Project Subjects
Next Generation Electric Power Equipment for Distribution System
Background and Objective
Next generation electric power transmission and distribution system must be ﬂexible enough to deal withchanges such as connection of large amount of solar cells to build a low carbon emission society. Moreover, innear future replacement of electric power equipment will be signiﬁcant problem. Therefore, technology menu forreplacement should be prepared.
In this project, super conductive fault current limiters and equipment for transformer substrate are developed to add to a list of technology menu for replacement.

Main results
1. Development of superconductor for fault current limiter
The optimum condition to fabricate Bi2223 superconductor for magnetic ﬁeld shield type fault current
limiter which is adequate for a large system was obtained. Detachment of Bi2223 superconductor ﬁlm from a substrate can be suppressed with conserving superconductivity performance, by using a substrate with rough surface
for producing superconductors (Fig. 1). Moreover, with optimizing temperature and number of baking during
a sintering process, critical current density of each crystal forming a sinter of superconductor was improved
to 8,000A/cm2 which has margin of 2,000A/cm2 against the minimum value for fault current limiters (Fig. 2,[H09019]). Bulk performance of super conductor will be improved by reducing electrical resistivity between eachcrystal.
2. Development of element technology for an all solid insulated transformer
All solid insulated transformers are very attractive because of its high safety, compact and low environmental loading due to their oil-free insulation (Fig. 3). However, to develop an all solid insulated transformer with
operation voltage of more than 33kV, new insulation material with high electrical insulation property and thermalconductivity, and material property suitable for molding process must be invented. Moreover, molding method ofmetallic conductors as coils and metallic plates as ground plates with high precisions must be developed. In thisproject, new transformer structure which can be produced by molding process without reducing electrical insulation performance by optimizing material and conﬁguration of spacers supporting conductor coils and groundmetallic plate. Using this structure, a 60 kV-class 20 MVA all solid insulated transformer with the same size withconventional oil insulated transformer can be designed by selecting material (such as nitride aluminum particle)
and concentration of ﬁller.
3. Development of hybrid gas-insulated transmission line
CRIEPI is developing a new type of electric insulation method called hybrid gas-insulation. The hybrid
gas-insulation is expected to have the electrical insulation performance close to that of conventional gas-insulation,
without using SF6 which has a high global warming potential. However, in this insulation method, connection ofconductor can be a weak point lowering electrical insulation property. So far, detailed electric ﬁeld of conductor
connection has been analyzed, and design and fabrication of model electrodes simulating conﬁgurations of real
hybrid gas insulated transmission line were performed. Electrical insulation properties of model electrodes arebeing evaluated experimentally for designing a prototype model of 257kV class hybrid gas-insulated transmission
line.
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Environmental and Energy Utilization Technology
Conventional Method
ScratchBi2223
Bi2212
Reaction of Bi2212 withBi2223 by thermal process

1.0

Bi2223
Reacted layer

Bi2212MgO
Although detachment was suppressed 、 reacted ｌ ａ ｙ ｅ ｒ
ｒｅｄｕcｅｄ ｃｒｉｔｉｃａｌ current density lower than2,000A/cm2.

New method
Bi2223
Surface preprocessing

MgO(a. u.)(a.u.)
Critical臨界電流密度
current density

MgO

By roughing substratesurface detachment can besuppressed without Bi2212
buffer layer

Fig. 1 Suppression of superconductive thickﬁlm
By roughing substrate surface, detachment of superconductive ﬁlm can be suppressed without lowering propertyof superconductor.

0.8
0.6
0.4
0.2
0.0

123
Number焼成回数of sintering

4Fig. 2 Dependency of critical current density on
number of sintering process
Critical current densities are normalized by the value after
the 3rd sintering process. The maximum critical current
density was obtained after the 3rd sintering.

Parameter area of property of electricalinsulation and thermal conductivity todesign 60kV class all solid insulatedtransformer with the same size withconventional oil insulated transformer.

3
Aluminium nitride(micro and nanosize mixture)
40%vol2

Aluminium oxide(micro size) 35%vol1

00～～

Thermal Conductivity(W/m/K)

4

Base epoxy resin406080

Dielectric Breakdown Strength(kVrms/mm)

Fig. 3 Conceptual design of 60kV class all solid
insulated transformer
Transformer model designed on the basis of the electric insulation property under high temperature of epoxy resin ﬁlling with
AlN nano-structured particle, which is developed by CRIEPI.

Fig. 4 Insulation material for molding all
solid insulated transformer
60 kV class 20 MVA all solid insulated transformer
can be designed by using epoxy resin ﬁlled with
AlN composite particles or AlN fractured particles.

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