Article
Engineering, Electrical & Electronic
Jose E. Contreras, Josue Rodriguez, Carlos Gaytan
Summary: Currently, the use of new biodegradable dielectric liquids as an alternative to conventional mineral oil in transformers is being considered. However, the higher viscosity of ester liquids compared to mineral oil requires modifications in the impregnation process of insulation materials.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2022)
Article
Energy & Fuels
Kamil Lewandowski, Hubert Moranda, Radoslaw Szewczyk
Summary: One possible cause of transformer failures is high moisture in the winding insulation system, which can lead to a sudden release of water vapor, known as the bubble effect. This study analyzed the initiation temperature of the bubble effect in different solid insulation materials immersed in two electro-insulating liquids. The moisture content of the solid insulation was found to be the main factor affecting the initiation temperature, with high-temperature materials having slightly lower initiation temperatures compared to cellulose. However, the differences in initiation temperature among the tested materials were very small after considering uneven water absorption.
Article
Engineering, Electrical & Electronic
Chong Guo, Qiaogen Zhang, Rui Zhang, Xiaohui He, Zhicheng Wu, Tao Wen
Summary: The study investigates the generation characteristics and mechanism of characteristic gases in transformer oil under strong vibration, as well as illustrates misdiagnosis of insulation status caused by vibration. Increasing vibration pressure leads to higher concentration of characteristic gases.
IET GENERATION TRANSMISSION & DISTRIBUTION
(2022)
Article
Engineering, Electrical & Electronic
C. Oria, C. Mendez, I Carrascal, A. Ortiz, D. Ferreno
Summary: This study investigates the effects of thermal aging with vegetable oil on commonly used components in power transformers and finds that vegetable oil has a protective effect on the mechanical properties of paper insulation.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2022)
Article
Engineering, Electrical & Electronic
Heng Zhang, Jiefeng Liu, Chuhan Geng, Xianhao Fan, Yiyi Zhang
Summary: This study investigates the furfural partitioning in oil-paper-pressboard insulation under partial oil change conditions, proposing an initial furfural partitioning equation and a modified model, as well as providing a correction scheme. Results indicate that the modified model is not suitable for certain insulation materials.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2021)
Article
Acoustics
Bakrutheen Moosasait, Willjuice Iruthayarajan Maria Siluvairaj
Summary: The study demonstrates that ultrasonic treatment can significantly reduce the pour point of vegetable oils, meeting the standard value for liquid insulation and providing a new pathway for the application of low pour point vegetable oils as liquid insulation in power transformers in cold climate areas.
ULTRASONICS SONOCHEMISTRY
(2021)
Article
Engineering, Electrical & Electronic
Shigeyoshi Yoshida, Masahiro Kozako, Masayuki Hikita
Summary: This study investigates the effect of white trace on partial discharge inception voltage (PDIV) of the composite insulation system using high-speed optical observation and electrical measurements. It reveals the impact of the white trace on discharge propagation and discusses the mechanism of discharge progression.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2021)
Article
Computer Science, Information Systems
Jose M. Guerrero, Alejandro E. Castilla, Jose A. Sanchez Fernandez, Carlos A. Platero
Summary: Condition monitoring of large power transformers is crucial in power systems, with moisture content being a common aging indicator. A capacitive sensor for online moisture measurement, along with Frequency Response Analysis, was introduced for determining oil degradation levels. The prototype sensor demonstrated the ability to accurately estimate moisture content and assess oil degradation.
Article
Energy & Fuels
Yannaphol Kittikhuntharadol, Norasage Pattanadech, Sakda Maneerot, Korraya Jongvilaikasem, Kittipod Jariyanurat, Siwakorn Jeenmuang, Patt Udomluksananon, Komin Chumpiboon, Chanin Bunlaksananusorn
Summary: This paper investigates the physical and chemical properties of natural ester (NE) and palm oil (PO) used as alternative liquid insulations in a transformer for 21 months. The physical properties including interfacial tension, viscosity, and particles count, as well as the chemical properties including moisture content, acidity, corrosive sulfur, and furanic compound (2-FAL), were examined. The test results showed deterioration of the liquid insulations in terms of interfacial tension, particles count, moisture content, acidity, and 2-FAL, but no changes were observed for particles amount and acidity of NE.
