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The requirements for the construction of a new power system inevitably pose significant challenges and changes to the operation and maintenance of the power grid. To ensure the safe and stable operation of ultra-high voltage (UHV) transmission equipment, this work reports on the principles and preliminary results of using electroluminescence (EL)-based photon counting (PC) methods for early detection of micro-defects in GIS/GIL insulation spacer. In this study, the impact of voltage, gas pressure, and gas composition on the photon response of insulation is examined. Furthermore, the corresponding relationship between defect status and photon response characteristics is explored, along with the discussion of the EL mechanism and its evolution induced by defects. The research results demonstrate that PC measurement exhibits high sensitivity to variations in millimeter-scale defect size, position, and morphology at lower electric fields before partial discharge (PD) initiation. With this regard, this paper reveals promising prospects for the early detection of micro-defects in UHV transmission equipment using PC measurement-based methods.

Abstract Herein, the surface charge characteristics of a tri‐post insulator in a ± 500 kV direct current gas‐insulated transmission lines (DC‐GIL) filled with SF6 are thoroughly studied. The influences of volume and surface conductivity of the insulator on the surface charge and consequent electric field distribution are discussed. An improved method is introduced to obtain the distribution of surface charge with considerable accuracy and efficiency for the calculation. It is found that with increasing the volume conductivity, the dominative conduction mechanism changes from surface conduction to bulk conduction, while the inverse variation appears with increasing the surface conductivity. During the variation of electric conductivity, obvious effect of surface charge accumulation is found on the electric field distribution involving the variation of peak electric field strength and its location. Besides, high charge density usually appears along with low peak field strength during this variation. It can be concluded that the surface charge accumulation should be paid special attention when analysing the insulation characteristics of tri‐post insulators. The variation of volume and surface electric conductivity should be thoroughly considered.

Herein, the surface charge characteristics of a tri‐post insulator in a ± 500 kV direct current gas‐insulated transmission lines (DC‐GIL) filled with SF6 are thoroughly studied. The influences of volume and surface conductivity of the insulator on the surface charge and consequent electric field distribution are discussed. An improved method is introduced to obtain the distribution of surface charge with considerable accuracy and efficiency for the calculation. It is found that with increasing the volume conductivity, the dominative conduction mechanism changes from surface conduction to bulk conduction, while the inverse variation appears with increasing the surface conductivity. During the variation of electric conductivity, obvious effect of surface charge accumulation is found on the electric field distribution involving the variation of peak electric field strength and its location. Besides, high charge density usually appears along with low peak field strength during this variation. It can be concluded that the surface charge accumulation should be paid special attention when analysing the insulation characteristics of tri‐post insulators. The variation of volume and surface electric conductivity should be thoroughly considered. [ABSTRACT FROM AUTHOR]

Abstract An investigation is made of the influence of an accumulated charge sprinkled on the surface of an epoxy resin plate in corona mode on partial discharge inception and its forms as analyzed by optical imaging at DC voltage. The effects of the polarities of both the deposited hetero‐ and homocharges were investigated. The occurrence of first streamer discharges was detected electrically and observed by optical imaging. The various forms of streamers were acquired by optical imaging and associated with the polarity and intensity of the accumulated surface charges. Surface charge sprinkling on the epoxy specimen surface was quantitatively evaluated by surface charge mapping. In addition, the effect of the subsequent discharges occurring in a heterocharge configuration above the inception voltage was observed. In terms of their directions and lengths, the kinetics of the streamer filaments revealed a strong dependence on both the polarity and the intensity of an accumulated charge. Compared with the reference charge‐free surface, the strongest drop in dielectric strength in the interelectrode space with a sprinkled charge was obtained for the heterocharge configuration. The presented results provide a contribution to the assessment of streamer behaviour in the presence of accumulated surface charges, including its polarity and intensity.

