Origin
Electrification of dielectrics by friction can occur when two dissimilar substances come into contact due to differences in atomic and molecular forces (due to differences in the electron work function of the materials). In this case, a redistribution of electrons (in liquids and gases, also ions) occurs with the formation of electric layers with opposite signs of electric charges on the contacting surfaces. In fact, atoms and molecules of one substance, which have a stronger attraction, remove electrons from another substance.
On the other hand, such voltages can be dangerous for elements of various electronic devices - microprocessors, transistors, etc. Therefore, when working with radio-electronic components, it is recommended to take measures to prevent the accumulation of static charge.
Lightning
As a result of the movement of air currents saturated with water vapor, thunderclouds are formed, which are carriers of static electricity. Electrical discharges are formed between differently charged clouds or, more often, between a charged cloud and the ground. When a certain potential difference is reached, a lightning discharge occurs between clouds or on the ground. To protect against lightning, lightning rods are installed that conduct the discharge directly into the ground.
Notes
see also
Links
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See what “Static electricity” is in other dictionaries:
Static electricity- see Static electricity... Russian encyclopedia of labor protection
STATIC ELECTRICITY, a certain amount of ELECTRIC CHARGES in a state of rest, and not in motion, as is the case with ELECTRIC CURRENT. As a rule, uncharged ATOMS have the same number of positive and negative ELECTRONS.... ... Scientific and technical encyclopedic dictionary
static electricity- 3.1 static electricity: A set of phenomena associated with the separation of positive and negative electrical charges, the conservation and relaxation of free electrostatic charge on the surface or in the volume of dielectrics or on... ... Dictionary-reference book of terms of normative and technical documentation
static electricity- rus static electricity (с) eng static electricity fra électricité (f) statique deu statische Elektrizität (f) spa electricidad (f) estática … Occupational safety and health. Translation into English, French, German, Spanish
static electricity- statinė elektra statusas T sritis fizika atitikmenys: engl. static electricity vok. statische Elektrizität, f rus. static electricity, n pranc. électricité statique, f … Fizikos terminų žodynas
Electricity is static- Static electricity: a set of phenomena associated with the separation of positive and negative electrical charges, the conservation and relaxation of free electrostatic charge on the surface or in the volume of dielectrics or on... ... Official terminology
Electricity- (Electricity) The concept of electricity, the production and use of electricity Information about the concept of electricity, the production and use of electricity Content is a concept that expresses the properties and phenomena determined by the structure of physical... ... Investor Encyclopedia
Noun, s., used. compare often Morphology: (no) what? electricity, why? electricity, (I see) what? electricity, what? electricity, what about? about electricity 1. Electricity is the type of energy that people use to power... ... Dmitriev's Explanatory Dictionary
- (from the Greek elektron amber, since amber attracts light bodies). A special property of some bodies that appears only under certain conditions, for example. by friction, heat, or chemical reactions, and is revealed by the attraction of lighter... ... Dictionary of foreign words of the Russian language
The daily activity of any person is connected with his movement in space. At the same time, he not only walks, but also travels by transport.
During any movement, a redistribution of static charges occurs, changing the balance of internal equilibrium between the atoms and electrons of each substance. It is associated with the process of electrification, the formation of static electricity.
In solids, the distribution of charges occurs due to the movement of electrons, and in liquid and gaseous bodies, both electrons and charged ions. All of them together create a potential difference.
Reasons for the formation of static electricity
The most common examples of the manifestation of static forces are explained in school during the first physics lessons, when they rub glass and ebonite rods on woolen fabric and demonstrate the attraction of small pieces of paper to them.
There is also known experience in deflecting a thin stream of water under the influence of static charges concentrated on an ebonite rod.
In everyday life, static electricity manifests itself most often:
when wearing woolen or synthetic clothing;
walking in shoes with rubber soles or woolen socks on carpets and linoleum;
using plastic items.
The situation is aggravated by:
dry indoor air;
reinforced concrete walls from which multi-storey buildings are made.
How is a static charge created?
