The discussionobout High-rise buildings in electrical
grounding system
1 The species of high-rise building grounding system
With the development of social and technology, Especially the emergence of large intelligence building,the more higher requirement of Docking land system design is put forward.in order to make good grounding system design, we need a clear understanding of theclassification of the high-rise uilding between different grounding system,We also need to know the role of the relationship between each other, Only in this way,Can we have a effectively guarantee to the the quality of the electrical engineering grounding systems designing of the high-rise buildings .the species and function in High-rise building grounding system,Especially high and intelligent buildings requires lots of grounding equipment and components ,and the request is different, But the role of from grounding can be divided into three categories.
Lightning proof grounding, work grounding and protection grounding. Lightningproo f grounding is very important in high-rise building grounding system, when the block is stroked by the lightning,it can lead the current into the earth effectively,thereby protect each component of the block ang also protect people from being lightnen in the block.due to the instant current can reach decades to several hundred thousand amp,instantaneous induced voltage can achieve decades to several hundred kv, May make the equipment within the stuctures suffer the lightning counter-attack or the destruction of induction overvoltage.especially electronic equipment. Therefore lightningproof grounding system must also make building equipment has pressure, equipotential and multi-layer shielded lightning protection structure. In the entire building grounding system design, make lightningproof grounding system design should be in the first place, and based on lightningproof grounding within the building and in the same time make the equipment work grounding and protect the grounding system, give people to create a safe environment.
Work grounding , its function is to essure the electrical equipment within the
building can work normally ,need earthed system, work grounding can be divided into exchange work grounding grounding and dc work grounded. The exchanges in residential construction work within an ac ground is a low-voltage distribution system in power transformer neutral point (independent substation) or introducing building the ac power neutral wires directly grounded, thus making the electrical equipment within the building won 220/380V normal and stable working voltage. Dc work within the building grounding is to let the amplification of electronic equipment, signal transmission and digital circuits of various gate information to deliver a stable benchmark potential, thus make structures within the elv systems can stable work normally.
Protect grounding refers to protect the person within the structures from indirect contact with electric shock (i.e. distribution lines and equipment in the ground fault cases occurred in the shock) and when earthing fault cases for avoiding metal shell arising between unshaven potentials of fires. When distribution circuit meet earthing fault,it will generate enough ground-fault current distribution circuit, the protection switch rapid action, thus removed fault circuit power in time to protect purpose. However, in some cannot be removed in time the place, fault circuit power grounding potential protection measures adopted to realize its protection.
2the attentive matters In the design of high-rise building grounding system The neutral-point earthing ways of high power system mainly divided into two categories: : direct grounding and not grounded.Direct grounding system have a low safety ensurrence because this kind of system safety low when one-phase ground fault happens in neutral, then place and will form the loop, thus grounding phase short-circuit current will be very high. No grounding system without the above phenomenon when one-phase ground fault phases, but for the no-fault proster the voltage will rise as that of the square root of three times and require electrical insulation level, In voltage high system, raise the level of insulation will make the cost incresse greatly ,so the system commonly adopts high voltage neutral grounding method directly. we should pay attention to the problems occured in the designing of the high-rise building below: 1) due to the high-rise buildings support lighting and
air-conditioning load heavly , such as transport equipment, elevator, water supply and drainage equipment, in the same time the requirements of the reliability to power supply electricity use is high. 2) in high-rise buildings, lighting and power basically don't share route. Dynamic load used more radiation type power supply, lighting load mostly use bar with power distribution, separate from the driving force. 3) with big column on the structure, mostly forming large space, make metope installed equipment, will make the ground pipeline increased the increase.4) because of the construction component prefabricate assembly and dry construction; Shorten the construction period, and ceiling generally uses standardized, systematic condole supports. 5)the electrical equipment pipelines should take precautions against fire. 6) air conditioning equipment mainly electrical equipment, most request centralized management scattered, which requires using computer management and monitoring system. 7) take shockproof measures. 8) fire requirement is high. 9) save energy is a major policy in our country's economic construction and the electricity energy saving is an important aspect of work, it's directly related to the economic benefit of enterprise and People's Daily life.
3 the designing of high-rise building lightningproof grounding system
The lightningproof grounding system design is very important in high-rise building grounding system design.we devide the building to three types in building lightningproof design standard: class a ,class b and class c lightning protection. High civil buildings according to category commonly be the class b lightning protection design, when buildings has explosion danger, should regard as the first lightning protection design. High-rise building lightningproof grounding system is usually made up of terminal equipment ,lead referrals, grounding body and pressure device component ring. General in the ridge, eaves, etc is susceptible to be struck by lightning site installation. All exposed roof metal pipe and metal components should connected with the nearby corona.the terminal equipment should pick up on the roof with lead referral welding connectivity. High-rise buildings should be preferred using led referrals reinforced the coagu-flocculation column rebar with the referral. Using the column diagonal two main cables for referrals diameter steel leads should not be
less than 12mm, Reinforced with steel, lead referrals is used to connect the construction of the binding law connection or welding all can, In buildings around the periphery of the proper position led referrals set up several point for measurement, Connection artificially grounding body and equipotential connection with the proper position of the bottom of the set several for measurement, The grounding body,the reinforce in pillar for equipotential connection should be uniform layout ,The number of leads referral makes no specific provisions, But lead referrals span should not be greater than 18m(usually is 12m). Lead with roofing referrals corona device should be top welding, ends shall be welded with grounding body. This led referral design need many lightning current leak ,save materials, and don't damage the exterior of the building and construction is convenient. Grounding body design is the key, the grounding system of high-rise building grounding body usually use each of the pile foundation reinforcement as natural grounding body, this design can save the project investment, construction is convenient, grounding the effect is good.
