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The charge phenomena under sine and half‐wave sine voltages within the frequency range of 500 Hz are studied here. Based on the pulsed electro‐acoustic method, the traditional circuit design under high‐frequency voltages is first analysed. It is found that the selection of a 186 pF protection capacitor and a 333 kΩ protection resistor can ensure that the actual voltage applied to the sample is consistent with the expected input. Based on this design, experimental results show that the polarity of the charge accumulated in the depth of the sample is determined by that of the upper electrode. Comparison results under special voltages with different amplitudes and frequencies indicate that the amount of accumulated charge under sine voltages are larger than those under positive and negative half‐wave sine and DC conditions, and the samples under lower‐frequency conditions show more charge accumulation. The maximum electric field strengths appear at 90 and 270 degrees of the sine voltage with a frequency of 10 Hz, and their values are 68.55 and 81.82 kV/mm, respectively. Therefore, the charge characteristics are easily affected by the voltage’s waveform and frequency parameters. The results obtained here can provide guidance for the application of insulating materials under special voltage environments.

This paper reports the effect of DC and pulse wave voltages on space charge characteristics of polyimide material for high-frequency insulation. The pulsed electroacoustic method is used to measure the charge distribution inside the material under the pulse wave voltages with different amplitudes, polarities, frequencies and duty ratios. Comparative results show that positive charge is more likely to accumulate inside the polyimide. The amount of accumulated charge under pulse wave voltages is larger than that under DC voltages. With frequency, more space charge is accumulated under negative pulse wave voltages with a frequency above 50 Hz, while it is not larger than 100 Hz under positive voltages. The maximum distortion of electric field appears under the negative pulse wave voltage with the frequency of 500 Hz, which is 1.19 times the applied field strength. When the duty ratio of the pulse wave voltage exceeds 50%, the distribution of accumulated charge tends to be stable. The research results can provide a reference for the practical application and modification design of polyimide materials in power electronic equipment.

In this paper, space charge behavior over a large range of electric field and temperature, of two kinds of epoxy resins are investigated using an improved pulsed electro-acoustic method. Significant influence of high electric field and high temperature on the space charge accumulation in epoxy are found. Hetero charge accumulation starts to build up at 80 °C under 120 kV/mm for amine-type hardener cured epoxy (EP-AM), while at 140 °C under 60 kV/mm for anhydride-type hardener cured epoxy (EP-AH). The accumulated charge increases with the increasing of electric field and temperature. The maximum enhancement of local electric field of is 135 and 123 % at 140 °C for EP-AM and EP-AH, respectively. Quantum chemical calculation is performed to clarify the mechanism of space charge characteristics in the two types of epoxy. It is indicated that ionization of remnant unreacted hardener and electrode injection may be the main sources of space charge. The interaction between molecular chains of EP-AH is stronger than that of EP-AM, which makes it have better space charge characteristics even under high temperature.

In this paper, we studied the space charge phenomena of a solid polymer under thermal and electrical stresses with different frequencies and waveforms. By analyzing the parameter selection method of a protection capacitor and resistor, the newly built pulsed electro-acoustic (PEA) system can be used for special electrical stresses under 500 Hz, based on which the charge phenomena are studied in detail under positive and negative DC and half-wave sine and rectangular wave voltages. Experimental results show that the charge accumulated in the polyimide polymer under DC conditions mainly comes from the grounded electrode side, and the amount of charge accumulated with electric field distortion becomes larger in a high-temperature environment. At room temperature, positive charges tend to accumulate in low-frequency conditions under positive rectangular wave voltages, while they easily appear under high-frequency situations of negative ones. In contrast, the maximum electric field distortion and charge accumulation under both half-wave sine voltages occur at 10 Hz. When the measurement temperature increases, the accumulated positive charge decreases, with a more negative charge appearing under rectangular wave voltages, while a more positive charge accumulates at different frequencies of half-wave sine voltages. Therefore, our study of the charge characteristics under different voltage and temperature conditions can provide a reference for applications in the corresponding environments.

