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Two sets of 6500m3 / h air separation plant
Use of DCS system control, put into operation in early 2004. 2004
Between July to August, there have been three times due to a general cessation of induction caused by lightning
Production accidents, and cause the transmitter, on-line analytical instruments and so on more than one instrument
Instrumentation of damage, direct economic loss of more than 20 million yuan. In addition, because
ASU parking, resulting in steel plant was halted and seriously affect the
A long process steel production lines running.
An induction of direct damage by lightning
(1) on-site once a meter is damaged: The main on-site pressure, differential
Pressure transmitter within the circuit board damage.
(2) The second instrument input and output channels damage: mainly
Flow Totalizer output section of the transmission channel, shaft vibration data logging devices
Output channel, the transmission-line analysis instruments as well as the output part of the channel
Part of the DCS analog input channels.
Two causes of damage caused by lightning analysis of induction
211 direct damage induced voltage meter
The air breakdown voltage of 500kV / m, so to puncture the air,
Voltage to reach hundreds of thousands of volts or more.
Nevertheless, the damage to circuit boards do not have charred, burning black phenomenon, says
Out the introduction of over-voltage, and not tens of thousands of volts; Furthermore Waichuan gas path parts
Brass grounding, it is impossible to introduce the gas path from the 10000-volt over-voltage. Therefore,
Can exclude a direct lightning induced voltages caused by damage to instrumentation.
212 from the power supply part of the introduction of lightning damage to instrument
From the site analysis, the entire instrument control system uses a separate power supply
Cabinets, and after the supply by the UPS rectifier voltage regulator controller and transformer to use,
Transformer Output 24V DC power supply voltage to the on-site instrumentation. From the Instrument Control
Power supply cabinet to the control rooms are air-switch control cabinet, UPS with over-voltage
Protection. The inspection of all air switches, UPS over-voltage protection are not
Take any action, but will control the control cabinet power supply board and no damage,
From the analysis shows that there is no strong from the power supply part of the introduction of lightning.
213 to counter potential damage to instruments
Then there any place of grounding resistance, measured by the control cabinet access
Ground resistance is 113Ω and 112Ω, meet the required standard, but all are
Field when the transmitter is installed there is no separate ground, simply by connecting
The bolt and shielded cable to connect the wire mesh layers. The grounding system
Basic components shown in Figure 1.
Figure 1 a basic component diagram grounding system
Assume A transmitter at bolt and shield cables are not reliable with
Then there is the grounding resistance, A Division then flashing lightning current I = 10kA, Ra
= 4Ω, resulting in Ra at the voltage V = 40kV, while in control
System flash R0 Agency had not received mine, grounding resistance is also smaller, R0 Service Electric
Pressure theoretically 0, then Ra and there is a high potential difference between R0;
Similarly, although the Rb missed flash Department of Mines, and Rb Department voltage is also smaller.
Ra at a high but there is potential, the currents generated by larger, can be divided into
Do not follow the control system signal cable diversion, and this current is much larger than
Instrument operating current 4 ~ 20mA, thus causing electrical components of the
Damage.
The analysis found that the damaged equipment, analytical instruments, transmitters, etc.
Are transmission output partially damaged and some of the transmitter release by the right to
After power-up, can return to normal, there are strong currents typical over, leaving
Instrument to enter the work dead-zone. And control system, AI (analog input
Income) channels also have varying degrees of damage, but also show that the channel has been
There is a strong current through a short time.
Are more a result of on-site open-air meter, there is an on-site equipment then flash Lei
Later, there are strong currents into the apparatus, equipment grounding resistance and the higher
Produce high voltage, other instruments of static pressure is almost 0, on the letter
No. voltage cable at both ends there is a big difference, thus leading to higher electricity
Flow. The current through the control system and other instrumentation output channels
Diversion, because too much damage to the instantaneous current the output part of the instrumentation.
Owing to the safety of air separation industry, specificity, when the pressure of other important parameters
Occurred a few exceptions, for the protection of equipment and production safety will be automatically protected
Of parking.
3 of mine-action programs
311 Equipotential
Equipotential bonding is to eliminate strong voltage difference and the sharing of strong currents in the main
To means, can be divided into lightning protection equipotential bonding and electrical safety, with potential
Access. They are to separate the various parts of conductive device connected with the equipotential
Equipotential bonding conductor to do next in order to reduce the lightning or electrical installations under
Failure might arise between these parts of the potential difference. But lightning
Equipotential connection also includes the live conductor is not directly connected, and information
Cable, when there is threatening the potential of wiring insulation and equipment, through
Install surge protection devices (SPD) to achieve transient equipotential bonding, that is, a
Are potential dangers when, SPD moves to reduce the potential difference at both ends.
