Thermocouples are used in industrial field, in the case of using to different temperature gradients apparatus, there is a happening measurements errors due to inhomogeneity such as by mechanical strain. On the other hand, because it does not depend on the using time and temperature, it may doubt the thermocouple defect defects and measurement system itself becomes a trouble. Therefore, in order to realize the failure or accident analysis of the thermocouple, it was realized to evaluate inhomogeneity measurement.

Solid Oxide Fuel Cells (SOFCs), which work at 600 ∼ 1000°C and have efficiencies of over 60%, are expected to be larger capacity. However, expanding SOFCs will rise operating voltage and increase the risk of insulation failure. Extending creepage distance is one of the ways to reduce the risk. In order to clarify the effect of extending creepage distance on dielectric strength, it is indispensable to elucidate the mechanism of creepage distance dependency for electrical breakdown in high temperature and non-uniform electric field.

In this paper, surface breakdown voltage for alumina (Al₂O₃) at 700 ∼ 900°C was measured, changing creepage distance from 4 mm to 20 mm. As a result, at 4 ∼ 8 mm, breakdown voltage was proportion to the 0.4 ∼ 1.2th power of creepage distance. However, at 8 ∼ 12 mm, breakdown voltage decreased with extending creepage distance and indicated dependency on Paschen's law. At 12 ∼ 20 mm, breakdown voltage was proportion to the 0.25 ∼ 0.3th power of creepage distance. At creepage distance of 8 mm, breakdown voltage was over 3 kV. Therefore, the voltage of primary insulation part should be 3 kV or less to prevent increase in size and cost.

It is desired to establish an insulation diagnosis method for cast resin transformers (CRTr), which is often used in distribution systems. Partial discharge (PD) detection is considered to be an effective method, but its phenomenon has not yet been clarified. This paper presents investigation on the frequency characteristics of PD generated inside CRTr to improve PD detection technology. It is clarified that dominant frequency of PD signal detected by a high frequency CT depends on the frequency characteristics of the impedance between the primary and secondary windings. It is suggested that the dominant frequency could be predicted in advance by analysis using a high-frequency equivalent circuit model of CRTr. PD diagnostic technology that utilizes the frequency characteristics of the CRTr impedance has also been proposed. It is found that a PD generated external to CRTr does not have resonance at the dominant frequency of the CRTr itself, even though it passes through the CRTr. In conclusion, it is suggested that the frequency analysis of CRTr impedance could identify degraded CRTr and external noise.

This paper reports AC breakdown properties of the vegetable-oil-based insulating fluid (FR3) contained NaCl aqueous solution and particles. These results were showed as the following. (i) AC electric strength (Fb) of FR3 with 50 to 100 ppm of NaCl aqueous solution showed constant value and 200 ppm of that slight decrease when the concentration of the aqueous solution increased. (ii) When FR3 contained 300 ppm of the aqueous solution, Fb decreased in the concentration of 0 to10 wt%, and turned to rise in 26.4 wt% of that. (iii) Fb increased with adding 1×10^-3 to 2×10^-3 wt% of NaCl particles. (iv) Fb of 400 to 600 ppm water contained FR3 improved substantially with adding more than 1×10^-3 wt% of the particles.

We compared the lightning impulse (LI) breakdown voltages (BDVs) and/or breakdown characteristics of mineral oils treated by three different methods using Rogowski electrodes. These mineral oils had been treated to nitrogen gas filling, nitrogen bubbling addition, and nitrogen fine bubbles (FBs) addition respectively after degassing. As a result, it was found that there was almost no effect on LI BDVs by the difference of the nitrogen addition treatment methods. Additionally, there was almost no difference in the Formative time lag, the Statistical time lag and the distribution of discharge marks for each sample oil. Therefore, nitrogen FBs used in this study were not considered to be a factor in reducing BDV of mineral oil, similar to our previous report using spherical electrodes.