Article
Engineering, Electrical & Electronic
Hanbo Zheng, Yongji Feng, Xufan Li, Hang Yang, Weijie Lv, Songjiang Li
Summary: Natural ester insulating oil, with a biodegradation rate of almost 100% and meeting carbon emission requirements, is considered a good substitute for mineral insulating oil. However, its higher kinematic viscosity in low-temperature environments limits its application in cold regions. This study establishes a model to predict the kinematic viscosity of natural ester insulating oil through experiments and molecular dynamics simulation. It provides a convenient tool for predicting and improving the low-temperature kinematic viscosity of the oil.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2022)
Review
Energy & Fuels
Enze Zhang, Jiang Liu, Chaohai Zhang, Peijun Zheng, Yosuke Nakanishi, Thomas Wu
Summary: Chemical compounds dissolved in insulating oil can excellently monitor the aging condition of paper, which has attracted increasing interest in the field of transformer condition monitoring and fault diagnosis. This study provides a comprehensive insight into the indicators of insulating paper aging, including aging characteristics, physico-chemical characteristics, shortcomings of different compounds, generation pathways and mechanisms, and monitoring technologies. It is expected that these chemical indicators can provide better guidance for evaluating paper insulation performance and transformer aging. The study also outlines the latest research progress, current challenges, and future prospects.
Review
Engineering, Electrical & Electronic
Marina N. Lyutikova, Sergey M. Korobeynikov, U. Mohan Rao, Issouf Fofana
Summary: Due to growing environmental concerns, synthetic and natural esters have become the focus for high-voltage equipment insulation in the past two decades. These ester liquids are biodegradable, non-toxic, safe for the environment and human health, and derived from renewable sources with high fire resistance. However, their use is limited in electrical equipment due to factors such as high cost, viscosity and density, electrostatic charge, and faster propagation of streamers in an inhomogeneous electric field. This article presents a comprehensive review on the blend of mineral oil and alternative dielectric fluids, discussing research progress, challenges, and tutorial elements. This is valuable for researchers, utilities, and transformer owners concerned with ester liquids and retrofilling.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2022)
Article
Engineering, Electrical & Electronic
Haoxi Cong, Yuxin Wang, Hao Pan, Xuefeng Hu, Qingmin Li
Summary: In this study, multiple sulfur corrosion was simulated on the oil-paper insulation system to investigate the mechanical properties and hydrogen bond of the insulating paper, as well as the mean square displacement (MSD) and shear viscosity of the insulating oil under different electric and thermal fields. The electric field had a significant impact on the degradation of the elastic modulus of cellulose, with the dc electric field showing a more obvious influence than the ac electric field. Temperature also played a significant role in the modulus parameters, with a considerable decrease in the elastic modulus as temperature increased. The study's findings provide valuable insights into the microscopic mechanism of multiple corrosive sulfides and effective protection techniques against sulfur corrosion.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2023)
Article
Energy & Fuels
Pawel Zukowski, Przemyslaw Rogalski, Tomasz N. Koltunowicz, Konrad Kierczynski, Marek Zenker, Alexander D. Pogrebnjak, Matej Kucera
Summary: This study investigated the conductivity and permittivity of electrical pressboard-insulating liquid-water composites and compared them to water. The presence of water increased the permeability of the composites below 100 Hz, and the conductivity of the composites exponentially increased with increasing water content. The activation energy of the composites' DC conductivity was higher than that of liquid water, and the dielectric relaxation times of the composites were significantly longer than those of water.
Article
Engineering, Electrical & Electronic
U. Mohan Rao, Issouf Fofana, Pawel Rozga, Patrick Picher, Dilip K. Sarkar, Rajan Karthikeyan
Summary: The focus of this study is on the oxidation aspects (gelling) of natural esters and its impact on the performance of transformer insulation systems. Even though natural esters are not suitable for breathing units, the scenario considered simulates a defect in the sealing system, allowing direct contact with atmospheric air. Commercially available natural ester liquids are thermally degraded under controlled aging conditions to observe the formation of sol and gel. The influence of sol and gel on the insulation is analyzed through physicochemical and electrical characterizations.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2023)
Article
Energy & Fuels
Benjamin Adam, Stefan Tenbohlen
Summary: PRPD patterns are commonly used to assess power transformer condition, but multiple PD sources can complicate classification. A system based on LSTM neural networks can classify overlapping PRPD patterns accurately, even with imbalanced datasets. This method can identify the main PD source and potentially classify secondary sources, using conventional electrical measuring devices.
