Analysis on lightning protection and grounding of

2022-08-23
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The intelligent control technology of instrument and control system lightning protection and grounding can be said to be the most important and critical software resource in the measurement and control system. Electrical engineers must see it

[Abstract] electrical engineers must see the analysis of lightning protection and grounding of instrument and control system

I. overview of surge protector grounding

1. Name of surge protective device

surge protector is also known as surge protector or surge protective device. It is a device that contains at least one nonlinear voltage limiting element to limit transient overvoltage and shunt surge current. During normal use, the power supply and signal can pass unimpeded basically. When the surge of abnormal overcurrent and overvoltage occurs in the circuit, the surge protector will automatically start quickly to discharge the surge current and prevent it from entering the equipment, so as to achieve the purpose of protection

the origin of the name of surge protective device or surge protective device varies with the understanding of domestic standard and specification preparation units and individuals on translation and application occasions

2. Development of lightning protection

in the past 10 years, the attention and application of lightning protection in the petrochemical industry have mushroomed, forming a wealth of standards and specifications, which are used to guide lightning protection projects. However, there are differences and differences in grounding methods between some standards and specifications, which will cause confusion that there is no unified grounding method

3. The setting of surge protector

lightning protection works mainly include:

1) meet the lightning protection grade requirements determined by lightning protection zoning and classification

2) equipotential bonding and grounding protection measures should be taken

3) adopt shielding and reasonable wiring measures for instruments, control systems and cables

4) appropriate surge protectors should be adopted according to the actual application. The setting of surge protector is only a part of lightning protection project

4、 Standard specifications mainly used in lightning protection engineering

GB 15599 code for safety of petroleum and petroleum facilities lightning

GB 18802.1 surge protective devices (SPDs) for low voltage distribution systems Part 1: performance requirements and test methods

GB 18802.21 low voltage surge protective devices Part 21: surge protective devices (SPDs) for telecommunications and signal networks ----Performance requirements and test methods

GB 18802.22 low voltage surge protective devices Part 22: surge protective devices (SPDs) for telecommunications and signal networks Guide for selection and use

gb/t 19271.3 protection against lightning electromagnetic pulse Part 3: requirements for surge protective devices

gb/t 21714.1 lightning protection part 1: general provisions

gb/t 21714.4 lightning protection part 4: Electrical and electronic systems in buildings

gb 50057 code for design of lightning protection of buildings

gb 50343 technical code for lightning protection of electronic information systems in buildings

sh/t 3164 Petrochemical instrument system lightning protection engineering design Design specification for instrument system grounding

hg 20513

iec 61312 International Electro technical Commission, protection against lightning electromagnetic impulse

iec 62305 International Electro technical Commission, Protection against lightning

ul1449 UL -- underwriter Laboratories Inc., surge protective devices

ieee (c62.41), IEEE -- Institute of electrical and electronic engineers, Recommended Practice on surges in low voltage AC power circuits

II. Lightning protection and grounding of control system

1. Lightning protection measures for power lines

1) overhead lines should not be used for power lines entering and leaving the computer room of electronic information system

2) when the electronic information system equipment is powered by TN AC distribution system, the distribution line from the main distribution cabinet (box) in the building must adopt the grounding form of TN-S system

3) the impulse voltage rating UW of the equipment in the distribution system is selected according to table 1

Table 1 impulse voltage rating of various equipment in 220v/380v three-phase distribution system UW

4) the installation of surge protectors for distribution lines of electronic information system equipment is generally divided into three levels, the first level is installed in the low-voltage main distribution board (lpz0a or lpz0b at the junction of lpz1), the second level is installed in the front end of ups and the power distribution box of information system, and the third level is installed at the power incoming line of information equipment

5) the first level surge protector should be set as voltage switching surge protector or voltage limiting surge protector; The second and third level surge protectors shall be equipped with voltage limiting surge protectors

6) the voltage protection level up value of the surge protector shall be less than the impulse withstand voltage UW of the protected equipment

7) the maximum discharge current Imax shall not be less than 2 times the nominal discharge current in

8) the impulse current IIMP of the surge protector of the power line, so we are also constantly strengthening the competitiveness of this base or the recommended parameter value of the nominal discharge current in should comply with the provisions of Table 2

Table 2 recommended parameter values of impulse current IIMP or nominal discharge current in of power line surge protector

9) when providing power to electronic information equipment installed in the open air, surge protector shall be installed at the site power inlet and equipotential connection shall be carried out. AC power surge protector implements the third level SPD protection parameters in Table 2, and DC power surge protector implements the SPD protection parameters in Table 2

10) the connecting wire between the surge protector and the power line should be straight, its length should not be large, and it should be perpendicular to the axis of the sample by 0.5m. When the length of the line from the voltage switching surge protector to the voltage limiting surge protector is less than 10m, and the length of the line between the voltage limiting surge protector is less than 5m, a decoupling device should be installed between the two-level surge protectors

2. Lightning protection measures for process control system

1) surge protectors should be installed at both ends of analog signal, pulse signal and communication signal circuits between different buildings and outdoor places

the SPD of the signal line shall be connected to the signal port with the initial distance between the clamps corresponding to the marking distance in the standard of the protected equipment within 80 ~ 115mm. The SPD output end of surge protector is connected with the port of the protected equipment. SPD can also be installed in the cabinet and fixed on the equipment rack or nearby supports

2) the SPD grounding terminal of the signal line surge protector should be connected with the local equipotential grounding terminal board in the equipment room with a copper core conductor with a cross-sectional area of not less than 1.5mm2, and the grounding wire should be straight

3) the performance parameters of the signal surge protector of the process control unit (PLC or RTU) shall meet the requirements of Table 3

Table 3 requirements for performance parameters of signal surge protector

note:

1) UOC is open circuit voltage, ISC is short-circuit current

2) in lpz0b area, surge current test with waveform of 8/20 s (class II test) or appropriate combined wave test (Class III test) can be used to simulate induction effect

3) in the area of lpz1 and lpz2, the induction effect can be simulated by surge current test with waveform of 8/20 s (class II test) or appropriate combined wave test (Class III test). For switch SPD, it is necessary to consider that the previous SPD triggers a 10/350 s surge applied to the suffix SPD

3. Surge protector grounding

the surge protector is connected in series between the protected equipment and the signal transmission line, and should be installed close to the end of the protected equipment. The grounding of the protected equipment should be connected to the main grounding of the station through the surge protector grounding guide rail. See Figure 1 for the grounding principle of surge protector

Figure 1 grounding schematic diagram of surge protector

the signal SPD installation guide rail in the control room is grounded, and the guide rail is reliably connected with the working ground busbar in the cabinet through 16mm2 multi strand copper wire

for the signal SPD not installed through the guide rail at the side of the control room, its grounding wire should be reliably connected with the working grounding busbar in the cabinet, and the length of the grounding wire should not be greater than 0.5 m

see Figure 2 for the grounding connection of surge protector in the cabinet:

the above content is: analysis of lightning protection and grounding of instrument and control system, which must be seen by electrical engineers! For your reference only. For more free information, click free download>;>;>; Electrical engineer test questions/test site essence

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