Partial Discharge Detection by TEV Sensors and Signal Propagation Analysis in Transformer Model

This paper deals with a detailed study on partial discharge (PD) generated in transformers using transient earth voltage (TEV) detection method. Experiment and numerical analysis are carried out using an iron box model which simulates a tank of an actual transformer. In the test model, propagation properties of TEV signal caused by PD occurring inside and outside of the transformer model are examined. Results reveal that the electromagnetic waves generated by PD in the model can leak from the opening window, having special frequency determined by the size of the opening window. It is also found that TEV sensor placed on the surface of the tank detects a TEV signal originating from the leaked electromagnetic wave. On the other hand, TEV signal by electromagnetic waves generated by an external PD source is found to have a wider frequency band than that by leaked electromagnetic wave. In addition, electromagnetic field and surface current analysis are performed using finite difference time domain (FDTD) method and simulated results are compared with experimental ones. As a result, it is shown that leaked electromagnetic wave excites a surface current on the outer tank wall of the transformer model. It is also found that there exists difference in the time required for TEV signal to arrive at the inside and outside sensors. The results indicate that PD emitting electromagnetic waves leaked from the dielectric discontinuities can be detected by the TEV method. Furthermore, these results suggest a combination of the detected waveform and its frequency band could lead to highly reliable diagnosis of the apparatus by TEV detection method.The 19th International Symposium on High Voltage Engineering (ISH 2015), August, 23 – 28, 2015, Pilsen, Czech Republi

Simulation of Electrical Characteristics for Misalignment of Coil in Wireless Power Transfer System Using Repeating Coil

This paper compares the electrical characteristics of the S-P type and the repeating coil type wireless power transfer (WPT) system. The features of the two types of WPT systems are described if the output power is same value using the same coil model. The current and voltage values of resonance capacitor are high, and the output power decrease when misalignment of coil occurs. Therefore, compensation method for misalignment is investigated to suppress this burden of resonance capacitor when misalignment of coil occurs. These results are calculated from circuit equations based on the results of electromagnetic analysis and are investigated for automatic guided vehicle (AGV) applications. Thus, if the repeating coil maintains the center position between the primary and secondary coils, the repeating coil type can suppress the burden of the resonance capacitor and improve the transmission power.6th IIAE International Conference on Industrial Application Engineering 2018, March 27-31, 2018, Okinawa, Japa

PD Behaviors of Monoester Insulating Oil under Different Moisture Contents

One of the problems encounters in implementing vegetable oils (natural esters) as a transformer insulating oil is their viscosity which is high. To address this problem, monoester derived from vegetable oil was introduced. This paper deals with partial discharge (PD) behaviors of dry and moist samples of a monoester type insulating oil, palm fatty acid ester (PFAE), under AC high voltage utilizing a needle plane electrode configuration. Variations of average PD charge and PD number against the variation of voltage application, as well as their polarity discrimination under both dry and moist sample conditions are analyzed. PD pulses phase distributions of both dry and moist sample oils are elaborated. Finally, a mechanism of the water molecules effect on PD behavior is proposed based on experimental results and shown schematically

Co-fired AlN–TiN assembly as a new substrate technology for high-temperature power electronics packaging

New wide-band gap semiconductors (SC) for power electronics such as SiC, GaN and diamond will allow higher power densities, leading to higher operating temperatures. However, the surrounding materials will also undergo an increase in temperature, meaning that a parallel effort is needed in SC packaging technologies research. One of the essential components, the substrate, is used to insulate electrically the SC from the rest of the system, drain the generated heat and provide a path to connect the SC to the rest of the system. Direct bonded copper (DBC) and active metal-brazed (AMB) substrates have limited temperature and cycling operation, owing to the large differences in the thermal expansion coefficients between the ceramics and the metals. In this work we propose a new and original substrate technology based on two co-sintered ceramics: an insulating ceramic (AlN) and a conductive one (TIN). The microstructure, the chemical compatibility and the electrical properties indicate that the proposed substrate could operate at a temperature above 200 1C the current substrate technologies, which makes it particularly attractive for high-temperature power electronics applications

Comparison of the effect of thermal aging on dielectric properties of vegetable oils and impregnated Kraft paper

In this paper, dielectric properties (BDV and permittivity) of two vegetable oils (Palm Fatty Acid Ester and FR3) used in power transformers are studied. Also, partial discharge inception voltage (PDIV) of Kraft paper impregnated with these oils is measured. All the tests were carried out at room temperature and the samples were prepared following the same procedure. Both the impregnated paper and the vegetable oils were aged at 140°C for 11 days to study the evolution of the dielectric properties with the thermal aging. PDIV has been also measured for different number of paper sheets (from 4 to 6), analyzing the dependence of PDIV on the thickness of solid insulation. Dielectric characterization of the oils showed that they are suitable to use in power transformers. BDV of the oils decreased with the aging and PFAE performance was better. Dielectric constant of both oils is almost the same. PDIV results showed that both oils are suitable for the impregnation of Kraft paper in terms of dielectric properties. PDIV of FR3 insulating system was higher than PFAE system in all the studied cases. FR3 insulating systems showed a decrease of PDIV value after the aging process, whereas PFAE one remained almost constant.This research is under BIOTRAFO project, which has received funding from the European Union’s Horizon 2020 Research and Innovation Program under the Marie Sklodowska-Curie Action-Research and Innovation Staff Exchange (MSCA-RISE) grant agreement No 823969. The authors of this research wish to thank the Ministry of Economy for its financial support for the National Research Project: Improvement of Insulation Systems in Transformers Using Dielectric Nanofluids. Thermodynamic Characterization and Modelling (DPI2015-71219-C2 1-R). Also, the authors thank the Council of Universities and Research, Environment and Social Policy for its support for the Project: Impregnation of Dielectric Solids with Biodegradable Fluids Used in Power Transformers 2019-2

