Conference Agenda

IEEE PES EMC standards are well-known in the industry for guiding work on generators and motors. The EMC is the Electric Machines Committee. The authors of this paper are the present leadership for IEEE PES EMC Materials Subcommittee (MaSC). The focus of this paper is to review the general topics of the standards in this committee, with a particular focus on the new standards of the last 5 years, as well as a couple that will be going to ballot in the next year or two. The paper will include a grouping of the IEEE PES EMC MaSC standards as to general use. In addition, an overview of the hierarchy of the IEEE PES EMC will be discussed. The goal of this paper is to provide the novice with a general education of this area of IEEE Standards activities, hopefully, to generate interest to participate. For those more knowledgeable about IEEE standards, this paper plans to provide a review of new standards and activities on the existing works.

This paper compares high-voltage electrical coils from hydroelectric generators after approximately 36 years of service with newly manufactured replacement coils. The original coils are part of the US Army Corps of Engineers' renovation of the Chief Joseph Dam in Washington State, where 16 generator units (92,920 kVA, 13,800 V) will be rewound. Preformed Windings will supply the new coils, designed to sustain decades of renewable energy production. With the average age of hydroelectric power station in the U.S. approaching 50 years, this paper is to create a reference for the industry of the expected benefits that can be achieved in the rewinding of the fleet using resin rich coils manufactured with modern techniques.

Four coils removed from generator Unit 10 were inspected for signs of operational degradation, measured using 3D laser scanning technology and tested for key electrical insulation parameters, including insulation resistance (IR), Tan Delta, and Partial Discharge (PD). Additionally, the coils were dissected to evaluate the condition of the insulation system at various points along their cross-sectional areas.

The paper will present the results of these tests, quantifying the many effects of prolonged operation on insulation integrity by comparing the in-service coils with coils stored since their original manufacture. Further comparisons are made with newly fabricated coils, highlighting advancements in insulation materials and manufacturing techniques. Improvements in insulation performance, as evidenced by the enhanced Tan Delta, PD, and Phase-Resolved Partial Discharge (PRPD) measurements, are discussed in detail.

This paper aims to inform the industry on the impact of generator operation on electrical insulation, discuss what are good indicators of quality for high voltage coils and finally, the benefits of rewinding hydroelectric generators with modern resin rich insulation systems and improved manufacturing methods, which offer better control of main wall insulation quality.

Dissolved Gas Analysis (DGA) and offline electrical testing are fundamental tools for diagnosing faults in power transformers. Although these two techniques differ in their approach, they complement each other by providing a comprehensive view of the equipment's operational condition, which is crucial for ensuring its reliability and extending its service life.

DGA does not require the transformer to be disconnected and is highly sensitive to early-stage thermal and electrical faults. It allows detection and quantification of gases generated in the insulating oil due to overheating, electrical arcing, or partial discharges, among other phenomena. These gases, such as hydrogen (H₂), methane (CH₄), ethane (C₂H₆), acetylene (C₂H₂), and other gases are analyzed to identify the type and severity of the fault. On the other hand, offline electrical tests provide a detailed evaluation of the transformer’s electromechanical and dielectric condition. These tests include winding resistance , transformer turns ratio (TTR) , tan delta (tan δ) , and dielectric response tests, among others. However, unlike DGA, offline electrical testing requires the transformer to be de-energized and isolated from other devices, which can present a limitation in situations where service interruption is complex or undesirable.

It is common for an unusual increase in certain gases detected by DGA to indicate an internal problem that is then confirmed with greater accuracy through offline electrical testing. For instance, if the DGA reveals an increase in gases related to partial discharges, such as hydrogen, tests that assess insulation conditions could confirm this deterioration. Similarly, an abnormal value in winding resistance measurements may correlate with hot spots detected through DGA, suggesting loose connections or thermal dissipation issues.

However, there are cases where an abnormal condition diagnosed by DGA is not confirmed by an electrical test, or vice versa. This discrepancy can occur because each technique has its own limitations and sensitivity to different types of faults. For example, a low-magnitude dielectric fault may not produce enough gases to be detected by DGA, but it could be identified through a dielectric response test.

This paper presents various case studies illustrating the correlation (or lack thereof) between DGA results and electrical tests. The combination of both techniques allows for a more comprehensive and accurate diagnosis, helping to improve decision-making in predictive maintenance. Furthermore, this correlation aids in interpreting potential discrepancies between methods, optimizing inspection intervals, and managing assets more efficiently. In conclusion, the integration of these tools enhances fault detection accuracy, resulting in more reliable transformer management.

The dynamic thermal modelling of transformers is subject to many constraints which have always been a challenge to match the design phase with the real operation under different conditions such as variable loading, short- and long-term emergency loading. With the increasing awareness of real-time modelling and the growing trend nowadays to use accurate and detailed models that give a clearer picture of the thermal behavior of the transformer in service, the improvement of the available models has become essential.

One of the most important key factors that affecting the performance, lifetime and health condition of transformers is the thermal performance. Temperature affects the insulation system by increasing ageing factors such as moisture distribution, gassing, bubble formation, degree of polymerization, etc. The insulation system mutually interacts with the cooling process and therefore the health condition of the insulation system is essential to maintain its main functions.

Natural ester liquids that are characterized by higher biodegradability and lower CO2 footprint compared to other liquids beside relatively lower market price, leading to a significant growth in their demand. Therefore, the operational reliability for asset management and lifetime expectancy of a transformer filled with natural ester is essential to achieve a higher sustainability value. On the other hand, compared to mineral and synthetic ester liquids, natural esters present more challenges in cold climate operation due to their relatively high pour point. Monitoring requires a reliable dynamic transformer thermal model (DTTM) to accurately determine the response to the real-time loading profile under environmental conditions for different insulating liquids allowing energy maximization without compromising sustainability.

The DTTM has been receiving increased attention because it has a direct impact on the lifetime of the transformer and is dependent on the transformer load profile and environmental conditions which cannot be easily estimated when evaluating transformers onsite. The implementation of sophisticated and rapid computational models for monitoring dynamic thermal behavior provides opportunities for real-time control and optimization of transformer performance, maintenance, and loadability while ensuring insulation system integrity and avoiding misleading operational decisions.

This study presents investigations of the dynamic thermal behavior of a 66 kV KFWF transformer filled with natural ester insulating liquid, designed for offshore wind applications operating in cold climates. The transformer is equipped with fiber optic sensors to monitor the temperature distribution of the winding and liquid during the heating and cooling processes. The case study transformer is investigated through a heat run test by injecting a load while the transformer is exposed to sub-zero temperatures for 100 hours, with the entire transformer placed in a controllable temperature cold chamber. The study includes an extended DTTM that considers the variation of liquid properties with temperature to predict the dynamic temperature behavior of the entire transformer during the test.

Polyimide (PI) is extensively used in aerospace applications owing to its exceptional properties. However, exposure to harsh environmental conditions, including heat and humidity, can significantly affect its performance. Understanding the effects of aging on PI is important for ensuring its long-term reliability in aerospace systems. This research presents the impact of thermal oxidative aging and humidity on the dielectric performance of polyimide (PI). Aging was conducted at 250°C for 170 hours under controlled humidity conditions, facilitating thermal oxidative degradation and moisture absorption in polyimide. The results of Scanning Electron Microscopy (SEM) analysis revealed surface degradation in aged PI, characterized by micro-voids and cracks that facilitated moisture ingress into the bulk material. The aging process led to the formation of polar molecules, including moisture-induced hydroxyl groups, which enhanced the polarization ability and AC conductivity of PI. To analyze these conductivity changes, Jonscher's Power Law and the Almond-West formalism were employed. The fitting of AC conductivity data using these models provided insights into the frequency-dependent charge transport behavior in fresh and aged PI. The extracted parameters, including DC conductivity, crossover frequency, and relaxation time, demonstrated that aging resulted in increased charge transport and a shift in the frequency response. While the bulk resistivity decreased, the carrier density and mobility were notably enhanced, leading to an increase in leakage current density. At high electric fields (100 MV/m), the leakage charge density increased by 8.4% due to the aging process. These findings highlight the impact of both thermal oxidative and humidity-induced aging on the dielectric and microscopic properties of PI, which is essential for assessing its reliability in aerospace applications under harsh environmental conditions.

High-voltage circuit breakers (HVCBs) are critical components in power systems. They safely isolate and connect electrical networks. Their primary function is to open or close circuits, controlling electrical current flow under normal conditions and preventing damage during faults. HVCBs interrupt currents from very small values up to the maximum rated short-circuit current. The interruption process uses arc energy to generate gas pressure, which is necessary for extinguishing the arc and preventing re-ignition. The residual arc energy is dissipated through heating and ionization of the surrounding gas, vaporization of metals from arcing contacts, and ablation of nozzles.

Understanding the energy balance in an HVCB is crucial for designing efficient and reliable circuit breakers. This involves determining how the arc energy is distributed among the different dissipation mechanisms. This work investigates the energy balance of an HVCB using computational fluid dynamics (CFD) simulations. The simulations are performed for power test duty with 100% of the short-circuit current (T100a). The results show that the energy balance is complex and depends on several factors and estimating it can highlight necessary design changes to enhance the performance. By using CFD simulations and understanding the energy balance within an HVCB, engineers can develop more reliable and efficient circuit breakers that can meet the demands of modern power systems.