Abstract Gas‐filled internal crack might appear in thermoset materials like epoxy resin during the equipment manufacturing, which would become a vulnerable local region to initiate the electrical tree, thus prone to cause insulation failure. The withstand voltage test was carried on epoxy samples with artificial cracks based on a rod‐plane electrode arrangement. Simultaneously, surface state variation and tree evolution with crack were observed by an optical microscope in conjunction with a charge‐coupled device camera. The changes in morphology and chemical status of the crack surface were characterized by scanning electron microscopy, laser Raman spectrometer and energy dispersive spectrometer, respectively. It was found that the erosion and tree started from the borderline of crack under a relatively low electric field strength; however, the area near the electrode had relatively little damage. The breaking of epoxy molecular chains coarsens the crack surface and further forms deep channels on a micro‐level, which is the forerunner of the electrical tree inception. Based on these, the initiation mechanisms of the crack‐induced electrical tree and the reasons for the erosion near the borderline have been revealed. This study provides a train thought for the polymer degradation opening up into the initial tree channel during tree evolution processes.

Epoxy aluminium nitride (AlN) nanocomposites were prepared to understand the influence of thermal ageing on dielectric and space charge performance of the material. It is observed that the real relative permittivity values of epoxy AlN nanocomposites are higher than epoxy resin when wt% of AlN is >1 wt%. Also, the epoxy AlN nanocomposites depicted an increase in dielectric loss compared to the neat epoxy specimen. The space charge variations in the test specimens are analysed by adopting a pulse electro‐acoustic technique. It is observed that the nanocomposites have lesser space charge in the bulk volume of insulating material compared with pure epoxy resin. Also, it is realised that the local electric field is less with nanocomposite material in both virgin and thermally aged specimens. The threshold electric field is observed to be lesser with epoxy resin compared to nanocomposites. Laser‐induced breakdown spectroscopy (LIBS) analysis clearly indicates the reduction in plasma temperature with epoxy AlN nanocomposites compared to pure epoxy resin. Principle component analysis (PCA) has classified the nanocomposite materials having different filler concentrations from the pure epoxy resin, qualitatively based on their LIBS spectra. Thermally aged epoxy AlN nanocomposites are successfully classified from unaged nanocomposite specimens, using PCA. [ABSTRACT FROM AUTHOR]

In this study, the relationship between thermal ageing and charge trapping properties of epoxy-based nanocomposites has been investigated. With ageing, any dielectric material undergoes thorough degradation. This degradation significantly affects the space charge accumulation and charge trapping behaviour of the dielectric, which are very important parameters for insulation health under high-voltage direct current (HVDC) environment. In this work, an improved model based on the isothermal relaxation current (IRC) has been developed to study the charge trapping behaviour of pure epoxy and epoxy alumina (Al(2)O(3)) nano-composites at different ageing conditions. A methodology based on polarisation–depolarisation current (PDC) measurements has been proposed to identify the current component due to a dipolar relaxation in measured total IRC. This will help to identify the trap distribution characteristics more accurately compared to conventional IRC measurements. It was experimentally observed that the addition of nanoparticles significantly reduces trapped charge formation and reduces thermal degradation. It is observed that aging leads to the generation of deeper traps, while the addition of Al(2)O(3) nanoparticles mainly enhances the density of shallow traps. Results presented in this work indicate that epoxy–alumina nanocomposites are very much suitable in HVDC applications from the perspective of trapped charge accumulation.

High permittivity materials are currently in use for mitigation of electrical stress in high-voltage apparatus and energy storage systems. In this work, epoxy-based high permittivity nanocomposites with Barium titanate (BaTiO(3)) nanofillers are considered, for the purpose of stress mitigation. Uniform dispersion of the fillers in the polymer up to 10% by volume is achieved. Apart from the use of as-received fillers, the effect of using surface-functionalised nanoparticles (with 3-glycidoxypropyltrimethoxy-silane) before use is also investigated. The nanocomposite is characterised in terms of its complex permittivity, DC conductivity, short-term AC breakdown strength and space charge accumulation, to gauge its suitability for use in high-voltage insulation. Complex permittivity is measured using broadband dielectric spectroscopy over a broad frequency range of 1 mHz to 1 MHz. DC conductivity is studied from polarisation–depolarisation current measurements. Short-term AC breakdown strength tests are performed at power frequency (50 Hz). Space charge density along the sample thickness is obtained using pulsed electro-acoustic technique. A computational case-study is presented to show the feasibility of using the high permittivity nanocomposite for electric stress control in high-voltage equipment (viz., at mounting flanges of 69 kV bushings).

