Study on Conductor Creep Characteristics and Test Model of UHVDC Transmission Line

Abstract

UHVDC transmission has the capacity of point-to-point, ultra long distance and large capacity power transmission. In order to further improve the transmission capacity and reduce the line loss, 1000mm2 and 1250mm2 large cross-section conductors are used in ± 800kV UHVDC transmission project constructed by State Grid Corporation of China in recent years. After the conductor is erected, under the action of long-term stress, besides elastic elongation, plastic elongation and creep elongation will also be produced, which is called plastic creep elongation. Plastic creep elongation will cause permanent deformation of conductor and lightning conductor, that is, the elongation of these two parts will not disappear after the tension is removed. It is related to the size of tension and the length of action time. In the process of operation, with the change of conductor tension and the passage of time, the elongation gradually extends, and finally tends to be stable after 5–10 years. Obviously, the existence of plastic creep elongation increases the length of the conductor in the span, thus making the sag permanent increase. As a result, the distance between the conductor and the ground and the object to be crossed becomes smaller, which endangers the safe operation of the line. In the construction of new line erection, the plastic creep elongation of overhead conductor must be compensated, so that the sag will not increase due to plastic creep elongation after long-term operation. Due to the lack of experience and theoretical basis, it is more difficult to estimate the conductor elongation in line design. Aiming at the 1250 mm2 large cross-section conductor used in ± 800 kV UHVDC transmission project from Lingzhou-Shaoxing, the internal and external factors affecting the creep characteristics of the transmission line are analyzed in detail, and the creep test research of the large cross-section conductor is carried out. According to the test results, the creep calculation model of 1250 mm2 conductor is proposed.