Article
Engineering, Electrical & Electronic
Mehran Tahir, Stefan Tenbholen, Satoru Miyazaki
Summary: Frequency response analysis (FRA) is widely used for evaluating the mechanical integrity of power transformers. Recent studies have standardized measurement procedures, but interpretation of results remains limited. Evaluation and comparison of numerical indices can help identify more suitable indices for calculating changes in FRA signatures.
IEEE TRANSACTIONS ON POWER DELIVERY
(2021)
Article
Energy & Fuels
Mehran Tahir, Stefan Tenbohlen
Summary: This study introduces an intelligent fault detection and classification algorithm using FRA results, based on numerical indicators and ANN for power transformer condition classification.
Article
Engineering, Electrical & Electronic
A. K. Pradhan, S. Tenbohlen
Summary: This paper presents an advanced technique for calculating the activation energy of oil-impregnated pressboard through dielectric response current measurement under switching impulse voltage at different temperatures. The proposed technique analyzes the equivalent circuit parameters and curve shifting to estimate the activation energy, and its effectiveness is confirmed through laboratory testing.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2021)
Article
Engineering, Electrical & Electronic
Denis Mueller, Michael Beltle, Stefan Tenbohlen
Summary: Rising voltages and wide bandgap semiconductors lead to increased electromagnetic interference (EMI) emissions from dc-dc converters in electric vehicles. This article proposes a method using a simple half-bridge gate-driver IC to compensate for EMI, demonstrating effectiveness in suppressing EMI during both stationary and dynamic operation of the converter.
IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY
(2021)
Article
Engineering, Multidisciplinary
Hadi Tarimoradi, Hossein Karami, Gevork B. Gharehpetian, Stefan Tenbohlen
Summary: Frequency response analysis is an effective method for diagnosing mechanical defects in power transformer windings. This study investigates the sensitivity of different components of the transfer function (TF) to defects, finding that the phase, imaginary, and real components are more accurate for classification than the amplitude. A new index based on fitting performance is proposed, showing the best classification accuracy compared to high-usage indices.
Article
Engineering, Electrical & Electronic
Saeed Khandan, Malte Gerber, Stefan Tenbohlen
Summary: Due to the energy transition and the expansion of renewable energies, transformer stations need to be expanded with new transformers more frequently. The thermal overload capacity of transformers is being investigated to give the grid operator a better overview of the overload capacity. Numerical calculations and laboratory measurements are used to determine the hot spot temperature and analyze the thermal behavior of transformers. The analysis of temperature, power, and ambient measurement data allows for the creation of thermal models, which can calculate the overload capacity of transformers at different ambient temperatures. The overload curve generated can ensure that transformers can be operated with a higher load without increased risk.
ELEKTROTECHNIK UND INFORMATIONSTECHNIK
(2022)
Article
Energy & Fuels
Chandra Prakash Beura, Michael Beltle, Philipp Wenger, Stefan Tenbohlen
Summary: Ultra-high-frequency (UHF) partial discharge (PD) monitoring is advantageous for onsite/online applications, and the possibility of three-dimensional PD source localization is highlighted. This study analyzes and compares the signal attenuation and propagation characteristics of two transformers with the same rating but different internal structures, and finds that transformers with the same rating have similar attenuation characteristics even if they have different internal structures.
