电气专业毕业设计外文翻译--防雷接地

Lightning protection groundingAbstract The significance of lightning p.rotection and mitigation on very little money to prevent large losses, and its function is to use scientific means avoid natural disasters. Grounding is to make the system has been included in the lightning protection lightning energy discharge into the earth, and good grounding can effectively reduce the online guide overvoltage, avoid counterattack. Avoid ground is the most important aspect of technology, whether sings rem, induction lightning, or other forms of ray, ultimately the lightning current into the earth. Therefore, no reasonable and good grounding device is can't reliably the lightning strikes. The smaller the grounding resistance, come loose flow is quicker, lightning objects the time to maintain high potential more short, the less riskKey W ords:Lightning protection; Grounding; Current; potential1 introductionIn recent years, many domestic and foreign standards do not advocate information equipment using independent grounding device, recommend the use of common earthing system. For example, the 2000 edition of the GB50057-94" design code for protection of structures" in point out clearly:" every building itself should adopt common earthing system" to be the buildings within the various grounding are unified to buildings based on, or outdoor grounding device. When the building was hit by lightning, power system voltage and electrical equipment grounding voltage rises at the same time, keep the equipment working voltage constant, so that the electronic equipment from lightning strikes can work normally. Common earthing system usually use the building foundation grounding electrode, the grounding resistance less than 1 ohm in general, if the equipment grounding resistance requirement is lower, should take the minimum value.The ground that has been incorporated into the lightning protection system of lightning energy drain into the earth, good grounding downlead to effectively reduce the voltage on the back, to avoid the occurrence of. In the past some requirements of electro nic equipment grounding alone, the purpose is to prevent stray current and transient current in power network disturbance of the normal work of equipment. Before 90 time, forces of the communication navigation equipment electronic tube device, using analog communication mode, analog communication on particularly sensitive to interference, interference, so will take power and communications grounding separate way. Now, the lightning protection engineering fields do not advocate a separate ground. In the IEC standards and ITU standards are not advocating a separate ground, American Standard IEEEStd1100-1992more sharply pointed out: not recommended the use of any kind of so-called separate, independent,computer, electronic or other such incorrect ground as equipment grounding conductor of a connection point. Grounding is the most fundamental aspect of the lightning protection system. The ground is not good, all the measures of lightning protection effect can play. Lightning protection grounding is ground communication stationCode for construction and acceptance of the basic safety requirements, the grounding of PLC belongs to a low-voltage electrical equipment of single point grounding modeLow voltage electrical equipment of single point grounding mode can be divided into: tandem type single point grounding, parallel type single point grounding, multiple branching of single point grounding.2 single point grounding methodTandem type single point grounding: or first grounding ways. Method : the number of low voltage electrical equipment grounding terminal equipment with the same root near the ground wire connecting, then through this grounding and grounding device. The grounding system is: save manpower, material resources; while the disadvantage is that: when the public grounding line open circuit, if the grounding system has a device leakage, can cause other equipment which occurred on voltage, a threat to the safety of personnel.B ackup ground terminal introducing a grounding line, and then the number of lines at the same time received a grounding device. The grounding system is: when the grounding system in which a device grounding wire broken circuit, will not cause other equipment enclosure voltage, to ensure personal safety. This grounding mode is: if it is not perfect on the interference of high frequency electronic equipment or other highly sensitive electrical equipment, high frequency interference from other devices ( such as converter, intermediate frequency stove thyristor converter parts) will be from the common place of string, causing the device is not working properly.Multiple branching of single point grounding: or third grounding ways. Grounding method: each equipment grounding terminal alone received a grounding device. Earthing method and second kinds of grounding is the difference: the device has a separate grounding body ( or a change of: received directly from the grounding body recent grounding device ( or grounded source office ), each device in the electrical ground loop on the distance is far more (for example, more than 50meters ) ). This effectively avoids the mutual electrical equipmentMagnetic interference.But this grounding mode time-consuming, laborious and separate grounding the source is not good for.In the usual construction, in fact the grounding of PLC way adopts the second grounding ways, as for electromagnetic interference: if the cabinet is provided with a plurality of high power frequency converter, can be in the PLC power supply is installed in front of a single-phase power filter can be, generally designed in the inverter PLC near the front end are equipped with power supply filter.The interference effect of DC and AC equipment, can be connected together -- even if the DC and AC circuits because of some reason connectivity, because they are not the same as a loop ( grounding is not part of the loop ), will not cause damage to the equipment. People have AC220V power and DC24V circuit connected to it, but the equipment work remains normal.Digital and analog ground suggested separately ( unless you're a low-voltage electrical equipment power supply voltage only a few tens of volts ), because the digital circuit belongs to positive and negative 5V,12V,24V level, are vulnerable to interference, and once the external abnormal voltage once the series will very possible equipment damage. I just go to work in the factory has a 1000 tons of SACMI press, because other equipment and digital ground causes the electronic facilities burned down last several times, Italy sent technicians ( just graduated from secondary school students ) and replacement equipment, conductor of the in situ dug a pit, buried a piece of ground the brass and the earthing filler, engage in a separate grounding.3 Lightning proof grounding device for part of a concept(1) Lightning receiving device directly or indirectly accept the lightning rod ( flash ), such as lightning, lightning protection zone ( net ), overhead ground wire and arrester. (2) lead: for the lightning current from the lightning arrester is conducted to the grounding conductor.(3) grounding: electrical equipment, tower grounding terminal and a grounding body or the zero line connected with the normally not current-carrying metal conductor.(4) grounding body ( polar ): buried in the soil and directly touch the earth metal conductor, known as the grounding body. Divided into vertical grounding electrode and level of grounding body.(5): grounding device grounding and grounding. (6): grounding grid by vertical and horizontal grounding body composition having discharge and pressure equalizing function network grounding device. (7): grounding resistance of grounding body or natural grounding resistance to the ground of the sum, a grounding device resistance, its value is equal to the grounding device of voltage to the ground and through the grounding body into ground current ratio. At the same time the grounding resistance of grounding device is a constant level indication.4 The grounding device is easy to corrosion location mainly(1) equipment grounding downlead and connecting screws; (2) each welding head; (3) cable channel equalizing zone; (4) the horizontal grounding body,Anti corrosion measures,grounding body using copper, copper clad steel earth body or hot galvanized materials; welding brush asphalt paint or powder coating; use of cathodic protection.One, ground resistance test requirements: a. AC grounding, grounding resistance should be less than4 ohm; b. Safety grounding, grounding resistance should be less than4 ohm; C DC grounding, grounding resistance should be according to the computer system specific requirements determined; lightning protection to D. Grounding resistance should be less than10 ohm; e for shielding system if the joint grounding, grounding resistance should not be greater than1 ohms.Two, ground resistance tester ZC-8grounding resistance meter is used for measuring the power system, electrical equipment, lightning and grounding resistance value. Also measuring low resistance conductor resistance and resistivity of soil.In three, the instrument by hand generator, current transformer, a slide wire resistor and galvanometer etc., all arranged in the plastic shell body, and the shell is convenient for carrying. Accessory auxiliary probe wires, installed in the accessory bag.The working principle of the voltage comparing type.I n four, before use to check whether the complete tester, tester comprises the following device. In 1, ZC-8 type grounding resistance tester, a2auxiliary grounding rods two root of 3,5m,20m,40m wire aGround resistance tester, usually hand ZC-XX series, including a short black lines, a20M line, a40M line, testing line connected at one end of a tested object whose the other end is connected with a shake table on each of two short connecting terminals, and the remaining 2terminal 20M line with P terminal,40M line C terminal to terminal, after the 20M and 40M line according to the ribbon (that is, to shake table for the endpoint of a triangle ) or linear completely out, hit good probe. In the shake table select file and then to 120RPM speed swing table, side table edge with a shake shake table can dial0, until the pointer on a shake table center scale 0, with