Insulating materials are frequently used in spacecraft's structure and especially as thermal blanket which are protecting the electronic devices. Their behavior in relation to an electron beam irradiation due to space environment must be clearly elucidate. For example, when the electron beam is irradiated to the material, it charged up and a large electric potential difference generate between the charged and uncharged surfaces. If the difference in potential becomes very large, a discharge sometimes occurs between them. Such discharge is very harmful for the spacecraft. Therefore, at designing stage of spacecraft, it is important to understand the charging characteristics of the surface material of the spacecraft. In this paper, we focused on the charge accumulation in the materials under an irradiation of high energy electron beam. In the experiments, some fluorine materials are used which are ordinary used for the spacecraft. Judging from the measurement results, it was found that the amounts of accumulated electrons gradually decreased ever during an electron beam irradiation. In addition, we tried to explain for this phenomenon using an idea of RIC (Radiation Induced Conductivity).

Polyimide is widely used insulation materials, such as power equipment, motor windings, multi layer insulated, and so on. As the operation environment is high temperature, high humidity, radiation, the dielectric insulation characteristic is decreased compared with pristine one. Especially, the space charge characteristics are obtained big different. Furthermore, the breakdown phenomenon is frequently produced. In this chapter, we discuss the dielectric phenomena through the viewpoints of charge accumulation under the following environment. High temperature, High humidity, DC application, PWM application, Radio-active rays (electron, proton).

Recently, the high performance and high reliability materials on the power electronics devices have been studied. Those devices are used in severe environments, such as high temperature, radiation, vacuum environment, and so on. In this study, we focused on the effect of space charge accumulation in the bulk of dielectrics by the radiation, such as the proton and/or the electron beams. So, we measured space charge distributions on insulating materials for the power electronics devices irradiated by proton/electron using the pulsed electroacoustic (PEA) method. As a result, the charges due to irradiated protons and electrons were confirmed to accumulate in the bulk at the calculated penetration depth, and the electric fields were emphasized 1.3 and 1.2 times larger than that of non-irradiated samples for the proton and electron irradiations, respectively. It is considered that those appearances of the electric field distribution had been occurred by charge accumulation by irradiation, modification of molecules structure, radio activation, and an increase of conductivity. To clarify this assumption, further investigation will be carried out in our future study.

Polypropylene (PP) is one of the candidate materials for cable insulation instead of XLPE, which is remarked as a thermoplastic material with high melting temperature. In our previous studies, it is shown that space charge injection and conduction current in PP based flexible copolymers are both reduced at high temperatures and under high DC electric fields by adding an inorganic filler or a polar group into them. In this report, we tried to analyze the state of trap sites formed in the PP copolymers using the quantum chemical calculation to understand the effect of the inorganic filler and the polar group added into PP copolymers.

Recently, some next-generation semiconductors such as SiC, which can be operated at high temperature under high electric field, have been developed, and power devices using these semiconductors have been reduced in size with higher power output. However, while the semiconductors themselves are available at high temperature under high electric stress, there is no suitable material which shows a good performance as the insulating material under such a severe condition. Therefore, to realize the usage of the next-generation semiconductors with the inherent ability, it is required to develop the insulating material that shows an excellent characteristic even under such severe conditi ons. Generally, epoxy resin is used as such a molding insulation material, and this study also evaluated the insulating performance of the epoxy resin. For this purpose, several imide type hardeners for the epoxy resin were developed provide the characteristics of both high heat resistance and low dielectric properties. A feature of the imide type hardener is that an imide group is introduced into the hardener to maintain high heat resistance without lowering the crosslinking density. In this study, we estimated the insulating properties of those epoxy resins by observing space charge accumulation behaviors in them at high temperature under high electric field. From the measurement results, it is found that some of them shows a good performance as the insulating materials even under such severe conditions.

