In this work, the vibrations on the surfaces of the tank wall, stiffeners, and the cover of a 5 MVA transformer experimental model were measured during open-circuit and short-circuit transformer tests. Vibration measurements of a transformer tank side were conducted at discrete points using two different voltage sources in no-load test. Using interpolation functions, the RMS values of acceleration and vibration velocity are visualized and compared for each considered measurement configuration (no-load and load tests and two different excitation sources). Significant differences in mode shapes and amplitudes of vibrations at different frequencies are observed. The maximum RMS values of acceleration, velocity and displacement in the open-circuit test are 0.36 m/s², 0.31 mm/s, and 0.42 µm, respectively. The maximum values in short-circuit test are 0.74 m/s², 1.14 mm/s, and 1.8 µm, respectively. In the short-circuit test, the frequency component of 100 Hz is dominant. In the open-circuit test, the first few 100 Hz harmonics are significant (100 Hz, 200 Hz, and 300 Hz). In addition to the visualization of RMS values during the open-circuit and short-circuit tests, animations of the vibrations are created. Fourier analysis and phase comparison between frequency components are also used to show vibration animations at dominant frequencies in the spectrum (100 Hz harmonics). The visualization of the vibrations at the tank wall surfaces is transferred into 3D space in such a way that all 15 surfaces are mapped to the spatial coordinates of the surfaces so that a 3D model of the acceleration, vibration velocity, and displacement of the transformer tank is shown.

Relevant international instrument transformer standards specify internal arc testing to prove the transformer behavior under internal fault conditions. However, the test is defined in a way that does not recognize that it is possible to limit and reduce the total fault energy. For such instances, testing, as currently defined, is mostly inapplicable. The purpose of this paper is to address this issue by presenting a testing sequence that is applicable for verifying the behavior of transformers with sectioned active parts that contain energy-limiting features. Furthermore, the acceptance criteria for the successful completion of the test are also introduced. Every step of the proposed test sequence is discussed in detail and presented on a 145 kV inductive transformer, selected specifically for this purpose. This paper is a part of a continuous broad research with the aim of developing and specifying adequate routine, type and special testing sequences for qualifying paper-oil insulation systems that limit internal arc energy, with the aim of improving the performance of such systems and introducing test methods and criteria that exceed the practices of current standards.

The aim of this paper is to present the findings and compare the results of two types of tests, both of which are designed to test the instrument transformer insulation during disconnector operation. The first one is the multiple/endurance chopped test as given in the IEC/IEEE standards, and the second one is the repeated flashover testing procedure, as presented in the 2021 IEEE Electrical Insulation Conference (EIC) by the same group of authors. The goal is to determine whether the standardized tests are adequate in addressing the real-life stresses on insulation during disconnector operations. The research will be presented on four full-scale 123 kV voltage instrument transformer insulation systems.

During their lifespan all the primary equipment installed in power system is subjected to transients. Therefore, it is necessary to adequately dimension and protect the equipment. However, in the networks with high share of renewables, power electronics, cables or near GIS, the failure can occur even though good practice of insulation coordination are fulfilled. In this paper high frequency power transformer model is presented. Such model is based on measurements of admittance matrix and is adequate for simulation of fast front transient in EMTP like software. Additionally, simulations of lightning and switching overvoltages are given for the observed power transformer unit.

The aim of this research is to develop a physical model useful for measuring the influence of ageing, temperature and water content on the high voltage behavior of oil-paper insulation. The insulation model, made in accordance with the instrument transformer design practice, is placed in a specifically designed capsule in which those parameters can be controlled. All the parts of the capsule were electrically optimized using finite element method-based software. A procedure for insulation preparation that quantifies the water content has been developed. The partial discharge tests verify the applicability of the designed capsule. Thermal testing verifies the model’s useful temperature range up to 120 °C.

In this paper, the mode shapes of an empty and oil-filled transformer experimental model tank are obtained using 3D finite element method (FEM) modal analysis. For verification of the FEM analysis results, experimental modal analysis (EMA) is carried out in both cases using appropriate impact hammers and accelerometers. Simulated and measured results are visualized and compared for mode shapes in a frequency range of interest for both empty and oil-filled tanks. In order to avoid overly stiff FEM models of transformer tanks, the welded joint modeling technique is presented and analyzed in detail. For an oil-filled tank, the most accurate results are calculated in the model where the welded joint is modeled as half the tank wall’s thickness. In that case, the mean absolute error for the given ten-mode shapes is 1.7 Hz. Also, mesh sensitivity analysis is performed. It is concluded that a 10 mm maximum element size is an optimal solid (3D) mesh. However, shell mesh can be used to reduce computing requirements.