【導讀】附錄B樓宇的電氣保護與接地......

　　

【正文】 mon get a equipotential benchmark and other measures, so TN C S system can serve as a kind of intelligent building grounding system. 3. TN S system TN S is a threephase fourwire add PE line grounding system. Usually buildings which are equipped with independent transfering amp。transforming when using this system into line. TN S system characteristics are, neuter line N and protection in PE except transformer neutral point mon ground outside, two lines and no longer have any electrical connections. Neuter line N is charged, and PE line not charged. This grounding system has all the safety and reliable benchmark potential. Just like TN C S grounding system, take the same technical measures, TN S system can be used as intelligent building grounding system. If the puter and other electronic equipment without special requirement, generally use this grounding system. 4. TT system Usually says TT system for threephase fourwire grounding system. This system is used for building the place from public power supply. TT the characteristics of the system 畢業(yè)設計 24 is neutral grounding wires with protection line N no point electrical connections, PE neutralpoint earthing and PE lines that separate grounding. This system in normal operation, no matter when unbalanced threephase load balance in neutral wires N charged cases, PE line won39。t charged. Only when onephase ground fault protection grounding sensitivity low, because cannot promptly, fault can cut off, equipment shell TT system normal operation similar to TN S system, also can obtain the safety of people and things and getting qualified benchmark grounding potential. With the capacity of the emergence of leakage protector, the system would also more and more as intelligent building grounding system. According to the current situation, because of public power grid power quality is not high, to meet the requirements, so intelligent equipment by intelligent building systems rarely TT adopt. 5. IT system IT system is threephase threewire grounding system, this system of transformer or by impedance ferroresonance, no neutral ground, only line voltage wire N (380V), no photograph by pressing (220V), the protection of ground wire PE independent grounded. The advantages of this system is when a connect, doesn39。t make the crust with a larger fault current system can run as usual. Defect is can39。t match the neuter line N. So it is not applicable to have large of the intelligent building singlephase equipment. In intelligent building, demanding grounding within very much, have the equipment specialized equipment, extralow equipment, and some does not normally charged of conductive equipment and ponents, all must adopt effective protection grounded. If using TN C system, will TN C system of N line also used as grounding lines。 Or in TN S system with PE line will N line connected together with, again connected to the motherboard up。 Then or not setting electronic equipment, and the dc grounding leads to dc grounding directly to the PE online。 Some simply put N line, PE line, dc grounding wires connected together with practices are not accord with grounding requirements, and is wrong. It has already been analyzed, in intelligent building, many devices and singlephase singlephase power greater proportion, threephase load load is often not balanced, so in neutral wires N with random current. In addition, because of using fluorescent lighting, its produced three times in N online, the harmonic superposition of increased N online, if will N electrical flow line received equipment enclosure, can cause shock or fire accident。 If in TN S system will N line together with PE line again, receiving equipment who received more dangerous, the equipment, the shell PE 畢業(yè)設計 25 online are charged。 Will expand the scope of electric shock accidents。 If will N line, PE line, dc grounding lines are connected together with the dangerous except happen outside, electronic equipment will be disturbed and cannot work. So intelligent building shall set up electronic equipment, the dc grounding munication grounding, safety protection grounding, and ordinary buildings also should have the lightning protection grounded. In addition, because more inside of intelligent building with requires antielectrostatic programcontrolled exchange room,Computer room, fire and fire alarm monitoring room, as well as a number of vulnerable to the electromagic interference, so precision electronic equipments in intelligent building design and construction, still should consider antistatic grounding and shielding grounding request. And then, we then analyze intelligence building should adopt the earthing measures. 一、 Exchange work grounding: somewhere in power system, directly or through special equipment (such as impedance, resistor etc) and the earth for metal connection, called work grounded. Grounding refers to the work transformer neutral point or neuter line (N line) grounded. N line must use TongXin insulation line. Existing in the distribution of terminal blocks, auxiliary equipotential potential terminals on the box normally enclosure. Must note, this terminals can39。t exposed。 Can39。t and other grounding systems, such as dc grounding, grounding screen, antistatic grounded mix meet。 Also can39。t connect with PE line. In high pressure system, adopt neutralpoint earthing ways can make the grounding relay protection accurate movement and eliminate singlephase grounding overvoltage of arc. Neutralpoint earthing can prevent the zero sequence voltage offset, maintain threephase voltages for the basic balance, lowpressure system is very meaningful, can ease of use singlepha