Employing of dielectrical losses measurement for insulation of high voltage rotating machines is widespread for the most manufacturers of the winding for high voltage rotating machines. Typically trending over of the dielectrical losses versus losses allows to qualify for extend of the insulation cure and insulation integrity. Losses in the end turns grading system creates significant impact on the measurements and does not allow to use this test without guarding out losses created by the current thought the end turns voltage grading surfaces.

North American standard IEEE 286 and European standard IEC 60034-27-3 recommends different guarding techniques in some extent mitigating of losses due to current though the voltage grading surfaces. Interference to the dielectrical losses measurements depends on guarding technique in different ways and depends also on the basis of the measurements.

Influence of the higher harmonics especially third harmonic both in the test voltage and test set supplied voltage creates additional problem in the testing.

Employing of inner corona protection for single turn coils such as Roebel bars also distort the dielectrical losses measurements.

All these interferences influencing on the routine test of dielectrical losses creating unpredictable distortion of the actual dielectrical losses increasing of the dielectrical losses measured values and sometimes creating negative tip-up of dielectrical losses.

Some specifications inherited from the past restriction on the negative dielectrical losses tip-up. Negative dielectrical losses tip-up was typical in the past in the asphalt matrix micasplitting insulation related. Measured dielectrical losses start to decrease at double of corona inception voltage. Thus, insulation with vast delaminations had dielectrical losses reduction at the higher test voltage. With epoxy or polyester matrix insulation negative dielectrical losses tip-up relates most of the time with distorted measured values.

The present work is attempting to summarize the potential problem with measurements of dielectrical losses using different guarding techniques and different testing devices.

Thermal cycling testing was performed on turbine generator stator bars according to IEEE 1310. Case studies are presented spanning multiple different insulation systems. These case studies encompass varying designs and manufacturing methods (resin rich autoclave, resin rich press cure and vacuum pressure impregnation). These case studies and the results of thermal cycling tests of each are summarized and statistically compared to the performance of non-thermal cycled bars of the same design. The results show that de-bonding of the insulation at the conductor interface does not correlate to a statistically significant change to the dielectric breakdown strength or voltage endurance performance of the thermal cycled bars compared to non-thermal cycled bars. Likewise, a statistical increase of dissipation factor and tip up did not correlate to a statistically significant change in dielectric breakdown strength or voltage endurance performance. The results also demonstrate that the dielectric breakdown strength and voltage endurance tests have a large standard deviation. This indicates that caution must be taken when assessing data from a limited sample size of test and control bars. These case studies challenge the common perception that de-bonding at the conductor interface and the associated increase of dissipation factor after thermal cycling has a significant impact on the stator bar or winding life. These results also reinforce that the critical result of the thermal cycling test is the impact of the test on the dielectric breakdown strength or voltage endurance performance of bars compared to non-thermal cycled bars. This supports that the diagnostic testing described in IEEE 1310 should remain informative as data does not support that these tests correlates to bar or winding life.

The presence of partial discharges (PD) in an insulation system has been a cause for concern in equipment for decades. Some dielectric materials have stronger resistance to degradation from PD than others, hence the many works that discuss partial discharge and its methods of measurement, such as PDIV as well as PD magnitude.

This paper seeks to investigate the affect of partial discharge on dielectric material chemical and mechanical aspects.

Aging theories discussed include parameters from partial discharge activity, such as electric field effects, mechanical degradation as well as chemical aspects caused by corona emission due to exposure of nitric acid, ozone, etc.

The chemical aspect includes components from the degradation of the chemical structure of the dielectric material, such as epoxy, as well as components generated thru interaction with environmental constituents, such as moisture. Additionally the influence on local metallic constituents will be discussed.

Recent developments in instrumentation have demonstrated that it is feasible to monitor the condition of energized cables online using frequency domain reflectometry (FDR) and spread spectrum time domain reflectometry (SSTDR). However, the response spectra from these measurements are complex to interpret and do not lend themselves to simple threshold alarms. To address this challenge, machine learning (ML) techniques have been used, demonstrating high accuracy in predicting normal or anomalous cable behavior when using binary normal and anomalous training and test data. A more plausible scenario for cable insulation damage, however, involves a slowly developing material change due to long-term exposure to thermal or radiation stresses, subtly altering material properties and resulting in an altered reflectometry response. The practical challenge lies in recognizing when such changes are significant enough to raise concern. The Pacific Northwest National Laboratory (PNNL) Accelerated and Real-Time Experimental Nodal Analysis (ARENA) cable motor test bed was used to measure the FDR and SSTDR responses of an energized cable as a section of it was thermally aged over 70 days. Online reflectometry spectra were collected and post-processed to simulate real-time analysis, aiming to distinguish normal from anomalous behavior. These spectra were also contrasted with off-line and direct conductor-coupled reflectometry tests. For use with ML algorithms, it was necessary to label the reflectometry results as either normal or anomalous. This was accomplished with witness samples, which were aged alongside the main cable and periodically tested for elongation at break and tensile strength—two offline destructive tests indicative of cable damage. These destructive tests revealed a natural breakpoint for differentiating the two conditions at ~35 days. Both supervised and unsupervised ML methods were applied. The results indicated that the ML methods could effectively classify cable data as normal or anomalous and that there was a strong correlation between the reflectometry results and the elongation at break and Fourier transform infrared spectroscopy destructive off-line tests of the witness samples. In addition, the online testing was nearly as clear and effective as off-line tests. These findings suggest that the integration of ML techniques with reflectometry can provide a reliable method for monitoring and early detection of cable insulation damage.

In Gas lnsulated Switchgear (GIS), basin-type insulators serve as critical components, providing both insulation support and sealing functions. Due to their complex geometrical structure, these insulators are highly sensitive to electrical field distribution under extreme operating conditions. The details of the geometric model directly influence the concentration and uniformity of the electrical field, making optimized design essential for improving insulation performance and preventing flashover and breakdown. To address the issue of automatic annotation of the geometric model's physical properties, this paper proposes a refined construction method for basin-type insulators based on the integration of 3D reconstruction and numerical simulation. The results show that the proposed automated reconstruction method can effectively calculate the electric field distribution，providing a new avenue for electrical field simulation and design optimization of basin-type insulators.

Over the past 25 years, thousands of kilometres of installed XLPE High Voltage (HV) and Extra High Voltage (EHV) cable systems have been subjected to after-laying commissioning testing prior to energization. The commissioning test usually consists of a combination AC withstand (HiPot) & Partial Discharge (PD) testing. This paper presents more than two decades of experiences with non-monitored and monitored withstand testing on HV and EHV cables obtained globally with withstand levels and durations as in accordance with IEC standards and PD monitoring in accordance with IEEE & CIGRE recommendations.

The paper discusses influence of level and frequency of the applied withstand voltage for successfully identifying typical life limiting laying or installation related defects in newly laid HV & EHV Cable systems both in terms of dielectric break-down and also in terms of detection of partial discharge sources from same defects. The paper further provides statistical summary of tests performed on more than 10,000km of HV and EHV cable systems including failure rates and non-pass PD rates of accessories distinguishing between HV and EHV cable systems. The paper also provides several case studies of PD detected in cable accessories during AC HiPot commissioning testing. The paper also discusses the influence of PD sensitivity on the results obtained especially considering that different types of PD sensors and measurement instruments have been used.

Bis(trifluoromethyl) sulfides, i.e., CF3SCF3, was proposed to be a potential alternative to refrigerant fluids. Moreover, the significant attachment cross section of low-energy electrons for CF3SCF3 is to make it good gaseous dielectrics and also good electronegative gas for the electrical applications. CF3SCF3 has high uniform field breakdown strength 1.35 times that of sulfur hexafluoride (SF6), a potent greenhouse gas being phased out of all frivolous applications due to environmental concern. The global warming potential (GWP) of CF3SCF3 was estimated to be 2.8 by an empirical structure-reactivity relationship and thus CF3SCF3 has been designated to be a potential eco-friendly replacement gas for SF6. However, such an empirical estimation on the GWP of CF3SCF3 is highly problematic because the models trained with alkanes, alkenes, and thioethers might be inapplicable to the fluorinated compounds. Based on the solid ab initio quantum chemistry calculations on the reactions of CF3SCF3 and CH3SCH3 with OH radicals in the atmosphere, it is revealed that the reactivity of CF3SCF3 is completely different from CH3SCH3 in terms of both degradation mechanisms and kinetic behavior. Besides the absence of hydrogen abstraction mechanism, CF3SCF3 reacts with OH through the shallow wells (0.7 kcal/mol) rather than the stable complex (9.1 kcal/mol for CH3SCH3), forming the less stable tri-coordinated S(III) covalent intermediates before the endothermic S-C bond fission. The room-temperature rate coefficient for the CF3SCF3+OH reaction is four orders of magnitude lower than that for the CH3SCH3+OH reaction. The atmospheric loss of CF3SCF3 has been retarded considerably with a lifetime around 300 years. Together with the significant radiative efficiency, 0.463 Wm-2ppb-1, the GWP of CF3SCF3 is predicted to be approximately 14000, as indicative of a super greenhouse gas. The present work not only reveals the significance of fluorination effect on the reactivity of thioethers but also realizes that the empirical structure-activity models without the mechanistic insights should be taken with caution.

