Electro-thermal Aging Research Articles

Nonlinear torsion-dominated deterioration behavior of wind generator output cable under electrothermal aging

Nonlinear torsion-dominated deterioration behavior of wind generator output cable under electrothermal aging

Effects of electrothermal ageing on dielectric performance of metallised biaxial orientation polypropylene film capacitors in strong magnetic fields

Effects of electrothermal ageing on dielectric performance of metallised biaxial orientation polypropylene film capacitors in strong magnetic fields

Electrothermal Aging of All-Organic PEI/ITIC Composite Films for Dielectric Energy Storage

Electrothermal Aging of All-Organic PEI/ITIC Composite Films for Dielectric Energy Storage

Space Charge Characteristics of Electrothermally Aged Oil-Paper Insulation Under Slightly Nonuniform Electric Field

To study the change characteristics of space charge in oil paper insulation under a slightly non-uniform electric field and a uniform electric field, the existing space charge measuring device was improved, and sphere–plate and column–plate electrode models were prepared. Oil paper insulation samples at different aging stages were obtained via electrothermal aging. The real-time waveforms of the space charge distribution in the samples at different aging stages were measured in the process of polarization with a direct-current (DC) voltage and depolarization with a DC voltage, and the effects of different electric-field types on the charge distribution and motion characteristics of oil paper insulation samples at different aging stages were examined. The results indicated that the existence of a slightly non-uniform electric field accelerated the change in the charge-density peak at the interface and increased the fluctuation range of the charge-density curve in the process of applying a DC voltage. With the aggravation of electrothermal aging, the amount of charge injected into the sample increased, and the slightly non-uniform electric field intensified this process, affecting the accumulation and dissipation of space charge in the sample. Electrothermal aging increased the trap distribution density and energy-level depth. However, for an oil paper insulation sample at the same aging stage, compared with the uniform electric field, the slightly non-uniform electric field had no obvious effect on the trap energy-level depth, but it increased the amount of trapped charge and changed the trap density distribution in the sample. The results of this study provide a theoretical basis for examining the influence of slightly non-uniform electric fields on the space charge distribution characteristics of oil paper insulation subjected to AC/DC combined electrothermal aging.

A Dynamic SOH-Coupled Lithium-Ion Cell Model for State and Parameter Estimation

The health assessment of Lithium-ion batteries (LIBs) is critical for battery management systems (BMSs) to ensure safe and reliable operation and predict life-cycle. State-of-health (SOH) monitoring is challenging since it is governed by several internal and external degradation factors, such as temperature, aging, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$C_{rate}$</tex-math></inline-formula> , and faults. In this paper, we propose a SOH-coupled nonlinear electro-thermal-aging (ETA) model of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LiFePO_{4}$</tex-math></inline-formula> /graphite battery, which can be employed to simultaneously estimate the state of charge (SOC), state of health (SOH), temperatures, and internal resistance using a filtering-based approach. The coupling between the equivalent circuit model (ECM) and the SOH is established using an empirical capacity fade model of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LiFePO_{4}$</tex-math></inline-formula> /graphite battery and its effects on SOC dynamics. In contrast to a constant usable capacity, the proposed model employs a SOH-dependent variable capacity ECM, thereby incorporating the influence of battery aging on the ECM. The SOH-coupled ECM model is then integrated with the thermal model to develop the ETA model. The ETA model is further extended by augmenting the ohmic resistance dynamics to enable monitoring of the evolution of the internal resistance. The proposed SOH-coupled model is validated with numerical simulation and experimental data. Estimation results for SOC, SOH, temperature and ohmic resistance are included to show the model's potential for monitoring and control applications.

