Electrical Insulation Layer Research Articles

Electrical Insulation of 500-m High-Tc Superconducting Power Cable

Electrical insulation is one of the essential technologies for the electric power apparatus. Determination of testing voltages and design method of the electrical insulation layer are inextricably linked each other, and are critical to developing and realizing a cold dielectric (CD) type high-Tc superconducting (HTS) power cable. The authors had proposed the electrical insulation design method with concepts of partial discharge-free designs for ac voltage condition. This paper discusses the testing voltages for a 77 kV 1000 A HTS power cable with a length of 500 m, and describes results of various voltage withstand test. As a result, it is concluded that the proposed electrical insulation design method is appropriate for the HTS power cable.

Allowable Repetition Frequency of Pulse Heating in Microactuators Using Rapid Boiling (Effect of Electrical Insulation Layer beneath Heater)

High-frequency pulse heating of heaters in microactuators utilizing the rapid expansion of boiling bubbles causes a gradual increase in the temperature of the heater and the substrate material in the immediate vicinity of the heater, resulting in a loss of reproducibility of the boiling phenomena. In the present report, the maximum frequency at which the steady increase in heater temperature can be maintained within the allowable limit for the succession of pulse heating is obtained by numerical simulations based on the heat conduction from the heater to the adjacent materials in the system having an electrical insulation layer between the heater element and the silicon substrate. Calculations are carried out using a model in an axisymmetrical system for two different heating conditions, that is, transient heating by a single pulse and steady heating by the time-averaged power during repetition of pulses, instead of the direct calculation of the entire repetition process. The effects of heater size and pulse width on the allowable repetition frequency are examined over wide ranges of these parameters. The influence of the insulation layer on allowable repetition frequency is investigated by comparing the calculation results with those of the case of without the insulation layer. Approximate correlations for the allowable repetition frequency are also derived based on an analytical examination.

低温絶縁超電導ケーブルの絶縁設計とその実証

A High Temperature Superconducting (HTS) cable has a bulk power transmission capacity as a candidate for the replacement of the aged cable and/or for the increase of the power transmission capacity, and its diameter is prefer to be smaller than inner diameter of the duct for the existing cables. To reduce the diameter of HTS cable, the cold dielectric (CD) type electrical insulation in which a cable core is immersed into liquid nitrogen (LN2) should be adopted, and the thickness of its electrical insulation layer has to be optimized. Since a partial discharge (PD) in the electrical insulation layer of the CD type HTS cable is considered as a major causes for the aging of the insulation layer, PD-free design must be adopted for the CD type HTS cable.This paper describes a design method for the electrical insulation layer of the CD type HTS cable adopting the PD-free design under ac stress, based on the experimental results such as a PD inception stress (PDIE), an impulse breakdown stress, and PD extinction characteristics under ac stress superimposed with an impulse stress. Moreover, the proposed design method was applied to a 500-m HTS cable and was verified by a field test.

High-frequency proximity heating for injection molding applications

High-frequency proximity heating was used to rapidly heat injection molds. The principle is based on the proximity effect between a pair of mold inserts facing each other with a small gap and forming a high-frequency electric loop. Because of the proximity effect, the high-frequency current will flow at the inner surfaces of the facing pair, thus selectively heating the mold surface. With this method, the electrical insulation layer beneath the mold surface can be eliminated, resulting in a mold insert made of a single metal. A mold with a cavity of 25 × 50 mm2 was constructed with careful design on its electrical, structural, and thermal performance. Air pockets with reinforcing ribs were embedded right beneath the mold surface for enhancing the heating performance. The resulting mold cavity can be rapidly heated from room temperature to about 240°C in 5 s with an apparent heating power of 93 W/cm2. The new mold heating method was applied to thin-wall molding and micromolding, and in all testing cases, short cycle times less than a minute were achieved. POLYM. ENG. SCI. 46:938–945, 2006. © 2006 Society of Plastics Engineers

Dielectric Properties of 500 m Long HTS Power Cable

The 500-m high temperature superconducting (HTS) cable has been constructed in the Yokosuka area, CRIEPI, by CRIEPI, The Furukawa Electric Co. and Super-GM. Its design voltage is 77 kV and the thickness of the electrical insulation layer should be 8 mm made of semi-synthetic paper (polypropylene laminated paper). During cooling, the capacitance and dielectric loss tangent were measured periodically. After cooling, which means that the HTS cable was fully filled with liquid nitrogen (LN/sub 2/), the initial voltage withstand test was carried out. This paper describes the design method of the electrical insulation layer including determination of the testing voltage and the result of the initial voltage withstand test, and the permittivity calculated from the capacitance, and dielectric loss tangent.

