Protective Measures to Oil Depot Against.doc

此文档收集于网络，如有侵权，请联系网站删除NWEPDI_Protective Measures to Oil Depot AgainstLightning Stroke and Electrostatic SparkYu Pengfei,Northwest China Design Institute此文档仅供学习与交流IntroductionLightning can cause great destruction. According to the record in the northern China, more than 150 lightning strokes occur on a power system annually. High voltage (millions of volts) and large current (hundreds of kA) associated with lightning, will damage property and even kill people and livestocks. It will be very dangerous if a lightning stroke strikes oil depot of power plant or substation. In addition, the high voltage induced by the electrostatic charge generated due to oil flowing will probably cause damage unless the electrification has been limited and drained off.Protective Measures to Oil Depot Against Lightning StrokeThe most frequently used lightning- protection measures to oil tank is the lightning rod system. It consists of a group of lightning rods at proper locations on a structure.There are two ways of setting the lightning rods. One is to set it at the top of oil tank; another is on the ground level around the oil tank.If setting the lightning rods at the top of oil tank, the oil tank will be subject to high voltage when lightning strikes. The potential difference may result sparking on the metal tank, igniting oil gas and causing fire accident. Fixing lightning rods on the top of the tank is also equivalent to increase the structure height thus the probability of lightning stroke on oil tanks increases. For example, oil tanks built in Kelamayi Oil Field, Xinjiang Uygur Autonomous Region in 194CT s has never been suffered from lightning stroke without any lightning rod on the tank. However, years after, tanks installed with lightning rods were struck unexpectedly by lightning. It is obvious that lightning rods at the top of oil tanks is not a good protective measure against lightning stroke.The criteria for setting lightning rod had been studied by the author together with the experts from Electrical Engineering Institute of Chinese Academy of Sciences and XT an High-Voltage Electrical Equipment Research Institute from August 1980 to March 1981 when preparing the Code for Design of Petroleum Depot”. A test of imitating lightning stroke with a current of 146.6 kA to 220 kA (energy 133.40 J to201.8 J, electricity 6.68 C to 10.69 C ) was applied on a steel plate, a 0.0715 to 0.352 mm hollow on the steel plate had been melted by absorbing heat energy of 31.8 Cal to 48.1 Cal. Only warm but not scalding can be felt when touch the back of the struck plate.Considering the nature of lightning stroke as carrying electricity of 100 C and heat energy of 477 Cal, the melted depth of the plate would be approximately 1.55 mm.Metal tanks are generally considered to be capable of protecting against lightning if the thickness of the steel plate is not less than4.8 mm where flammable liquids are stored, but all sealing shall be gas-tight, and electrical conductivity be provided, Where these provisions can not be met, the structure shall be grounded for safety against contact voltage and be protected against lightning stroke by overhead shielding wires or an independent lightning rod system located on ground level, and the protection zone shall cover the whole oil tank.We should also pay more attention to ihe lightning protection of non-metal oil tanks, as a large number of lightning stroke accidents happened on non-metal oil tanks in China. For example, on August 12, 1989, lightning struck at Huangdao Oil Depot, Shandong Province, causing 2 big underground non-metal oil tanks, 5 big metal oil tanks, oil pump house, switchgear room and laboratory etc. destroyed and some operating staff killed or injured.By analysis, the reason seems to be that lightning struck at the underground nonmetal oil tanks, induced high potential difference between any two metal parts (between steel bars of RC. and cover plate), caused spark over which ignited oil gas with explosion inside the gas tank.Presently in China, the non-metal tanks are no longer used to store oil. Independent lightning rods located on ground level, or overhead shielding wires, or a metal grid made of steel bars of 8 mm minimum in diameter with 6 mm x 6 mm spacing covering the non-metal oil tank has been used as successful measures, and all metal parts should be continuous in electrical conductivity and led to the ground grid.Measures for Protecting Oil Tanks Against Electrostatic SparkElectrostatic charge induced due to the friction when the petroleum products are loading or flowing in pipe, may cause hazard if it had not been drained off before well accumulated.An oil tank in one oil refinery exploded, and caused a fire on Dec. 8,1977 because oil was filled so quickly and so fully in the tank that the voltage on oil-surface even reached as high as 7000 V, and when the three metal level floaters went up closing to the top of tank, initiated sparkover and subsequent explosion.In order to avoid electrostatic charge accumulation, it is necessary to control the oil flowing speed. The