Eugeniusz Kornatowski

Mechanical-Condition Assessment of Power Transformer Using Vibroacoustic Analysis

This paper presents a method for vibroacoustic analysis of a transformer in the steady state. The standard approach to this problem has been based on analysis of the vibration frequency spectrum recorded with an accelerometer mounted on the transformer’s tank. To improve legibility of measurement results, the paper suggests the analysis method for the relative coefficient of harmonic frequency contents hnorm(f). The conducted experiment showed that high values of hnorm within a wide frequency range testify to deformation of windings and degradation of solid insulation.

Transformer Windings Diagnostics with Combined Frequency Response Analysis and Vibroacoustic Methods

The paper presents the idea of performing combined analysis of measurements results conducted with FRA and V-SSM methods. Both of them give some information on the mechanical condition of transformer’s active part. However none of these methods allows for direct and straightforward interpretation of measured data. The application of FRA and V-SSM measurements together may give detailed information of the mechanical condition of windings. The idea has been experimentally verified on the real transformer, during controlled deformations.

Method of vibroacoustic signal spectrum optimization in diagnostics of devices

The vibroacoustic method of device diagnostics is most often based on spectrum analysis of digitally recorded vibration signal of their mechanical elements. In the steady-state, depending on the test object, the signal may contain only fundamental frequency and harmonics. Then, in case of poor mechanical condition, diagnostic signal contains also some foreign frequencies. Using signal of finite length for computing its spectrum causes some deviations in spectrum structure. It can be the reason for misinterpretation because of array frequencies occurring in DFT, which in fact do not exist in the signal and existing frequencies, which have incorrect amplitude. To reduce this effect, the window function can be used. Taking into consideration the special spectral structure of diagnostic signals in the steady-state, it is possible to adjust parameters of signals in such a way to eliminate any distortion for regular frequencies. For this purpose, if further analysis requires a fixed number of signal samples, by signal resampling, spectral resolution can be adjusted to the harmonics existing in the signal, especially, when processed are signals already recorded with unwanted sampling frequencies.

Detection of the Transient Vibrations Amplitude of Power Transformer’s Active Part

The vibroacoustic diagnostics is currently one of the most important methods used for assessment of the mechanical condition of power transformers’ active part (windings and core). The analysis of transformer’s tank vibrations is performed for the steady state (stable load or no load) and for the transient state, during the first couple of seconds after unloaded transformer energization. Vibrations signal is recorded with accelerometric sensor attached to the transformer tank. In the case of transient state it is very important to determine the envelope of tank vibrations recorded signal. There is very often used for this purpose amplitude detector AM-DSB, which algorithm is based on the Hilbert filter. However recorded signal of vibrations (proportional to the acceleration) does not fulfill conditions of AM-DSB signal. Using the standard envelope detection (Hilbert filter) leads to wrong conclusions. In this paper a modified algorithm of envelope detector is presented, which can be used each time, where there is a need to determine signal’s envelope, that does not fulfill conditions of amplitude modulation AM-DSB. The quality of proposed algorithm was experimentally verified on the example of two transformers: low and medium power (0.8 MVA and 16 MVA).

Failure Issues in WiFi Networks Applied in Intelligent Home Systems

Abstract This article presents current research on failure issues in the IEEE 802.11g wireless network that can be easily applied in the intelligent home system. Different systems in different communication models coexisted with each other in the same time of operation. As a result of many observations the new statistical model of communication system failures was developed. During normal operation there should be no connection loss in the ideal case. However, when transmitting devices are located on the edge of the wireless network range, the connection could be lost. The problem of reconnections cannot be ignored in the process of automation devices control, especially when dealing with sensitive data transmitted using e.g. Internet of Things technologies. One of the possible scenarios that could take place after link failure is the stability loss of the system or issues with data integrity. All research presented in this work could help in performing new computer simulations, and as a consequence - by appropriate designing of queueing systems - preventing data loss.

Transformer diagnostics with combined measurement methods based on different physical phenomena

The paper presents the concept of transformer diagnostic based on complementary methods with two measurements related to different physical phenomena. Two separate approaches are described. The first one allow the assessment of moisture content, ageing level and sludge presence in paper-oil insulation with joint measurement employing Return Voltage Measurement (RVM) and Polarization Depolarization Currents (PDC) methods. The second approach uses complementary measurements with Frequency Response Analysis (FRA) and Vibroacoustic Method (VM) to assess mechanical condition of an active part. Such approaches allow to perform more reliable and exact diagnostics. The results obtained in each pair of methods analyzed together show additional processes, which are impossible to detect with a single method. The paper describes basics of all four methods and gives directions for combined assessment. There are also some examples given of measurements from real cases.