Relation between Electrical and Physical Properties of XLPE
It is well known that PE has excellent electrical properties, while XLPE maintains this electrical performance. At the same time, XLPE has higher performance than PE in other aspects, such as heat shrinkable tube. Its volume resistivity is above 1015Ωcm, much higher than that of PVC and oil-paper insulation. The dielectric loss angle is below 10-4, and does not change with temperature (or slightly increase) at normal temperature. According to the data, the breakdown strength of PE and XLPE develops with the change of temperature. There is no electrical strength of PE through the base wood at 105 C, and there is a sudden change in the breakdown strength of XLPE, which can be explained by the obvious molecular loosening and the change of structural tightness of XLPE materials in this temperature range.
In addition, the thermal expansion coefficients of organic synthetic insulating materials such as XLPE and PE are relatively large, and both PE and XLPPE are in the range of 1.3*10-5℃~-20*10-5℃. Therefore, under heavy load operation, XLPE itself has a great thermal expansion due to the rise of temperature, but the expansion coefficients of metals outside the insulation are relatively small ((0.7*10-5℃). Thus, the insulation expansion is uneven and the insulation table is seriously distorted. The uniformity of the original electric field of the cable is changed, and the cable life is changed accordingly.
Secondly, according to the data, the electric field strength of polymer materials corresponds to the elastic modulus of materials with temperature. That is to say, the rapid decrease of the elastic modulus makes the electrical strength of XLPE materials decrease correspondingly, and the higher the temperature, the more obvious the change is.