speed limit of gasoline, kcrvSene and light-diesel oil filling in tank or pipe shall not be over 4.5 m/s. When filling oil into 200 liters bucket, it shall take one minute (flowing at 3.0-3.5 liter per second). For 4000 liters bucket, it shall take five to eight minutes (flowing at 8.5-】3 liter per second). For lubricant, because of its high viscosity and large resistance to flow, it shall take 3 minutes (1.11 liter per second).It is very important to remove the floating substances from oil. The substances are easy to be charged because the oil is normally a good insulator. The substances will probably tend to be electrified and sparkover when there are too large amount of charge on it. It is a safe way to fill the oil into tank from bottom in order to ensure less charge on oil surface.In order to avoid too much charges accumulated, it is safe for all kinds of tanks,ELECTRICrTY-CSEE/OL 7 N0.3 25SPECIAL ISSUEeither metal or non-metal tanks which are used to store oil, gasoline, diesel, kerosene, etc. to be connected to the grounding grid with a resistance of less than 100 Q for discharging electrostatic charges. Railroads on which loading-unloading oil products shall be equipped with electrostatic protection grounding and the resistance shall be less than 30 Q. All the pipes for oil transportation shall be grounded by connection to the ground grid with conductors at both ends and every 200 m to 300 m in the straight line portion, the grounding resistance shall be less than 30 Q.Three Gorges Dam project in great progress as plannedIt hasnt been easy, but almost all of the work on the Three Gorges Project is on schedule, according to a corporation overseeing construction of the dam.The China Yangtze Three Gorges Project Development Corporation has reported that contractors and other staff are working hard to ensure that the flood season does not slow the dam project.The company recently detailed the mammoth tasks that have taken place so far this year on one of the worlds biggest construction sites.-More than 7.24 million cubic metres of earth and rocks have been excavated, accounting for 38 per cent of the years earthworks.-794,000 cubic metres of concrete have been placed, meeting 47 percent of the target set for 1996.-24,600 square metres of walls have been built to prevent water seepage, comprising 39 per cent of the years work.Contractors are now preparing for the damming of the Yangtze in November of 1997.Projects for the dry season were also completed on schedule. Concrete was poured in major parts of the project before the wet season.Preparations have been made for the second-phase of the project, from 1997 to 2003. This work also is pushing forward as planned.Officials said high temperatures and heavy rains in the second quarter of this year made concrete work difficult. But due to efforts of the design and overseeing departments and other workers, the concrete work on sections on a crucial cofferdam onthe right bank was completed in time.The Xiling Yangtze River Bridge has spanned the river, and is expected to open to traffic in the near future. The Datuo road on the right bank has also been finished.The speed of construction on a major highway, exclusively built to link the dam site with the outside world, is scheduled to open on October 1. But theres still a lot of work to do on it, officials said.Tests for the damming of the Yangtze are being carried out day and night.The China Yangtze Three Gorges Project Development Corporation also said that the excavation work for the temporary shiplock and shiplift has been relatively slow, while the excavation work in one area of the downstream navigation channel has lagged behind.The State Power Grid Development Ltd Corp. officially establishedThe establishment of the State Power Grid Development Corp Ltd(SPG) was officially announced on June 18, marking the governments determination to form a nationwide united power network to make the best of power generating capability.The State-owned corporation, with 2.5 billion yuan ($301 million) worth of operating capital raised by the government, will be responsible for investment, construction and management of the power transmission and substation projects involved in the construction of the Three Gorges Project.The construction of the Three Gorges Project is providing a good opportunity to shape an united power network nationwide; as a power hub, the project is creating conditions for linking up grids between different regions and areas throughout China.Construction of transmission and substation of 500 kV to stretch 9,100 kilometres, from inland China to coastal regions, will keep up w ith the pace of the construction of Three Gorges Power Stations to ensure the even transmission of electricity to other parts of the country.Upon completion, the installed power capacity in the network will account for 40 per cent of the nations total.As part of a significant economic development strategy, the State is making every endeavour to optimize energy resources through extra-high voltage transmission of electricity from western power bases to eastern a