Influence of Combined Electrothermal Aging on Dielectric and Thermal Properties of HVAC XLPE Cable

To explore the influence of electrothermal aging on the properties of HVAC XLPE cable during its normal operation, two circuits of 110 kV XLPE cable were subjected to a combined electrothermal accelerated aging test for 180 days. The test voltage was set at 95 kV, and the test temperature was set at 90 °C. The constant temperature aging mode was adopted for one circuit, and the periodic thermal cycle aging mode was adopted for the other circuit. The dielectric property of the cable was diagnosed with dielectric spectroscopy measurement, and the thermal property was diagnosed with thermal parameters (thermal capacity and thermal resistance) measurement. Combined with Fourier infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) measurements, morphological changes in the insulation under different electrothermal aging modes were analyzed to construct the correlation with the dielectric and thermal properties. The results show that the short-term electrothermal constant temperature aging mode effectively enhances the dielectric and thermal properties of the cable by modifying spherulite morphology and migrating polar compounds; the short-term electrothermal cycle aging mode also enhances the thermal properties of the cable due to the drop in small polar compounds. However, different distributions of polar compounds and crystal interfaces in the insulation lead to extreme distortion in the electric field distribution.

A Novel Approach to Estimate Electrothermal Aging of Epoxy–Alumina Nanocomposites Using Dielectric Relaxation Current Analysis

In this article, an advanced technique is applied to estimate the aging state of epoxy–alumina nanocomposite insulation. For this purpose, several epoxy–alumina nanocomposite samples are prepared in the laboratory. Samples are undergone into artificial electrothermal aging conditioning up to duration of 600 h. After each 100-h instant, the relaxation current is measured under 1-kV/mm dc stress through the developed experimental setup in the laboratory. From the experimentally measured current data, relaxation frequency distribution (RFD) function of the test samples is computed. Based on the relaxation distribution function, two aging sensitive parameters are evaluated. In order to correlate these two aging sensitive parameters with the aging state of insulation, two empirical relationships are proposed based on the experimental investigation. The effectiveness of these two empirical relationships is validated with the laboratory prepared epoxy nanocomposites (EPNCs) insulation having a definite aging state. The experimental investigation shows that the proposed method can effectively be applied for estimating the aging state of nanocomposites insulation used in real-life high-voltage equipment.

Correlation between Terahertz Dielectric Properties of XLPE and Its Composition Structure during Electrothermal Aging

Correlation between Terahertz Dielectric Properties of XLPE and Its Composition Structure during Electrothermal Aging

Effects of Electrothermal Aging on Surface Morphology and Dielectric Properties of Poly(Ethylene Terephthalate) in Laminated Busbars

Poly(ethylene terephthalate) (PET) used as an insulating medium of laminated busbars is subjected to combined stresses of the dc electric field and elevated temperature. The coupling effect induces the electrothermal aging of PET, which weakens the busbar performance and thus threatens the long-term reliability of power electronics equipment. In this article, the dc electrothermal aging tests of a 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> PET film are carried out at varied aging temperatures of 60 °C, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$80~^{\circ }\text{C}$ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~^{\circ }\text{C}$ </tex-math></inline-formula> and a fixed electric field of 120 kV/mm. The surface becomes rougher with ongoing electrothermal aging. It is found that the surface roughness <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Sa</i> of samples increases from 95 to 2100 nm and the PET surface energy drops from 46.7 to 43.9 mN/m. Moreover, dc breakdown strength and volume resistivity decrease from 807 kV/mm and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.75\times 10^{{16}}\,\, \Omega \cdot \text{m}$ </tex-math></inline-formula> to 556 kV/mm and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.97\times 10^{{16}}\,\,\Omega \cdot \text{m}$ </tex-math></inline-formula> , respectively. The aging performance of dc breakdown strength and volume resistivity is discussed based on trap characteristics, which are involved in the evolution of aggregation structure and molecular chain during electrothermal aging. The results of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) reveal that in the initial aging stage, recrystallization leads to the increased deep trap depth and the crystalline region destruction, and the molecular chain scission results in the decreased deep trap depth in the late aging stage.