This paper provides an overview on stringent requirements for stator windings that are used in petrochemical, utilities and nuclear plants. For nuclear applications, it is critical that a machine must be designed for a Design Basis Accident (DBA) refers to a specific accident scenario that a plant design must consider and prepare for, such as a Loss Of Coolant Accident (LOCA) and built to withstand without loss to the systems, structures, and components necessary to ensure public health and safety. Stator winding insulation system can be quite complex due to the interactions of materials and geometry; therefore, testing is the most appropriate method for qualification. To carry out qualification tests for motor or motor stator winding insulation system, IEEE Std. 323 & 334 along with several other industry standards were followed. In addition to other qualifications tests and to achieve environmental qualification, a test program was performed on statorettes with two distinct types of insulation systems. The qualification program comprised of voltage aging, radiation aging, thermal aging, mechanical vibration aging, seismic testing and a DBA. The statorettes used as test specimens successfully completed the required qualification program and met the specified acceptance criteria. The integrity of the insulation system demonstrated that the motor stator will perform its safety related function when subjected to a DBA at the end of its service life. The qualified insulation system has been widely used in services industry with outstanding thermal, electrical and dielectric performance.

The demand for medium voltage direct current (MVDC) systems is rising as they enable lighter, more efficient electric ships and aircraft. However, medium voltage levels generate high electric fields that challenge insulation system reliability. In high voltage systems, the presence of triple points, sharp edges, bubbles, and air gaps can intensify electric fields, leading to partial discharge (PD) and space charge injection and accumulation within insulation materials. PD accelerates insulation aging and raises the risk of system-wide failures, while space charge causes electric field distortions, insulation degradation, and early device failure. Our recent findings suggest that incorporating electrets between electrodes and insulating materials effectively mitigates PD, space charge injection, accumulation, and space charge-induced breakdown of insulating materials. Electrets, materials with embedded positive or negative charges, generate electric fields that counter harmful fields created by system voltage, thereby blocking charge injection into insulators.

This study further explores the charge stability of electrets under high temperatures, varying electret thickness, and charging duration during fabrication. We fabricated electrets using Parylene HT through triode corona charging and measured embedded charge with an electrostatic voltmeter. To assess high-temperature effects, we placed electrets on a hot plate and monitored the normalized surface potential for over 30 hours. The effect of thickness on charge retention was analyzed by varying material thickness, fabricating samples, and measuring their normalized surface potentials. Additionally, we examined the impact of extended charging duration at high temperatures on electret charge stability during the fabrication process.

Thermocycling (TC) of the major windings elements: coils, and bars for High Voltage Rotating Machines (HVRM) became a highly employed test required to verify the reliability of the windings for these machines.

The IEEE 1310 standard, introduced in 2012, provides guidelines for thermal cycle testing of form-wound stator bars and coils in large rotating machines, emphasizing temperature uniformity across test samples. However, the standard specifies only one test assembly without accounting for alternative setups that may achieve similar or superior uniform temperature distributions. Our team has developed and tested a modified setup to improve temperature uniformity during TC tests, involving actual reassembly and reconnection of samples.

This paper extends our prior research presented in 2024 at the IEC conference, focusing on thermocycling (TC) tests for large turbo bars with 3-inch copper cross-sections and 6 mm ground wall insulation thickness. These TC tests, critical for verifying the reliability of high-voltage rotating machines (HVRM) windings, are conducted to compare calculated and measured temperatures across various setups and cooling modes.

This study explores an empirical and simulation-based approach, utilizing Finite Element Analysis (FEA) to identify optimal setups that predict uniform temperature distributions. This dual approach aims to reduce the need for physical sample reconfiguration and streamline the testing process. We propose that future revisions of IEEE 1310 prioritize temperature uniformity criteria, with setup guidelines relegated to the Annex to allow greater flexibility in achieving standardized results across the industry.

The health and safety of workers using chemical compounds (resins, paints and solvents) when installing, refurbishing or maintaining hydro generators is paramount. Recently observations have necessitated technological development to better achieve this goal. The uses of such chemical compounds include generator rewinds, painting of the stator winding and core, stator frame, rotor field poles, rotor mechanical assembly, etc. and the clean up when the work is ongoing and finally completed.

An analysis of the types of chemical compounds shows significant health and safety risks for workers such as Carcinogens, Mutagens and Reproductive (CMR). While Personal Protective Equipment (PPE) is reasonably effective in minimizing short time exposure, longer term exposure is still a concern. A new and preferred approach is the reformulation of the chemical compounds to eliminate the substances that pose risk. The authors of this paper have been working collaboratively to develop and qualify chemical compounds that eliminate these known health risks while still ensuring that the technical efficacy remains as good or better than the original.

While this work does not eliminate the need for PPE for site workers, the newly formulated and qualified chemical compounds eliminate the worst chronic risks for workers. The use of PPE to control more acute hazards such as eye, throat, and respiratory irritation will be maintained.

This paper will present the work done to qualify a family of products developed that eliminate the CMR risks. All chemical compounds presented will have been subject to laboratory and field testing with good overall technical performance that meets or exceeds the existing. Most important is solid feedback from personnel at site performing the work.

While this work presents new chemical compounds and technology, a list of currently qualified materials and their suggested applications will be provided so that users may start to take advantage thus reducing personnel risk at site.

It should be recognized that studies of the health affects of various chemical compounds continues, and as studies continue, new and further materials may be identified that have more extreme risks for workers. The materials currently presented are CMR free based on today’s technology, but overall, this type of work and mindset must continue into the future.

Electricity distribution is essential to modern society, with medium voltage (MV) power cables playing a critical role in delivering power from transformer stations to end users. However, these cables often operate under adverse conditions, that can compromise their performance and longevity. One of the primary stresses for MV cable insulation is water treeing, a process that occurs when polymeric materials are exposed to high humidity and electrical stress. Water treeing is characterized by the formation of microchannels within the insulating material, which can eventually lead to electrical treeing and material breakdown. For these reasons, it is essential to understand the mechanisms of water treeing formation in order to identify preventive strategies to optimize cable efficiency and durability.

This study investigates water treeing within the EPDM (Ethylene Propylene Diene Monomer) insulation, widely used in medium voltage cables through a water blade electrode test cell, which generates a localized high electric field able to accelerate the initiation and propagation of water trees. This method enables the reproduction accelerated aging conditions in the lab, subjecting samples to electrical stress, to observe long-term effects in a shorter timeframe. The goal is to establish a testing methodology which can compare different insulating materials in flat sample form, identifying the best candidates for the standard Accelerated Water Tree Test (AWTT) a time-intensive and costly test typically conducted on actual cables

To assess change in material properties due to aging, the study applied various diagnostic techniques, including dielectric spectroscopy, DC conductivity measurement, and FTIR spectroscopy. The results showed an increase in dielectric loss factor (tanδ) and insulator capacitance, which are attributable to the increase in complex permittivity of the material. The rise of ε’’, the imaginary part of the complex permittivity, indicates increasing energy dissipation with the presence of relaxation peaks associated with dipolar polarization, associated with water absorption. Conductivity analysis further supports the observed deterioration in insulating properties and the increase in dielectric losses within the material. FTIR analysis revealed new peaks associated with hydroxyl groups related to water absorption. These structural changes demonstrate how moisture absorption degrades dielectric properties, suggesting that these diagnostic techniques could be effective for ongoing insulation monitoring, In conclusion, the proposed method can be seen as a valuable tool for the preliminary investigation of insulation systems' resistance to water treeing. It may assist in distinguishing between different polymeric compound formulations, helping to select materials more likely to succeed in the AWTT, and contributing to the improvement of cable design and durability.

One important milestone for a wider acceptance of DFR (Dielectric Frequency Response) in condition assessment of capacitance graded bushings was the publication of IEEE C57.12.200 in 2022. Since then, additional experience has been collected.

Baseline testing using DFR for new bushing installations to allow for more accurate condition assessment during service is a well-established method which is encouraged by the authors. It is however important to understand the influence of fringing effects caused by the different electrical context when testing is carried on installed bushings, compared to the separate routine testing in the manufacturer’s facility required by the bushing standards.

Some examples of bushing degradation and methods for result analysis are outlined in IEEE C57.12.200 however additional are available for both oil impregnated as well as dry concepts. The additional findings are based on extensive practical use of DFR. The most important conclusion is that testing at 1400 V provides more reliable results when accessing the condition of bushings, compared to testing at lower voltages.

The trend towards higher power density motors and electronics has resulted in manufacturers looking for more efficient ways to cool their products during operation. Due to the size of these components and the need to keep them light weight, polymer solutions for heat dissipation have been growing in popularity. Polymers are already present in these designs due to their ability to protect from environmental hazards, function as an adhesive, and provide electrical insulation. These same polymers can be modified to be thermally conductive through the addition of various fillers. However, the effects of thermally conductive resins when used in a thin film are still unclear. In this study, the thermal conductivity of an epoxy-based system with traditional silicas vs high performance alumina-based fillers at various loading levels were measured. These thermally conductive resins were then coated as a thin film onto copper magnet wire windings using a dip method. An electrical current was then applied to the windings and the dissipation of heat was observed using an infrared camera. The data obtained from observing the heat removed from the windings when under load was used to determine the thin film effects of thermally conductive polymers.