Typically, the physical body contains an equal number of positive and negative particles, due to which a balance is created in it, ensuring its neutral state. When it is violated, the body acquires an electrical charge of a certain sign.
Static means a state of rest when the body does not move. Polarization can occur inside its substance - the movement of charges from one part to another or their transfer from a nearby object.
Electrification of substances occurs due to the acquisition, removal or separation of charges when:
interaction of materials due to friction or rotation forces;
sudden temperature change;
irradiation in various ways;
dividing or cutting physical bodies.
They are distributed over the surface of an object or at a distance from it of several interatomic distances. For ungrounded bodies they spread over the area of the contact layer, and for those connected to the ground loop they flow onto it.
The acquisition of static charges by the body and their drainage occur simultaneously. Electrification is ensured when the body receives a greater energy potential than it expends into the external environment.
A practical conclusion follows from this provision: to protect the body from static electricity, it is necessary to remove the acquired charges from it to the ground circuit.
Methods for assessing static electricity
Physical substances, based on their ability to form electrical charges of different signs when interacting with other bodies by friction, are characterized on the scale of the triboelectric effect. Some of them are shown in the picture.
The following facts can be cited as an example of their interaction:
walking in wool socks or shoes with rubber soles on a dry carpet can charge the human body up to 5÷-6 kV;
the body of a car driving on a dry road acquires a potential of up to 10 kV;
the drive belt rotating the pulley is charged up to 25 kV.
As we can see, the potential of static electricity reaches very high values even in domestic conditions. But it does not cause us much harm because it does not have high power, and its discharge passes through the high resistance of the contact pads and is measured in fractions of a milliamp or a little more.
In addition, it is significantly reduced by air humidity. Its effect on the amount of body stress upon contact with various materials is shown in the graph.
From his analysis, the conclusion follows: in a humid environment, static electricity appears less. Therefore, various air humidifiers are used to combat it.
In nature, static electricity can reach enormous values. When clouds move over long distances, significant potentials accumulate between them, which manifest themselves as lightning, the energy of which is enough to split a century-old tree along the trunk or burn down a residential building.
When static electricity is discharged in everyday life, we feel “tingling” in our fingers, see sparks emanating from woolen items, and feel a decrease in vigor and efficiency. The current to which our body is exposed in everyday life has a negative effect on well-being and the state of the nervous system, but it does not cause obvious, visible damage.
Manufacturers of industrial measuring equipment produce instruments that make it possible to accurately determine the voltage value of accumulated static charges both on equipment housings and on the human body.
How to protect yourself from static electricity at home
Each of us must understand the processes that create static discharges that pose a threat to our body. They should be known and limited. For this purpose, various educational events are held, including popular television programs for the population.
They show, using accessible means, methods for creating static voltage, principles for measuring it, and methods for performing preventive measures.
For example, given the triboelectric effect, it is best to use natural wood combs for combing your hair, rather than metal or plastic, as most people do. Wood has neutral properties and does not form charges when rubbed against hair.
To remove static potential from the car body when driving on a dry road, use special antistatic tapes attached to the bottom. Various types of them are widely available on sale.
If there is no such protection on the car, then the voltage potential can be removed by briefly grounding the body through a metal object, for example, a car ignition key. It is especially important to perform this procedure before refueling.
When a static charge accumulates on clothing made of synthetic materials, it can be removed by treating the vapors from a special canister containing “Antistatic” composition. In general, it is better to use such fabrics less and wear natural materials made from linen or cotton.
Shoes with rubberized soles also contribute to the accumulation of charges. It is enough to put antistatic insoles made of natural materials into it, and the harmful effects on the body will be reduced.
The influence of dry air, characteristic of city apartments in winter, has already been discussed. Special humidifiers or even small pieces of dampened cloth placed on the battery improve the situation and reduce the formation of static electricity. But regular wet cleaning of premises allows you to promptly remove electrified particles and dust. This is one of the best ways to protect yourself.
Household electrical appliances also accumulate static charges on their bodies during operation. A potential equalization system connected to the general grounding loop of the building is designed to reduce their impact. Even a simple acrylic bathtub or an old cast-iron structure with the same insert is susceptible to static and requires protection in a similar way.
