Y. Muramoto

Estimation of carrier mobility using space charge measurement technique

The carrier mobility in a ethylene-vinylacetate copolymer (EVA) film was measured by a new technique. The time-dependent charge distribution in an EVA film was monitored by the pulsed-electroacoustic method when a pulse voltage was superposed on a DC bias voltage. A positive charge packet injected from the anode was observed soon after the pulse application, and traveled towards the cathode. It was suggested from the movement of the charge packet, that the mobility of the positive carrier at 0.1-0.6 MV/cm was in the order of 10/sup -9/ cm/sup 2//Vs at room temperature. When the pulse voltage was very high, a charge packet appeared originating from the bulk, suggesting that the carrier dissociation takes place.

Influence of Absorbed Gas in Silicone Rubber on Electrical Tree Initiation

Silicone rubber (SiR) has various excellent characteristics. The use of SiR is increasing as an insulating material of cable joint in power transmission line in recent years. In SiR, the electrical tree initiation voltage is increased by vacuum evacuation, and it decreases with time after air is again impregnated. In polyethylene, it is known that electrical tree initiation voltage is increased by SF6 impregnation. In this paper, we will report the influence of SF6 impregnation on electrical tree initiation characteristic in SiR with and without vacuum evacuation. Without vacuum evacuation, the electrical tree initiation voltage of SF6-impregnated specimen is a little higher than that of untreated specimen. With vacuum evacuation, the electrical tree initiation voltage of SF6-impregnated specimen is a little lower than that of air reimpregnation. In SiR, unlike in polyethylene, the increase of the electrical tree initiation voltage by SF6 impregnation is not clear.

Influence of Vacuum Evacuation on Electrical Tree Initiation in Silicone Rubber

The usage of silicone rubber is increasing for insulating material of power cable joint in recent years, although ethylene propylene rubber has been used for that purpose. In this paper, we will report the influence of vacuum evacuation on electrical tree initiation in silicone rubber. The electrical tree initiation voltage of silicone rubber increases after vacuum evacuation. However, when air is impregnated again, the electrical tree initiation voltage decreases with time. Finally, the electrical tree initiation voltage goes down nearly to the same value as the original one without vacuum evacuation. This tendency is observed in silicone rubber with secondary cross-linking treatment as well as in sample without secondary cross-linking treatment.

Influence of electric field on plant weight

This paper reports the influence of D.C. electric field on plant growth. We used the white radish sprout as the sample. The seeds of white radish sprout were grown under two circumstances; one is under electric fields, and the other is without electric fields. We have confirmed the following things: 1. The application of D.C. electric field improves the germination rate. 2. The D.C. electric field increases the length and the weight of the sample. 3. However, after removal of water by vacuum treatment, the weight of the sample subjected to the D.C. electric fields turns to be lower than that of the sample not subjected. This result suggests that the D.C. electric field accelerates the growth of the plant; it does not increase the real plant weight, but just improves the stem elongation by water absorption, and encourages the consumption of substances stored in the seed. The D.C. electric field probably activates the work of phytohormone called Gibberellin, which is reported to induce germination, and to encourage the stem elongation by absorbing water.

Effect of gas impregnation in silicone rubber on electrical tree initiation

We consider that electrical tree initiation is caused by collision impact of electrons which are accelerated in polymer free volume by electric field. It is expected that gas in free volume in SiR affects the electrical tree initiation characteristics. The electrical tree initiation voltage is increased by vacuum evacuation, SF6 impregnation, and air re-impregnation after vacuum evacuation. It is important to investigate the influence of gas impregnation for the improvement of the electrical tree resistance in SiR. In this paper, we will report the effect of gas impregnation on electrical tree initiation in SiR.

Influence of degradation on electroluminescence in polyethylene

Electrical treeing is responsible for the breakdown of power cables with polymeric insulation. Electroluminescence (EL) and the degraded region are observed in the initiation phase of the electrical tree before partial discharge starts. The degraded region has a larger number of microvoids and polar groups than the normal region dose. We studied the EL characteristics of PE (XLPE and LDPE) with the degraded region, and compared them with those in virgin PE. The specimen with the degraded region has higher EL activity, namely lower EL inception voltage and higher light intensity. We considered that EL is caused by the process in a micro cavity of sub-micron size, namely by collision impact of electrons accelerated in that space. These results suggest that electron acceleration is emphasized by the increase of microvoids in the degraded region.

Influence of D.C. electric field on growth of arabidopsis thaliana (thale-cress)

This paper reports the influence of D.C. electric field on plant growth. In previous paper, we had reported that the D.C. electric field improves the growth of Raphanus sativus longipinnatus (daikon radish). We also reported that the D.C. electric field improves the seed germination rate of Arabidopsis thaliana (thale-cress). In this paper, the results for the thale-cress will be confirmed. Furthermore, we will show the new result that the D.C. electric field exerts no effect on seed germination when the electric potential of the sample is grounded by insertion of the grounded stainless steel plate into the seed bed.

Electroluminescence properties of water-treed XLPE under long time voltage application

Electroluminescence (EL) occurs in initiation phase of electrical tree and is considered to be a probe of the degradation of polymer insulating materials. We consider that EL is caused by electron impact; namely, electrons injected from electrode are accelerated in micro cavity of sub-micron size and causes bond scission and excitation of luminescence center. Under existence of water, water treeing takes place when subjected to a high electric field. Water tree provides a starting point of electrical tree, and therefore is responsible for the final breakdown of power cables with polymeric insulation. But the relation between EL and degradation in water-treed region is still unclear. We studied the EL properties of cross-linked polyethylene (XLPE) with a water-treed region after drying process. Wepsilall discuss the relation between EL properties and progress of material degradation in water treed region.

Sterilization of liquid by high electric field pulse

There are two methods for sterilization of foods, heating and non-heating. The heating sterilization is now widely used for liquid food such as milk and juice. However this method has some problems. One of them is the changes in nutrition and quality of food caused by heating up to temperature for example 63°C to kill bacteria. The large energy consumption is also a drawback of heating sterilization; the heating sterilization needs to heat up whole volume of liquid. The non-heating sterilization such as UV irradiation, ion beam irradiation, and chemical methods are proposed to avoid these problems of heating method. The pulse sterilization, one of the non-heating methods, attracts attentions because it causes little change in nutrition of liquid food, and low energy consumption. We have studied the sterilization of liquid using high electric field pulse. Sample was liquid medium including Escherichia coli. E. coli was used because of easy cultivation. We used nonpoisonous K coli. We applied high voltage pulse to a coaxial cylindrical tank containing sample liquid. After application of 50 pulses, the survival rate of K coli was reduced to 0.01%. This value of 0.01% is far superior to 1%, which is reported for milk sterilized at 63°C for 30 minutes.

Suppression of Electrical Tree in Silicone Rubber by Gas Impregnation

It is expected that gas in free volume in silicone rubber influences the electrical tree initiation characteristics. The electrical tree initiation voltage was examined in the silicone rubber treated by vacuum evacuation, SF6 impregnation and air re-impregnation after vacuum evacuation.