[Show abstract][Hide abstract] ABSTRACT: Space charge behavior has been investigated in LDPE/MgO composite films including the different size of MgO particles with a diameter of several tens nm (nano) or a few mum (micro) when a dc high stress is applied to the sample at high temperature. It is believed that a positive packet-like charge is injected from the anode, and after that a negative packet charge is injected from the cathode. In the samples with relatively low content of MgO, the apparent velocity of positive packet-like charge in LDPE/MgO (nano) is faster than that in LDPE/MgO (micro) at a field of 150 kV/mm. Such generation of charges causes the enhancement of local electric field in the sample. However, almost no packet-like charge was observed in the sample with relatively high content of MgO irrespective of the filler size. It is considered that the addition of MgO filler to LDPE plays a role to reduce the enhancement of the electric field in the sample by suppression of both the positive and the negative charge injection into the sample.
[Show abstract][Hide abstract] ABSTRACT: Recently, authors have developed the simultaneous observation system which is combined a photomultiplier tube (PMT), a high performance CCD camera and the dissipation current waveform detecting circuit. In this study, the observations of the dissipation current waveform and EL of LDPE/MgO nanocomposite material under AC high field were carried out. LDPE and the concentration of LDPE/MgO nanocomposite were 1 and 5 phr respectively, were prepared. Electric field dependence and time variations of EL pulses were examined by using the system. As the results of these experiments, the incorporation of MgO nanoparticles in LDPE matrix makes elevate the EL inception level and makes increase the number of EL pulses, especially negative half cycle. But there were no dependences of the relaxation time tau at 60 kV/mm 50 Hz with MgO contents under AC field.
[Show abstract][Hide abstract] ABSTRACT: This paper deals with a water tree retardant characteristic of magnesium oxide (MgO) nano-filler addition to a low-density polyethylene (LDPE) and a cross-linked polyethylene (XLPE). Water tree retardation of both LDPE and XLPE at 313 K was improved with adding the MgO nano-filler at the content of more than 2 phr, while it was almost the same level at the nano-filler content of less than 2 phr. From the comparison of the result with MgO/XLPE and MgO/LDPE, the water tree retardation of MgO/XLPE was superior to that of MgO/LDPE at the nano-filler content of less than 2 phr, where MgO nano-filler shows no remarkable water tree retardant property. When the nano-filler content is 5 phr, however, water tree retardations of both XLPE and LDPE due to MgO addition became almost the same level and shows remarkable improvement with adding MgO nano-filler. As for the influence of temperature, the water tree at 333 K tends to grow faster and the retardation of water tree due to MgO addition became less effective than those at 313 K. Finally it was also found out that the growth rate of water tree became smaller with increasing MgO nano-fillers, showing the water tree retardant property of MgO nano-filler addition.
[Show abstract][Hide abstract] ABSTRACT: This paper deals with initiation of light emission and electrical trees in LDPE/MgO nanocomposite. Specimens were prepared in such a way that a tungsten needle of 50 mum phi and 1mumR was inserted into dielectrics with a spacing of 0.4 mm between high voltage and ground. Light emission was observed by an ICCD camera, and tree shapes were examined by an optical microscope. As a result, it was found that light emission originates from electrical trees rather than electroluminescence in our experiments and that initiation of electrical trees and light emission are affected by the addition of nano MgO fillers. That is, it was clarified that applied voltage or electric stress for tree initiation tends to increase, as filler content increases in the range of 0 to 1 phr. In addition, tree length is shortened due to inclusion of nano-fillers.
[Show abstract][Hide abstract] ABSTRACT: It has been proved earlier that electric properties of polymer insulation can be improved by addition of nano-sized inorganic filler. These materials have attracted a lot of attention. With the addition of nano sized MgO filler in Low Density Polyethylene (LDPE), several improvements in material properties were observed and were already reported. In this paper, investigations on the volume resistivity and space charge distribution in XLPE/MgO nanocomposite (MgO nano-filler mixed with Cross Linked Polyethylene) material are reported. Investigations on packet like charge, observed earlier in LDPE, are also made both for XLPE and XLPE/MgO nanocomposite materials. The results indicate the suitability of XLPE/MgO nanocomposite material for HVDC insulation.