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: Tapan Kumar Saha, Oct 03, 2014
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    • "When inferring the transformer LOL acceleration rate using these methods, the calculation of the winding hot-spot temperature (HST) is the most critical issue [3], [4]. The methods proposed in [1], [2] were followed by a series of papers [5]–[7], [12], [13], [15] dealing with more accurate calculations of HST. Although deterioration of insulation is a function of temperature , moisture content, oxygen content and acid content, the model presented in this paper is based only on the insulation temperature [9]. "
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    • "The switching device was designed and operated based on the PDC measurement technique as recorded in many previous general literatures [1] [2] [3] [4] [5]. It consists of hardware (the switch; Fig 5), software (the computer program, LabVIEW), computer & the voltage source/ammeter. "
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    • "The DDF (also known as tan δ) is propriety of an electrical insulation system; low values of it are usually regarded as proof of good quality of the insulation. The progressive increase of the DDF is closely related to the chemical degradation which accompanies thermal ageing of the insulation system [1] [2] [3] [4] [5]. "
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