S. Mitsumoto

Effects of acetophenone on high-field electrical properties in polyethylene

This paper describes the effect of acetophenone, one of the curing decomposition by-products, on high field electrical conduction and space charge distribution in low density polyethylene (LD-PE) films. When the applied field was relatively low, the current after polarity reversal with the positive acetophenone-coated Au electrode was much larger than that with negative one. The time dependence of leakage current has a peak. With the increase of the time from the acetophenone coating to the voltage application, the time from voltage application to the current peak appearance became short. When voltage was applied just after the acetophenone coating on the sample, space charge was formed in the vicinity of the positive electrode. On the other hand, when voltage was applied at 30 min after coating on the sample, space charge was formed from the positive electrode to near the negative electrode within 1 minute after the voltage application. From these results, it is concluded that the acetophenone promotes both carrier injection at the electrode interface and carrier transport in the bulk.

Space charge distribution of polyimide films in high temperature region

We have been studying the breakdown characteristics of polyimide (PI) films. The purpose of this study is to clarify the effect of space charge on breakdown mechanism of PI films in the high temperature region. The electric strength (Fb) decreased with temperature and the DC conduction current (I) increased with temperature. Between room temperature and 100/spl deg/C, there is no space charge detected in PI films. In the high temperature region, hetero space charge tends to be formed near the anode under the high electric field approaching to the breakdown field, but it decreases just before breakdown. These results show a thermal breakdown process based on the space charge modified conduction current is considered as a possible breakdown mechanism of PI films in the high temperature region.

High-field conduction and space charge distribution in acetophenone-coated polyethylene film

This paper describes the effect of polarity of applied field and electrode metal on electric conduction and space charge formation in one-sided acetophenone-coated low density polyethylene (LDPE) film. Up to an electric field of about 0.5 MV/cm with Au electrode, the acetophenone-coated positive electrode gives much larger conduction current than the negative one, suggesting that the existence of acetophenone at electrode interface enhances the hole injection rather than the electron injection. In the case of Al electrode this polarity dependence is opposite, suggesting the electron injection is more enhanced for Al electrode. Above about 0.5 MV/cm, however, these polarity effects changed. This change of polarity effect in high field region is explained by considering the space charge distribution and carrier injection from the acetophenone non-coated-side electrode. With the polarity where the current above 0.5 MV/cm became much larger, the dc electric strength showed significant decrease, showing that the dc breakdown is governed by the thermal process caused by Joule heating.

Effect of temperature and voltage application time on space charge decay of HDPE

Polyethylene is a material that is widely used as insulation for power cables. In this paper, the effect of temperature and voltage application time on space charge decay in HDPE is described. Negative charge was found to be retained by the samples when a field of 50kV/mm was applied at temperatures of 25 and 40 degC, with an amount that increased with increasing voltage application time. The same field applied for 4800s at 60degC gave both negative and positive space charge, but only positive charge at 90 degC The decay time of the negative charge increased as the amount of negative space charge retained after voltage removal increased. This indicates that much of the trapped negative charge could not be de-trapped easily. In contrast positive space charge was observed following the application of 180 kV/mm and 300kV/mm. The speed of positive charge decay in these cases was much faster than that of the negative charge accumulated under 50kV/mm. It was also observed that the decay time of positive charge decreased with increases in the cathode field measured just before short-circuiting at 25 and 40degC, but not at 60 and 90degC.

Breakdown and space charge distribution in polyimide film

We have been studying the breakdown characteristics of polyimide (PI) films. The purpose of this study is to clarify the effect of space charge and heat treatment on breakdown mechanism of PI films in room temperature region. The space charge distribution in a 125 /spl mu/m thick PI film was measured up to electrical breakdown with a semi-conducting and Al plate electrode under dc voltage by using pulsed electroacoustic (PEA) method. In room temperature region, hetero - charges were formed near the cathode, when the electric field approached the breakdown field. The conduction current shows large increase with increase of electric field near breakdown field. These results show a thermal breakdown process where the high-field conduction current is modified by the space charge effect is considered as a possible breakdown mechanism of PI films; in room temperature region.

