Insulation Magazine
    • "Above all, these measurements so far discussed are applied on de-energized transformers, which require the transformers under test shut down for days and disturb the continuous power supply. Although efforts in1011121314have been put on investigations of influence factors of dielectric response, such as temperature and geometric structure, results are rarely reported for dielectric response of a transformer under an energized condition. Therefore, one objective of this paper is to improve the FDS to measure the dielectric response in an energized environment by carefully designing the measurement circuit. "
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    ABSTRACT: Frequency domain spectroscopy (FDS) is being used to assess the insulation condition of oil-paper power transformers. However, it has to date only been implemented on de-energised transformers, which requires the transformers to be shut down for an extended period and may cause significant costs. To solve this issue, a newly improved monitoring method based on the FDS principle is proposed to implement the dielectric measurement on energised transformers. Moreover, a chirp waveform excitation and its novel processing method are introduced. Compared with the conventional FDS results, dielectric results from the energised insulation system have higher tanδ values because of the increased losses. To further understand the insulation ageing process, the effects of the geometric capacitance are removed from the measured imaginary admittance of the insulation system to enhance the ageing signature. The resulting imaginary admittance is then shown to correlate well with the central time constant in return voltage measurements results. The proposed methods address the issues on techniques used on energised transformers and provide a clue for on-line FDS diagnostic application.
    No preview · Article · Jan 2015 · IET Science Measurement ? Technology
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