中英文对照外文翻译
Reliability of Lightning Resistant
Overhead Distribution Lines
Lighting cont矫正身姿
inues to be the major cau of outages on overhead power distribution lines. Through laboratory testing and field obrvations and measurements, the properties of a lightning stroke and its effects on electrical distribution system components are well-understood phenomena. This paper prents a compilation of 32 years of historical records for outage caus, duration, and locations for eight distribution feeders at the Oak Ridge National Laboratory (ORNL) .
Distribution type lightning arresters are placed at dead-end and angle structures at pole mounted wormer locations and at high points on the overhead line. Station class lightning arresters are
ud to protect underground cable runs, pad mounted switchgear and unit substation transformers. Resistance to earth of each pole ground is typically 15 ohms or less. At higher elevations in the system, resistance to earth is substantially greater than 15 ohms, especially during the dry summer months. At the high points,山东崂山
ground rods were riven and bonded to the pole grounding systems in the
1960's in an attempt to decrea lightning outages. The attempts were only partially successful in lowering the outage rate. From a surge protection standpoint the variety of pole structures ud (in-line, corner, angle, dead end, etc.) and the variety of insulators and hardware ud does not allow each 13.8 kV overhead line to be categorized with a uniform impul flashover rating (170 kV, etc.) or a numerical BIL voltage class (95 kV BIL; etc.). For simplicity purpos in the analysis, each overhead line was categorized with a nominal voltage construction class (15 kV, 34 kV, or 69 KV). Six of the eight overhead lines (feeders 1 through 6) were built with typical REA Standard horizontal wood cross arm construction utilizing single ANSI Class 55-5 porcelain pin insulators (nominal 15 kV insulation). The shield angle of the overhead ground wire to the pha conductors is typically 45
degrees. One overhead line (feed蜂蜜妙用
er 7) was built with transmission type wood pole construction becau the line extended to a rearch facility which was to have generated electrical power to feed back into the grid. Pole structure of this line are of durable wood cross a construction which utilize double ANSI 52-3 porcelain suspension insulators to support the conductors (nominal 34 kV insulation). The shield angle of the overhead ground wire to the pha conductors for feeder 7 is typically 30 degrees. In 1969, an overhead line (feeder 8) was intentionally built with "lightning resistant" construction in an attempt to reduce lightning caud outages. Pole structures of the line h
ave pha over pha 24-inch long fiberglass suspension brackets with double ANS护眼高清壁纸
I 52-3 porcelain suspension insulators to support the conductors (nominal 69 kV insulation). The shield angle of the overhead ground wire to the pha conductors for feeder 8 is typically 30 degrees. The failure data was compiled for each of the eight 13.8 kV feeders and is prented in Table, along with pertinent information regarding feeder construction, elevation, length, and age.
A key finding of the failure analysis is that weather-related
events account for over half (56%) of the feeder outages recorded. Fifty-ven of the 76 weather-related outages were attributed to lightning. Insulation breakdown damage due to lightning is also suspected in at least a dozen of the equipment failures obrved. The data indicates感恩节图片
overhead lines which pass over 桌面提醒
high 嘴巴周围的痣面相
terrain are less reliable becau of the greater exposure to lightning. For example, feeder 3 had the most recorded outages (48), of which two-thirds were due to weather-related events; this feeder is also the highest line on the plant site, rising to an elevation of 450 above the reference valley elevation. Overhead lines that are longer and to which more substations and equipment are attached were also obrved to be less reliable (more exposure to lightning and more equipment to fail). The age of the line does not appear to significantly lesn its reliability as long as adequate maintenance is performed; none of the lines have had a notable increa in the fre
quency of outages as the lines have aged. As would be expected, the empirical data prented in Table I confirms the two overhead lines which have been insulated to a higher level (34 or 69 KV) have significantly better reliability records than tho utilizing 15 kV class construction. Feeder 7 (insulated to 34 KV)
and feeder 8 (insulated to 69 kV) have bad only 3 outages each over their 32 and 23 year life spans, respectively. The lines follow similar terrain and are comparable in length and age to the 15 kV class lines, yet they have a combined failure rate of 0.22 failures per year versus 4.32 failures per year for the remaining feeders.
On typical 15 kV insulated line construction, lightning flashovers often cau 60 cycle power follow and feeder trip. With the higher insulation construction, outage rates are reduced by limiting the number of flashovers and the resultant power follow which caus an over curre怎样在电脑上打字
nt device to trip. This allows lightning arresters to perform their duty of dissipating lightning energy to earth. The number of re clor actions and their resultant momentary outages are also reduced. This is beneficial for critical facilities and process which cannot tolerate even momentary outages. An additional benefit is that outages due to animal contact are also reduced becau of the greater distance from pha conductor to ground on pole structures. Distribution line eq班主任心得
uipment to increa l
ine insulation values are "off the shelf" items and proven technology. New lightning resistant construction typical by utilizes horizontal line posts, fiber老北京炸酱面的做法及配料
glass standoff brackets