Humidity has been considered as one of the main influencing factors that determine the conduction processes and electric strength of gas-insulated systems. Whereas in the past, various studies focused on the change in the partial discharge inception voltages, breakdown strength of homogeneous and inhomogeneous field arrangements, and insulator flashover voltage, recent studies have investigated the changes in ion currents measured through different gas gaps. In the framework of this contribution, a highly precise humidity control circuit has been developed to analyse the significance of humidity in the range from −25 to −5°C frost-point, which is fully applicable to operating gas-insulated devices. Using sulphur hexafluoride (SF(6)) as the insulation gas at 0.45 MPa, Al(2)O(3)-filled epoxy resin insulators, and technically rough electrodes, the humidity was found to significantly influence the intensity of microdischarges at interfaces. Charge generation from microdischarges at the interfaces substantially increased with increasing humidity. For an electric field of 5 kV/mm that were applicable to the dimensioning of gas-insulated devices, humidity strongly influences the charge provision from technically rough interfaces and potentially contributes to the surface-charge accumulation at insulator surfaces. On the other hand, for low-field conduction phenomena, no increase in the ion currents from natural ionisation or electrophoretic conduction was observed. For the investigated range of parameters, humidity is expected to be highly relevant for the design of gas-insulated devices.

In this paper the behavior of partial discharges (PDs) on epoxy insulation under AC and impulse superimposed voltages are experimentally investigated in SF 6 gas. The lightning impulse (LI) and the switching impulse (SI) voltages with different polarity are superimposed on different phases of the AC voltage. PDs are measured by three sensors, a 50 Ω measurement impedance, an ultra-high frequency sensor and a photomultiplier tube. The max PD amplitude, PD pulse number and PD duration under AC voltage after an impulse voltage are summarized and analyzed. The effect of the impulse superposition phase, the impulse type and the impulse polarity on the characteristics of AC PDs are discussed. Results show that after a positive impulse voltage was applied on the positive semi-wave of AC voltage (0 to 180°), PDs in the negative half cycle of the AC voltage can be remarkably excited. A negative impulse voltage was applied on the negative semi-wave (180 to 360°), AC PDs can be initiated in the positive half cycle of AC voltage. PDs excited by a LI voltage is severe than excited by a SI. PDs excited by a positive impulse is intense than excited by a negative impulse. [ABSTRACT FROM AUTHOR]

Layered dielectric materials are currently in use for electric field stress control, but are limited by charge accumulation at the dielectric–dielectric interfaces. The current work uses micrometric particles to modify the effective permittivity of epoxy resin samples. Two broad kinds of samples are considered: discrete layered material (DLM) samples and functionally graded material (FGM) samples. DLM samples are obtained by bonding layers of epoxy resin with different filler loadings such that abrupt variation in permittivity might occur along the sample thickness. FGM specimens are prepared by hot pressing a comparatively large number of very thin layers of micro‐filled epoxy resin with very small differences in permittivity one over the other, thus creating a gradual spatial permittivity gradation. Dielectric properties of FGM and DLM specimens are compared in this study. Space charge accumulation is studied using the pulsed electroacoustic method; the accumulated charge density is seen to be lower in FGM. The uniformity of electric field distribution under applied electric stress is computed, and the field utilisation factor in FGM is seen to have a higher value. Also, the dissipation factor is lower and the short‐term breakdown strength is higher in FGM than in DLM samples, providing reason to prefer FGM for insulation to control electric stress. [ABSTRACT FROM AUTHOR]

