1、外文文献：Lightning Protection against Winter Lightning1. Introduction Most of transmission line outages in Japan are caused by lightning. The mountainous areas along the Sea of Japan coast are affected by winter lightning in particular. Winter lightning has often caused multiphase outage including doubl
2、e circuit outage, and even strand fusing of overhead ground wire (OGW) has occurred . There have been several methods to analyze the transmission line outage. However, the outages due to winter lightning have been difficult to explain with these methods. Therefore, observations of winter lightning s
3、trokes and measurements of lightning surges on transmission lines have been conducted since the end of the 1970s and the early of the 1980s, respectively. These observations have revealed winter lightning has several specific characteristics (large maximum value and long duration of lightning curren
4、t, large electric charge, frequent upward flashes etc.). And then the lightning performance of various protection methods has studied by experiments and analyses. Taking into account these studies, the lightning protection measures for transmission lines against winter lightning have been improved.
5、Installation of transmission line arresters is one of the effective measures against double circuit outage from lightning. These conventional arresters were developed against summer lightning, and might be damaged by a very large electric charge of winter lightning than that of summer lightning. Mea
6、surements of lightning surges, caused by natural lightning and rocket-triggered lightning in winter, were carried out at the 275 kV Okushishiku Test Transmission Line equipped with transmission line arresters for a 154 kV line in Hokuriku, Japan from 1993 to 1999 . The measurement results have demon
7、strated that the conventional arrester designed against summer lightning is effective against winter lightning, and an arrester with reduced withstand capability is a reasonable option to realize a line of high lightning performance . In recent years, the number of installing transmission line arres
8、ters is increasing not only in summer lightning areas but also in winter lightning areas. On Japanese distribution lines, surge arresters and/or an OGW are utilized to protect equipments against lightning. The lightning outages of distribution lines due to flashover have been gradually decreasing wi
9、th increasing surge arresters. However, several arresters are damaged by direct lightning strokes, especially in winter. Installing an OGW is more effective to reduce the arrester failures caused by direct lightning . Though the OGW is installed on distribution lines located in mountainous areas fac
10、ing the Sea of Japan, winter lightning has often damaged surge arresters, and lightning outages have occurred at many poles by a single lightning flash in some cases . Winter lightning strokes are concentrated on tall structures located in mountainous areas, such as radio and TV broadcasting station
11、s on hilltops and have very large electric charge as compared with summer lightning. Most lightning outages in mountainous areas are caused by backflow lightning current flowing into a power distribution line from a tall structure. Thus lightning protection for equipments at poles supplying power to
12、 tall structures should be given special consideration in the case of these lines. The failure probability of an arrester, which is installed at the electric pole nearest the tall structure, due to backflow lightning current is calculated using the Electro-Magnetic Transients Program (EMTP). And the
13、n the lightning performances of various protection methods have been studied. As a result, multiple OGWs in addition to the conventional OGW and increasing the withstand capability of arresters have been applied as the effective measures against arrester failures caused by direct strokes and backflo
14、w currents . In summer, similar lightning outages sometimes have occurred on Japanese distribution lines in Engineering Research & Development Center mountainous area, the above described lightning protection methods are effective.2. Lightning Protection of Transmission Lines against Winter Lightnin
15、gLightning Protection of Transmission Lines against Winter Lightning Fig. 1 shows the lightning outage rate of 500 kV double-circuit balanced insulation lines in Japan from August 1974 through March 1980 . The total length of these lines was approximately 11,700 km. Winter lightning area is the coas
16、t of the Japan Sea north of Wakasa Bay, summer lightning area is the other area. Winter was defined as from November to March, and summer was from April to October. The lightning outage rate of winter lightning area in winter was approximately 4 times larger than that of summer lightning area in summer. The percentage of double circuit outages of winter lightning area in winter was much larger than that of summer lightning area, and winter lightning with large maximum value of lig
