Discussion on lightning protection design of the h

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Discussion on lightning protection design of gas station system

through the analysis of the environmental characteristics of the automobile gas station and the factors of lightning disaster in the system characteristics, according to its characteristics, the direct lightning protection and grounding of the fuel shed, oil tank and auxiliary buildings, the lightning protection of the power supply and signal system of the gas station, etc., according to the requirements of GB 50057 and iec61 312 standard for lightning protection under the load of 1.86mpa, this paper puts forward a systematic solution

with the rapid development of China's economy, urban comprehensive disaster prevention planning and urban construction planning have become one of the main contents of urban construction planning by local governments. With the development of local economy and the improvement of people's living standards, the number of motor vehicles in various places is also increasing rapidly, and the urban motor vehicle public gas stations, which provide energy for them, are also increasing at a faster speed. Gas stations play an important role in urban traffic construction and are also an important energy base in urban disaster relief. However, in recent years, the frequent occurrence of lightning disasters and accidents in gas stations directly threatens the safety of people and buildings around gas stations and weakens the function of gas stations as urban energy hubs. Therefore, the comprehensive lightning protection of gas stations is very important

1. Environmental characteristics of gas stations

gas stations usually have the following characteristics:

1) geographical location: gas stations are usually located in open areas in urban areas or in open areas along roads such as suburbs, mountains, villages and highways

2) implementation conditions: whether there are sediment areas in the process flange of urban transmitters or villages, these gas station buildings often do not have lightning protection implementation that meets the requirements (including external lightning protection, internal lightning protection and grounding, etc.). In addition, the business building area of gas stations is generally very small, which is not convenient for the implementation of multi-level lightning protection scheme

3) power supply system: generally, the 380V AC power supply line of the gas station is connected to the nearby station area by overhead open line and then buried into the building. Some gas stations are connected by 10kV power line overhead and then buried into the building after passing through the transformer. In rural and mountainous areas, sometimes there is no burial measures at all, so it is very easy to induce lightning electromagnetic pulse

4) communication network system: ISDN and other communication lines introduced into gas stations are usually introduced by outdoor overhead open lines, and special surge protective devices (SPD) are usually not installed as lightning protection measures

will directly affect the large deformation and elongation after fracture 2 This is only the realization of physical meaning. It is not difficult to find from the above characteristics. From the perspective of lightning protection, gas stations generally operate in a "high-risk" environment, that is, the "exposure" to the risk of lightning damage is very high, so strong protective measures need to be taken. According to GB code for design of lightning protection of buildings, GB code for lightning safety of petroleum and petroleum facilities, GB code for design of oil depots and other national standards and iec61312 protection of lightning electromagnetic pulse, its power line should adopt at least two levels of lightning protection, and its signal line should adopt at least one level of lightning protection to meet the requirements of lightning protection. However, the current situation is that most gas stations do not have lightning overvoltage protection for power lines and signal lines

in view of the above characteristics and requirements of gas stations, it is generally considered that the maximum nominal discharge current greater than 15ka (10/350) should be selected for areas with moderate thunderstorm intensity (annual thunderstorm days more than 40 days) μ S) As the first level lightning protection of the power supply system, the protection level of the surge protector should be less than 2000V. At the same time, meeting the requirements of these two aspects can ensure the reliable operation of the power supply of the gas station equipment. Since most communication signal lines are incoming from the outside, they will also be threatened by lightning. Therefore, special communication signal series surge protectors are also required for lightning protection. The following figure shows the system diagram of the gas station:

2. Confirmation of lightning protection grade of the gas station

according to GB code for design of lightning protection of buildings, the estimated number of lightning strikes in a building is calculated according to the following formula: n = kngae; Ng = 0.024td, where n is the estimated number of lightning strikes on buildings (times/a)

k correction coefficient of lightning stroke times; In this case, take 2

ng the annual average density of lightning strike on the earth in the area where the building is located [times/(km2 • a)]

ae and the equivalent area of the building intercepting the same number of lightning strikes (km2)

td the annual average number of lightning days in this area

K takes the corresponding value under the following circumstances:

a. take 2 for isolated buildings located in the wilderness

b. 1.7 for brick and wood structure buildings with metal roof

c. take 1.5 for buildings located by rivers, lakes, under hillsides or in mountains where the soil resistivity is low, where the groundwater is exposed, at the top of earth mountains, at Valley vents, etc., and especially humid buildings

according to the estimated number of lightning strikes in the past years, for areas with moderate or above thunderstorm intensity (with an average annual thunderstorm day of more than 40 days), the estimated number of lightning strikes for conventional gas stations with an area of about 3000 square meters next to the highway and a building height of less than 15 meters is: n = kngae ≈ 0.15/a

according to the above calculation, with reference to the requirements of article 2.0.3 of GB code for design of lightning protection of buildings, It belongs to the "building with explosion hazardous environment in zone 1, and the electric spark is not easy to cause explosion or cause great damage and personal casualties". Therefore, it should be classified as a class II lightning protection building, and its explosion-proof and fire-proof rating should be IA (IA) Ⅱ at3

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