Design of Hilbert Fractal Antenna for Partial Discharge Classification in Oil-Paper Insulated System (original) (raw)
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UHF PD Experiments on Real Power Transformer and its Frequency Characteristics Results
Engineering, Technology & Applied Science Research
A number of methods have been used in partial discharge (PD) detection and recognition. Among these methods, ultra-high frequency (UHF) detection and recognition based on a single signal have attracted much attention. In this paper, a UHF PD detection system is built, and samples are acquired through experiments on a real power transformer. The received signal is decomposed into different frequency ranges through wavelet packet decomposition (WPD). In each frequency range, a pattern recognition neural network is built, and then the relationship between the information in that frequency range and PD type is described. By comparing the recognition accuracy of these networks, frequency range selection is optimized. In this specific case (the specific transformer, PD sources, and UHF sensors), results show that low frequency (156.25 MHz to 312.5 MHz) and high frequency ranges (1093.75 MHz to 1250 MHz) contain the most information for recognition. If a PD detection recognition system is ...
Detection of partial discharge acoustic emission in power transformer
International Journal of Electrical and Computer Engineering (IJECE), 2019
Partial discharge is one the most important factor that leads to deteroration and failure of the power transformer transformer. Acoustic emission detection is effective method to evaluate the health index of the power transformer using acoustic emission (AE) sensors for partial discharge (PD) measurement is considered as one of the most promising techniques to detect and localize PD activities inside the transformer tank. On the other hand, AE waves suffer from high attenuation and reflections while traveling from the PD source to the AE sensor. The modeling of the AE wave can help to understand the behavior of the AE PD signal during its travel. In this paper, the AE PD signal is assumed to be composed of different frequencies. This work aims to investigate the influence of the frequency value on the attenuation and arrival time of the acoustic wave. 1. INTRODUCTION Monitoring of PD is one of the tools to identify the health condition of transformer insulation system. When PD activities are initiated, the resulting energy is transformed into different forms as mechanical, electrical, and chemical energy. Among all PD detection techniques, there is a growing interest in the PD acoustic detection method because it overcomes several disadvantages of using electrical methods like low susceptibility to electromagnetic noise and cost effectiveness. A significant effort has been exerted to understand the behavior of the PD acoustic wave while travelling from its source to the sensor. A mathematical model was introduced in [1] by solving the acoustic wave governing equations through finite elements technique. The presented model describes the propagation of PD acoustic wave in the whole medium (oil and steel) with contour plots to show the attenuation at different locations. Moreover, it examined the propagation properties under the effect of changing oil density as the temperature increased. The effect of frequency on acoustic PD attenuation was studied in [2] by applying pulses with different widths. As the frequency of PD pulse increases, this resulted in higher attenuation. This understanding of the PD behavior can be very helpful to predict the actual frequency ranges of the generated PD based on the received one. An approach in [3] presented the PD as a multiple of different sine waves with different frequencies and attempted to understand the interaction between them as it happens in PD pulse. This approach considers that all these sine waves will travel with the same velocity which is not accurate because each frequency will travel with different velocity as discussed by reference [4]. It has been mentioned that each frequency component of the PD wave will travel with different velocity and hence will arrive to the tank wall at different time which will lead to a higher degree of distortion of the received PD wave.
Energies
The article presents a novel on-line partial discharge (PD) monitoring system for power transformers, whose functioning is based on the simultaneous use of three unconventional methods of PD detection: high-frequency (HF), ultra-high frequency (UHF), and acoustic emission (AE). It is the first monitoring system equipped in an active dielectric window (ADW), which is a combined ultrasonic and electromagnetic PD sensor. The article discusses in detail the process of designing and building individual modules of hardware and software layers of the system, wherein the most attention was paid to the PD sensors, i.e., meandered planar inverted-F antenna (MPIFA), high-frequency current transformer (HFCT), and active dielectric window with ultrasonic transducer, which were optimized for detection of PDs occurring in oil-paper insulation. The prototype of the hybrid monitoring system was first checked on a 330 MVA large power transformer during the induced voltage test with partial discharge ...