Dielectric response analysis, performed in time domain and frequency domain is one of the interesting methods used for condition assessment of high voltage equipment. In this article, the degradation of epoxy-mica composite insulation which is widely used in rotating machines has been investigated through frequency domain spectroscopy measurements. Artificial ageing of the carefully prepared stator bar insulation sample was performed through simultaneous application of high temperature and electric field in a designated environmental chamber for specific durations. To study the effect of temperature, the measurements were performed at temperatures ranging from 20 to 60°C at different ageing status. Following experimental work, the measurement results were modelled using Havriliak–Negami model and ageing sensitive parameters were extracted. To study the effect of temperature, the measurements were performed at temperatures ranging from 20 to 60°C. The modelled results matched well with the experimental measurements and certain model parameters sensitive to the ageing condition were identified. The numerical relationships between the insulation status of the stator bar and the aforementioned parameters were identified. It was observed that the nature of the numerical relationship remains identical in the investigated temperature range, although the coefficients vary to some extent.

A saturable reactor is one of the important components of converter valves in high-voltage direct current transmission systems. With the ever-increasing capacities of converter valves, the heat losses generated by saturable reactors are also increasing. Thus, a thermal–fluid mechanics coupled heat dissipation model for saturable reactors is proposed. In order to study the factors affecting the thermal dissipation in the saturable reactor, the epoxy resin insulating layers with different thermal conductivity were considered in this work. The simulation results showed that the hot spots in the saturable reactor are on the iron core and close to the pipe inlet that most of the generated heat can be extracted by a cooling pipe and that the effect of heat dissipation can be improved by raising the thermal conductivity of the epoxy resin. The thermal conductivities of the epoxy resin used in the two reactors were 0.8 and 1.2 W/mK, respectively. The time dependence of the iron core temperature was in accordance with the simulation results and the maximum temperatures of the saturable reactor were also consistent with the simulation results. By increasing the thermal conductivity of the epoxy insulation layer, the temperature of the iron core could be significantly reduced.

Identification of partial discharge (PD) sources in stator insulation is an important and challenging task. Distinct phase‐resolved PD (PRPD) pattern of different PD sources are well established at power frequency (50/60 Hz) and can help to identify each source. In this study, different sources of PD commonly found in stator insulation were created on a 6.6 kV epoxy‐mica stator coil. Each PD source was experimentally investigated at a variable excitation frequency in the range of 50–0.1 Hz. PRPD pattern and PD parameters such as integrated charge per cycle and number of discharge pulses per cycle of each discharge source were compared at different frequencies. The comparison suggests that the parameter of each PD source was dependent on excitation frequency. Some discharge sources have shown a distinct variation in their characteristics with excitation frequency. These distinct characteristics are additional information to the existing ones, which will help to correlate PD characteristics with the source of PD in stator insulation. [ABSTRACT FROM AUTHOR]

Epoxy MgO nanocomposites exhibit high surface discharge inception voltage (SDIV) in SF6 gas ambience. Increase in SDIV is observed with 3wt% of MgO‐added epoxy nanocomposites, especially when the SF6 ambient gas pressure is high. Impact of thermal ageing of epoxy nanocomposites on SDIV is minimum. Dielectric response studies were carried out experimentally and compared with modelling studies. The surface potential decay and charge trap characteristics of epoxy nanocomposites vary with percentage of nano filler. Thermal aging of epoxy nanocomposites has less influence on surface potential decay characteristics for 1 and 3 wt% MgO‐added epoxy nanocomposites, indicating anti‐thermal aging characteristics. Surface discharge activity generates UHF with its dominant frequency at around 1 GHz. The UHF signal magnitude formed due to SD activity is minimum with 3 wt% MgO‐added epoxy nanocomposites. Laser‐induced breakdown spectroscopy (LIBS) studies indicate that plasma temperature and threshold fluence increases with increase in wt% of MgO in epoxy resin. Tensile and flexural properties are greatly improved for nanocomposite compared to epoxy. The dynamic mechanical analysis (DMA) indicates increased storage modulus and reduction of tan δ with epoxy nanocomposites. The glass transition temperature (Tg) and activation energy increases with wt % of nano filler. [ABSTRACT FROM AUTHOR]