Space charge distribution measured with short period interval up to electrical breakdown in polyethylene

The paper describes the space charge behavior measured with short period interval up to electrical breakdown in polyethylene film. Positive space charge was formed from the anode near the opposite electrode within 1.2 seconds after voltage application of 30 kV in a HDPE film. Up to electrical breakdown, this positive space charge formulation did not change. From this result, it is considered that there is the possibility that electrical breakdown in HDPE film is caused by hetero space charge, which enhances the cathode field just before electrical breakdown. The amount of homo space charge accumulation near both electrodes increased with time of voltage application in the LDPE film. Space charge distribution was remarkably changed with time. Electrical breakdown occurred when the negative space charge layer reached the cathode after hetero space charge was formed in the bulk. There is a possibility that hetero space charge formation may be a pre-breakdown phenomena in LDPE films.

Effect of acetophenone on electric conduction in LDPE film

We study the effect of an acetophenone coating on high field dc conduction of LDPE films. The existence of acetophenone at the electrode interface and the bulk of LDPE significantly promotes both electronic carrier injection from the electrode and its transport. When the polarity of the applied field is reversed, it is supposed that the current behavior is associated with the balance between the electron injection promoted by the hetero space charge and the hole injection which is relatively easy for the gold electrode.

Effect of voltage rise rate on space charge distribution in HDPE film [electrical insulation applications]

This paper describes the effect of voltage rise rate on space charge distribution in high-density polyethylene (HDPE) film. The observation of space charge distribution just before breakdown of HDPE films was carried out with short period interval (1 s) PEA measurement. A positive space charge was formed near the negative electrode irrespective of the difference of voltage rise rate. Up to electrical breakdown, this positive space charge formation was not remarkably changed at room temperature. The cathode electric field modified by the space charge effect was enhanced above the average field in the high field region. It was found that the average value of electric strength was about 4 MV/cm regardless of voltage rise rate at room temperature (25/spl deg/C). From these results, it is considered that the electrical breakdown in HDPE film is possibly caused by positive hetero space charge, which enhances the cathode electric field just before the electrical breakdown.

Observation of electrical breakdown and space charge formation in acetophenone-coated LDPE film under AC voltage application

This paper deals with the effect of acetophenone on dielectric properties such as tan /spl delta/ and capacitance and on space charge formation up to electrical breakdown under the AC voltage application in acetophenone-coated low density polyethylene (LDPE) film. The existence of acetophenone at the electrode interface enhance tan /spl delta/. Tan/spl delta/ increased with electric field and decreased inversely proportional to the frequency in the high field and high temperature region in acetophenone-coated specimen. AC breakdown test gave the result that the electric strength in non-coated specimen was higher than that in acetophenone-coated one and that the electric strength also decreased with temperature.

Observation of space charge distribution up to electric breakdown in acetophenone-coated polyethylene film

This paper describes the effects of polarity of applied voltage and electrode metal on electric conduction and space charge formation up to electric breakdown in one-sidedly acetophenone-coated low-density polyethylene (LDPE) film. Up to the electric field of about 0.5 MV/cm with Au electrode, the acetophenone-coated positive electrode gives much larger conduction current than the negative one, suggesting that the existence of acetophenone at electrode interface enhances the hole injection rather than the electron injection. In the case of Al electrode this polarity dependence is opposite, suggesting the electron injection is more enhanced for Al electrode. Above about 0.5 MV/cm, however, these polarity effects changed oppositely. This change of polarity effect in high field region is explained by considering the space charge distribution and carrier injection from the acetophenone non-coated-side electrode. With the polarity where the current above 0.5 MV/cm became much larger, the dc electric strength showed significant decrease, showing that the dc breakdown is governed by the thermal process caused by Joule heating.