This paper aims at the measurement of the time dependence of the internal space charge and analysis of radiation induced conduction (RIC) in polyimide caused by electron beam irradiation. Both the normal PEA method and an “on-line” PEA system were employed to detect the space charge profiles after and during the electron irradiation. In view of that, a small size PEA device with a ring high voltage electrode was used for the “on-line” measurement. In addition, the electric conduction was discussed by the RIC theory. Negative charge accumulations were introduced by the irradiated electrons, which increase with the increase of electron energy and density. The behaviors of RIC depend on electron energy, indicating an enhancement with high electron energy. These phenomena are closely related to the charge deposition and electron-hole pairs. High energy and density of the electron beams introduced large amounts of negative charge accumulations. Meanwhile, they contributed to the high level of RIC. Consequently, the space charge would maintain the dynamic equilibrium in polyimide film.

DC current integrated charge measurement (Q(t) method) is applied to evaluate the performance of insulating layer used in power module at high temperature under high DC stress. It is said that a s pace charge accumulation is one of important factors to evaluate the insulating materials, and the Q(t) measurement is an effective method that is available to the actual devices. Therefore, the Q(t) method was attempted to be applied to evaluate the insulating layers in some actual IGB T modules. As the result, it is found that the Q(t) method is effective to evaluate the insulating materials used for actually devices.

Investigation of space charge accumulation processes in a chemically cross-linked polyethylene for ac usage (XLPE) and a modified XLPE for dc usage (DC-XLPE) at voltage polarity reversal was carried out using pulsed electro-acoustic (PEA) measurement system. We found that a huge amount of so called packet-like charge, some of which partially increased the electric field in the material to more than twice of the average applied stress, generated in XLPE at the polarity reversal of DC stress. It enhanced the electric stress locally in the sample by almost twice of the applied average stress. On the other hand, we also found that the packet-like charge was not observed in DC-XLPE under the same experimental condition.

We developed a compact system for evaluating the deterioration of insulating materials used in high-voltage dc power apparatuses. The developed system can be used for simultaneous determination of three basic parameters important for evaluating the deterioration of high-voltage insulation materials, i.e., conductivity, dielectric constant, and charge accumulation. Charge accumulation, which is detrimental to high-voltage dc electrical apparatuses, such as power devices, transformers, and power cables, can be evaluated using this system. With this system, the charges accumulated are measured by integrating the current through a capacitor inserted between the highvoltage power source and the high-voltage apparatus to be tested. The obtained information is transmitted to the unit placed at ground potential. The evaluation is carried out by comparing the amount of initial charges in the insulating material with that of charges accumulated at a certain time after application of a high voltage. When the ratio of the charges accumulated at time (t) to that of the initial charge is 1, it is assumed that there was no charge accumulation; thus, no deterioration of the insulating material is assumed. However, when the ratio is greater than 1, the insulating material is considered to have deteriorated. Using the evaluation system, we developed, we examined the deterioration of insulating materials used in coaxial cables by exposure to 1) γ-rays and 2) high-temperature conditions. From these two experiments using the developed system, the deterioration of insulating materials was found to have advanced substantially when the charge accumulation ratio exceeded approximately over 2.0.

We have investigated a space charge distribution and a conduction current characteristics in copolymerized materials of propylene and ethylene under high DC electric field at various temperatures, which are considered as one of candidate insulating materials for HVDC cable. The materials show excellent mechanical flexibility and relatively low conductivity at room temperature. However, at high temperature under very high DC applied electric field, electric field distortion induced by accumulated space charges in the bulk was observed. We attempted to improve the insulating properties of them by adding inorganic fillers into them. In this report, we describe measuring results of space charge distribution and conduction current in the composite materials under high DC electric field at high temperature.

It is said that a space charge accumulation in an insulating material for motor windings decreases the partial discharge inception voltage (PDIV). Therefore, the space charge distribution measurement is important in the insulating material under square wave voltage, which is applied to an actual motor. In this study, we tried to understand the relationship between the space charge accumulation and the change of PDIV by comparing the experimental results obtained using PEA (pulsed electroacoustic) method and PDIV testing systems.

