1、 外文资料翻译 Reliability of Lightning Resistant Overhead Distribution Lines Lighting continues to be the major cause of outages on overhead power distribution lines. Through laboratory testing and field observations and measurements, the properties of a lightning stroke and its effects on electrical dist
2、ribution system components are well-understood phenomena. This paper presents a compilation of 32 years of historical records for outage causes, duration, and locations for eight distribution feeders at the Oak Ridge National Laboratory (ORNL) . Distribution type lightning arresters are placed at de
3、ad-end and angle structures at pole mounted wormer locations and at high points on the overhead line. Station class lightning arresters are used to protect underground cable runs, pad mounted switchgear and unit substation transformers. Resistance to earth of each pole ground is typically 15 ohms or
4、 less. At higher elevations in the system, resistance to earth is substantially greater than 15 ohms, especially during the dry summer months. At these high points, ground rods were riven and bonded to the pole grounding systems in the 1960s in an attempt to decrease lightning outages. These attempt
5、s were only partially successful in lowering the outage rate. From a surge protection standpoint the variety of pole structures used (in-line, corner, angle, deadend, etc.) and the variety of insulators and hardware used does not allow each 13.8 kV overhead line to be categorized with a uniform impu
6、lse flashover rating (170 kV, etc.) or a numerical BIL voltage class (95 kV BIL； etc.). For simplicity purposes 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 wit
7、h typical REA Standard horizontal wood crossarm construction utilizing single ANSI Class 55-5 porcelain pin insulators (nominal 15 kV insulation). The shield angle of the overhead ground wire to the phase conductors is typically 45 degrees. One overhead line (feeder 7) was built with transmission ty
8、pe wood pole construction because the line extended to a research 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 condu
9、ctors (nominal 34 kV insulation). The shield angle of the overhead ground wire to the phase 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 caused outages. Pole struc
10、tures of the line have phase over phase 24-inch long fiberglass suspension brackets with double ANSI 52-3 porcelain suspension insulators to support the conductors (nominal 69 kV insulation). The shield angle of the overhead ground wire to the phase conductors for feeder 8 is typically 30 degrees. T
11、he failure data was compiled for each of the eight 13.8 kV feeders and is presented 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 out
12、ages recorded. Fifty-seven 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 observed. The data indicates overhead lines which pass over high terrain are less reliable because o
13、f 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 l
14、onger and to which more substations and equipment are attached were also observed to be less reliable (more exposure to lightning and more equipment to fail). The age of the line does not appear to significantly lessen its reliability as long as adequate maintenance is performed； none of the lines h
15、ave had a notable increase in the frequency of outages as the lines have aged. As would be expected, the empirical data presented 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 those utilizing 15
16、 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. These lines follow similar terrain and are comparable in length and age to the 15 kV class lines, yet they have a combined failure
17、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 cause 60 cycle power follow and feeder trip. With the higher insulation construction, outage rates are reduced by limiting the number of fl
18、ashovers and the resultant power follow which causes an over current device to trip. This allows lightning arresters to perform their duty of dissipating lightning energy to earth. The number of re closer actions and their resultant momentary outages are also reduced. This is beneficial for critical
19、 facilities and processes which cannot tolerate even momentary outages. An additional benefit is that outages due to animal contact are also reduced because of the greater distance from phase conductor to ground on pole structures. Distribution line equipment to increase line insulation values are o
20、ff the shelf items and proven technology. New lightning resistant construction typical by utilizes horizontal line posts, fiberglass standoff brackets or any other method which world increase the insulation value. The replacement of standard pin insulators with line post insulators of greater flasho
21、ver value is an effective means to retrofit existing wood cross arm construction. The doubling and tripling of dead end and suspension insulators is also a means of increasing flashover values on existing angle and dead-end structures. Current fiberglass, polymer, and epoxy technologies provide an affordable means to increase line insulation. While the use of increased insulation levels to reduce lightning flashovers and the resultant outages on overhead distribution lines has been thoroughly
