Electrical Protection Of Intelligent Building And Earth.doc

桂林电子科技大学毕业设计（论文）报告用纸 第 15 页 共 15 页编号： 毕业设计(论文)外文翻译（原文）学 院： 机电工程学院 专 业： 电气工程及其自动化 学生姓名： 黄潇毅 学 号： 0800120115 指导教师单位： 机电工程学院 姓 名： 张彤 职 称： 副教授 2012年 05月25日Electrical Protection Of Intelligent Building And EarthYang Yi, Senior Member, IEEEAbstractThis article through introduced to several kind of power supplies earth system summary that, screens suitably took the intelligent building the power supply earth system, and to each kind of earth measure which its should adopt has given a more exhaustive explanation and the analysis, should adopt the electrical protection and the earth method to the intelligent building put forward the suitable proposal. Keyword: Power supplies earth system; The power supply earth system; Electrical protectionIn the construction commodity supply power distribution design, the earth system design holds the important status, because it relates to the power supply system reliability, security. No matter which kind of building, always contains in the power supply design has the earth system design. Moreover, along with building request different, each kind of equipment function different, the earth system corresponding is also different. Enters after especially for the 90s, the massive intellectualized building appearance docking system design proposed many new contents. In the commonly used several seed grafting place in the formula, which one kind can suit the intellectualized building? We might as well analyze one after next surface several seed grafting systems.1. TN - C system TN - C system was called the three-phase four systems, this system neutral axis N and protective earth PE combines, is generally called the PEN line. This seed grafting system although docks the breakdown sensitivity highly, the line economy is simple, but it is only suitably used in the three-phase load balanced place. In the intellectualized building, the single-phase load accounts for the proportion in a big way, realizes the three-phase load balance with difficulty, the PEN line the circulating current does not add on in the line to exist because the fluorescent lamp, the crystal transistor (silicon-controlled rectifier) and so on the equipment causes the higher harmonic current, in the non- breakdown situation, can superimpose on neutral axis N, causes the neutral axis N voltage undulation, also when electric current big when is small is extremely unstable, creates the neutral point earth electric potential not stably to drift. Not only can cause the equipment outer covering (with PEN line connection) charged, creates to the person not safely, moreover also is unable to take to an appropriate electric potential reference point, the sophisticated electronics are unable the accurate reliable movement. Therefore TN - C earth system can not take the intellectualized construction the earth system.2. TN - C - S systemTN - C - S system is composed by two earth systems, the first part is TN - C system, the second part is TN - S system, divides the contact surface in the N line and the PE line junction. This system uses generally in the building power supply the place which brings in by the region transformer substation, in front of the buyer uses TN - C system, the buyer place makes the repetition earth, after the buyer turns TN - S system. TN - in front of the C system has made the analysis. TN - S system characteristic is: Neutral axis N and the protection meets grounding PE after the buyer earths together, cannot again have any electrical connection. In this system, neutral axis N often can charged, protects meets grounding PE not to have the electricity the origin. PE line connection equipment outer covering and steel work when system normal operation Can not throughout charged Therefore TN - S earth system obviously enhanced the human and the thing security .At the same time so long as we adopt the earth lead wire. Each one all from meets the terrain to draw out, And the choice correct earth resistance value causes the electronic installation to obtain measure together and so on an equivalent reference point, Then TN - C - S system may take the intelligence building a seed grafting system.3. TN - S system TN - S is three-phase four adds the PE line the earth system. In the usual building is equipped with independently changes when the substation the coil in to use this system. TN - S system characteristic is outside, neutral axis N and the protection meets grounding PE except to earth together in the transformer neutral point, two no longer have any electrical connection. Neutral axis N is charged, but PE line not charged. This earth system has safe and the reliable datum electric potential completely. So long as looks like TN - C - S earth system, takes the similar technical measure, TN - S system may serve as the intelligent building the earth system. If computer and so on time electronic installation not special request, all uses this seed grafting system generally.4. TT system The TT system is Usually called the three-phase four earth system. This system commonly used the place where the power comes from the public electrical network. The TT system characteristic are neutral axis N and the protection meets grounding PE not to have an electrical connection, namely the neutral point earth and the PE line earth is separated. This system when normal operation, no matter the three-phase load balance is not balanced, in the neutral axis N charged situation, the PE line cannot charged. When single-phase earth fault, because protective earth sensitivity low, the breakdown cannot promptly shut off, the equipment outer covering only then is possible charged. Time the normal operation TT system is similar to TN - S system, also can obtain the human and the thing security and obtains the qualified datum earth electric potential. Along with the large capacity leakage