Space charge accumulation characteristics in super engineering plastics, the polymer materials available at 150 oC or more, were investigated under dc high stress at high temperature to apply them as insulating materials of power electric devices. Since the materials must show a good insulating properties under such severe condition, the space charge accumulation behavior, which is one of important factor to evaluate insulating performance, were observed.

Space charge accumulation properties were investigated on epoxy resin under high dc stresses at high temperature. Due to the recent improvement in operable temperature of semiconductors, it is required to develop a new insulating material for semiconductor packaging, which exhibit a high insulation performance even at high temperature under the high electric stress. To estimate the insulation performance, it is said that the space charge accumulation is characteristic one of important factors for the evaluation of the materials. Therefore, in this study, the space charge behavior in epoxy resin, that is widely used as a semiconductor packaging material, is evaluated using PEA (Pulsed Electro Acoustic) method at high temperature under high electric field. While there are many demand to know the insulating properties in epoxy resin at relatively high temperature like more than 100 °C the ordinary PEA system was applicable to the measurement at temperature from room temperature to about 80 °C. Therefore, we improved the PEA system available to the measurement at 100 °C. In this report, two types of epoxy plate samples were used: one is made using an amine type curing agent (EP-A) and another is made using acid anhydride curing agent (EP-NH). As a result, it was found that an obvious amount of space charge accumulation was observed in EP-A, while it was not observed in EP-NH even under the dc stress of more than 100 kV/mm at 100 °C.

While many kinds of polymeric materials have been developed for being used at high temperature in various devices, there is a few cases that they are used as an electric insulating material for dc high electric stress. However, according to the development of power electric devices in recent years, the demand of an insulating material which show a good performance even at high temperature more than 100 °C has been increasing. Under such severe condition, especially in HVDC (high voltage DC) systems, the space charge accumulation property must be a key factor to evaluate the performance of them. Therefore, we tried to measure the space charge distributions in many kinds of polymers at high temperature (∼ 140°C) under high electric stress (∼ 120 kV/mm) using the originally developed PEA (pulsed electroacoustic) system for high temperature measurement. Judging from the results, the obtained data can be available to evaluate the performance of them under such severe condition.

While many kinds of polymeric materials have been developed for being used at high temperature in various devices, there is a few cases that they are used as an electric insulating material for dc high electric stress. However, according to the development of power electric devices in recent years, the demand of an insulating material which show a good performance even at high temperature more than 100 °C has been increasing. Under such severe condition, especially in HVDC (high voltage DC) systems, the space charge accumulation property must be a key factor to evaluate the performance of them. Therefore, we tried to measure the space charge distributions in many kinds of polymers at high temperature (~ 150 °C) under high electric stress (~ 120 kV/mm) using the originally developed PEA (pulsed electro-acoustic) system for high temperature measurement. Judging from the results, the obtained data can be available to evaluate the performance of them under such severe condition.

In this paper, we tried to evaluate the charge accumulation in insulating materials used for electronic power devices. Space charge accumulation is said that one of important factors to evaluate the insulating materials under dc high electric fields, especially at high temperature. While, the space charge accumulation in insulating materials has been measured using pulse electro acoustic (PEA) method, the PEA method has been mainly applied to sheet shape samples. Therefore, it is difficult to apply the PEA method to an insulating layers used for an actual electronic devices, which are usually composed of complicated shape. Therefore, we have tried to apply a direct current integrated charge measurement which is newly developed measurement method to evaluate the charge accumulation in the insulating layers. Using the method, we tried to estimate the charge accumulation in the insulating layer of actual power electronic devices under various electric stresses at various temperature. As the result, it was found that the method was preferably available to evaluate the characteristics of charge accumulation in the insulation layers of the power electronic devices.