Partial discharge (PD) can be detected using ultra high frequency (UHF) method to increase the detection threshold and to improve the performance of on-line measurement of PD in noise environment. The PD emitted energy as electromagnetic emission, acoustic emission and ozone and nitrous oxide gases. We can use this emitted energy to detected PD signal. The best method to detect PD in gas insulate substation, power cable and transformer is by using UHF electromagnetic wave. UHF method have advantages such as high sensitivity, a good signal –to- noise ratio (SNR). On the other hand, there are still some issues to be solved in the UHF methods, such as a clear understanding of the propagation characteristics of electromagnetic waves arising from the structure of the equipment, optimization of antenna design and calibration of charge. Furthermore, in on-site measurements and laboratory experiments it has been that UHF method gives avery moderate signal attenuations. In this paper, a review on UHF PD sensor connected at extra high voltage-termination of cables, UHF PD signals in a 132 kV gas insulated substation (GIS) transformer are described. Results from the measurement show that this method can give the precise value of PD signal
Sensors, 2016
A well-defined condition-monitoring for power transformers is key to implementing a correct condition-based maintenance (CBM). In this regard, partial discharges (PD) measurement and its analysis allows to carry out on-line maintenance following the standards IEC-60270 and IEC-60076. However, new PD measurements techniques, such as acoustics or electromagnetic (EM) acquisitions using ultra-high-frequency (UHF) sensors are being taken into account, IEC-62478. PD measurements with antennas and the effect of their EM propagation in power transformer tanks is an open research topic that is considered in this paper. In this sense, an empty tank model is studied as a rectangular cavity and their resonances are calculated and compared with their measurement with a network analyser. Besides, two low cost improved monopole antennas deployed inside and outside of the tank model capture background noise and PD pulses in three different test objects (Nomex, twisted pair and insulator). The average spectrum of them are compared and can be found that mainly, the antenna frequency response, the frequency content distribution depending on the PD source and the enclosure resonances modes are the main factors to be considered in PD acquisitions with these sensors. Finally, with this setup , it is possible to measure PD activity inside the tank from outside.
Practical experiences with and without the help of UHF measurement technology
2015
Detecting partial discharges in the insulation system of a power transformer at an early stage reduces the risk of total breakdown. One method to detect partial discharges is acoustic measurement. With this technique detection and localisation of partial discharge is possible by placing acoustic sensors on the surface of the transformer tank. The low impact of electrical interferences from outside the measurement set-up constitutes one of the strengths of the acoustic method. A further advantage is the ability to identify the position of the partial discharge source, which is needed to estimate the risk and to enable a fast and effective repair. The sensitivity and accuracy of the PD localisation can be improved with a combination with conventional electrical measurement or with Ultra High Frequency (UHF) measurement method. Since the UHF measurement method is more advantageous for measurement environments with heavy interferences in the field, the combination with acoustic localisa...
Proceedings of the 25th IMEKO TC4 International Symposium and 23rd International Workshop on ADC and DAC Modelling and Testing, 2022
Considering increasing the reliability of electrical systems, continuous equipment maintenance is essential, thus ensuring longevity and avoiding failures that can cause irreparable damage to the equipment. Partial discharges are physical phenomena that cause short circuits in power equipment. There are techniques that use the detection of partial discharges as a condition monitoring techniques for electrical equipment. One of these techniques is the detection of partial discharges in power transformers by means of antennas. Thus, different antennas were analyzed for different coupling to the sensor into the high voltage equipment, either via dielectric window or oil valve. In comparison, the L-probe antenna obtained the best result, at −10 dB, while at −5 dB the log spiral performed better, for insertion via the dielectric window. For coupling via oil valve, the monopole obtained the best result, at −10 dB, considering the bandwidth at −5 dB the conical 70 mm did better.