Epoxy resin impregnated paper (RIP) bushings are widely used as transformer bushings and wall bushings, but this type of bushing is easy to be dampened. In order to study the effect of moisture on the bushings' insulation performance, a test device was established to simulate the moisture absorption process in the air or N2 gas. Based on the frequency-domain dielectric spectroscopy (FDS) method, FDS curves that indicate the dielectric loss factor (tan δ) and capacitance (C) under different frequencies were tested and analysed. The results demonstrated that the FDS curve moves to the high frequency direction with the increase of the moisture content, and there exist minus tan δ and a negative peak in low-frequency band. Since the moisture content is much lower than in the air, tan δ and C under power frequency of the bushing almost unchanged in the N2 gas. However, the tan δ under 0.1 Hz increases sharply with the increase of trace moisture, and the higher moisture content, the greater increase rate. A damp diagnosis method for RIP bushings is proposed based on the FDS curves' frequency translation characteristics and tan δ variation law. Also the results can give references for RIP bushings' insulation diagnosis. [ABSTRACT FROM AUTHOR]

Corona inception voltage (CIV) due to water droplet sitting over the surface of epoxy nanocomposite material depends on supply voltage frequency, the conductivity of water droplet and the contact angle of the test specimens. The contact angle of the specimen and CIV due to water droplet has a direct correlation. It is realised that the CIV is high under negative DC and the least under AC voltages. Surface charge accumulation studies indicate that the accumulated charge and its decay time constant reduces in the damage‐caused zone due to corona activity. The ultra‐high frequency (UHF) signal generated due to water droplet‐initiated corona activity has frequency content in the range of 0.8–1 GHz. The localisation of incipient discharges is demonstrated by using the non‐iterative technique and the cross recurrence plot (CRP) technique is used to estimate the time difference of arrival (TDOA) of UHF signals generated due to water droplet‐initiated discharge. Laser‐induced breakdown spectroscopy (LIBS) depicts the elemental composition and reveals the difference in plasma temperature and threshold fluence between all the test specimens. In short, the performance of ion trapping particle filled epoxy nanocomposite performance is found to be best followed by titania filled epoxy nanocomposite and the base epoxy resin. [ABSTRACT FROM AUTHOR]

Epoxy resin impregnated paper (RIP) bushings are widely used as transformer bushings and wall bushings, but this type of bushing is easy to be dampened. In order to study the effect of moisture on the bushings' insulation performance, a test device was established to simulate the moisture absorption process in the air or N(2) gas. Based on the frequency-domain dielectric spectroscopy (FDS) method, FDS curves that indicate the dielectric loss factor (tan δ) and capacitance (C) under different frequencies were tested and analysed. The results demonstrated that the FDS curve moves to the high frequency direction with the increase of the moisture content, and there exist minus tan δ and a negative peak in low-frequency band. Since the moisture content is much lower than in the air, tan δ and C under power frequency of the bushing almost unchanged in the N(2) gas. However, the tan δ under 0.1 Hz increases sharply with the increase of trace moisture, and the higher moisture content, the greater increase rate. A damp diagnosis method for RIP bushings is proposed based on the FDS curves' frequency translation characteristics and tan δ variation law. Also the results can give references for RIP bushings' insulation diagnosis.

Slot discharge studies are very important from the insulation diagnosis perspective. Further in practice, testing of rotating machines with power frequency requires sources which are quite bulky and costly. Instead if the diagnosis is carried out at lower frequencies (

In this letter, a test platform capable of generating superimposed voltage with controllable phase is presented. Surface partial discharge(PD) of epoxy insulation was measured and analyzed in SF6. The applied voltage is AC and switching impulse superimposed voltage. Results show that only PD of the negative cycles of the AC voltage is excited or accelerated after impulse. With AC voltage at 90% of partial discharge inception voltage(PDIV), AC PDIV is reduced after imposing the switching impulse. When AC voltage is kept at 110% of PDIV, AC PDs are obviously promoted after impulse. [ABSTRACT FROM AUTHOR]

