The influence of frequency of AC component on space charge behaviours in polyethylene under combined AC and DC electric fields
Combined ac and dc voltages may occur in high voltage power transmission system, which bring challenges to the dielectric materials. Generally speaking, space charge is well recognised under high voltage dc conditions but has received little attention under high voltage ac conditions. Under ac electric fields, the formation space charge in the material depends strongly on the frequency. The knowledge of space charge behaviour in dielectric materials under combined voltages is desirable in terms of both experimental and simulation. In this paper, a numerical model based on the bipolar charge injection/transport model is used to analyse characteristics of space charge in polyethylene under combined electric fields at room temperature. The DC component ratio and the overall root mean square (RMS) are kept the same, while the frequency of the AC component is altered from 0.05 Hz to 50 Hz. It has been found that the amount of the accumulated charges reduces with increasing frequency due to the more frequent polarity reversal. Moreover, the time to reach the steady states of charge amount increases with frequency as well.
Electric field and space charge characteristics of XLPE insulation doped with nanofillers
Various types of nanoparticles had been introduced as additive to polymeric 
insulator by previous researchers. As a result, the existence of nanometre-size particles 
is well acknowledged in enhancing the dielectric strength in insulation material. The 
remained unanswered that is concerning the nanometre-sizes in maximising the 
potential of nanocomposite insulator. The main criteria to dictate the dielectric 
performance is by measuring the level of electric field distribution. While, electric 
field properties also influenced by the accumulation amount of space charge. So, this 
study was conducted to evaluate the electric field and space charge distribution in 
within nanocomposite insulator. The primary purpose is to identify the finest size in 
each type of selected nanoparticles in optimising the dielectric properties, but selecting 
the best type of nanofillers as well. Three different sizes attributed from 100nm, 80nm 
and 50nm were selected from three different nanofillers which are nanometre silicon 
dioxide (NSD), nanometre titanium dioxide (NTD) and air. All these nanofillers were 
doped in XLPE separately for simulation based study. Electric field distribution and 
space charge tabulation on each selected size were measured and compared. 
Consequently, each type of nanofillers give a selection different of sizes for the best 
dielectric performance. Conclusively, the best size for NSD, NTD and air were 100nm, 
80nm and 50nm respectively. The dominant influence of nanometre-size is the 
intrinsic behaviour of an oxidised element in nanofillers. In term of type, NTD is 
performed in electric field distribution can correlated with its permittivity constant, e. 
But for space charge tabulation, NSD is better due its intrinsic behaviour and insulation 
structure.
A technique for large-field, superficial electron therapy.
The application of electron beams to radiation therapy has received increased attention in recent years. This interest stems largely from the special characteristics of the electron depth-dose distribution; the fall-off in depth dose near the end of the range of the electrons is particularly rapid for electron beams having energies less than about 10 Mev. Such an electron beam is suitable for the treatment of widespread, superficial lesions, where it is desirable to minimize the dose to deep tissues. All the common sources of super-voltage x-rays, apart from radioactive substances, are inherently capable of producing an external beam of electrons, though with varying degrees of complexity. Electrons of about the energy suitable for superficial therapy (several Mev) may be used to produce an x-ray beam which is sufficiently penetrating for the treatment of even the deepest lesions. The Stanford medical linear accelerator was designed to provide both x-rays and electron beams. The accelerator and its applic...