Development and Evaluation of Small Loop Sensor for Detecting Electromagnetic Field Caused by Partial Discharges in Simulated Insulation System of Inverter-fed Rotating Machine

This paper deals with development of small loop antenna sensors with 10 mm in diameter for detecting electromagnetic (EM) waves emitted by partial discharges in the insulation system of inverter-fed motors. Partial discharges (PD) were generated with a pair of crossed enamel wires under ac voltage at 10 kHz for examining various fundamental properties of the small loop sensors; i.e. the frequency response, the distance dependence from the PD source to the sensor. The sensitivity of the small loop sensor was also measured. As a result, it was found that the developed small loop antenna allows detection of EM waves over the frequency range up to 4 GHz and can detect PD current pulse with its peak magnitude as small as 12.6pC. It is also suggested that the array of the developed loop sensors can be applied for PD localization in practical rotating machines under the so-called repetitive voltage impulse. It was found that the developed loop sensor can be also applied to detect and locate the PD source.2011 International Symposium on Electrical Insulating Materials (ISEIM 2011), September 6-11, 2011, Kyoto, Japa

PARTIAL DISCHARGE INCEPTION VOLTAGE MEASUREMENT AND ITS ESTIMATION BY VOLUME-TIME THEORY FOR SF6/PET INSULATED WEDGE GAP UNDER IMPULSE VOLTAGE

Insulation properties of SF6 gas gap formed at the wedge gap of gas-insulated transformer has not been investigated well. So, the authors aim to study characteristics of partial discharge inception voltage (PDIV) of the wedge gap formed by two electrodes wrapped with polyethylene terephthalate (PET) film to simulate wedge gap insulation system of the gas-insulated transformer coil insulation. Applying a given magnitude of impulse voltage to a set of the electrode systems, discharge generation probability is obtained at different pressures (0.10, 0.22, 0.50 MPa) of SF6 gas. Partial discharge (PD) signal occurring at the wedge gap is detected using a number of 1 kΩ resistors connected in series of the electrode systems. An attempt is made to interpret these results in terms of the Volume-Time theory. It was found that the Volume-Time theory can explain the measured discharge inception probability quantitatively.20th International Symposium on High Voltage Engineering, August 28 - September 01, 2017, Buenos Aires, Argentin

Partial Discharge Induced Electromagnetic Wave Propagation Analysis and Detection Using UHF Sensor in Transformer

This paper deals with optimum UHF sensor design and fabrication suitable for oil-filled transformer as well as the sensor characteristics and sensitivity check. As one promising UHF sensor, we make design of small loop antenna and fabricate it, investigating antenna characteristics and sensitivity in detecting PD in a model transformer.18th International Symposium on High Voltage Engineering, ISH2013, August 25-30, 2013, Soul, Kore

X-ray Irradiation Induced Discharge of Spherical Void in Epoxy Resin

It is crucial for proper insulation design of cast resin transformer to consider voids and delamination which might exist in cast molding process and/or under long-term operation because of several surface boundaries between resin and conductor. Should such defects in the insulation system exist, it would lead to reduction of the life of the apparatus. In this report, we investigate the relation between the void size and apparent charge of partial discharge (PD) occurring in a model simulating the insulation system of cast resin transformer. It is also important to determine necessary PD detection sensitivity of PD test in a factory as well as in a field. In addition, we investigate X-ray irradiation induced discharge of spherical void in epoxy resin. Physical consideration of the effect of X-ray irradiation on void discharges in epoxy resin was also made. Time lag of void discharges in epoxy resin was also made with attenuation of X-ray irradiation dose considered.2011 Electrical Insulation Conference (EIC), 5-8 June 2011, Annapolis, M

Examination on the Denoising Methods for Electrical and Acoustic Emission Partial Discharge Signals in Oil

Partial discharge (PD) measurements either through electrical or acoustic emission approaches can be subjected to noises that arise from different sources. In this study, the examination on the denoising methods for electrical and acoustic emission PD signal is carried out. The PD was produced through needle-plane electrodes configuration. Once the voltage reached to 30 kV, the electrical and acoustic emission PD signals were recorded and additive white Gaussian noise (AWGN) was introduced. These signals were then denoised using moving average (MA), finite impulse response (FIR) low/high-pass filters, and discrete wavelet transform (DWT) methods. The denoising methods were evaluated through ratio to noise level (RNL), normalized root mean square error (NRMSE) and normalized correlation coefficient (NCC). In addition, the computation times for all denoising methods were also recorded. Based on RNL, NRMSE and NCC indexes, the performances of the denoising methods were analyzed through normalization based on the coefficient of variation (). Based on the current study, it is found that DWT performs well to denoise the electrical PD signal based on the RNL and NRMSE index while MA has a good denoising NCC and computation time index for acoustic emission PD signal