Both pressure and shunt is lightning over-voltage, over-current spread to the ultimate security
Protect the object channel (power lines and signal transmission lines) to set a ~
3 lightning security device, the front one, two security devices will be mine
Produced by lightning over-current leakage into the ground and over-voltage attenuation,
In order to reduce access to the ultimate object of protection of the lightning intensity, three lightning protection
Safety device for the remaining lightning over-voltage limit of pressure, to ensure the safety of equipment.
Specific implementation options are: in the main control room on the 3 row transmission corridor
Office set up installation equipotential bonding arrangement, as shown in Figure 2. Transmitter
Case, surge protectors and metal components of the earth are connected to the nearest
Equipotential bonding rafts, each row at equipotential connection with at least two
Received a metal hallway, metal walkways can be soldered to the common earthing system,
Equipotential bonding row using 30mm × 3mm square copper bars. Achieve
Gas purity analysis room, main control room of the other potentials, such as the walkway on the
Potential emission extended to the gas purity analysis room, master room, and gas
Body purity analysis room, main control room equipment enclosure grounding, static flooring
Grounding, surge protector grounding, grounding the transmitter case and metal structure
Pieces of ground are connected to the nearest equipotential bonding rafts, and each office
Equipotential bonding row there are at least two connected to the common grounding system.
312 Shield
Set room shielding, wire shielding, equipment or parts shielded
Will reduce the electromagnetic induction coupling to the device onto the over-voltage, over -
Currents caused by lightning electromagnetic pulse. In order to reduce electromagnetic interference in a sense of
Shall effect, shielding the measures taken to deal with lines, according to GB 50057 --
94 standard, the line through the shielding treatment, which reduce the intensity of electromagnetic induction
When they are not shielded to 30%. It should also be noted that when the cable Waichuan metal tube shield, should the role of the metal shield at both ends of earth, when the
System requirements grounded at one end should be using double-shielding measures, if the
Only the outer metal tube at one end grounded, the metal is only serve to prevent the electrostatic induction
Role and can not prevent lightning electromagnetic pulse attacks. Therefore, in all
A transmitter input armor layer should be reliable connection with the switch connector, and the
Both ends connected to the common earthing system, the same token, the introduction of gas path of gold
Is a layer of common ground should also be received on the body.
In the main control room, nitrogen pressure station, argon pressure points and analysis of the various room window
Outdoor set 10mm × 10mm of metal mesh shield, and reliable connection
To the common earthing system, all the outdoor installation of glass fiber reinforced plastic transmitter
Cover with wire mesh lining 10 the purpose of shielding methods and to achieve shielding
Ground.
313 Install surge protectors
Surge protectors in essence is a kind of equipotential bonding material
Material, its selection means lightning in a different area, in accordance with the thunder and lightning
Magnetic pulse intensity and the location of equipotential connection point, decided located in the
Electronic equipment within the region in what surge protection devices to achieve common -
Equipotential bonding with the grounding. Can be divided into power supply system and electronic information
System surge protection.
31311 Power Supply System Surge Protection
The accident took place against the lightning area distribution in the instrument panel
The three-phase master switch, the main control cabinet single-phase dual power input
After the master switch and the cabinet room in the analysis of single-phase input of the master switch after the
Power lightning protection box were installed in parallel to prevent the lightning from the power supply part of the
Into the instrument.
31312 DCS Information Systems Surge Protection
Analyzer in the field transmitter and the signal input at parallel installation of
Tube-fit shielding signal arrester, because the signal in parallel with special skills
Surgery, both the original test signal without attenuation and amplification, but also to prevent the
Lightning along the signal line into the instrument.
4 program implementation and effects of lightning
The use of cut-off opportunities, in May may be susceptible to lightning attacks on the electrical
Instrumentation installed in parallel with a series of lightning protection devices, the installation of three-phase electricity
Source Lightning Box 22, tubular shield signal arrester 178 and the rail
Signal arrester 12, while the corresponding region of the window and external
Transmitter box mounted shield installed network, set up Equipotential
Row, for equipotential bonding, so that these instruments are an effective instrument
Protection.
Improvements to the system through the implementation of lightning protection, effectively preventing the induction
Ray on the instrument the instrument is damaged, the summer of 2005 not occurred due to lightning
Attack caused by parking, cut-off accidents, not only reduces the Instrument Control System
Repair and maintenance costs, but also to ensure a regular supply of oxygen and long flow
Cheng steel production lines running, and achieved a good experience
And good value for money.