In the ordinary space charge distribution measurement using pulsed electro-acoustic (PEA) system, a semi-conductive (SC) layer is inserted between a high voltage metal electrode and a measurement sample to improve a mismatch of acoustic impedance between them. On the other hand, as a grounded electrode, an aluminum (AI) plate is usually used to increase a sensitivity of the measurement. However, in an actual XLPE (cross-linked polyethylene) cables, an inner and an outer SC layers are used as the electrodes, and XLPE insulating layer is sandwiched by them. Therefore, to understand the actual space charge effects in the actual cable on a breakdown property, it is important to study the space charge accumulation characteristics in XLPE using such electrode system. In this paper, we measured the space charge distribution and external circuit current density in XLPE sandwiched by the SC layers under dc high electric stress. As a result, a larger current was observed in the XLPE sandwiched by the SC layer, but the fracture strength appeared to be similar to that in the XLPE of a conventional electrode system. From this result, it is thought that even if XLPE is sandwiched between SC layers, it would not show any effect on the dielectric strength.

We have been investigating the insulating property of polymeric materials, especially polyethylene (PE) based materials, for power transmission cables under extra high AC and DC stresses. In this study, using a simultaneous measuring system for space charge distribution and external circuit current, we attempted to evaluate the properties of polypropylene (PP) based polymers, which are expected to apply to an insulating material for dc power transmission cable. As the results, we found that large amount of space charges accumulated were observed in some of PP and PE copolymers at high temperature under high dc stresses, while any charge accumulation was not observed at room temperature under the high de stresses.

Currently, epoxy resins are used as insulating materials for various electronic devices. However, when an epoxy resin is exposed to a high humidity environment, deterioration due to moisture absorption and ion migration occur, and it has been reported that the dielectric breakdown strength is greatly reduced. Therefore, it is important to investigate the influence of moisture absorption on insulating characteristics of the resin. In this study, space charge distribution measurement under DC stress was performed on hydrocarbon-based thermosetting resin, which is expected as a new insulating material instead of epoxy resin. We investigated how moisture absorption by humidification affects the space charge behavior in the resin. In addition, we also investigated the effect of oxidative degradation in the resin on change of moisture resistance.

In the automotive industry, a reduction in CO 2 and low fuel consumption are required from the environmental point of view. According to such demand, electric vehicle using an inverter fed motor is developed and widely used. However, partial discharge generates in motor winding, when the higher voltage is applied to the windings. Thereby, it may induce a fatal breakdown in the insulating coating layer of the windings. Judging from a published report, it was said that a decrease of partial discharge inception voltage (PDIV) was strongly related with space charge accumulation in the insulating layer. However, only few studies about the space charge accumulation characteristic in the insulating coating for the windings has been carried out in the past. In this study, we proposed a new space charge distribution measurement technique using Pulsed Electro Acoustic (PEA) method to evaluate the space charge accumulation characteristics in such layer. Using this technique, we can observe the pace charge distribution in an insulating film during the application of square wave, square wave with surge shape and half-wave of AC voltages of 50 Hz to the film. Judging from the obtained results, we found that the space charge accumulated in the film by applying above mentioned the voltages, and it might cause of the reduction of PDIV.

Insulation materials are used to keep the temperature inside the spacecraft constant. However, there is a possibility of causing a charge and discharge occurs operational abnormality by the charged particle on the orbit. In this study, we observed a space charge accumulation when high DC voltage is applied to the fluorinated insulating material which irradiated proton beam using PEA method. As a result, charge accumulation was observed in the proton beam irradiated sample. As a cause of this, irreversible change of molecular structure may occur due to proton beam irradiation and it may be caused by it, so structure analysis using XPS, FTIR is also done together and comprehensive consideration I went and report it.