In view of the great impact of sulfur hexafluoride (SF6) on global environment, the development of eco-friendly dielectric replacement gases has attracted considerable experimental and theoretical attentions. It is extremely difficult to identify an alternative gas that outperforms SF6 in all aspects because combining various mutually exclusive properties including dielectric strength, boiling point, global warming potential, arc interruption capability, toxicity, and flammability remains challenging. A variety of structure‐activity relationship models were developed to estimate the specific properties of the potential alternatives. However, these techniques either showed inadequate accuracy or employed the computationally intensive quantum chemical calculations. More reliable and efficient models are desired for the large-scale systematic virtual screening on the enormous number of all conceivable molecules. In this work, a valence-bond based structure‐activity relationship method is proposed for the first time to assess the dielectric performance from aforementioned six aspects by means of artificial neural network. From the mechanistic point of view, the dielectric-related physicochemical properties are determined predominantly by the electron-molecule and molecule-molecule interactions, which depend strongly on the inherent characters of the relevant chemical bonds as augmented by the bond-bond interactions. The chemical bonds are extracted straightforwardly from the simplified molecular input line entry specification (SMILES) and designated to be the descriptors for property prediction. Good correlations between theory and experiment have been obtained through the extensive machine-learning training on the well-established databases. The correlation coefficients for all the properties exceed 0.9. Using the present theoretical model, a multidimensional assessment on the performance of the potential alternative gas could be carried out efficiently with good accuracy in a consistent manner, shedding new light on the characteristic sought in SF6 replacement gases.

E-mobility is a key component nowadays to fulfil the goal of overall reduction of greenhouse gas emissions. An important step is to switch to regenerative energies and another is to make the vehicles as efficient as possible and feasible, technology wise.

Key components are installed in electric vehicles are the charging system, the battery and the electric motor. With regards to these components new developments and trends are introduced in recent times, such as an increase of the voltage level from 400 to 800 V and implementation of new materials for the multi-level inverter used in the drivetrain. By increasing the voltage level, the ohmic losses and charging times are reduced, whereas the usage of advanced materials, i.e. SiC-MOSFETs, the slew rate is increased to minimize the switching losses. In addition, a trend is to increase the switching frequency. These developments lead to higher electric and thermal stress especially in the enameled copper wires used in electric motors and will limit the resulting lifetime.

For investigation and qualification of new insulation system an inverter voltage generator was developed and comprehensive measurements were conducted to quantify the effects of temperature, switching frequency, voltage-level and rise time.

Depending on the capacitive load the inverter voltage generator is able to generate bipolar square-wave voltages in the range of 1-20 kHz with a rise time down to 50 ns and a voltage level up to 20 kVpk/pk. A big advantage of the generator is, that the rise time can be adjusted and the overshoot is quite low (<5 %).

The inverter generator is presented and basic results of the conducted lab testing are presented and discussed in this paper. During the testing we recognized that in some cases a high scattering of the lifetime results especially under inverter stresses is obtained, which is not consistent with the results under sinusoidal stress. Even if the guideline acc. IEC 60851 to manufacture the twisted pairs is tightly followed, we noticed a strong scattering in the PDIV, which can´t be explained by the test setup itself.

Therefore, we also did some investigation on a modified test setup acc. IEC 60851 and discuss these results.

Partial discharge (PD) magnitude and phase-resolved PD (PRPD) patterns are key indicators for on-line PD diagnosis for stator windings. These indicators can be influenced by generator operating conditions because generators are subjected to high temperatures and voltage distortion. This study investigates the impacts of voltage distortion and winding temperature on on-line PD diagnosis. We measure PDs in stator windings of a hydrogenerator. The voltage waveform and winding temperature varied with the load condition. Harmonic voltages of about 2-4 kHz are superimposed on the generator voltage. The temperature ranges from 27°C to 70°C. Although the superimposition of the harmonic voltages altered the PRPD pattern, its effect on PD magnitude remains negligible. In contrast, the shape of the PRPD pattern is independent of the temperature, whereas the PD magnitude decreases with the temperature. Based on these findings, we state notes for conducting on-line PD diagnosis under varying generator conditions.

Subsea cable connectors are critical components of offshore power delivery systems. The current-carrying components of these connectors are typically enclosed in solid insulation and protected by a liquid-filled diaphragm. Even though liquid dielectrics make pins and sockets more watertight and seal them from seawater, this solid-liquid interface may also be vulnerable to creepage discharges, which, by propagating over the solid insulator surface, can lead to flashover. It is therefore critical to understand the characteristics of these discharges, as well as their morphological evolution over time under sustained electrical stress. This could result in a better reference for the design and production of underwater cable connectors.

To investigate creepage discharges, a needle-to-plane electrode arrangement was adopted, and the gap distance was set at 25 mm. The sample under investigation consists of a block of Polyetheretherketone (PEEK) immersed in a synthetic ester liquid inside a 1.2 L polycarbonate test cell. The AC stress is ramped up to 30 kV at 1 kV/s and sustained for approximately 4 hours. In addition to recording PD apparent charges throughout the process, a camera captures surface tracking on the PEEK surface. Based on the results, phase resolved partial discharge patterns (PRPD) are analysed as well as PD magnitude and length of the tree growth over time.

PD magnitude and time were found to be related, indicating that the whole process can be divided into two phases. In the first stage, recordings were made above 3000 pC with a low repetition rate. At this stage of initiation, no trees were observed on the sample and the PRPD pattern was similar to that of an open liquid gap. This indicates that discharge in liquids was the primary cause of PDs. The second stage took place after approximately 65 minutes. During this propagation stage, PD magnitude abruptly decreased while tree length increased. In this phase, the number of PDs increased and the PRPD pattern changed into a turtle-like shape, with many PDs occurring at zero crossings, indicating accumulation of space charge on the PEEK surface. The final length of the tree was estimated at 14.3 mm, more than half the gap distance

This paper is about Partial Discharge (PD) measurement techniques for detecting insulation defects in oil-filled power transformers and reactors. Despite well-designed and properly dried insulation systems, discharges can occur due to defects such as moisture, voids, bubbles, delaminations, free or fixed particles and poor connections. The study examines both conventional (IEC 60270) and unconventional (UHF) PD detection methods, highlighting their effectiveness in identifying and localizing defects in laboratory and field conditions. However, challenges arise in interpreting results due to multiple PD sources and environmental noise. Recent advancements, particularly tools like 3PARD, have significantly improved the diagnostic capabilities for identifying PD sources. By using these tools alongside UHF and electrical PD tests, detailed analyses of measurement results can be conducted. The paper presents seven case studies that illustrate the application of these techniques in both field and laboratory settings. Results from these studies reveal various suspicious PRPD patterns, with many PD sources successfully identified using 3PARD. Subsequent visual inspections of the transformers and reactors confirmed serious insulation damages consistent with the observed PD patterns. This correlations between PD measurements and actual physical damages underscores the reliability of these diagnostic methods. Overall, the findings demonstrate that PD diagnostics are effective for identifying insulation faults, emphasizing the importance of ongoing monitoring and maintenance. The ability to clearly match PD patterns with visualized damage validates the robustness of these diagnostic tests in ensuring the reliability and longevity of power transformers and reactors. The paper ultimately highlights the critical role of advanced PD measurement techniques in enhancing the maintenance and operational integrity of electrical insulation systems.

The integrity and safety of pipeline infrastructure are critical for the reliable transportation of resources, and understanding the impact of external electrical phenomena is essential for effective risk management. Pipelines, often coated with insulating materials, can be subject to induced voltages resulting from electrical short circuits and lightning strikes. This paper examines how right-of-way (ROW) conditions influence the magnitude of induced voltages along pipelines, particularly in relation to power line faults.

Pipelines frequently traverse diverse terrains and run parallel to power lines, both overhead and underground. Faults in these power lines can induce electrical disturbances in adjacent pipelines, leading to potentially hazardous high-voltage levels. These induced voltages, if sufficiently high, can exceed the breakdown voltage of the pipeline insulation, causing failure and posing risks to personnel and landowners in contact with the pipelines. As such, effective ROW management and safety measures around power lines are crucial for mitigating risks associated with induced voltages.

This study, conducted in partnership with BC Hydro, focuses on a gas pipeline located alongside a transmission line. The paper investigates how short circuits and lightning strikes induce voltages in pipelines, paying particular attention to ROW factors such as soil resistivity and the proximity of other electrical infrastructure. The analysis is based on a planned 69 kV transmission line in British Columbia, which runs parallel to a FortisBC gas pipeline with an extruded polyethylene (PE) coating. This pipeline is located near residential and farming areas, heightening the need for careful evaluation of inductive interference risks to safeguard both public and worker safety.

A comprehensive model, developed using EMTP software, simulates voltage induction along pipeline segments, incorporating variables such as pipeline depth, coating type, distance from the ROW boundary, and soil conductivity. Simulations reveal significant variations in induced voltage levels based on these ROW parameters.

This research offers important insights into the interaction between ROW conditions and electrical disturbances, contributing to the broader understanding of pipeline safety and reliability. The findings provide valuable guidance for policymakers, engineers, and industry stakeholders to adopt best practices in mitigating induced voltage risks. Ultimately, the research aims to enhance pipeline safety, protect public health, and ensure the long-term reliability of energy infrastructure.

One of the advantages of the Roebel bar type stator winding is that in-service failures of the machine winding can be repaired by replacing the failed bars with spares. On large hydro-generators, access to the core face to allow replacement of the failed bars can be accomplished by either removing 2-3 of the rotor poles or by removing the rotor from the stator. This paper will describe an unusual situation in which neither of the normal repair access options were feasible, and how the specific winding failure location and Roebel bar design allowed for a novel approach to repair the winding. The paper will describe the initial testing and inspections performed, the reasoning that led to the novel repair approach, the repair work and in-process testing, the final testing, and observations made when returning the unit to service.