Electrothermal Aging Model of Li-Ion Batteries for Vehicle-to-Grid Services Evaluation

The growing interest in Electrical Vehicles (EVs) opens new possibilities in the use of Li-ion batteries in order to provide ancillary grid services while they are plugged to recharging stations. Indeed, Vehicle-to-Grid (V2G), Vehicle-to-Building (V2B), Vehicle-to-Home (V2H) as well as Vehicle-to-Vehicle (V2V) services can be carried out depending on the particular installation and on the connection to the distribution grid of the considered recharging station. Even if these are interesting and challenging opportunities, the additional charging/discharging cycles necessary to provide these services could decrease the expected life of EV batteries. For this reason, it is of paramount importance to study and develop reliable models of the batteries, which take the aging phenomena affecting the reliability of the Li-ion cells into account to evaluate the best charging/discharging strategy and the economic revenues. To this aim, this paper focuses on a battery pack made up with Li-ion nickel–manganese–cobalt (NMC) cells and proposes a semiempirical Electrothermal Aging Model, which accounts for both calendar and cycle aging. This modeling phase is supported by several experimental data recorded for many charge and discharge cycles at different C-rates and for several temperatures. Thus, it is possible to analyze and compare scenarios considering V2G services or not. Results show that the considered battery is subjected to a life reduction of about 2 years, which is a consequence of the increased Ah charge throughput, which moves from 120,000 Ah over 10 years (scenario without V2G services) to almost 230,000 Ah over 8 years (scenario with V2G services).

Optimization of charging strategy for lithium-ion battery packs based on complete battery pack model

This study focuses on a charging strategy for battery packs, as battery pack charge control is crucial for battery management system. First, a single-battery model based on electrothermal aging coupling is proposed; subsequently, a battery pack cooling model and battery pack equilibrium management model are combined to form a complete battery pack model that describes the state parameters of the battery pack and the interaction between the individual batteries in the battery pack. Then, a multi-objective optimal charging strategy considering charging time, aging, and energy loss is proposed, and the equilibrium management, temperature, and battery parameters are restricted. A genetic algorithm method was used to optimize the adaptive multi-phase constant-current constant-voltage charging strategy. A fast charging strategy based on the shortest charging time is proposed. The results show that the fast charging strategy can significantly reduce charging time but leads to aging and increases energy loss. The contradictory relation between charging time and aging and the interaction between charging time and energy loss are revealed. The balance optimization charging strategy appears on the left side of the Pareto curve. Finally, a balanced charging strategy considering charging time, aging, and energy loss is obtained. In comparison with single batteries with the same average initial current charging, the constant current phase order decreases because of battery pack state parameters and equilibrium management, resulting in different charging strategies.

The Role of Trapping-Detrapping Space Charge in Electrothermal Aging of XLPE

In this paper, we focus on the effects of trapping-detrapping space charge on electrothermal aging. A physical quantity, free energy increment, is introduced to quantitatively describe the aging rate. Two aging effects of trapping-detrapping process are expressed by the free energy increment. The effects of the trapping-detrapping process on aging is identified on the basis of the energy features of traps and the free energy increment through experiment. The free energy increment can be a quantitative description of the aging effect of trapping-detrapping space charge on materials. It is positively related to the maximum density of traps, indicating that the trapping-detrapping process is hazardous to insulation health.

Research on electric thermal aging resistance new energy material transformer oil based on steady quality engineering technology

The aim of this study was to investigate the electrical resistance of polycarbonate film and polyester film materials in new energy materials during electrothermal aging in transformer oil. Insulating paper was used as a comparative material to compare the breakdown voltage and initial voltage of insulating paper, polycarbonate film, and polyester film in electrothermal aging at 90 °C, 110 °C, and 130 °C. The best performance in the test was achieved by polycarbonate film, followed by polyester film, while the worst performance was that of insulating paper. Polycarbonate film can be used as an insulating material in transformers, and it has great application value and commercial prospects.

