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Demand on the usage of HVDC cables in the past was very low, this is because at that time most its application is only for underwater cable installations. However, when there are an increased in demand for using renewable energy such as solar energy, the use of polymer-based as insulaton material for HVDC became increased. This have attracted more cable manufacturers try to improve this cable quality and attract more market penetration in order make the development costs recoverable. This paper presents a review the used of polymer-based material for HVDC cable application. Comparison and discussion from previous researcher and manufacturer was done in term of material properties and quality was presented and discussed. The review was focused 4 types of polymer-based material which are: cross-linked Polyethylene (XLPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE). Each material tests result were discussed for the best usage as HVDC insulation systems. The review found, polymer based material with additional of nana filler or difference type polymer can improve dielectric properties of HVDC cable insulator. This is because these material have very good indication of the conductivity and dielectric strength of high voltage insulation for HVDC application.

The application of mineral oil in transformer is prominently act as and insulator and a coolant liquid. More often, petroleum based oil is used because most its elements are good to act as insulator such as excellent heat transfer and low in viscosity. Anyhow, the usage of mineral oil in transformer is possibly hazardous to the environment considering that it is poor biodegradable liquid where when a spill or leakage happens, it could pollute the environment surroundings. Moreover, it is known as a non-renewable energy sources, the world will be out of it someday near future. For this reason, a new option of transformer insulation liquid is studied. Vegetable oil is a fully biodegradable insulating liquid and for this paper, coconut oil is used as the insulator. In this paper, it concentrates on the performance of the transformer before and after virgin coconut oil is applied in a single-phase step down transformer that use the 220 V supply and 50 Hz frequency. Transformer is connected to 110V induction motor as load and has been test in two conditions, dry and after virgin coconut oil is applied. Comparison is made from both results and clearly shown a good improvement when virgin coconut oil is used as insulation oil.

This paper reports the improvement of open circuit voltage stability of solar cell using InN based quantum dot in the active layer of the device structure. We have analyzed theoretically the temperature dependence of the open circuit voltage of the solar cell to investigate its fluctuation using Ge and InN based quantum dot in the active layer of the solar cell. Numerical results obtained are compared. The comparison results reveal that the open circuit voltage has been reduced a little bit but the fluctuation of terminal voltage has been reduced significantly by using InN quantum dot in the active layer of the device structure. Therefore InN is proved to be an excellent material to fabricate solar cell to provide higher stability in the open circuit voltage of the solar cell in very near future.