stalls multiplied by the dial corresponding numerical result this grounding grounding resistance.Wire grounding is an important electrical safety technical measures, the operation should be serious, serious, comply with the requirements of technical specifications, must not be careless. Therefore, correctly use the ground, normative hanging, remove grounding behavior, consciously cultivate rigorous safety work style, improve their awareness of safety, to resistthe danger from thousands of miles away, in order to avoid the ground causes electrical accident.A ccording to the practical work, ground use should pay attention to the following matters.1work must be checked before grounding wire. Soft copper wire is broken, the screw loose connections, hook line stretch is normal, do not meet the requirements should be replaced or repaired before use.2 hanging wire must be a priori power, not checking cable grounding is the base of common habitual violations, in suspension when the grounding body and physical contact.3 in the work place two segment ends hanging earthing, lest the user would send electric, induction electricity, suffer a number of examples.4 in the play ground pile, you should dial can borrow to physical fast dredge accident current, grounding the quality guarantee.5to protect the earth. Grounding wire in use in the process may not be twisted, should not soft copper wire wheel, grounding in removed, not from the air leaving or anywhere to fall, use rope transfer, pay attention to ground cleaning work.6new staff must go through ground wire using the training, learning, after passing the examination, can the individual engaged in ground operation or use of the work.According to the different voltage levels corresponding to7specifications of the grounding wire selection.8prohibited the use of other metal wire instead of grounding wire.The 9 grounding wire has two sides, it has a safety function, improper use will produce destructive effect, so after work to timely removal of ground wire. With the earthing switch may damage electrical equipment and the destruction of the power grid stability, can lead to severe malignant electric accident.10field work not less hanging earthing conductor or alter the articulated ground location.5 Lightning protection system construction methods and technical measuresLightning protection system grounding engineering major required close coordination, interspersed with civil completed. In civil unit beam, column and reinforced structure modeling is to follow up the grounding body ( line ) of the lap welding and grounding lead welding. In order to prevent the welding fault leakage, during each lightning protection on the ground ( body ) after welding, are on the main reinforcement is painted in eye-catching mark, for the benefit of a layer.Wire, mesh welding.Lightning protection construction methodAccording to the design institute to provide the drawings, using the foundation steel (including pile steel mesh cage bars ) as the lightning protection and grounding, using column within 2main bar as lead, using concrete foundation beam reinforced bar as electrode connection, use of roof beam reinforcing steel bar and reinforced parapet coping as dark installed lightning protection belt.Flank-Striking lightning protection construction method:1straight buried metal pipes and metal top and lightning protection device.2into the building of buried metal pipeline, roof all the metal pipeline and its structure also and lightning protection device.3note that in the construction of grounding body ( line ) of the lap length must comply with the following provisions:3.1flat to2 times its width ( and at least 3edge welding);3.2bar is connected by double lapped continuous welding of , weld length not less than 6 times the diameter, good weld appearance;3.3round steel and flat steel connections, its length is6 times the diameter of round steel;3.4flat steel and steel, flat steel and angle steel welding, in order to reliable connection, except in the contact area on both sides of the welding, and welding to steel bent into arc ( or angle ) clips or directly by the strip itself curved surface arc ( or angle ) and steel ( or angle ) welding.3.5 exposed lightning strip galvanized special clamping support code support, avoid the support member and lightning belt welding.3.6steel pipe for lightning protection grounding device (including needle, etc. ), tube wall thickness not less than2.5mm. The butt welding of the tube, pipe is provided suitable liner pipe diameter. And connecting pipe diameter dovetails, lining length not less than4 times the outside diameter.From3.7in the first layer of ground1.51.8m leads to easy operation and maintenance of the permanent test. Test points are obvious grounding mark and reliable and anti-corrosion measures.The 3.8grounding resistance should be performed to detect, plus or minus 0part test point were tested individually, + 0above part can use test point of each of the three layer is a detection, i.e. each completed a lightning arrester grading ring or band is installed you can use e lectrode leading-out wire of a test work. The grounding resistance measurement requirements of