Ageing state identification and analysis of AC 500 kV XLPE submarine cable based on high‐voltage frequency dielectric response

Carrying out the insulation condition measurement and analysis is important for the safe operation of the submarine cable. In this study, the high-voltage frequency dielectric response is used to identify the ageing state of the AC 500 kV cross-linked polyethylene (XLPE) submarine cable. The complex capacitance and tanδ in the low-frequency area for the new, thermal ageing, electro-thermal ageing cable all increase with the testing voltage increased from 200 to 2000 V. It is founded that the dielectric response at high voltage is more likely to detect the ageing differences. Based on the carbonyl index and the dielectric loss of the XLPE specimens at different position of the insulation layer, the non-uniform ageing phenomenon of the cable insulation is presented for the thermal ageing and electro-thermal ageing cable. The loss quantity parameter and its changing behaviour with testing voltage based on the frequency dielectric response could be used to identify the ageing state. The comparison of the modified Cole–Cole model parameter under 200 and 2000 V also indicates that the higher voltage dielectric response is helpful to identify the ageing differences.

Electro-Thermal and Aging Lithium-Ion Cell Modelling with Application to Optimal Battery Charging

This paper deals with optimal charging versus aging minimization for lithium-ion batteries. The optimal charging strategy proposed involves charging controllers whose design relies on a battery model. The model, especially designed for automotive battery management systems applications, is recalled in this paper. It provides the voltage response of a cell to an input current. It also models side reactions that produce degradation mechanisms and thus decrease battery performance. Side reaction modelling involves taking into account the temperature cell variations, which are thus also modelled. The association of the three above-mentioned sub-models leads to an electro-thermal battery aging model used to design an optimal charging strategy that simultaneously takes into account the minimization of charging time and maximization of battery lifetime. Thus, to achieve a charging controller that manages battery health, an appropriate charging trajectory was computed by solving an optimization problem minimizing aging. Then, a charge control loop was designed. The nonlinear behavior of the battery was taken into account through the linearization of the electro-thermal aging model in different operating conditions. To take into account the resulting linear model family, the CRONE design methodology was used. The principles of this methodology are recapped and the design of the charging control loop is explained. The efficiency of the resulting charge controller is illustrated by several simulations.

Influence of electrical and thermal ageing on the mineral insulating oil performance for power transformer applications

In the present work, a new electrothermal combined stress test cell has been designed and fabricated to conduct accelerated electrothermal ageing. The fabricated test cell includes all possible real working conditions of the transformers. The effects of accelerated electrothermal ageing on the performance of power transformers with thermally upgraded Kraft (TUK), Nomex-910 and Nomex-410 solid dielectrics in conjunction with mineral oil have been investigated. The accelerated electrothermal ageing has been performed for a temperature range of 100°C to 220°C, along with 10 kV electrical stress. Subsequently, several electrical, thermal, mechanical and chemical properties of transformer oil and different paper dielectrics have been determined. It has been observed from the diagnostic test results that Nomex impregnated mineral oil samples have better electrothermal performance as well as oxidation stability when compared to the thermally upgraded Kraft oil samples. Therefore, Nomex insulating materials in conjunction with mineral oil are suggested as alternative solid dielectrics for power transformers in order to achieve better oxidation stability, improved thermal performance for long service runs and reduced operating and maintenance costs. It is envisioned that the present experimental study will be very beneficial to utility managers and end-users of power transformers.

Emergent failure patterns at sub-critical fields in polymeric dielectrics

A generalized physical framework is presented for the simulation of electro-thermal ageing in large-size samples of polymeric dielectric by discretizing them into small-size elements using an orthogonal matrix. The individual elements are treated as thin-film samples with assigned generic morphological parameters, whose distribution in the matrix obeys their fitted thin-film distribution probabilities obtained from experiments. This allows the effect of spatial inhomogeneity in large-size samples to be included in the model. Quantitative simulations of the evolution of direct-current ageing up to eventual catastrophic failure are studied at sub-critical fields, and it is shown that the criterion for the onset of a deterministic runaway event is the enhancement of the local field, caused by self-organized degradation, to a temperature-dependent critical value. The lifetime is effectively the time taken to reach the critical value, and its statistics are fitted to the Weibull distribution. The failure patterns produced during ageing were found to be strongly dependent on the applied electric field, but not on temperature whose increases accelerated the ageing process instead. The global inhomogeneous properties of the dielectric were found to control the ageing process with stochastic percolation behaviour below the critical point at low applied fields. Increasing the applied field gradually strengthened the influence of local deterministic factors.

