Theory of petrochemical instrument system lightning protection system # 3 - — The basic principles and measures of protection of lightning protection instrument equipment

Read through the above two articles, we type of lightning for violations of the instrument system have probably understanding, and sorted out for lightning protection grounding method types, this chapter we'll for what some of the appropriate measures for lightning protection. For the control measures of instrument system are various, mainly including flash, equalizing, shunt, grounding and shielding, etc. Must be integrated use of these measures, can we truly achieve the instrument system of lightning protection. Petroleum enterprise instrument system lightning protection measures should be taken is mainly from the following several aspects to consider: 3. 1 flash should be according to the instrument control system, the structure of the control room and field devices and other related factors, comprehensive lightning protection measures. Automatic control system of lightning protection, such as the field instruments should be around the lightning protection measures such as process equipment design together, and according to the actual situation of considering joint ShanQi category ( The lightning rod, lightning protection belt or lightning protection network) 。 3. 2 all pressure to prevent the transient current flows through a conductor and its surrounding counterattack discharge between metal objects, cause the damage of the instrumentation equipment, interfere with the normal operation of the instrument control system, through the lightning protection shall be protected areas of the ground of the instrument control system control room metope, instrumentation, equipment, pipeline, such as processing equipment for equipotential connection, and with the instrument control system connected to the grounding system of the control room, to form a more perfect equipotential connection. 3. 3 grounding earthing is an important application in lightning protection measures, should fully consider various factors, make the grounding system can ensure the electric potential gradient is small, as far as possible to achieve the effect of equilibrium potential. For floating, multipoint earthing grounding measures, such as in case of strong lightning, due to the instrument or DCS equipment enclosure protection grounding, instrument and DCS equipment between shell and the internal circuit will form a high potential difference, the two gap insulation breakdown, damage to the circuit. Therefore, you can connect protective grounding and work, and access the lightningproof grounding system. The current domestic oil chemical instrumentation system there are two main types of grounding measures: float, multipoint earthing. If the system of communication & other; Work & throughout; 、“ Sites throughout the &; And & other Lightning protection throughout the &; Are installed respectively, each connection, form a system, called & other; Separate grounding systems & throughout; 。 The prominent advantage of grounding method is can nearby ground, ground wire of parasitic inductance is small. But if strong thunder electric wave through sites into the system, electronic circuit will also damage due to bear high pressure. If the three merger in together, forming a unified grounding system, it is called a & other; Fellow grounding system & throughout; 。 Fellow grounding system eliminates the different ground there may be a potential difference, in the case of lightning, can better suppress discharge phenomena happened between different ground. 3. 4 block due to chemical instrumentation automation control system USES a large number of semiconductor components, integrated circuit and the power, signal transmission cables, the shielding of instrumentation and control on the spot, therefore, should not only consider the direct lightning strike damage, also should consider the influence of lightning electromagnetic pulse produced by radiation. Lightning transient electromagnetic pulse radiation can be made directly to these components, can also be on the power supply or signal cable induced transient overvoltage wave, along the cable loop into instrumentation equipment, and instrumentation equipment damage. By using shield attenuation or stand in the way of electromagnetic pulse energy transmission is a kind of effective protection measures. Lightning shielding instrument automation control system mainly include the following three aspects. 1) Shielding field instruments field instruments lightning shielding is realized by using the instrument protection metal box, instrument protection box access the lightningproof grounding system. 2) Control room shielding instrument automation control system control room for lightning electromagnetic pulse generated by the strong sensitivity. Therefore, to deal with the instrument control room wall steel structure node in electrical connection, constitute the shielding cage, and in a circle around the indoor along the wall to do grounding protection ring, at the same time grounding ring and the electrical connection in the shielding cage should be effective, after the lightningproof grounding system access. 3) Signal circuit and power supply circuit shielded to prevent lightning electromagnetic pulse in signal circuit or power back to the road induced transient overvoltage, all of the power supply circuit and signal circuit should be used with a metal shield cable. At the same time because of the shielding layer multipoint earthing will be at the core of the cable and suites produce low-frequency interference, therefore can only adopt single point grounding along the shield. Therefore, the power supply circuit and signal circuit should use double shielded cable, its shielding layer can be used in a single point grounding, the outer shield can be used in a multipoint earthing. 3. 5 shunt due to welding flash, mainly through the shunt and induction lightning current release in two ways, so by setting the reasonable number of lightning protection downlead, shunt after lightning rheological small, thus will occur back flashover and the influence of induction fell to a low. 4. Conclusion in petrochemical enterprise in the future construction of instruments, the construction and acceptance shall be strictly in accordance with the standards of acceptance specification for construction of the instrument to carry out, check and acceptance, ensuring high quality of each link operation, enhance the entire instrument system the conductor of the conductive effect, in order to reduce the possibility of lightning damage occurred. The escort for the enterprise's safe production. ( In this paper, published by the embellish of instrument science and technology co. , LTD. )