Density change and viscous flow during structural relaxation of plasma-enhanced chemical-vapor-deposited silicon oxide films

The structural relaxation of plasma-enhanced chemical-vapor-deposited (PECVD) silane-based silicon oxide films during thermal cycling and annealing has been studied using wafer curvature measurements. These measurements, which determine stress in the amorphous silicon oxide films, are sensitive to both plastic deformation and density changes. A quantitative case study of such changes has been done based upon the experimental results. A microstructure-based mechanism elucidates seams as a source of density change and voids as a source of plastic deformation, accompanied by a viscous flow. This theory was then used to explain a series of experimental results that are related to thermal cycling as well as annealing of PECVD silicon oxide films including stress hysteresis generation and reduction and coefficient of thermal-expansion changes. In particular, the thickness effect was examined; PECVD silicon oxide films with a thickness varying from 1to40μm were studied, as certain demanding applications in microelectromechanical systems require such thick films serving as heat∕electrical insulation layers.

In Situ Thermocouples in Macro-Components Fabricated Using SALD and SALDVI Techniques. III. Fabrication and Properties of the SiC/C Thermocouple Device

Fabrication of a SiC/C thermocouple embedded in an arbitrarily-shaped SiC macro-component has been demonstrated using an integrated Selective Area Laser Deposition (SALD) with the closely related Selective Area Laser Deposition Vapor Infiltration (SALDVI) process. SALD is used to make the embedded thermocouple devices in situ and SALDVI to fabricate the macro-components. The thermocouple elements, silicon carbide and carbon lines, and the electrical insulation layer, Si3N4, have been deposited from tetramethylsilane (TMS), acetylene, and a gas mixture of TMS and ammonia, respectively. It is found that the fabricated in situ thermocouples respond sensitively to temperature variation. Furthermore, the electric signal of the embedded thermocouple is very stable and reproducible in response to thermal cycling. This is not the case when the thermocouple is not embedded in the SiC matrix because of the oxidation of the thermocouple elements.

A monolithic series-connected solar cell on an organic polymer film substrate

A new fabrication process of a monolithic series-connected a-Si:H solar cell was investigated. In this process, an Al/SS/a-Si:H/ITO solar cell structure is produced on an organic polymer film substrate by a roll-to-roll sputtering method and a roll-to-roll GD-CVD method. A conversion efficiency of 10.1% was obtained in the small area cell (1.2 cm 2). To make a large size monolithic series-connected solar cell, this cell on the film substrate is divided into some unit cells by a combination of YAG laser scribing and screen printing of an organic electrical insulation layer and then each unit cell is inter-connected in series by screen printing of a grid electrode and bonding by the YAG laser. So far, a practical conversion efficiency of 5.5% was obtained in a 20 × 60 cm monolithic series-connected cell on a poly(ethylene terephtalate) (PET) substrate. Various types of modules (flexible, lightweight) were obtained by laminating with another PET film, a polycarbonate sheet, or a glass sheet.

Absolute measurement of the thermal conductivity of electrically conducting liquids by the transient hot-wire method

An apparatus for precise and absolute measurement of the thermal conductivity of electrically conducting liquids using the transient hot-wire method has been developed. In the present apparatus, a metallic wire coated with a thin electrical insulation layer has been used as a heating element and a resistance thermometer instead of a bare metallic wire. The effects on the thermal conductivity measurement caused by the thin insulation layer have been analysed. In the analysis, it was found that the effects can be negligibly small if the instrument is adequately designed. The usability of the method for electrically conducting liquids has been tested to measure the thermal conductivity of an aqueous NaCl solution in the temperature range 0 to 45 degrees C at atmospheric pressure. The accuracy of the present measurement was estimated to be +or-0.5%.