A high surge impedance loading technique approach for uprating transmission lines

Resumo

This paper presents a study involving a viable unconventional transmission line (TL) uprating concept,
named High Surge Impedance Loading (HSIL). This technique is based on the understanding of the variation
of the electric field produced by the TL, regarding the geometric position of the conductors. It proposes the
adoption of unconventional geometric bundles design, by reducing the distance between phases and increasing the
distance between conductors of the same phase. An analytical model for transmission lines is developed for the
soil effect determination on the estimate of electric field magnitude at ground level and at the conductors’ surface
of TLs. The model is submitted to a stochastic evolutionary optimization technique called Differential Evolution,
aiming at maximizing the Surge Impedance Loading. However, many constraints as minimum distances among
TL components and soil determined by NBR 5422 are considered, as well as the magnitude of the electric fields
for human exposure of the general public at ground level, established by NBR 25415. Also, using altimetry
data supplied by the Brazilian Geodetic System, maximum levels of the surface electric field are determined and
compared with the values of the critical electric field, from which the Corona effect occurs. The results acquired
from the developed computational tool suggested new bundle geometric configurations for an existing transmission
line, with enhanced surge impedance loading and with electric fields at ground level and at conductors’ surface
below the thresholds values and defined by the norm.