Review
Energy & Fuels
Stefan Tenbohlen, Chandra Prakash Beura, Wojciech Sikorski, Ricardo Albarracin Sanchez, Bruno Albuquerque de Castro, Michael Beltle, Pascal Fehlmann, Martin Judd, Falk Werner, Martin Siegel
Summary: Although there are uncertainties about the frequency range of partial discharge (PD) radiations and the appropriate frequency range for measurement, this paper discusses UHF PD frequency ranges obtained from laboratory experiments and practical use cases. The literature review reveals a range of 200 MHz to 1 GHz, and newer publications extend this range from 3 to 6 GHz. Practical use cases show that the common frequency range for signal power is approximately 400 MHz to 900 MHz, with significant variations in individual cases. Based on the discussed experiments and observations, UHF PD measurements using valve or window antennas are feasible methods for PD detection according to Cigre.
Article
Energy & Fuels
Mehran Tahir, Stefan Tenbohlen
Summary: Currently, the assessment of transformer winding condition using frequency response analysis (FRA) requires skilled personnel. However, there is still a lack of definitive methodology for interpreting and assessing the condition of transformer windings based on FRA results, which poses a challenge for industrial applications. To address this challenge, this paper proposes a transformer condition assessment (TCA) algorithm that utilizes numerical indices and supervised machine learning to interpret FRA results automatically. The algorithm includes random forest (RF) classifiers that can identify various faults in transformer windings and classify their condition. Through the analysis of 139 FRA measurements from over 80 power transformers with different ratings, sizes, designs, and manufacturers, the results demonstrate that the proposed TCA algorithm can effectively assess transformer winding condition with up to 93% accuracy without extensive human intervention.
Article
Engineering, Electrical & Electronic
Felipe L. Probst, Michael Beltle, Malte Gerber, Stefan Tenbohlen, Kai A. Alsdorf
Summary: This paper presents a case study of measuring switching transient overvoltages using a capacitive electric field sensor. After the failure of a surge arrester during the energization of a 420 kV transmission line, a measurement system was developed and installed in a substation. The results show that the system is capable of measuring switching transient voltages and can be considered a flexible solution for the long-term monitoring of transient overvoltages in substations.
ELECTRIC POWER SYSTEMS RESEARCH
(2023)
Proceedings Paper
Energy & Fuels
S. Tenbohlen, C. P. Beura, M. Siege
Summary: Partial discharge (PD) measurement is used to detect localized defects in oil/paper insulation. PD can be measured using electrical PD measurements or electromagnetic measurements in the ultra-high frequency range (UHF). The importance of PD measurements is reflected in the electrical measurement standard. However, current UHF technology is not yet used as an acceptance criterion for testing.
2022 9TH INTERNATIONAL CONFERENCE ON CONDITION MONITORING AND DIAGNOSIS (CMD)
(2022)
Proceedings Paper
Engineering, Electrical & Electronic
Inti Runa Supa Stoelben, Jonas Bertelmann, Michael Beltle, Stefan Tenbohlen, Christian Bersch, Konstantin Spanos
Summary: This paper presents different setups for conducting electromagnetic compatibility (EMC) testing during the charging process of electric vehicles (EVs) on-board AC chargers. The study investigates both component measurements on the vehicle side and grid side interferences according to CISPR 25 and IEC 61851-21-1 standards. A second reference ground plane is introduced to simulate stray capacitances between the car body and the anechoic chamber's ground potential in these setups. Additionally, a simplified chamber filter is modeled to analyze its effects on noise level and consider loads installed outside the anechoic chamber. Structural impedance measurements between ground plates are carried out to visualize the impacts of ground connections and assign resulting disturbances.
2022 INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC COMPATIBILITY (EMC EUROPE 2022)
(2022)
Article
Engineering, Electrical & Electronic
A. K. Pradhan, S. Tenbohlen
Summary: This article discusses an advanced method for estimating the dc conductivity of oil using parameters evaluated under switching impulse voltage, and verifies its effectiveness and limitations under experimental conditions.
IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
(2022)
Proceedings Paper
Engineering, Electrical & Electronic
Jan Schabel, Michael Zerrer, Martin Kull, Michael Beltle, Stefan Tenbohlen
Summary: This study examines the impact of different measurement setups on radiated emissions testing according to CISPR 25. The most suitable method found among those investigated is exciting the wiring harness with a broadband impulse.
2021 JOINT IEEE INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC COMPATIBILITY, SIGNAL & POWER INTEGRITY, AND EMC EUROPE (EMC+SIPI AND EMC EUROPE)
(2021)