protector appearance, this system also can more and more take the intelligence building the earth system. Is not in light of the present circumstances high as a result of the public electrical network power source quality, satisfies the intellectualized equipment with difficulty the request, therefore the TT system is short very much by the intellectualized building use.5.IT system The IT system is the three-phase three earth system, this system transformer neutral point does not earth or after the impedance earth, does not have neutral axis N, the wired voltage (380V), does not have only presses (220V), protects meets the grounding PE respective independence to earth. This system merit is works as when a docking, cannot enable the outer covering to have the big fault current, the system may move as usual. The shortcoming cannot match neutral axis N. Therefore it is not suitable in has the massive single-phase equipment the intellectualized building.In the intellectualized building, the request protective earth equipment are extremely many, has the strong electricity equipment, the weak electricity equipment, as well as in some normal conditions not the charged electric conduction equipment and the component, must use the effective protective earth. If uses TN - C system, line with makes TN - C in at the same time the system N meets the grounding; Or system meets in TN - in the S the N line and the PE line in the same place, again connects to the ledger wall comes up; Again or does not establish the electronic installation the direct current earth lead wire, but receives directly the direct current earth PE on-line; Some the N line, the PE line, direct current meets the grounding to mix simply meets in the same place. Above these procedures all are do not conform to the earth requirement, is precisely wrong. Front already has analyzed, in the intellectualized building, the single-phase current collector many, the single-phase load proportion is big, the three-phase load usually was not balanced, therefore has the stochastic electric current in neutral axis N. Moreover, because massively uses the fluorescent lamp illumination, its produces the triple frequency superimposition in N on-line, has enlarged the N on-line amperage, if receives the N line in the equipment outer covering, can create the electric shock or the fire accident; If in TN - S system N line and PE line in together again receive in continually the equipment outer covering, then the danger is bigger, every is receives PE on-line the equipment, the outer covering charged; Can expand the electric shock accident the scope; If the N line, the PE line, direct current meets the grounding to meet in the same place besides can occur the above danger, the electronic installation will be able to receive the disturbance but to be unable to work. Therefore the intelligent building should establish the electronic installation the direct current earth, the exchange working earth, the safekeeping of security earth, and the ordinary construction also should have anti-radar protective earth. In addition, because in the intelligent construction is equipped with has guards against the static electricity request the stored program controlled switching engine room, computation? In the room, the fire prevention and the fire report to the police room, as well as are massive easily the electromagnetic wave disturbance precise electronic instrumentation equipment, therefore in intellectualized building design and construction, but also should consider guards against the static electricity earth and the bonding request。Under, we then analyze various seed grafting measure which the intellectualized building should adopt.1. Anti-radar earth: In order to rapidly inducts the thunder electric current earth, by prevented the lightning damage is called the anti-radar earth for the goal earth. In the intellectualized building has the massive electronic installation and the wiring system, like the correspondence automated system, the fire reports to the police and the fire prevention coordinated control system, the building automated system, the security supervisory system, the office automation system, the closed circuit television system and so on, as well as their corresponding wiring system. From the building which completes looked that, building each roof, the ledger wall, the spandrel wall, in the suspended ceiling is covered entirely nearly by each kind of wiring. These electronic installations and the wiring system belong to the pressure resistance rank to be low generally, guards against the disturbance to request high, most feared receives part which is struck by lightning. No matter is straight strikes, the string strikes, the counter-attack all can cause the electronic installation to receive the varying degree the damage or the serious disturbance. Therefore must be strict to the intellectualized building anti-radar earth design, reliable. The intellectualized building all functions earth, must take the anti-radar earth system as the foundation, and the establishment is strict, complete anti-radar structure. The intelligent construction belongs to level of loads much, should according to level of anti-radar buildings protective measures designs, meet dodging to use needle belt group connecting dodging, evades the mine belt to use 254 (mm) galvanizes the flat steel in the roof composition = 1010 (m) the grid, this grid and the roofing steel work makes the electrical connection, makes the electrical connection with the building column head steel bar, in the down use column head the steel bar, the grid steel bar, the floor steel bar and the anti-radar system connection, outside the wall surface all steel work also should with the anti-radar system connection, the column head steel bar with meet the terrain connection, the composition has the multiple shield the cage shape