Aging of insulation systems of rotating machines controlled by voltage source converters is an issue becoming of utmost importance due to the broader and broader application of speed-controlled rotating machines. Since one of the major concerns for machine reliability is the appearance of partial discharge (PD), this paper investigated how PD behave under multi-level inverter waveforms, and what is their impact on insulation life. PD patterns under sinusoidal and repetitive impulse voltage, considering two, three and five level inverters, are presented showing that PD phenomenology is deeply different, and its impact on insulation life changes depending on number of levels and voltage impulse rise time. This holds for both Type I and Type II insulation.

Cables used as severe accident management equipment in nuclear power plants are required to maintain their intended electrical insulating function under severe accidents (SAs) after having aged in normal operating conditions during their service life. To examine the electrical insulation behavior of the cables under SA environmental conditions, two types of cables were first pre-aged by simultaneous thermal and radiation exposure in accordance with the procedure prescribed in “The Guide for Ageing Evaluation of Cables for Nuclear Power Plants” (JNES-RE-2013-2049, 2014), irradiated to simulate radiation exposure during SA, and then subjected to two steam exposure conditions: 155°C and 0.444 MPaG for 14 days, and 200°C and 0.620 MPaG for 7 days. In addition, electrical insulation resistance was measured for the cables during the steam exposure. As a result, all the cables passed the voltage withstand test conducted in accordance with JIS C 3005, which is prescribed as a final cable evaluation test in the JNES Guide for the design basis accident. It was found that the minimum insulation resistance per meter of the cables during the steam exposure at 155°C is around 10⁸ Ωm, confirming that the cables have sufficient insulation performance. In contrast, the resistance falls to as low as 10⁵ Ωm during the test at 200°C due to the increase in leak current.

The electrostatic adsorption method can be used to produce composite materials with an arbitrary structure, and their properties may be tuned by changing the size of the individual components, which in turn alters the composition of the material. To develop a thermally conductive and electrically insulating composite material with high thermal conductivity and acceptable breakdown strength, polymethylmethacrylate (PMMA)/hexagonal boron nitride (h-BN) composite materials were produced by electrostatic adsorption method. The breakdown strength of the composite which the flaky surfaces of h-BN was oriented parallel to the thickness direction, was smaller than that of the composite which the flaky surfaces of h-BN was oriented perpendicular to the thickness direction. On the other hand, the thermal conductivity exhibited the inverse trend to the breakdown strength. The thermal conductivity also increased with the increasing of the molding temperature. The properties of the composite material can be easily changed as necessary controlled by each factors.

Reduced dimensions of Gas Insulated Substation (GIS) implies a relatively high electric field in the enclosure. To suppress metallic particles movement in the GIS tank, a nonlinear resistive coating has been developed that contains microvaristor fillers. It is important that understanding the effect of putting several second fillers into the composite. In this paper, the effects to the electrical properties of adding microvaristor / second filler content in the composites were investigated. Additionally, measurement of inner structure in the composite and calculation of the homogeneous dispersion were conducted. Moreover, the relation of experiment results and calculation results were discussed.

Space charge penetration into bulk of cable insulation is known as the cause of insulation breakdown thus affecting the cable power delivery capability. Penetration of packet-like positive space charge enhances local field and when the field increases up to 5 MV/cm before breakdown occurs. Exactly before the breakdown occurs, space charge penetration seems stagnant as it is prevented to penetrate further into cathode. The generated Maxwell force is assumed to press the free volume of the insulation thus reducing the size of the free volume itself. A pulsed-electroacoustic (PEA) equipment capable to press the sample up to 5 tons is developed. Sample used in this study is a 150 µm low-density polyethylene (LDPE) sheet. The sample is stressed with positive dc voltage so that the mean applied field is equal to 1.5 MV/cm. The range of pressure applied to the sample is from 0.1 MPa and 32 MPa. The penetration gradually reduces with the increase of pressure. Sample pressed with 32 MPa showed the least penetration depth as little as 5% of the sample thickness. As a comparison, space charge penetration of sample with 0.1 MPa pressure is as depth as 85% of the sample thickness. This shows that space charge penetration is restricted when sample is pressed. The result obtained shows that it requires at least 24 MPa to suppress space charge penetration.

The consideration of space charge accumulation characteristics in DC cable systems are important. However, there have not been many reports on the space charge accumulation characteristics at the joints, although there have been many reports at the cables itself. Therefore, space charge accumulation characteristics at the joints must be put into account, since interface charge accumulation caused by the difference in permittivity, conductivity, etc. is likely to occur, since two different types of insulating materials are being used. It is also likely that a polarity reversal of the applied voltage to the insulating material causes an unexpected accident at the joints in the cable system, while in some power transmission systems, the polarity reversal is an inevitable procedure. Therefore, in this paper, we investigated the influence of polarity reversal upon space charge distribution and electric field distribution in two-layered samples composed of different materials, to identify issues in cable joints under DC voltage.