Recently, some next-generation semiconductors such as SiC and GaN, which can be operated at high temperature under high electric field, have been developed, and power devices using these semiconductors have been reduced in size with higher power output. However, while the semiconductors themselves are available at high temperature under high electric stress, there is no suitable material which show a good performance as the insulating layer for the semiconductors under such a severe condition. Therefore, to realize the usage with the inherent ability of the next-generation semiconductors, it is required to develop the insulating material that shows an excellent characteristic even under such severe condition. In this study, we focused on insulating properties of Dicyclopentadiene (DCP) resin and Tricyclopentadiene (TCP) resin which are hydrocarbon-based thermosetting resin. These resins exhibit stable dielectric properties at high temperatures. Furthermore, these resins are characterized by high formability because of their low viscosity. However, polymer insulation material has a possibility of dielectric breakdown by accumulating a space charge under a high DC stress. Since, there are few investigations of space charges formed in epoxy resins and hydrocarbon-based thermosetting resins under high DC stress at high temperature, especially near the glass transition temperature of them. the space charge distributions in DCP and TCP under high DC stress at high temperature were measured using the pulsed electro-acoustic (PEA) method. As a result, it was observed that a significant amount of space charges accumulated in all resins at high temperature under high DC stress. At temperature of 100 °C or higher, it was found that the space charge accumulation property in hydrocarbon-based thermosetting resins was different from that observed at lower temperature below 80 °C, while the space charge behaviors in hydrocarbon based thermosetting resins at higher temperature than 100 °C were not much different from those observed in epoxy and thermosetting resins. It suggested that the insulating performance in the epoxy resin may be changed at such high temperature, while the DCP and TCP may show their good performance as insulating material.

XLPE (Cross-Linked Polyethylene) cable is expected to be applied to a long distance power transmission in HVDC systems. DC transmission system is effective for a long distance power transmission, and XLPE cable is not necessary to give a periodical maintenance procedure. However, when a DC high voltage is applied to XLPE, it is said that an electrical breakdown may occur due to an effect of space charge accumulation. In the previous research, the space charge distribution and an external circuit current in the XLPE including the by-products were observed simultaneously in a same sample using PEA (Pulsed Electro-Acoustic) measurement system under a DC high electric field. Although many dielectric breakdowns were observed in this investigation, they occurred in the state when the enhanced field by the accumulated space charge was relatively lower than that observed in LDPE. On the other hand, a large conduction current was observed in the XLPE sample, and it was predicted that a thermal breakdown may occurred due to an energization by the large current flowing in the XLPE at the breakdown. Therefore, in this paper, we tried to understand the relationship between the dielectric breakdown and the time dependence of the energy consumption distribution. Judging from the time dependence, it was found that the increase rate of the average consumption energy in bulk of XLPE was larger, the time to breakdown was shorter. By observation of the dissipation power distribution, it was also found that the large dissipation power zone was constantly localized in the part of the bulk in XLPE at the breakdown. Judging from the results, we considered that the process until dielectric breakdown occurred as follows; at first, a rapid heat increase generates intensively in a part of the bulk of the sample in the thickness direction, then, at a weak point in the layer, a melting happens and finally the dielectric breakdown occurs at the point.

In this paper, we investigated the space charge accumulation properties in double-layered dielectrics composed of EPR placed on top of LDPE, using PEA and Q(t) measurement systems. This was conducted to identify issues when using cable joints which have an interface of different dielectrics for DC transmission. As a result, we confirmed that the electric field was locally enhanced just by placing two different dielectrics when the polarity of the applied electric field was reversed, showing a dangerous state. Furthermore, we used Quantum Chemical Calculation to analyze the experiment results and revealed that this was caused by the difference in trap levels and charge injection barriers of EPR and LDPE.

In the automotive industry, a reduction in CO2 and low fuel consumption are required from the environmental point of view. According to such demand, electric vehicle using an inverter fed motor is developed and widely used. However, partial discharge generates in motor winding, when the higher voltage is applied to the windings. Thereby, it may induce a fatal breakdown in the insulating coating layer of the windings. Judging from a published report, it was said that a decrease of partial discharge inception voltage (PDIV) was strongly related with space charge accumulation in the insulating layer. However, only few studies about the space charge accumulation characteristic in the insulating coating for the windings has been carried out in the past. In this study, we proposed a new space charge distribution measurement technique using Pulsed Electro-Acoustic (PEA) method to evaluate the space charge accumulation characteristics in such layer. Using this technique, we can observe the pace charge distribution in an insulating film during the application of square wave voltage of 50 Hz is applied to the film. Judging from the obtained results using the technique, we found that the space charge accumulated in the film by the square wave voltage application, and it might cause of the reduction of PDIV. In this experiment, the space charge measurements were carried out by applying the square wave voltage to the samples of polyimide (PI), polyamide-imide (PAI) and polyester-imide (PEI), those are commonly used for coating material. Judging from the observed results, the tendency of space charge accumulation depends on the kinds of the materials. Furthermore, it was found that the duty ratio may strongly affect the partial discharge generation when polyamide-imide was used for the insulating layer for the windings.

