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Overhead transmission lines are important carriers of electric energy transmission. Their icing, galloping and shedding in winter and spring seriously threatened the safe operation of Shanxi power grid. Especially in the recent years, compact lines and double circuit lines on the same tower, typical types of overhead transmission lines in Shanxi Power Grid, were affected by frequent trips induced by icing, galloping, and shedding appeared in their conductors repeatedly, which seriously reduced the capacity of power energy transmission in Shanxi and caused trillions of power load losses. Through detailed investigation and analysis of the characteristics and historical fault cases of compact lines and double circuit lines on the same tower in Shanxi Power Grid, the key causes and main laws of two types of lines in Shanxi Power Grid are clarified, which could provide support for the follow-up line anti-ice technical transformation and capacity improvement.

The key to fabricating conductive polymer/carbon nanotube (CNT) nanocomposites is controlling the distribution of CNTs in the polymer matrix. Here, an effective and simple approach for controlling the distribution of multiwalled CNTs (MWCNTs) is reported to largely improve the electrical conductivity of biodegradable poly(l-lactide) (PLLA) through crystalline morphology development by addition of high-melting-point PLLA (hPLLA) crystallites. hPLLA crystallites are efficient nucleating agents, increasing the crystallinity and crystallization rate of PLLA/MWCNT nanocomposites. Furthermore, the diameter of spherulites decreases from 9.7 to 1.0 μm with an increase in the concentration of hPLLA from 0.03 to 3.0 wt %. The electrical conductivity of PLLA/MWCNT nanocomposites with 0.3 wt % MWCNTs greatly increases from 1.89 × 10-15 to 1.56 × 10-8 S/cm with an increase in the matrix crystallinity from 2.4 to 46.8% on introducing trace amounts of hPLLA (0.07 wt %). The percolation threshold of PLLA/MWCNT nanocomposites is reduced from 0.51 to 0.21 wt % on addition of 0.07 wt % hPLLA. The high electrical conductivity and low percolation threshold of PLLA/MWCNT nanocomposites incorporated with hPLLA are related to the high crystallinity and crystalline morphologies of the PLLA matrix. Big spherulites lock a lot of MWCNTs at the intervals in the spherulites, which is harmful to the electrical conductivity. Small spherulites, with large surface areas, also need more MWCNTs to form conductive networks in the amorphous regions. Most MWCNTs that are bundled together to form conductive paths are found in samples with mid-sized spherulites of ∼6.7 μm. More interestingly, the high crystallinity and reconstructed MWCNT network also enhanced the Young modulus, elongation at break, and elastic modulus at high temperature of PLLA/MWCNT nanocomposites with small amounts of hPLLA. [ABSTRACT FROM AUTHOR]