anti-radar system. Like this not only may effectively prevent is struck by lightning in the damage building the equipment, moreover also can prevent the external electronmagetic interference. Each kind of anti-radar grounding labor frequency earth resistance, should act according to falls when the thunder the counter-attack condition generally to determine. The antimine device like when comes in handy an always counterpoise with the electrical equipment working earth, the earth resistance should conform to its minimum value requirement.2. Exchange working earth: Electrical power system in some, is direct or after the specific installation (for example impedance, resistance and so on) makes the metal connection with the earth, is called the working earth. The working earth mainly refers is the transformer neutral point or the neutral axis (the N line) earths. The N line must use the copper core insulated wire. Has the assistance equivalent binding clamp in the power distribution, the equivalent binding clamp generally in the coffer. Must pay attention, this binding clamp cannot a equivalent pear externally; Cannot with other earth systems, like the direct current earth, the bonding, guard against the static electricity earth and so on to mix meets; Also cannot and the PE line connection. In the high tension system, selects the neutral point earth method to be possible to cause the earth relay protection accurate movement and the elimination single-phase electric arc earth over voltage. The neutral point earth may prevent the zero foreword voltage excursion, the maintenance three phase voltage basic balance, this has the significance very much regarding the low pressure system, may facilitate the use single-phase power source.3. Safekeeping of security earth: The safekeeping of security earth is partially with meets the electrical equipment not charged metal between the terrain to do the good metal connection. Soon in nearby the building current collector as well as the equipment some steel works, connect with the PE line, but strictly prohibits the PE line and the N line connection.In the intellectualized building, the request safekeeping of security earth equipment are extremely many, has the strong electricity equipment, the weak electricity equipment, as well as some non- charged electric conduction equipment and the component, must take the safekeeping of security earth measure. When has not made the safekeeping of security earth the electrical equipment insulation damage, its outer covering has the possibility charged. If the human body touches this electrical equipment the outer covering on possibly to wound by the electricity or to create the life danger. Like chart 6 shows. In the neutral point direct earth electrical power system, the earth short-circuit current passes through the person, the big subcrust current returns to the neutral point; In the neutral point non- direct earth electrical power system, the earth current flows in the earth after the human body, and after the line earth capacitance constitution circuit, these two kind of situations all can create the person to receive an electric shock.When is loaded with the grounding the electrical equipment insulation damage causes the outer covering charged, the earth short-circuit current at the same time along meets the terrain and the human body two circuits has flowed, Id=Id + IR, we knew that, In a parallel circuit, has the inverse ratio through each leg magnitude of current and the resistance size, namely, In the formula: In Id - earth return electric current resultantId - along meets the terrain has flowed the electric current IR - flows after the human body electric currentrR - human body resistance rd - grounding earth resistanceMay see by the previous type, earth resistance smaller, flows after the human body electric current slightly, the usual human body resistance must also flow earth resistance big several hundred times after the human body electric current has met the terrain electric current to be smaller than several hundred times. When the earth resistance is minimum, flows the human body electric current to be equal to the zero nearly. Namely Id Id . In fact, because earth resistance very small, the earth short-circuit current flows the pressure drop which obsolete produces to be very small, therefore the equipment outer covering to the earth voltage is not high. The human stands bumps when the earth touches the equipment the outer covering, the human body withstands the voltage is very low, cannot have the danger.Installs the protective earth installment and to reduce its earth resistance, not only safeguards the intelligent construction electrical system security, effective movement effective action, also is safeguards in the non- intelligent construction the equipment and the personal safety essential method. 4. Direct current earth: In a intellectualized building, contains has the massive computers, the communication equipment and has the computer the building automatic equipment. In carries on the infed information in these electronic installations, transmits the information, the transformation energy, the signal amplification, the logical movement, outputs the information and so on in a series of processes all is fast carries on through the micronormal or the micro electric current, also between the equipment often must carry on the work through the internet. Therefore in order to cause its accuracy high, the stability is good, besides must have a stable electric power supply, but also must have a stable datum electric potential. May use the big section the insulation copper core to take the lead wire, an end with the datum electric potential connection, another end supplies the electronic installation direct current earth directly. This lead wire not suitably with the PE line connection, strictly prohibits with the N line conne