less than 1ohm.6 Lightning protection engineering construction quality defects and Its CountermeasuresRoofing exposed metal pipe and equipment and component without lightning protection connection, or the connection does not meet the requirements, there is the potential for harm of thunder and lightning.Construction countermeasures:1strictly implement the" design code for protection of structures" ( GB5005794) concerned regulation, ensure the impulse grounding resistance to meet the requirements.The 2connecting leads not directly in galvanized steel pipe welding, suitable for welding or bolt connection in the special grounding wire card ( or metal pipe bracket ).The 3lightning protection connection lead should be concealed, grounding bar welding not fusion, resulting in effective contact area is reduced, the lightning will fuse risk.Construction countermeasures:Construction should pay attention to the appropriate electrode angle, swing, pay attention to the melting of lap joints on both sides.,Earthing and equipotential connection:1 all electrical equipment metal shell, frame, line pipe, cable bridge must have good ground, make it a good grounding path.2used for outdoor grounding bar welding length not less than 6times the diameter of round steel, flat steel two surface welding; the connection between the flat width for2 times, three surface welding; round steel and flat steel bar connection for6 times, two surface welding.3potential galvanized round steel welded beam in foundation of the main grounding bar, and small ground lines are connected, in the connection equipotential box galvanized plate, welding seam must be full. Indoor draught to the equipotential box is connected with the circuit to be connected is complete, the grounding wire specifications of not less than 4mm2, and ensure reliable contact.4 ground connection of all welds must oil antirust paint two times ( with the exception of concrete structure welding ); galvanized grounding bar, flat steel in the underground buried depth should not be less than0.8m.7 Importance of grounding and lightning grounding resistance testingLightning protection and grounding technology,In order to solve the communication network (including the user terminal ) overvoltage protection for the purpose, has developed a variety of lightning protection and grounding technology, these are to ensure the reliability of telecommunication network technology, is the important basic technology in the field of communication. Now commonly used by telecommunications building integrated earthing( grounding ) and introduces a variety of lightning protection device. But, now has access to the optical fiber communication era, even in the communication network of the user terminal, at the same time, and connected to an AC power line, at the user terminal using the large scale integrated circuit is more and more, the new features of the lightning protection and grounding, raised new requirement, we must try to adapt to these new characteristics.Grounding resistance test technology.In recent years, because of digital technology and the development of optical communication technology, so that the original installation in a telephone exchange part of the exchange, transmission equipment to the user mobile, and often these devices are mounted to the general residential buildings and overhead, so ask them with the telephone exchange room floor with.The shielding effect, it is obviously not possible, then how to do? Now hand requires these devices improve the adaptability, on the other hand, in order to prevent the leakage of electricity and lightning voltage on human body and equipment hazards, gro unding and lightning protection is vital.From the grounding purposes, especially for outdoor equipment grounding, leakage current and lightning protection is particularly important. The grounding resistance requirements, technical standards are clearly defined, it is. In order to ensure that the grounding resistance value to meet the requirement, after construction of the grounding resistance testing work is very necessary. But with the progress of the modernization of city, now the city roads and sidewalks are all concrete pavement asphalt pavement or covered now, if still use auxiliary electrode method to test the ground resistance, it is difficult to too much. The new ground resistance test method are introduced.In 1, the existing ground resistance test method.Wire grounding resistance is equal to the grounding electrode potential and the injected current ratio. The current earth resistance test method, as shown in figure 1. Where E is the grounding electrode, C is injected into the current of the auxiliary electrode, P is to test the potential of the auxiliary electrode imaginary reference point. Test, signal device in the E ~ C electrode with500 ~ 2KHz AC current by the dotted line into a flow, a current meter and a voltage meter readings, we can find the grounding resistance value.In order to test the value of accurate, the distance between the electrodes shall be not less than 10meters. The distance, in the downtown area of the city, is often difficult to do.防雷接地摘要防雷减灾的意义在于用很少的钱预防大的损失，其作用在于使用科学的手段规避自然灾害。