Changes on structural and electrical properties of retired cross-linked polyethylene (XLPE) cable insulation under electro-thermal aging test

In order to study the insulation performance of two retired high voltage cross-linked polyethylene (XLPE) cables with service years of 16 and 32 and evaluate the reliability of reusing these cables for actual operation, a 180-day electro-thermal aging test was exerted on a section of these two cables to inspect the changes on structural and electrical properties. Several diagnostic measurements including fourier infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and breakdown field strength were carried out on the untreated and treated samples. The measured results show that the crystalline structure of the 16 years cable has been improved after the accelerated aging test probably because of the reduction of the impurities and the annealing effect, which further improve the electrical property. Even though the molecular chains of the 32 years cable insulation has been damaged and a slight degradation happens on the crystalline structure under the intensive aging test condition, which is responsible for the decline in the electrical property, the cable still have the potential to resist the stresses properly under the actual operation condition for a long time from the perspective of the XLPE. Therefore, it can be expected that the rest of these two retired cables still have the ability to reuse in the long-term actual operation condition.

Electrothermal aging characteristics of epoxy resin under bipolar exponential decay pulse voltage and its insulation life evaluation based on Cole-Cole model

The epoxy resin insulation in saturable reactors in a HVDC transmission converter valve is subjected to a bipolar exponential decay pulse voltages under normal operating conditions and its aging mechanism is still unclear. In this paper, an electrothermal aging experiment of epoxy resin was carried out under bipolar exponential decay pulse voltages at high temperature. The dielectric properties of epoxy resin before and after aging were measured using frequency-domain spectroscopy. To quantitatively study the aging characteristics, the double-relaxation Cole-Cole model was used to fit the dielectric spectra. As a result, an exponential function relationship between the relaxation time constant and the aging time of epoxy resin under various aging conditions was obtained. This relationship can be used as an empirical formula to evaluate the degree of aging. Furthermore, a comparison of the aging life characteristics of epoxy resin under pulse and sinusoidal voltages with the same peak value was performed. The results show that the electrothermal aging rate of epoxy resin under a pulse voltage is lower than under a sinusoidal voltage. The effect of the measurement temperature on the insulation life evaluation of epoxy resin was also analyzed.

Electrothermal aging characteristics of epoxy resin under bipolar exponential decay pulse voltage and its insulation life evaluation based on Cole-Cole model

The epoxy resin insulation in saturable reactors in a HVDC transmission converter valve is subjected to a bipolar exponential decay pulse voltages under normal operating conditions and its aging mechanism is still unclear. In this paper, an electrothermal aging experiment of epoxy resin was carried out under bipolar exponential decay pulse voltages at high temperature. The dielectric properties of epoxy resin before and after aging were measured using frequency-domain spectroscopy. To quantitatively study the aging characteristics, the double-relaxation Cole-Cole model was used to fit the dielectric spectra. As a result, an exponential function relationship between the relaxation time constant and the aging time of epoxy resin under various aging conditions was obtained. This relationship can be used as an empirical formula to evaluate the degree of aging. Furthermore, a comparison of the aging life characteristics of epoxy resin under pulse and sinusoidal voltages with the same peak value was performed. The results show that the electrothermal aging rate of epoxy resin under a pulse voltage is lower than under a sinusoidal voltage. The effect of the measurement temperature on the insulation life evaluation of epoxy resin was also analyzed.