Failure of the stator winding and core happens more often in service than it can be predicted during offline and online diagnostics. Failures in stator assembly can be caused by various factors mainly affecting its insulation system, and include electrical stress, mechanical stress, and temperature exposure. On large machines above 100MVA, online stator failures may result in significant equipment downtime and repair costs.

This paper outlines the methodology for effective investigation, repair and testing of the stator failures to minimize the economic losses and extend useful life of the equipment following the failure. Moreover, asset management strategy is described to assist generation owner/operator with full lifecycle management of the stator assembly.

Abstract — High Voltage Rotating Machines (HVRM), generator stator cores, are susceptible to various operational issues that require thorough investigation and analysis. This paper focuses on different problems that can occur during operation: overfluxing, overheating of the end regions and spark damage. While these issues arise from fundamentally different causes, their visual symptoms can sometimes appear similar, making accurate diagnosis essential. This paper provides a comparison of these two failure mechanisms, clarifying their distinguishing characteristics with real-world examples. The specific case of 22 kV, 200 MW generator stator core overheating is presented, including failure analysis, root cause identification, repair methodology, and post-repair evaluation. To ensure the long-term reliability of the generator, computational analysis was performed to validate the effectiveness of the repair solution. The results demonstrate that the chosen approach is both feasible and capable of extending the operational life of the machine.

If the polarity of the PD impulses is accurately recorded and the polarity of the applied voltage at that time is known, it is possible to infer some information about the location of the PD. Specifically, in some situations, it can indicate whether the PD is originating from the insulation connected in series with the measuring impedance. In practical applications, this information can help determine if the PD is occurring within or outside the equipment being tested or, in some cases, if it is coming from a specific accessory.

This publication examines if and how this information can be utilized for PD diagnostic of shielded power cables, power transformers, and stator windings. It begins with practical measurements conducted on simple test circuits to explain the underlying theory of the direct and indirect PD measurement circuits. Later, it presents measurements taken from medium voltage cables, power transformers, and stator windings done to investigate if there are advantages of assessing PD polarity. Additionally, it discusses the challenges faced by PD instruments in achieving accurate detection of PD polarity.

Aged oil-filled (OF) cables are used in Japan; therefore, on-line condition monitoring for them becomes more important than before. A large-scale blackout occurred due to insulation breakdown of oil-impregnated paper insulation inside a joint of OF-cables in 2016. It is reported that the insulation breakdown was caused by partial discharges (PD) occurring in the oil-impregnated paper insulation.

We have been developing a radio interferometer system to detect PDs occurring in the joints of OF-cables. The sampling frequency, quantization bit rate, memory of acquisition of the system are 10 GHz, 10-bit, and 100 Mpts/channel, respectively. The acquired digital data can be stored directly into solid state drives (DDSs) and sent to the operation center through local area network (LAN) as well. The radio interferometer system can be controlled from the operation center through LAN.

In this study, the radio interferometer system was used to detect PDs generated in a hole of insulation papers set in a joint of 154 kV OF-cables and that of 275 kV OF-cables. Currents and electromagnetic (EM) waves of PDs generated in the joint were simultaneously measured using a high-frequency current probe and the radio interferometer system, respectively.

It is planned that the measurement for PDs is conducted on the upper floor than the floor on which underground cables arranged; therefore, the antenna-array of radio interferometer system was set behind a concrete wall with the width of 30 cm placed in a mock-up tunnel. This concrete wall was supposed to be the floor. The mock-up tunnel, of which size is 2 m×2 m×6 m, was used for consideration of actual usage of the radio interferometer system. All sides of the tunnel are made of aluminum plates; therefore, it is a severe environment for measuring the EM waves because the EM waves reflect on the surface of all sides, i.e., multipath effects appear. Although reinforced concrete and other metal materials are used in actual tunnels in which underground cables are arranged, it is thought that the environment in the mock-up tunnel is more severe than that in actual tunnels from the viewpoint of measuring the EM waves.

It was confirmed that the EM waves due to PDs leak from the flange of OF-cable joint by using the radio interferometer system. The characteristics of the PD currents and EM waves are also described.

Safety operation of superconducting magnetic levitation (SC Maglev) systems needs automatic insulation diagnosis for a large number of propulsion coils and levitation-guidance coils, which are arranged on both sidewalls of U-shaped guideways. We have been developing an on-board radio interferometer system with a vector-antenna to detect partial discharges (PD) occurring in propulsion coils and could locate a mock-up of propulsion coil with a PD source and/or insulation breakdown from a test bogie running at the speed of 212.3 km/h on the test track with the length of 500 m.

Two sets of an on-board radio interferometer system with a vector-antenna were newly developed in order to detect PDs simultaneously for both sidewalls of U-shaped guideways. The sampling frequency, quantization bit rate, memory of acquisition of the systems are 10 GHz, 10-bit, and 100 Mpts/channel, respectively. The acquired digital data can be stored directly into solid state drives (DDSs) and sent to the operation center through local area network (LAN) as well. The on-board radio interferometer systems can be controlled from the operation center through LAN.

In this study, the two on-board radio interferometer systems with the vector-antennas were used to detect PDs generated in a cylinder-shaped void composed of a cylinder-shaped electrode and a plane electrode, which was set in a mock-up of propulsion coil. As the previous studies, the cylinder-shaped electrodes with different diameters: 0.5 mm, 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm were used; the gap length between the cylinder-shaped electrode and the plane electrode was set to 3 mm. Apparent charges, currents, and electromagnetic (EM) waves of PDs generated in the mock-up of propulsion coil were simultaneously measured by using a commercial PD measuring system based on the IEC60270 standard, a commercial current probe, and the two on-board radio interferometer systems with the vector-antennas, respectively.

This paper describes the characteristics of the EM waves received by using the on-board radio interferometer systems with vector-antennas in order to use them for automatic insulation diagnosis.

The preparation of solid electrical insulating material samples for accelerated aging testing of liquid-immersed transformer insulation systems per IEEE Std. C57.100™ requires a guaranteed low moisture content, which is critical to achieve and interpret test results accurately. Multiple test methods exist to determine the amount of water present in solid electrical insulating materials, such as: the oven drying method, solvent extraction method, and Karl Fischer titration method. Even though the test standards describe sample preparation, measurement procedures, and interpretation of results, there can be variation in some specific critical parameters of these tests. Thus, this situation requires the development of so-called best practices that should be followed to ensure more reliable and accurate measurements of moisture content for such accelerated aging tests. This article describes the various test methods for measuring moisture content and their deficiencies/benefits and focuses on the development of optimum test parameters for the oven extraction method of the Karl Fischer titration moisture test to improve the accuracy of lower moisture content measurements in particular.

Bushings are one of the most important and essential equipment of power transformers. Statistics show that one of the main and major causes of transformer failures is due to bushing problems, so it has a significant impact on the safety and reliability of the power system. One of the main reasons for bushing failures is the penetration of moisture into its internal insulation system. Moisture usually enters the insulation system of oil-impregnated paper (OIP) bushings through the flange gasket and diffuses into it over time. The moisture affects the dielectric properties and leads to an increase in its leakage current. These effects lead to changes in the electric field of the inner insulating layers of the bushings, so it is necessary to investigate these effects. In this paper, the changes of the electric field in the insulating layers of a sample bushing have been investigated with considering the different moisture distribution between the layers. This evaluation has been done during the moisture diffusion time, from the start of penetration to the time of uniformity of moisture in all layers. Also, the moisture effects on the bushing leakage current under above conditions have been studied. For this purpose, an OIP bushing is modeled in COMSOL Multiphysics software, and the simulations are carried out based on Finite Element Method (FEM) and finally the obtained results are analyzed. The results show that the moisture distribution in the bushing can have an important effect on the internal electric fields. Also, according to the results, the moisture distribution inside the bushing does not have a great effect on the leakage current and this current is only affected by the volume of the moisture penetrated inside the bushing.

The transition toward sustainable aviation requires the electrification of propulsion systems, encompassing hybrid-electric, fully electric, and hydrogen fuel cell technologies. While high-voltage systems offer enhanced power density, they also introduce significant electrical insulation challenges under high-altitude conditions, where pressure, temperature, and humidity vary considerably. This study investigates partial discharge (PD) characteristics of motor winding insulation under low-pressure conditions (from atmospheric pressure down to 4 kPa) using both sinusoidal and repetitive pulse waveforms. An arrow-pair model with insulated conductors was tested in a controlled-pressure environment. The results indicate that reduced pressure increases PD current amplitude and expands the luminescence region, while also extending the PD current pulse width and shifting the frequency spectrum toward lower frequencies. Additionally, under repetitive pulse conditions, the PD extinction voltage (PDEV) decreases significantly relative to the PD inception voltage (PDIV) due to a reduced availability of initial electrons. These findings emphasize the necessity of considering the PD characteristics specific to low-pressure environments in insulation design to enhance the reliability of electric aircraft propulsion motors.

　Inverter-fed motors are increasingly utilized due to their energy-saving and high efficiency. However, electrical insulation systems are susceptible to premature failure when exposed to inverter surge voltages. These surges arise from impedance mismatches among the inverter, motor, and cables. Notably, inverter surge voltages with short rise times tend to be concentrated in the first coil, leading to increased voltage stress on turn insulation, potentially causing layer short circuits.

　In stator windings powered by a commercial power supply, voltage is evenly distributed. However, with an inverter power supply, the voltage distribution becomes uneven, resulting in higher turn-to-turn voltage in the first coil. To account for this, turn insulation is designed with a higher margin, increasing copper losses, and necessitating a larger motor frame size.

