Switching impulse discharge characteristics of UHV transmission line air gaps

Abstract

The design of external insulation for transmission lines is usually based on real-type experiments. With the increasing voltage level of the transmission lines, in order to better design the experiments and reduce the experiment workload in the future, this paper studies the switching impulse discharge characteristics of air gaps of an ultrahigh-voltage (UHV) transmission line. A long air gap switching impulse breakdown voltage prediction method based on the leader discharge mechanism is proposed in this paper, and a continuous leader inception model is fitted for the air gaps in UHV transmission lines by calculating the factor R of the conductor-plane gaps. The method and the model can effectively predict the air gap breakdown voltage of transmission lines. The influence of tower width and conductor structure on air gap breakdown characteristics of UHV transmission lines is studied by the method and the model proposed this paper. The results show that, as the width of the tower increases, the breakdown voltage decreases, and as the gap length increases, the influence of the tower width on the breakdown voltage decreases. The conductor structure has no obvious influence on the discharge characteristics of transmission line air gaps.

Modeling of Positive Switching Impulse Discharge of UHV Transmission Line Air Gaps

“…Subsequently, the shortest distance between the conductor and the tower was determined to be the breakdown path, and the gap length was the discharge path length d. Thereafter, on the breakdown path, a point charge Q 0 was set at a distance of s to the surface of the conductor. In this study, the initial leader length was about 0.7 m [22,23], and the value of s was in the range of 0.3-0.7 m and thus had little influence on the gap characteristic factor [15]. Therefore, the charge was considered away from the surface of the conductor 0.5 m in this paper.…”

“…Rizk calculated the gap characteristic factors of some typical gaps by a mathematical method [9,10]. A gap characteristic factor calculation method is proposed in [15]. This method sets an equivalent point charge in a finite element simulation software to determine the induced potential on the surface of the high voltage electrode so as to calculate the factor.…”

“…Therefore, the charge was considered away from the surface of the conductor 0.5 m in this paper. According to equations (8), (9), and (10), it can be considered that the value of the Q 0 has no effect on the gap characteristic factor [15], so the value of Q 0 was considered as 1C in this paper. That is to say, on the breakdown path, a point charge of 1C was set at the position of 0.5 m from the surface of the conductor.…”

“…In the gap of the conductor electrode with a gap length of 4-8 m, the general model of the continuous leader inception voltage is [15]:…”

“…In the 1980s, some scholars established a typical gap breakdown voltage calculation model based on the leader discharge mechanism [9,10]. Since the 21st century, with the continuous progress of technology, scholars have carried out long air gap breakdown voltage prediction calculation and observation tests [11][12][13][14][15][16][17][18][19], further promoting the research process of long air gap discharge. At present, scholars mainly adopt real tower discharge tests to obtain the positive switching impulse discharge characteristics of air gaps in UHV transmission lines.…”