Xuankun Song 1, Teng Feng 1, Liu Han 1, Travis M. Smith2, Xinzhou Dong3, Wenxuan Liu 1, Rui Zhang 1

1. State Grid Economic and Technological Research Institute CO., LTD., Beijing 102209, China

2. Oak Ridge National Laboratory, TN 37831, USA

3. Tsinghua University, Beijing 100084, China

Abstract: Half-wavelength AC transmission (HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the construction and operation of HWACT to analyze these fault features and corresponding protection technology. In this paper, the steadystate voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed when a three-phase symmetrical short-circuit fault occurs on an HWACT line. On this basis, the three-phase fault characteristics for longer transmission lines are also be studied.

Keywords: Half-wavelength AC transmission, Fault characteristics, Three-phase short-circuit, Fault distance, Overvoltage.

Introduction

Half-wavelength alternating current transmission (HWACT) is an ultra-long distance three-phase AC power transmission technology with an electrical distance near to half-wavelength at the system power frequency. In 50Hz system, the distance is 3000km, while it is 2500km in 60Hz system. The advantages of HWACT are infinite theoretical maximum transmission capacity, and no additional reactive power compensation. Hence it is suitable to serve as the long-distance backbone frame in the future Global Energy Interconnection.

The concept of HWACT is initially proposed by the experts from Soviet Union in 1940s [1]. After some following exploratory research in this field [2-4], the principal transmission characteristics and some correlative key technical problems, such as corona loss and overvoltage [5, 6], have been solved out. But the research on HWACT has not been continuously and deeply carried out due to the limited demand and lower technical level at that time.

In the new century, the ultra-long distance, large capacity transmission has attracted global attention because of the serious energy shortage problem. Many researchers in different countries focus on HWACT once again. In Brazil, HWACT is used as the backup scheme to transmit large scale hydropower from Amazon River basin to the load centers [7, 8]. And in China, the scheme of HWACT has also been proposed to transmit the coal and hydro energy to the east coast load centers [9-16]. In particular, the State Grid Corporation of China proposed the idea of building Global Energy Interconnection in July 2014. The UHV power grid serves as the backbone to mainly deliver clean energy and achieve a globally interconnected smart grid. Long distance UHV transmission lines are needed for the long distance power transmission or exchange. Therefore, the study on HWACT to satisfy the requirement of large capacity long distance point-to-point power transmission has broader significance and practical value. The fault characteristics of an HWACT line can be different from those of a conventional transmission line. It is very important for the construction and operation of HWACT to analyze these fault features and corresponding protection technology. References [13-15] all deal with the analysis of fault for HWACT line, but the studies are limited to overvoltage along the line. Reference [12] gives a simple analysis of the fault characteristics for HWACT line, but not further. When a symmetrical short-circuit fault occurs, the three-phase system can be regarded as a single-phase system in order to simplify the fault analysis. The symmetrical fault analysis is the basis of the asymmetrical fault analysis. Therefore, the steady-state voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed in this paper when a three-phase symmetrical short-circuit fault occurs on an HWACT line.