　To establish an optimal electrical insulation system, understanding voltage distribution across each coil is essential. Direct measurement is challenging, so simulation is a valuable alternative. This paper presents measurement and simulation results using impulse voltages with varying rise times.

　The charging voltage of the power supply’s capacitor was set to 1.0 kV, with an output impulse width of 20 µs, and rise times of 150 ns, 400 ns, and 850 ns. The impulse voltage was applied to the first coil of phase U, with both the neutral point and frame grounded. The waveform was recorded using an oscilloscope with a high voltage probe.

　An equivalent circuit was developed using LTspice. The motor’s circuit constants were determined through theoretical calculations. The circuit parameters of the impulse power supply were set according to design specifications. To ensure consistency, the rise times in the simulation were set to 150 ns, 400 ns, and 850 ns.

　Using measurement results, impulse voltage rise times were applied to simulate coil-to-coil voltage and turn-to-turn voltage of the first coil. A comparison revealed general agreement in voltage distribution and turn-to-turn voltage. However, a discrepancy of up to 20% was observed in the coil-to-coil voltage, likely due to the rising portion of the impulse voltage and mutual inductance between coils. These results suggest simulations are valuable for understanding voltage distribution, with accuracy improving by adjusting equivalent circuit constants. Model simplification is crucial for enhancing simulation efficiency.

　Future research will explore multi-level inverters, pulse width, winding temperature variations, and rotor influences on voltage distribution. Additionally, investigating insulation material properties and their aging degradation over time could provide valuable insights.

The flight control system is critical for ensuring aircraft safety and precise maneuverability, and the Electro-Hydrostatic Actuator (EHA) system represents a key technology for future more-electric and all-electric aircraft. This study takes a 270 V random-wound motor as the research object and establishes three-dimensional electrostatic field models of turn-to-turn, phase-to-phase, and main insulation using physical field simulation software. Electric field distributions and Partial Discharge Inception Voltage (PDIV) under various insulation gap sizes are analyzed by applying Paschen's law. The results indicate that the errors between measured and predicted PDIV values are within 15%, providing valuable guidance for insulation design, optimization, and reliability evaluation of EHA motors.

Transformers and instrument transformers are key equipment in the electrical grid. The condition of the insulation mostly decides its life and crucial for efficient energy transmission. Over time, the insulation inside the transformer may degrade due to various types of stresses such as thermal, electrical, mechanical and environmental that will reduce the transformer’s service life. Various monitoring and diagnostic techniques are available amongst which dielectric frequency response is an advanced insulation diagnostic technique based on the measurement of dielectric losses over a broad range of frequencies. Dielectric frequency response (DFR) provides comprehensive view on the condition of insulation having oil, paper and pressboard. This paper presents comprehensive studies to understand nature of dielectric frequency response. The different case studies include the impact of overhauling on dielectric frequency response (DFR) of a transformer and resin impregnated paper (RIP) bushing have been reported. The reported analysis is useful in insulation diagnostics to the practicing engineers to diagnose the abnormalities.

Dissolved Gas Analysis (DGA) has long been a cornerstone of transformer diagnostics, providing invaluable insights into the operational health and fault conditions of power transformers. However, the increasing complexity of transformer designs, coupled with advancements in insulating materials and diagnostic technologies, necessitates a reevaluation of traditional DGA methods. This paper presents a comprehensive framework that integrates established chemical principles, modern gas extraction techniques, and artificial intelligence (AI) to enhance the accuracy and reliability of transformer diagnostics.

The paper delves into the evolution of DGA techniques, emphasizing the transition from traditional partial vacuum extraction to Headspace methods paired with gas chromatography. While these advancements increase efficiency, they also introduce calibration challenges that can impact measurement accuracy. To address these issues, the study advocates for refined calibration protocols, including multi-level gas-in-oil mixtures (GIOM), to align diagnostic practices with contemporary transformer requirements.

A key focus of the paper is the refinement of the Key Gas Method, a well-established diagnostic approach that correlates specific gas patterns with fault types. By incorporating modern analytical chemistry principles, empirical patterns, and advanced diagnostic tools like Duval's Triangles and Pentagons, the Key Gas Method is extended to address multi-fault scenarios and accommodate the diverse gas behaviors associated with new insulating materials.

Moreover, the paper explores the potential of AI and machine learning in DGA diagnostics. By training AI algorithms on extensive datasets, diagnostic accuracy can be significantly improved, particularly in complex or ambiguous cases. AI also enables real-time analysis, facilitating proactive maintenance and reducing the risk of catastrophic transformer failures.

The proposed framework combines predictive, explanatory, and intuitive diagnostic methods to provide a comprehensive approach to transformer health monitoring. Predictive methods leverage historical fault data, explanatory methods focus on the thermodynamic and chemical mechanisms underlying gas formation, and intuitive methods incorporate expert insights. This multi-faceted approach ensures a balance between diagnostic precision and practical applicability.

Through case studies and comparative analyses, the paper demonstrates the efficacy of this integrated framework in enhancing fault detection, reducing diagnostic uncertainties, and optimizing maintenance strategies. By aligning traditional DGA methods with modern technologies and AI, this approach offers a robust and adaptable solution for ensuring the reliability of transformers in increasingly complex power systems

The ability to anticipate voltage-induced breakdown (BD) of electrical insulation is of critical importance to the power industry to maintain uninterrupted electrical service and ensure grid reliability. Gaseous voids trapped within the electrical insulation of power devices are an often unavoidable artifact of the manufacturing process. The compromising effect of voids on dielectric performance of motors and generators is difficult to predict as these effects are dependent on highly localized field geometries. Reported here are initial steps toward the development of a FEA simulation model which will help inform machine insulation design by predicting breakdown thresholds under device-specific configurations and conditions. Preliminary results consider a simplified test system of two opposing electrodes sandwiching an air gap. A finite element simulation was developed using COMSOL Multiphysics utilizing a newly released software add-on, the COMSOL Electric Discharge Module, to model the electric field generated within this simplified system under an applied DC terminal load. Electric field characteristics and associated gas breakdown thresholds were determined as a function of several geometric and environmental parameters. Modeled system geometry was specifically designed for rapid evaluation and experimental validation in the lab. Experimental air breakdown data was generated and found to be in agreement with simulated data.

The current electrical evaluation of power cable is generally decoupled from the mechanical loading such that the results of electrical measurement cannot reflect the dielectric condition of power cable under operation [1-5]. The dielectric response of a 15 kV power cable has been investigated in this study, while mechanical compression is being introduced in transvers direction. The work reported is part of a U.S. DOE WETO Incubator program with submarine dynamic power cable (SDPC or SPC) for floating offshore wind transmission. The SDPCs are typically subjected to hostile mechanical and environmental loadings in operation, including tension/ bending related to self-weight, anchor impact, wave, current, floater-cable interaction, and so on. The SPDCs shall have a high level of structural integrity to ensure reliable power delivery. This is critical, especially considering SPC failures accounted for 80% of financial loss and insurance claims for offshore wind farms, and the cable failure attributed to cable design constituted near 15% of total failures [6,7]. The project is proposed to address the technical challenge with design and application of submarine power cable. The dielectric breakdown time of power cores was focused and experimentally studied. Particularly, the response of power core has been examined under monotonic and creep mechanical loadings when a high voltage is applied. It has been shown that the breakdown of power cores was dominated by the equivalent circumferential strain induced to the outer layer of power core. Besides the external factors such as mechanical load level and environmental temperature, the breakdown of power cores was also related to the metal shield and outer sleeve for the given power core. The recovery of electrical resistance after a cable specimen was taken off testing machine showed that the mechanical unloading had altered the dielectric status of the insulation layer substantially and further suggested the significance of studying the electrical response of power cables with the mechanical load applied concurrently.

References

1 Worzyk, T., 2009. Submarine power cables: design, installation, repair, environmental aspects. Springer

2 Marta, M., Mueller-Schuetze, S., Ottersberg, H., Isus, D., Johanning, L. and Thies, P.R., 2015. Development of dynamic submarine MV power cable design solutions for floating offshore renewable energy applications.

3 Gao, Q., Duan, M., Liu, X., Wang, Y., Jia, X., An, C. and Zhang, T., 2018. Damage assessment for submarine photoelectric composite cable under anchor impact. Applied Ocean Research, 73, pp.42-58.

4 IEC 63026-2019, Submarine power cables with extruded insulation and their accessories for rated voltages from 6 kV (Um = 7,2 kV) up to 60 kV (Um = 72,5 kV) –Test methods and requirements.

5 NDV-RP-F140, Electrical power cables in subsea applications, September 2019.

6 Gulski, E., Anders, G.J., Jongen, R.A., Parciak, J., Siemiński, J., Piesowicz, E., Paszkiewicz, S. and Irska, I., 2021. Discussion of electrical and thermal aspects of offshore wind farms’ power cables reliability. Renewable and Sustainable Energy Reviews, 151, p.111580

7 Strang-Moran, C., 2020. Subsea cable management: Failure trending for offshore wind. Wind Energy Science Discussions, pp.1-11

For the past 37 years, cable rejuvenation has been integral in the system resiliency programs of more than 300 utilities worldwide. During that time, more than 50 million meters of their aged underground medium and high-voltage cable has been rejuvenated through silicone injection. This technology extends the reliable service of aged cable by more than 40 years through a non-invasive process that restores dielectric strength and retards future water-tree growth. As a result, utilities have extended the reach of their capital budgets, improved their reliability indices, exceeded rehabilitation targets and reduced carbon emissions by over 660,000 metric tons of global warming potential. This presentation will highlight the methodologies and key findings from a comparative study on the life-cycle analysis (LCA) of cable rejuvenation and cable replacement. The work was conducted by an independent firm according to the life cycle inventory (LCI) and life cycle impact assessment (LCIA) standards established by the International Organization for Standardization (ISO) life cycle assessment standards ISO 14040 series. Through comparison of the global warming potential (GWP) for these two options, the data reveals a 99.9% savings in kilograms of CO2-eq when cable rejuvenation is selected to extend the life of power cables over replacement.