We studied the trapping of positive and negative charges in the chemical structures of polymers under a high electric field using a space charge measurement system. Positive charges accumulated in low-density polyethylene (LDPE), whereas positive and negative charges accumulated in polyimide (Kapton) and also in ethylene tetrafluoroethylene (ETFE) subjected to electron beam irradiation. To determine the charge-trapping sites in the chemical structures, a quantum chemical calculation was carried out using Density Function Theory (DFT) with Gaussian 09. The relationship between the energy band and the isosurface of orbital electrons at various energy levels was obtained. A threedimensional (3D) electrostatic potential distribution map was obtained for positively and negatively charged polymers to determine the relationship between a trapping site and the charge accumulation center in the 3D potential distribution map. Positive and negative charges in Kapton and ETFE films are trapped in trapping sites in chemical structures and the positive charges in an LDPE film are trapped in physical defects.

SUMMARY Space charge behavior and conduction current in polyethylene under dc stress were investigated. One of the reasons for the different breakdown property in cross-linked polyethylene (XLPE) from that in low-density polyethylene (LDPE) may be based on the existence of cross-linking by-products in XLPE. Furthermore, a thermal history in cross-linking process for XLPE may also cause of the difference. It is generally accepted that the existence of the cross-linking by-products increase the conduction current in XLPE under dc stress. It is also said that an anneal treatment in air atmosphere may affect to the electrical properties under dc stress. Therefore, we investigated the effect of the cross-linking by-products and the anneal treatment on space charge behavior and conduction current in polyethylene under dc stress. In our research, it is thought that the increasing dissipation power in XLPE is the cause of the breakdown in it under dc stress. Therefore, to calculate the dissipation power in the bulk of test sample, we measured the space charge distribution and the external circuit current simultaneously. Based on the results, we discussed the reason of the difference of the space charge properties in XLPE and LDPE focusing on the cross-linking by-products and the oxidation of the test samples.

Recently, high performance electronic device is required insulating materials to show an excellent characteristic even at high temperature under high DC stress. In this study, we focused on insulating properties of Dicyclopentadiene (DCP) resin and Tricyclopentadiene (TCP) resin which are hydrocarbon-based thermosetting resins. These resins exhibit stable dielectric properties at high temperature [1]. Furthermore, these resins are characterized by high formability because of their low viscosity. On the other hand, polymer insulation material has a possibility of dielectric breakdown induced by accumulation of a space charge under high DC stress. Furthermore, the space charge behavior of hydrocarbon-based thermosetting resins may be affected by a heating degradation. So, we investigated the space charge accumulation behavior in a heat treated resin at high temperature under high DC stress using the PEA (Pulsed Electro-Acoustic) method, and use also evaluated the influence of high temperature on the insulating properties in the resins. Three kinds of samples with different blending ratios of DCP and TCP were used for the investigation. In this experiment, we observed the space charge distribution in untreated and heat treated samples. Furthermore, to confirm the change in the molecule structure of the heat treated sample, an IR absorption spectrum in the samples were measured using FTIR. As a result, in the samples with high TCP blending ratio, it wasn't observed any large change in space charge accumulation behavior and IR spectra based on the heat treatment. Therefore, hydrocarbon-based thermosetting resin is considered to be capable of suppressing degradation by increasing the blending ratio of TCP.

