Summary: petrochemical enterprise production automation instrument will heavily used in measurement control system, as the intelligent measuring instrument and automation degree continuously deepened, the degree of precision instrument is becoming more and more high, so to protect the instrument becomes very important in the production process of the work, in the subtropical areas in China, especially in the southern region of frequent thunderstorms weather, summer will be the instrument automation control system have a big impact damage, even lead to the production of enterprise seriously, make the enterprise economic losses.
In the north region will be because of dry climate in winter, have serious electrostatic interference, will also cause damage to system.
In this article, through systematic elaboration, thunder and lightning are introduced in the petrochemical enterprises instrumentation equipment such as electromagnetic flowmeter
and ultrasonic flowmeter equipment caused by the significant influence, and instrument automatic control system of the lightning protection system, instrument and petrochemical enterprises the basic principles and measures of lightning protection equipment.
This article in view of the space, divided into three chapters altogether, friends may, in accordance with this chapter three the contents of the study, to the related issues of the modified and optimized.
Thunder lightning protection put type what general mainly USES the method of shunt, through in the instrument control system signal circuits such as installing surge protector (
To achieve the goal of limiting instantaneous overvoltage and overcurrent.
But the characteristics of the unit the SPD is only for local circuit protection, such as installation in DCS control system of single channel SPD can only on the DCS system corresponding to the card channel provides protection;
Installed in the field of signal transmitting channel SPD can only provide protection for transmitter.
If every I/O channel installation of SPD, this will not only greatly increase the enterprise cost, and failure rate of SPD's can also lead to a complete set of instrument control system maintenance rate is greatly increased.
Therefore, chemical companies are usually only in some relatively important occasions using a surge protector, can't fully solve chemical instrumentation automatic control system of lightning protection.
1 direct lightning strikes a direct lightning stroke is in lightning activity region, lightning directly through the human body, buildings, equipment, etc of discharge produced by electric shock phenomenon.
In chemical enterprises, the lightning hit the instrumentation equipment directly, causing the instrument sensor or transducer electronic circuit damage.
Such as in the petrochemical enterprises will decorate in the outdoor many flow meter
, such as electromagnetic flowmeter, ultrasonic flowmeter, etc. , some of these instruments will be installed protection box, others are not.
In this case, the possibility of a lightning strike is very big.
So-called induction lightning is 2 lightning strike lightning did not hit any part of instrument control system, lightning conductor or near instrumentation equipment, due to electrostatic and electromagnetic induction in the conductor or overvoltage phenomenon is formed on instrumentation equipment.
Lightning strikes, as a result of the action of the thundercloud electric field, the ground metal type of cable conductor is induced a large amount of electric charge, after flashing a lot charge discharge, due to the instantaneous power is great, form a high potential difference, if the discharge current into the field instrumentation equipment, will cause the equipment damage.
Electromagnetic pulse radiation.
When meet ShanQi occurred after flash, huge lightning current will instantly through the ground down lead, and around the down lead a huge, tem field and electromagnetic wave radiation, the metal conductor in the electromagnetic field will sense how larger induction electromotive force, if there is a loop will produce the large surge current in the circuit, resulting in instrumentation equipment failure, lead to instrument control system failure.
Surge into 3 direct lightning or induction lightning can make the metal wire and metal pipe produces over voltage, over voltage influx can occur in the power supply circuit or signal circuit, caused the decrease of the quality of the power supply circuit, signal circuit conductor and the conductor and shielding layer between the transverse and longitudinal overvoltage, and signal interference and destruction by coupling circuit connection in the instrumentation equipment.
4 the counterattack of by ShanQi flash, great instantaneous over-current, introducing by downlead grounding lightning current in the process of release, connected on the conductor produces high voltage to other objects around its electric shock, this phenomenon is called back flashover.
Because the earth has a certain resistance, thunder and lightning to release the earth there will always be a process, in the process of the release, the local ground potential will instantly improve, if not two sets of grounding system design enough safe distance, can produce very high potential difference between a grounding pole, a huge moment of counter current, direct damage to the instrument automation control system to produce huge.
In this paper, published by the embellish of instrument science and technology co. , LTD. )
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