Surface flashover properties should meet stringent requirements for the use in electrical equipment under high voltage DC environments. With the aim of enhancing surface flashover properties and understanding the mechanisms involved at ambient conditions, epoxy nanocomposites with different weight proportions of nano-TiO2 were prepared. A silane coupling agent was selected to functionalize the TiO2, the effect of which on nanoparticles dispersion and distribution was perused through scanning electron microscopy and infrared spectroscopy. DC surface flashover measurements in five normally used ambient conditions (N2, air, CO2, SF6 and vacuum) were conducted and results were analyzed relating to loading content, gas parameters, surface trap parameters as well as electrical conductivity of nanocomposites. Outcomes indicate that with low content of nanoparticles, the density of deep traps was increased, showing a positive effect on inhibiting surface flashover. When the nanoparticle content is higher than 1 wt%, the overlapped transitional region reduced the energy level of traps, resulting in a poor display of surface flashover voltages. It was found that the nanoparticle content had a greater influence on surface flashover in vacuum. Electron negativity, ionization coefficient and mean free path of gases were taken into account to explain why surface flashover in SF6 appeared to be the highest, whereas in N2, it was the lowest. At last, effects of gas-solid interactions on surface flashover combining surface-trap characteristics, secondary electron-emission contributions and gas molecule impact-ionization characteristics were analyzed. [ABSTRACT FROM AUTHOR]

Epoxy disc‐type spacer, as the major insulator of gas insulated transmission line, plays a significant role in the reliability and safety of the entire power grid. While surface charge accumulation on the spacer could induce flashover and accelerate degradation of the insulator, which threats the operation of high‐voltage DC transmission and grid. In this study, a corona discharging system was employed to charge the epoxy samples before the charge dissipation measured, and the surface flashover voltages of samples with different modification time under DC voltage were also measured, the results are obtained from the research. It is found that the carrier mobility and surface flashover voltage of samples are affected by modification time, and maximum value of both can be obtained when the sample is modified for 60 min. Under the combined voltages, the initial surface charge density and carrier mobility are affected by both pulse voltage and modification time. It is indicated that surface modification is an appropriate method which can significantly inhibit the surface charge accumulation, and improve the flashover characteristics of epoxy sample by increasing carrier mobility. The trap distribution characteristics suggested that the modification treatment and charging condition have a significant effect on the depth and density of trap. [ABSTRACT FROM AUTHOR]

Heat dissipation becomes a critical problem because of the miniaturisation and the increase of power density in electronic devices and electric equipment, which calls for electrical insulating materials with high thermal management capability. Epoxy thermosets have been widely used as electrical insulating materials, but suffer from their low thermal conductivity. This study reviewed the research progress on the development of epoxy thermosets with high pristine thermal conductivity. First, the thermal conduction mechanism of polymers was briefly introduced. Second, the approaches used to enhance the thermal conductivity of epoxy thermosets were summarised, which mainly dealt with the formation of microscopically anisotropic but macroscopically isotropic structure in the epoxy thermosets. Third, the applications of high thermal conductivity epoxy thermoset resins were reviewed. Finally, the review provided the existing challenges and the future directions for the development of epoxy thermosets with high pristine thermal conductivity.

To enhance the toughness and electrical insulation properties of cured epoxy, carboxyl-terminated polybutadiene (CTPB) liquid rubber was used to modify epoxy in this study, and the thermal conductivity, mechanical and dielectric properties of modified epoxy were investigated. The results indicate that the CTPB-epoxy exhibits higher impact strength and lower dielectric constant and loss compared with pure epoxy. Further, hexagonal boron nitride (hBN) was used to reinforce epoxy modified with 20 phr CTPB. It is found that compared with the hBN/epoxy under the same filler loading, the heat conductive hBN/CTPB/epoxy possesses a lower dielectric permittivity and dissipation factor in all frequency ranging from 10^2–10^7 Hz, a higher electrical resistivity and dielectric breakdown strength, and improved mechanical toughness. Therefore, the prepared hBN/CTPB/epoxy composites are potentially useful in practical electrical insulation applications.

