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Experience with transformer diagnostics based on dielectric response measurements in time domain DOI:10.15199/48.2018.10.23

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Several different methods such as an oil analysis or/and different electrical measurements are available to perform the condition assessment of oil filled transformers. The estimation of the dielectric parameters of oil-paper insulation takes an important part of existing methods. The measurement of the dielectric response can be performed in the time or/and frequency domain [1, 2, 3]. The experimental results and modelling of the dielectric response in the time domain for transformer diagnostic known from the literature show high sensitivity of the results to the change of the basic material properties such as conductivity [4]. As it shown in [5] the moisture and contamination tend to increase the conductivity of the solid and liquid dielectric in the transformer. According to [6] the use of the measurement methods in the time domain show advantages especially for the condition assessment of complex transformer geometries. The measurement of dielectric response in the field conditions requires reliable solutions and technique to be able to minimize the influence of the surround conditions in the field and to reduce also the time needed for diagnostics. The new approach (PCRV) is based on combination of the measurements of the polarisation current (PC) and recovery voltage (RV). Figure 1 presents basic principle of the method and shows different stages of the measurement procedure. Fig.1. Basic principle of the measurements according to PCRV In the first step the polarisation of the dielectric is performed so that a DC voltage up to 2500 V is applied for about 1800 s and the polarisation current is measured. In the second step the dielectric is shorted via short circuit impedance to discharge the geometrical capacitance. The duration of the second phase is typically few seconds. And in the third step the recovery voltage is recorded. The combination of the results obtained from polarisation current and recovery voltage al[...]

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