The use of pulse width modulated (PWM) waveforms allows more flexible energy applications and management. The downside is that under such operating conditions the voltage stress imposed on the insulation systems increases, particularly as the frequency content is considerably higher than at the conventional 50 Hz sinusoidal waveform. Among various degradation mechanisms, electrical treeing is one important processes and it can be linked with a presence of partial discharge (PD) activity. In this paper, the changes in PD characteristics at different stages of degradation by electrical treeing were investigated for XLPE based insulation exposed to rapidly changing voltages of varying magnitude. The tested material samples were subjected to five square voltage shapes, each characterized by their rise-time. Here the shortest was 0.75 µs, followed by 40, 80, 250 and the longest 500 µs, all tests run at 414 Hz. To compare the voltage endurance, the voltage level was gradually increased until detectable PD activity and tree initiation could be observed, both electrically and optically. Typically, continuous PD appearance was observed between 23 and 32 kV_pp. The total number of PDs and their characteristics were monitored as the trees were gradually growing. Here the experimental results show that the PDs appears at lower voltage magnitudes for the shorter voltage rise times and that the trees had a significantly less branched appearance for these rise times as compared to longer rise times. These results resemble the observations that recently been presented with tests on DC voltage pre-stressed material samples exposed to impulses of reversed polarity. Additionally, the measured PD characteristics were distinct non-symmetric, having a clear polarity dependence for the shortest rise time. For 40 and 80 µs this tendency was much less clear and not observable for the two longest. This finding suggests a possibility to use the presented approach for a more detailed investigating of degradation processes in solid insulation systems suitable for both HVAC and HVDC applications.

Polyethylene (PE) is a hydrophobic polymeric insulating material. It has been found that adding hydrophilic additives can enhance the water tree resistance of PE. Such additives are most often surfactants that contain both hydrophobic and hydrophilic groups within their molecular structures. It is considered that a surfactant added to PE surrounds water molecules and stabilizes them. Hence, it is highly plausible that the solubilization of moisture in a supersaturated state leads to the suppression of water tree initiation in PE. In this study, we investigated the aggregation of water molecules and the orientation of surfactants toward water clusters by molecular dynamics (MD) simulation. In addition, quantum chemical calculations were performed to reveal the mechanism by which a surfactant suppresses water tree initiation. A comparison of the computational results with experiments suggests that the addition of a surfactant is extremely effective in suppressing bow-tie water trees.

This article is an overview on the sensitivity of the recently introduced EAR method for the measurement of space charge in thin dielectric films. Its principle is first recalled then an investigation of its sensitivity is made. It is shown that when the bandwidth of the network analyzer is 10 Hz, a signal-to-noise ratio above 50 is obtained even with an excitation as low as -50 dBm.

This paper presents a preliminary feasibility investigation, in the framework of a recent European project, GRIDABLE, aiming at the development of nanostructured Polypropylene, PP, materials as insulation for DC LV-MV capacitors and MV-HV cables. Results of electrical property characterization of various types of PP-SiO₂ materials for DC capacitors are presented in this paper, focusing on breakdown strength and space charge measurements. They indicate that the nanofiller may influence the degradation rate of materials, modifying the space charge accumulation dynamics and extent, as well as the threshold field value for space charge accumulation. Statistical analysis of breakdown voltage shows that the presence of nanoparticles may also improve noticeably the breakdown behavior.

Insulating materials are frequently used in spacecraft, especially as thermal blanket which are protecting the electronic devices from a drastic temperature change in space environment. While such insulating materials are working well to keep temperature stable, the electron beam is once irradiated to the materials, they are charged up and a large electric potential difference generates 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, their behavior in relation to an electron beam irradiation due to space environment must be clearly elucidate at designing stage of 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, which are ordinary used for the spacecraft, are chosen. Judging from the measurement results, it was found that the amounts of accumulated electrons gradually decreased during an electron beam irradiation. Therefore, we tried to explain the phenomenon with considering an idea of RIC (Radiation Induced Conductivity).

In this paper, a new decomposition method are developed for PCBs by high temperature pyrolysis method without using chemical substance such as metallic sodium. Pyrolysis in this decomposition system is by the following process. The thermal decomposition part is shielded from the outside by the quartz glass tube, and the interior is decompressed by the vacuum pump. The metal heating element in the glass tube is induction heated to 1,400 [℃] by the coil outside the glass tube. PCBs vaporized by heating from the evaporating part are decomposed thermally by passing through the heating element heated at 1,400 [℃]. Since the PCBs are decomposed in an oxygen-free atmosphere, generation of dioxin is also suppressed. In the experiment, tens of gram of PCBs was vaporized, and a decomposition rate of 99.9999 [%] was obtained. A basic mechanism of new PCB processing technology was established with low cost and no generation of dioxin.

This paper is the third report of gas-insulated switchgear (GIS) history from a view point of transition of the technological development and the practical application. This report focuses on the technologies and remarkable progress originated from the development of ultra-high voltage (UHV) - and high voltage (HV) DC-GIS.

First, outline of new technologies on UHV-GIS and their impacts on the other GIS of 550 kV and lower are mentioned. Various developments and the applications to GIS including its components are described together with 550 kV GIS with one-break gas circuit-breaker (GCB) and metal oxide surge arrester (MOSA). Secondly, a development of HVDC-GIS is introduced from a view point of reflecting the UHV-GIS technology on the HVDC-GIS as well as the impact on AC-GIS. Finally, the authors try to discuss the differences between domestic and overseas GIS in terms of the concepts of dielectric design and dielectric tests to ensure the dielectric performance of GIS.