Investigations have revealed that crosslinked polyethylene (XLPE) cable joints are susceptible to moisture intrusion, leading to interfacial wetting and subsequent discharge, which ultimately contributes to widespread insulation breakdown accidents. Despite these observations, the exact mechanism behind moisture-induced insulation failure of composite interfaces in cable joints remains elusive, contributing to a dearth of effective diagnostic methods for assessing joint moisture levels. This paper focuses on the effects of moisture intrusion on the discharge failure process of cable joints under operating conditions. An accelerated moisture aging platform for cable joints is constructed in this study. The Partial Discharge (PD) measurement is performed at AC 10kV power cable joints. The partial discharge test results show that normal cable joints do not exhibit significant partial discharge phenomena during the early to mid-stages of moisture ingress. The maximum discharge amplitude suddenly increases in the late period of moisture ingress. Through the finite element simulation of the cable joint, it is found that when moisture approaches the conductor shielding within the interface, early-stage interface insulation discharge phenomena are initiated, which coincides with the result of the PD test. Anatomical examination reveals early-stage insulation degradation, characterized by non-conductive regions and dendritic carbonization development, ultimately leading to complete interface insulation failure. Based on the results, this paper summarizes four stages of partial discharge in moisture-affected cable joints, providing a theoretical basis for monitoring partial discharge in actual moisture-affected cable accessories.

Novel and complex stator slot geometries demand precise forming of slot liner insulation materials to ensure a reliable interface with the ground-wall insulation, thereby optimizing electrical machine performance. This paper presents a new approach to forming liner materials within the stator slot using a custom-designed, additively manufactured insertion tool. The study evaluates the impact of this approach on the electrical and mechanical properties of five distinct slot liners. Experimental validation comprises of breakdown voltage, coefficient of friction and ultimate tensile strength at room and elevated temperatures (up to 220°C), revealing minimal degradation in both insulation and mechanical properties, with only minimal failure near the creased regions. Coefficient of friction tests also demonstrate variations in interaction forces between different slot liners, stator core pack and the bespoke insertion tooling. The findings confirm the suitability and effectiveness of this forming approach for low-volume or prototype level electrical machine manufacturing.

This study investigates the turn-to-turn insulation of hairpin windings in EVs under electrical stress from wide-bandgap power converters. A custom-built SiC-MOSFET pulse generator is used to induce continuous partial discharge (PD) by applying 2.5 kV unipolar pulses with a 40 ns rise time and 5 kHz frequency to corona-resistant magnet wire samples for 24 hours. The effects of 10% and 20% overshoot; and 20% and 50% duty cycles on insulation degradation are analyzed. Diagnostic techniques, including PDIV measurement, dissipation factor analysis, and surface imaging, are used in assessing the aging effects. Results indicate that voltage overshoot significantly accelerated PDIV reduction and increased the dissipation factor, underscoring its critical role in insulation aging.

This research studied the physicochemical and charge transport behaviour of composite natural esters derived from non-food grade oils for high-voltage insulation. Crude neem oil and palm kernel oil were purified and subjected to epoxidation, converting unsaturated carbon-carbon double bonds into stable epoxide rings, confirmed by Fourier Transform Infrared Spectroscopy. Purified palm kernel oil was further transesterified to reduce viscosity before epoxidation. Composite oils were synthesized by blending epoxidized neem oil with epoxidized palm kernel oil methyl esters in varying proportions. The physicochemical and dielectric properties were analyzed. The viscosity of the base oils and their blends show temperature dependence and there is also an improvement in the viscosity of the base neem oil with increase in the concentration of epoxidized palm kernel oil methyl ester. The optimum blend shows a viscosity less than that of mineral oil at transformer operating temperature. This is indicative that the optimal blend has a better heat transferability. Dielectric study revealed frequency dependent behaviour typical to DC conduction at high frequencies and at low frequencies below a characteristic frequency showing charge transport typical to interpolar polarization. The developed composite oil exhibits improved heat transfer property than the base neem oil. Its dielectric properties show similar behaviour as that of mineral oil, however, it has higher loss factor.

Wind turbines are critical components of renewable energy infrastructure, but they face operational challenges due to transformer, generator and powertrain defects. One cause of the defects is nacelle circulating currents. In this paper we will discuss how these currents impact generator stator and rotor insulation systems, gearbox gear and bearing, and main bearing reliability. The multi-year collaborative study included mapping circulating currents and component impacts as well as solutions attempted by OEMs, owners and vendors. Generator and transformer insulation defects related to circulating currents will be identified along with gearbox and main bearing discharge currents and the source of the circulating currents and their flow. The paper will explore mitigation strategies such as improved grounding and insulating techniques for these components for both on and off-short wind turbines.

Insulating systems under stress, both thermal and electric, break down yielding decomposition products, many of them in the gaseous form. These decomposition processes are chemical reactions and, as such, are subjected to its thermodynamics and kinetics laws and principles. It means that reaction products are dependent upon reaction’s temperature, pressure, and reagents concentrations, meaning that for each temperature or energy level involved in a given incipient fault in a transformer, a specific set of reaction products will be formed. Although stablishing a universal equation of gases formation for each type of transformer fault is not possible, due to differences in the other factors, pressure, and reagents concentration, several diagnostics methods have been developed based on statistic observation of failures related with gases generation. All those methods, however, are, as expected, related to basic chemical reaction thermodynamics. Therefore, transformer fault diagnostics based on mineral insulating oil (MIO) decomposition is well stablished and widely used. Knowing what fault is occurring, however, is not enough to allow a maintenance effective action; it’s also necessary to know how severe the fault is and if it does involve solid insulation. For oil/paper insulating systems, since cellulose-based papers thermal decomposition yields carbon monoxide and dioxide, these gases, and the ratio between them, are the most used criterium. Recently, the development of insulating systems for higher operating temperature transformers such as natural ester insulating oils (NEIO) with thermally upgraded kraft paper (TUK); aramid paper (AP), and hybrid paper (HP), as well as MIO with the same solid insulating options, have brought the need for further studies on incipient fault diagnostics. Several studies have been carried out to evaluate reliability of known diagnostic methods when applied to these new insulating systems and, on how to determine solid insulation involvement. In previous works, the authors have developed an experimental device able to simulate thermodynamics of a transformer thermal fault, in which a hot spot reaches high temperatures while the bulk oil temperature remains in normal transformer operating range. This setup allows heating of solid insulation to different fault temperatures keeping the bulk oil cool and, therefore, generating characteristic fault gases. In this work, the thermal fault generating device is used in studying thermal fault behavior in different insulating systems: MIO/TUK; MIO/HP; MIO/AP; NEIO/TUK, NEIO/HP and NEIO/AP. Results have shown that current diagnostic methods need to take into account the specific insulating system and that solid insulation plays an important role in fault development and characterization. As a conclusion, is suggested that diagnostic methods shall be adapted according to the specific insulating system in order to get best maintenance results.

Turn insulation of multiturn coils is often involved in machine failures. Until now, there has been no type test for detecting the long-term performance of turn insulation. Also, conventional diagostic tests such as partial discharge (DP) and dissipation factor (DF) tests are not accurate to detect degradation of the specific turn insulation.

The frequency response measurement technique, commonly called Sweep Frequency Response Analysis (SFRA), is based on the analysis of winding impedance in the frequency domain. This technique is used for the diagnosis of power transformer windings for more than 40 years and is currently the subject of research for its application in rotating machines.

The aim of this study is to evaluate the SFRA capability to diagnostic turn insulation degradation during long-term performance testing on coils by the insertion of fault resistances between turns and to develop an RLC model representative of the stator coil using MATLAB environment.

SFRA measurements were performed on a coil with inter-turn faults made by the introduction of resistances between turns at three locations. SFRA results were compared to the simulation obtained from the developed model. This validation ensured that the model was accurate and faithfully reflected the real behavior of the coil.

There are significant concerns regarding corona discharge, partial discharge, arcing, and minor arcing in medium- and high-voltage DC systems, as well as in battery energy storage systems (BESS). These issues may arise from various factors, including micro-voids in insulation, metal powder, loose connections in medium- and high-voltage buses, and internal short circuits in lithium-ion batteries. Detecting signals below 50 MHz presents challenges due to a low signal-to-noise ratio, making it crucial to differentiate between corona signals, partial discharges, arcing signals, and external noise. To address this challenge, the authors propose a novel signal differentiation analysis technique aimed at classifying signals and reducing unwanted noise. This analysis emphasizes four key parameters: repetition rate, signal frequency, signal duration, and magnitude. The authors apply high-voltage DC and overlapping harmonic voltage to a sample of epoxy insulation. To simulate the micro arc in a BESS, a positive electrode made of braided strand wire is paired with a flat metal piece as the negative electrode inside a transparent fiberglass tube. A new method classifies various signals and examines their behaviors using the aforementioned parameters. The process involves three steps. When the signal exceeds the alarm threshold, the device assesses whether to trigger an alarm by analyzing the signal’s behavior over several minutes, utilizing magnitude, time, and frequency (MTF) analysis. This paper presents the results of the experiment related to the classification of different discharges.