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A review of the literature on nanotechnology for the electrical power sector shows considerable hype in the technology, but the actual usage of nanomaterials in the sector is far below other industries. As an example, the automotive industry has made great strides in using nanomaterials because of their lower weight and higher physical strength. There are several reasons for this, the obvious one being the quantity of nanodielectrics is relatively small compared to nanomaterials in other industries. The second reason is that although there are clear improvements in some dielectric properties, for example resistance to partial discharges, the improvements in other properties are not so significant, or sometimes not even evident. Uniform dispersion of nano-sized inorganic fillers in nanodielectrics during manufacture is critical for repeatable electrical properties improvements, and this has been a problem in some of the reported properties such as breakdown strength. This comes about due to the fact that nanoparticles agglomerate easily because of the high surface energy, and conventional mixing techniques do not break apart the nanoparticle agglomerates. Another problem is the incompatibility of hydrophilic nanoparticles with hydrophobic polymers, such as silicone rubber, which results in poor interfacial interactions. [ABSTRACT FROM PUBLISHER]

A narrowband luminescent coating for germicidal 254-nm ultraviolet optical fiber sensors has been developed. A mixture of phosphor and epoxy is used for this coating. The luminescent-clad sensing principle uses a fiber, which has had its cladding and jacket both removed, and a photoluminescent coating replacing the cladding. As the coating luminesces, part of the emission is coupled to the fiber core through evanescent wave coupling. The combined absorption spectrum of the phosphor and the transmission spectrum of the epoxy result in a narrow sensitivity band of wavelengths being detected, centered around 254 nm. The absorption of the 254-nm radiation incident on the coating is emitted as visible light in the optical fiber sensor. This paper describes the development and testing of this narrowband coating using a spectrophotometer to examine its responsivity, and a luminescent-coated optical fiber sensor is compared with a UV photodiode when illuminated by a UV lamp. This optical fiber sensor monitors the output of UV lamps for stabilization and control purposes. [ABSTRACT FROM PUBLISHER]

Polyimides are commonly used as organic passivation layers for microelectronic devices due to their unique combination of low dielectric constant, high thermal stability, and excellent mechanical properties. Polyimides are well known to have poor adhesion to epoxy resins. Many surface treatment methods have been developed to increase epoxy-polyimide adhesion. These include various ion beam, plasma treatment, or chemical treatment methods. The goal of this research is to understand the strength of epoxy-polyimide interfaces by studying the effect of polyimide chemical structure on epoxy-polyimide adhesion. The four polyimides chosen in this study are commonly used in the microelectronics industry: poly (pyromellitic dianhydride-oxydianiline [PMDA-ODA], poly (3,3´,4,4´-biphenyltetracarboxylic dianhydride-phenylene diamine [BPDA-PDA], poly (hexafluoroisopropylidene-diphthalic anhydride-oxydianiline) [6FDA-ODA], and 5(6) -Amino-1-(4-aminophenyl)-1,3,3, trimethylindanbenzophenonetetacarboxylic dianhydride copolymer [BTDA-DAPI]. The adhesive strengths between an epoxy resin and these four polyimides were characterized using interfacial fracture mechanics and the critical interfacial strain energy release rates ranged from 20 to 179 J/m2 depending on the particular polyimide used. The loci of failure for these epoxy-polyimide interfaces were analyzed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR), and found to be at the interphase region for all four interfaces. It is interesting that the strength of the interfaces appears to be related to the predicted interfacial widths from solubility parameter theory. [ABSTRACT FROM PUBLISHER]

The paper presents application of newly developed three-dimensional (3-D) computer tool used for simulation of the automated pressure gelation process. The tool that is based on commercial CFD software-Fluent-enables the simulation of filling and curing stages and gives useful information helping to understand the phenomena occurring inside the mold. To simulate the complex rheology of the material, Macosko's model for viscosity and Kamal's model for curing kinetics were used and successfully applied in the software. First simulations were applied for arbitrary set parameters and formulated recommendations were later applied to approve the existing process. The simulation was performed for voltage transformer used in medium voltage applications and resulted in the optimization of the process parameters what allowed reduction of manufacturing time of the transformer considerably. Additionally the results of experimental verification of the simulation were presented in the paper showing very good agreement between simulation results and measured data. [ABSTRACT FROM PUBLISHER]