4 integrated wiring of highrise building grounding system
Integrated wiring as building intelligent indispensable infrastructure, The stand or fall of the grounding system will directly affect the quality integrated wiring system operation, so is particularly important. According to the commercial building grounding and connection request regulation: integrated wiring system grounding structure including grounding lines, grounding busbar (layer terminals), grounding, Lord grounding main bus (summary), grounding lead to terminals, grounding body rolled six parts in operation, the grounding system design, can press the above six factors to design competency.
(1) the ground
Grounding wire is refers to the integrated wiring system all sorts of equipment and the connection between the grounding bus, so grounding lines are copper wire, its section insulation should not be less than 4mm2. When integrated wiring system USES screened cable wiring, information socket grounding available cable shielding layer as grounding lines even to each layer distribution ark, if the comprehensive wiring cable adopts wear steel or metal trough laying, steel or metal trough should
keep electrical connections, and should be at the ends have good grounding.
(2)grounding busbar (layer grounding terminals)
Grounding busbar is the level of grounding wires in the system wiring of public center, each layer connections cabinets shall the floor with the floor grounding busbar phase welding and grounding generatrix of same wiring all integrated wiring between the metal frame and grounding in with this grounding main bus shall phase welding. Grounding busbar should be copper bus bar, its smallest size should be 6mm thick * 50 wide. Grounding busbar should try to adopt electroplating tin to reduce the contact resistance, if not electroplating, need to undertake handling,before fixed ,
(3) grounding route
Grounding lines drawn by total grounding bus, Grounding wires for Connect ing all the grounding busbar, When we design the grounded lines, we Should fully consider building structure form, The size of the building and building of routing and space configuration, And coordinate lines with integrated wiring cable laying . W hen building use two or more vertical grounding lines,Between vertical grounding lines every three layer and top need and grounding highways section insulation wire phase welding, TongXin conductor grounding lines should be insulated, Section should be no less than the minimum 16mm2,When in line and grounding,if the Grounding potential difference is greater than 1Vrm@S, Floor wiring workshop should connected to the main grounding bus using alone grounding lines
(4) the Lord grounding busbar (summary to terminal)
Normally, each building has a Lord grounding busbar, Lord grounding busbar as the turning point of integrated wiring grounding system grounding main and the grounding wires of equipment,The ideal position should set on exterior lines, or between building wiring, Lord grounding busbar should be decorated in linear path,And considering the Lord from protector of welding wire to grounding busbar shoulds not be too long. all ground between grounding into line, grounding main, dc distribution panel grounding lines, introduced the perimeter. The Lord, and the same wiring between the grounding busbar with all integrated wiring the metal frame should be good welding with the Lord grounding busbar,Lord grounding busbar
should adopt copper bus, its smallest section size for X100mm wide. 6mm thick.
(5)the line for grounding
Grounding into line with grounding bus refers to the connection line between the Lord and grounding body, Appropriate use 40mm wide * 4mm thick or 50 * 5mm galvanized steel Grounding lead referral should do insulating anticorrosive processing,In its place, should have unearthed mechanical damage prevention measures, and inappropriate setwith heating pipe ditch cloth.
(6). Grounding body
There are two kinds of grounding body :natural grounding body and artificially grounding body. When integrated wiring using a separate grounding system, with general grounding body only, then should be the artificial grounding body,should meet the following conditions:
1) The grounding body away from industrial frequency low voltage ac power supply system should be not less than 10m.
2)The grounding body stay away from the building lightningproof system should be not less than 2 m.
3) The grounding resistance should not be more than 40 Ω
When integrated wiring system, adopt combination grounding, On average,if we use reinforcement within Building foundation as natural grounding body, the grounding resistance should be less than 1 Ω. Usually used joint grounding systems in actual application, This is because, compared with the former joint grounding method,it has a few prominent advantages:
a. When the building suffers the thunderstroke, in the floor each spot position distribution quite is even, the staff and the equipment safety can obtain the good safeguard.At the same time, the building portal frame construction provides 10~40dB to the wave electromagnetism field energy the shield effect.
b. Easy to obtain the small earth resistance.
c. Can save metal materials, covers an area of less.