High-frequency, steep-fronted impulses generated by SiC inverters significantly increase the likelihood of insulation failure in hair-pin winding motors. To prevent partial discharge (PD) in Type I motor insulation systems, it is crucial to identify the maximum voltage drop in the motor stator and compare this voltage to the partial discharge inception voltage (PDIV) of the insulation. This paper presents a model of a stator with three-phase windings to analyze the voltage distribution in hair-pin winding motors. Simulation results indicate that: (1) the maximum phase-to-ground voltage occurs at the line end of the three-phase windings, accounting for approximately 70% of the input voltage; (2) the maximum turn-to-turn and phase-to-phase voltages are approximately 70% and 115% of the input voltage, respectively; (3) the error between simulation results and actual measurements is about 8%, verifying the accuracy of the calculations. The simulations identify the phase-to-phase voltage as the point where insulation failure is most likely to occur.

While holding several constructive similarities with power transformers, shunt reactors' thermal behavior differs significantly from transformers. Yet, the most common approach is to estimate the temperature distribution of shunt reactors using the same thermal model developed for power transformers. While adjusting some of the empirical coefficients of the model may lead to minimizing the deviations in the predicted temperatures, due to the exponential nature of the solid insulation life consumption, small deviations in the hottest spot temperature may represent several years or decades of difference in the expected lifespan.

A physics-based thermal model was included in the IEEE C57.91 in the 80s, traditionally referred to as the “Annex G” model. Rather than using time constants and exponential functions to predict the temperature gradients under different loading conditions, the model utilizes a model similar to a Runge-Kutta method, on a sequential calculation procedure based on an initial value, using small enough time steps. For each time step, equations are used to calculate the heat generated and dissipated by the different elements of the transformer, estimating the temperature variation for the average winding and the hotspot region.

Considering the differences in the variation of losses and heat dissipation as a function of the system voltage, the so-called “Annex G” model was adapted for shunt reactors. A comparison of the results with measurements and results from other models is presented in this article.

An inadequate isolation system (IS) design can result in transformer failures, which translate into severe economic repercussions due to the cost of repair or replacement, not to mention the interruption of the electric power supply.

The transformer insulation system is directly linked to its performance and useful life. Therefore, achieving the best possible IS design is a key objective. Appropriate design criteria can help accomplish this condition, and over the years, many criteria have been developed, such as the Weidmann® reference curves and safety margin calculation. This work focuses on the safety margins calculation of oil gaps, which are directly related to the probability of partial discharges in transformer oil.

The safety margins are directly related to the arrangement of the solid insulations immersed in the oil. In practice, safety margins must be properly estimated during the transformer design and optimization process. These margins must be adequate to guarantee that the equipment supports test levels and the dielectric stresses to which it will be subjected during its useful life.

A methodology supported by genetic optimization algorithms is developed to maximize safety margins in the arrangement of major insulation of a power transformer, considering restrictions such as the standard thickness of the barriers and typical sizes of oil ducts.

The work is divided into two main optimization stages. The first is the optimization of the major insulation between the windings, where the electrical stress is more critical. The second stage involves optimizing the insulation between the core and the low-voltage winding. The insulation stresses during applied potential and impulse tests were considered for each stage.

The configuration of the transformer's major insulation design was optimized through the genetic algorithm method (GA). The calculation of electrical stress was obtained through the finite element method (FEM).

The methodology was applied for the case study of a 20 MVA transformer of 115/13.8 kV of one Mexican manufacturer. The results show that optimal design presents a considerable improvement in the most critical safety margins compared to the original design of the transformer. The proposed developed methodology can be applied to any transformer immersed in oil.

Polarization and Depolarization Current measurements (PDC) are well-known in the industry. Hydro-Québec has been using PDC measurements as a diagnostic tool for more than 25 years. Since 2012, systematic PDC measurements are conducted every 6 years on the stator windings of all the hydrogenerator fleets. When the tool was first implemented, thresholds were defined to convert insulation resistance values into a condition health index. These limits were decided based on preliminary results obtained from a few hydrogenerators and laboratory measurements on accelerated-aged samples. However, with more than 500 PDC measurement results, the database can now help refine the limits for each type of insulation system (asphalt, epoxy and polyester). The purpose of this paper is to present the evolution of the insulation resistance value as global aging occurs and to observe the trending of insulation resistance over time. The influence of factors such as humidity, and the nature of the stress grading coating are also presented to describe how the limits can be managed for diagnostic purpose with statistical uncertainty.

In this paper we will discuss the use of electrical and current signature analysis on electric machinery for the detection of insulation defects. The project involved the practical study of electric machinery field testing and evaluation at repair facilities. In this paper we will identify the use of two different types of electrical signature and motor current signature analysis devices and how insulation system direct and inferred defects are detected. The use of expert and machine learning/AI for this type of analysis will be distinguished. Direct insulation system defects include electrical insulation system breakdown and inferred defects involves the identification of conditions that lead to breakdown. The study and results also includes results from both across-the-line clean, high harmonic, and inverter environments.

One of the major concerns in high-voltage power semiconductor modules is the high electric field stress at the edge of the metallization, where the substrate, encapsulation material, and electrode meet; commonly referred to as the triple junction. If this stress is not controlled, partial discharge may occur, eventually leading to insulation failure. To mitigate this issue, electric field grading techniques, such as the use of permittivity-graded materials in encapsulation, have been investigated. However, the optimal distribution of permittivity remains unclear. This study explores the effective distribution of relative permittivity (𝜀r) in permittivity-graded materials for reducing electric field stress at the triple junction. By comparing the stress-reducing effects of four different types of permittivity distributions, the study aims to identify and discuss the most effective approach.

Modern insulation systems for Hydro Generator Stators use mica-based insulations that are made with either a Vacuum Pressure Impregnation system or a system where resin is preloaded into the mica tapes using a Resin Rich insulation. Traditionally, these systems are based on binding the mica layers together with epoxy that is based on petroleum.

With advances in bio-based materials, there are now sustainable versions of epoxies that are available. Recent work has shown that some of the epoxies that are commonly used in our industry are now available in sustainable form.

Within Andritz, there is a CEO driven initiative to improve our ESG (Environmental, Social, and Governance) performance. Andritz recently has driven work such as removal of chemicals that have Carcinogenic, Mutagenic and Reproductive risks for workers and have invested heavily in businesses and technologies to improve environmental impacts for our customers. In our Hydro Power business more recently, we have teamed up with Isovolta to explore

A novel classification tool has been developed to analyze partial discharge patterns. This technique integrates features from the Peak Phase Dispersion Analysis (PPDA) Cross and the PPDA Cactus. It is intended to classify partial discharge patterns, including internal, slot, surface, and corona discharges. The PPDA Cross automatically generates key metrics, including the peak partial discharge (PD), the dispersion phase angle of the largest PD cluster, and the median phase angle of that cluster. On the other hand, the PPDA Cactus method clarifies the vertical characteristics of the phase-resolved partial discharge (PRPD) pattern in relation to the phase angle. This tool can simultaneously detect partial discharge signals from three-phase stator windings. A technique called three-phase signal discrimination (TPSD) has been introduced to improve measurement accuracy. This technique differentiates phase-related PD, external noise, and phase-to-phase PD, allowing PRPD data collection specific to each phase. Additionally, the instrument includes an innovative partial discharge sensor called the wide frequency band current transformer (WFBCT), which functions within a frequency range of 300 kHz to 60 MHz. This capability allows for acquiring PRPD patterns in voltage peak mode (VPM) and charge integration mode (CIM) under IEC60270.

The Insulation Resistance and Polarization Index test is routinely used to determine the condition of salient pole hydro generator field winding insulation. The current applicable IEEE standard, 43-2013 “IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery” notes that the Polarization Index test is not applicable to salient pole machines with strip-on-edge windings. A 2021 Electrical Insulation Conference Paper described the author’s experience with Polarization Index testing of strip-on-edge field windings over a 20-year period; this paper continues the effort to share hydrogenerator owner experience on this subject. The paper will briefly review the test theory as applied to strip-on-edge windings and test results reporting, and present several case studies in which the polarization index test results provided actionable information used to make decisions related to whether the salient pole generator field winding insulation was suitable for operation or testing at higher voltage. A brief discussion of possible minimum Polarization Index limits for salient pole strip-on-edge field windings is included.

To demonstrate the consistency of partial discharge (PD) measurements, a comparative study was carried out using two different PD instruments on several individual coils of various designs. Although PD measurements on individual bars and coils have been performed for many years, the quantification as well as reproducibility of the results are still a matter of debate. Proper use and understanding of the instruments are essential for obtaining reproductible PD results. Therefore, the main objective of this comparative study was to evaluate the effect of different parameters that can influence PD measurements, and to validate the reproducibility from one PD instrument to another. PD measurements were carried out in the laboratory on individual coils using capacitive couplers and an electromagnetic probe. Various parameters were studied, such as the impact of the value of the capacitive coupler, the frequency bandwidth, the amplitude of the calibrating pulse and the connection to the coil terminals. The results presented in this paper reveal close correlations between the two PD instruments, both for PD results obtained using the capacitive coupler and those obtained using the electromagnetic probe. Analysis of the Phase Resolved Partial Discharge (PRPD) pattern analysis in each case was also very similar between the two PD instruments.