As part of a general study on the possible use of UHV transmission lines in the range of 1200 kV for the James Bay Project, the corona performance of four conductor bundles -6 ×1. 823", 6 ×1. 998", 8 ×1. 63 " and 8 ×1.823"-has been studied in outdoor test cages under conditions of heavy artificial rain and fair weather. The radio interference, audible noise and corona losses of the four conductor bundles have been measured in the test cages, and the corresponding long line levels have been evaluated. The results show that of the four bundles tested the 8 ×1.63" conductor bundle gives the best corona performance. However, ice loading conditions may dictate the use of a six conductor bundle, in which case the 6 ×1.823" conductor bundle seems to give a marginally acceptable corona performance.

A Comparative Study of the Corona Performance of Conductor Bundles for 1200 KV Transmission Lines

Breakdown voltage of the air gap is of vital importance for the design of the external insulation in high-voltage transmission and transformation projects. In this paper, a new prediction method for the breakdown voltages of typical air gaps based on the electric field features and support vector machine (SVM) was proposed. According to the finite element calculation results of static electric field distribution, the electric field values in the whole region, discharge channel, surface of the electrode and the shortest path were extracted and post-processed, which constituted the electric field features characterizing the gap structure. Then, the breakdown voltage prediction model of the air gap was established by using electric field features as the input parameters to SVM, and whether the gap breakdown would happen as the output parameters of SVM, which changing the regression problem to a binary classification problem. This model was applied to predict the power frequency breakdown voltages of different short air gaps including sphere-sphere gaps, rod-plane gaps, sphere-plane gaps and sphereplane- sphere gaps. The power frequency breakdown voltages of longer air gaps which are affected by corona, and the 50% positive switching impulse breakdown voltages of long sphere-plane gaps and rod-plane gaps were predicted as well. The predicted results agree well with experimental values and simulated results of the published models, which validate the effectiveness of the proposed model. This method supplies a new possible way to obtain the breakdown voltage of air gaps.

A prediction method for breakdown voltage of typical air gaps based on electric field features and support vector machine

The paper deals with a laboratory investigation into the influence of rain on the switching impulse sparkover characteristics of large-sphere and toroid plane air gaps. Tests were also carried out on coneterminated rod-plane gaps for reference purposes. The factors investigated include the high voltage electrode geometry, nature of the surface, rain intensity as well as the impulse form and polarity. Attention is also paid to the influence of rain on the statistical dispersion of the sparkover voltage and on the nature of the cumulative probability curve. A general correlation, valid for a wide variety of electrodes, has been established between the mean spark-over voltage gradient for positive switching impulses under dry conditions, and the corresponding influence of rain on the breakdown voltage.

Influence of rain on switching impulse sparkover voltage of large-electrode air gaps

This paper presents the results of an analytical and physical study of the phase-to-phase strength based on experiments carried out at Renardieres.

Analysis of the Switching Impulse Strength of Phase-To-Phase Air Gaps

Investigation of positive streamer-leader propagation under slow front impulse voltages can play an important role in the quantitative research of positive upward lightning. In this work, we performed a large-scale investigation into leader development in a 10-m rod–plane gap under a long front positive impulse. To describe the leader propagation under slow front impulse voltages, we recorded the leader propagation with a high-speed charge coupled device (CCD) camera. It is important to figure out this phenomenon to deepen our understanding of leader discharge. The observation results showed that the leader mechanism is a very complex physical phenomenon; it could be categorized into two types of leader process, namely, continuous and the discontinuous leader streamer-leader propagation. Furthermore, we studied the continuous leader development parameters, including two-dimensional (2-D) leader length, injected charge, and final jump stage, as well as leader velocity for rod–plane configuration. We observed that the discontinuous leader makes an important contribution to the appearance of channel re-illuminations of the positive leader. To clarify the above doubts under long front cases, we carried out extensive experiments in this study. The comparative study shows better results in terms of standard switch impulse and long front positive impulse. Finally, the results are presented with a view toward improving our understanding of propagation mechanisms related to restrike phenomena, which are rarely reported.

https://www.mdpi.com/1996-1073/11/10/2636/pdf

Continuous and Discontinuous Streamer Leader Propagation Phenomena under Slow Front Impulse Voltages in a 10-meter Rod-Plane Air Gap

Tests were performed to evaluate the switching impulse (S.I.) breakdown voltage of tower window models of different sizes. Window models were tested with positive polarity S.I. and with conductor-to-structure clearances of 4.55, 5.90, 7.60 and 8.75 meters. With each size of model the 50% breakdown voltage was determined for seven different wave-fronts with a time-to-crest between 60 and 800 ps and a half-amplitude time over 3500 ps. The time-to-breakdown was also recorded and correlated to the time-to-crest of the applied wave and the breakdown voltage.

C. Menemenlis

Papers

Switching impulse Breakdown of EHV Trnasmission Towers