In the automotive industry, a reduction in CO2 and a low fuel consumption are required from the environmental point of view. According to such demand, electric vehicle using an inverter fed motor is developed and it used widely. However, partial discharge is generated in motor winding, when the higher voltage is applied to the windings. Thereby, it may induce a fatal breakdown in the insulating coating of the windings. Judging from a published report, it is said that a decrease of partial discharge inception voltage(PDIV) is related with space charge accumulation in the insulating coating. However, only few studies about the space charge accumulation characteristic in the insulating coating of the windings has been carried out in the past. In this study, we tried to apply a new space charge distribution measurement using Pulsed Electro-Acoustic(PEA) method to evaluate the insulating characteristics in such layers. In this measurement, the space charge distribution is measured with a square wave or a AC voltage with a contain frequency. By performing the measurement, we tried to analyze the mechanism of the space charge accumulation in polyamide-imide(PAI) film with applying the square wave and AC voltages. Also, we tried to investigate the influence of application of the square wave and AC voltage on insulation lifetime of PAI film. From the measurement results, it was found that the square wave voltage application was much affected to the PAI film degradation than the application of AC voltage.

In this research, we investigated the relationship between the amount of residual electron-hole-pairs inside the sample and the space charge storage characteristics in electron beam irradiated ETFE (Ethylene-tetrafluoroethylene) and FEP (Fluorinatedethylene-propylenecopolymer). Judging from the measurement results, it is found that the amount of electron-hole pairs in ETFE, which are excited by the electron beam irradiation, are gradually decrease during the relaxation time while those are quickly decrease in FEP.

In this paper, proton irradiated fluorinated polymer films are investigated. Space charge distribution on such materials has been studied. It was shown that pristine materials do not accumulate charges under DC voltage application. On the contrary, positive charges were observed in irradiated films. Concerning this paper, we focused to introduce the space charge behavior under DC stress in the bulk of proton irradiated fluorinated polymers. Furthermore, we have also many experience of measurement and analysis of charge accumulation in the bulk of electron irradiated ETFE and FEP. Therefore, we also compared the effect of electron and proton irradiation for space charge accumulation behavior in ETFE and FEP.

In this paper, proton irradiated fluorinated polymer films are investigated by physicochemical analysis, such as PhotoLuminescence (PL), FT-IR and Differential Scanning Calorimetry (DSC). It has been observed that proton irradiated fluorinated films have a positive charge accumulation in the bulk under DC stress. The origin of this charge storage seems to be due to molecular chain scission. Therefore, this paper focused on physicochemical analysis results obtained on ETFE and FEP irradiated films. From the data, the scission, oxidization and crosslinking phenomena have been confirmed.

In recent years, improvement of power density of a power semiconductor modules is required. However, it has been reported that dielectric breakdown occurs in the ceramic material used as an insulating substrate for the power semiconductor under the environment currently used. Therefore, to make it reliable and to improve its power density as the power module, it is necessary to elucidate the dielectric breakdown mechanism of the ceramic material. In this research, we tried to investigate the dielectric breakdown mechanism of the ceramic materials by measuring space charge accumulation characteristics using PEA method. However, it was found that the ceramic material a theoretically unexplainable behavior when shows it is measured using the PEA method. Therefore, we tried to estimate the charge behavior inside the ceramic material from a measurement result in multilayer samples composed of ceramic material and polymer material.

In this report, we study of fundamental research for a high positional resolution of pulse electro-acoustic (PEA) method. Positional resolution of PEA method depends on a pulse width of the applied pulse voltage and a traveling time of the acoustic signal through a piezo electric sensor. Our laboratory tried to develop a thin sensor using the polyvinylidene fluoride (PVDF). Consequently, we succeeded in developing a measuring device with a position resolution of ca. 2.5 μm using thin PVDF sensor which is 1 sm thick. However, since PVDF is polymer material, which is difficult to form a film thinner than under 1 sm. So, we focused on a depletion layer in semiconductor as a sensor material for further improvement of the sensor. The depletion layer is formed at the contact interface with the semiconductor and the metal. Which have space charge distribution inside, and it distribution is similar to an electric dipole. So we expect to apply the depletion layer for sensor. In this report, we tried to measure the space charge distribution of the depletion layer which is formed by contact a silicon substrate to an aluminum electrode. As a result, we succeeded in measuring the space charge distribution of depletion layer.