The paper presents results of diagnostic measurements on different transformers performed in time domain. New approaches for interpretation of the results are proposed and discussed. Modelling and calculations of different diagnostic values including dielectric response function are provided
Słowa kluczowe: dielectric response, polarisation current, recovery voltage, time constants, conductivity.
W artykule opisano wyniki badań diagnostycznych transformatorów metodą odpowiedzi dielektrycznej w dziedzinie czasu. Zaproponowano nowy sposób interpretacji uzyskanych wyników. Opisano sposób modelowania i obliczania parametrów diagnostycznych funkcji odpowiedzi dielektrycznej.
Keywords: odpowiedź dielektryczna, prąd polaryzacji, napięcie powrotne, stałe czasowe, przewodnictwo
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 . As it shown in  the moisture and contamination tend to increase the conductivity of the solid and liquid dielectric in the transformer. According to  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 [...]
 Houhanessian V.D., Zaengl W.S., Time domain measurements of dielectric response in oil-paper insulation systems, Conference Record of the 1996 IEEE Int. Symp. on Electrical Insulation, Montreal, Canada, 1996, 47-52  Zaengl W.S., Applications of dielectric spectroscopy in time and frequency domain for HV power equipment, IEEE Electrical Insulation Magazine, vol. 19, no. 6, 2003, 9-22  Gafvert U., Adeen L., Tapper M., Ghasemi P., Jonsson B., Dielectric spectroscopy in time and frequency domain applied to diagnostics of power transformers, Proceedings of the 6th International Conference on Properties and Applications of Dielectric Materials (Cat. No.00CH36347), Xi'an, 2000, 825-830  Frimpong G., Gafvert U., Fuhr J., Measurement and modeling of dielectric response of composite oil/paper insulation, Proceedings of 5th International Conference on Properties and Applications of Dielectric Materials, Seoul, 1997, 86-89  Saha T.K., Purkait P., Investigation of polarization and depolarization current measurements for the assessment of oil paper insulation of aged transformers, IEEE Trans. on Dielectrics and Electrical Insulation, vol. 11, no. 1, 2004, 144- 154  Kouzmine O., Kornhuber S., Niehus D., Comparison of timeand frequency-domain-based diagnostic procedures for condition assessment of distribution and power transformers, Conference: Grenzflächen in Elektrischen Isoliersystemen, 4. ETG-Tagung, 12-13.11.2013, Dresden, Germany  Measuring instrument manual DDA 2500, Formsmedia GmbH, 2017, Germany  Patsch R., Kouzmine O., Selection of Diagnostic Parameters in Return Voltage Measurements of Medium Voltage Cables, in WSEAS Conference on Power Systems and electromagnetic Compatibility, Corfu, Greece, Aug.23-25, 2005, 514-521