How to protect against static electricity in production
Factors that reduce the performance of electronic equipment
Discharges that occur during the manufacture of semiconductor materials can cause great harm, disrupt the electrical characteristics of devices, or even disable them.
In production conditions, the discharge can be random and depend on a number of different factors:
the size of the formed capacity;
energy potential;
electrical resistance of contacts;
type of transient processes;
other accidents.
In this case, at the initial moment of about ten nanoseconds, the discharge current increases to a maximum, and then it decreases within 100÷300 ns.
The nature of the occurrence of a static discharge on a semiconductor device through the operator’s body is shown in the picture.
The magnitude of the current is influenced by: the charge capacity accumulated by a person, the resistance of his body and contact pads.
During the production of electrical equipment, a static discharge can be created without operator participation due to the formation of contacts through grounded surfaces.
In this case, the discharge current is affected by the charge capacity accumulated by the device body and the resistance of the formed contact pads. In this case, the semiconductor is initially simultaneously affected by the induced high voltage potential and the discharge current.
Due to this complex effect, damage can be:
1. obvious, when the performance of the elements is reduced to such an extent that they become unsuitable for use;
2. hidden - due to a reduction in output parameters, sometimes even falling within the established factory characteristics.
The second type of malfunction is difficult to detect: they most often result in loss of performance during operation.
An example of such damage from the action of high static voltage is demonstrated by graphs of the deviation of the current-voltage characteristics in relation to the KD522D diode and the integrated circuit BIS KR1005VI1.
The brown line numbered 1 shows the parameters of semiconductor devices before testing with increased voltage, and curves numbered 2 and 3 show their decrease under the influence of an increased induced potential. In case #3 it has a greater impact.
Damage may be caused by:
excessive induced voltage, which breaks through the dielectric layer of semiconductor devices or disrupts the structure of the crystal;
high density of flowing current, causing high temperatures, leading to melting of materials and burning of the oxide layer;
tests, electrical and thermal training.
Hidden damage may not affect performance immediately, but after several months or even years of operation.
Methods for implementing protection against static electricity in production
Depending on the type of industrial equipment, one of the following methods of maintaining operability or a combination of them is used:
1. eliminating the formation of electrostatic charges;
2. blocking their entry into the workplace;
3. increasing the resistance of devices and components to the action of discharges.
Methods No. 1 and No. 2 allow you to protect a large group of different devices in a complex, and No. 3 is used for individual devices.
High efficiency in maintaining the operability of the equipment is achieved by placing it inside a Faraday cage - a space fenced on all sides with a fine-mesh metal mesh connected to a ground loop. External electric fields do not penetrate inside it, but static magnetic fields are present.
Cables with a shielded sheath work on this principle.
Static protection is classified according to the principles of execution into:
physical and mechanical;
chemical;
structural and technological.
The first two methods allow you to prevent or reduce the formation of static charges and increase the rate of their drainage. The third technique protects devices from the effects of charges, but it does not affect their drainage.
The drainage of discharges can be improved by:
creation of coronation;
increasing the conductivity of materials on which charges accumulate.
These issues are resolved:
air ionization;
increasing working surfaces;
selection of materials with better volumetric conductivity.
Due to their implementation, lines prepared in advance are created to drain static charges onto the ground loop, preventing them from reaching the working elements of devices. It is taken into account that the total electrical resistance of the created path should not exceed 10 Ohms.
If materials have high resistance, then protection is performed in other ways. Otherwise, charges begin to accumulate on the surface, which can be discharged upon contact with the ground.
An example of complex electrostatic protection of a workplace for an operator involved in the maintenance and adjustment of electronic devices is shown in the picture.
The table surface is connected to the ground loop through a connecting conductor and a conductive mat using special terminals. The operator works in special clothing, wears shoes with conductive soles and sits on a chair with a special seat. All these measures make it possible to efficiently discharge accumulated charges to the ground.
Working air ionizers regulate humidity and reduce the potential of static electricity. When using them, it is taken into account that the increased content of water vapor in the air negatively affects human health. Therefore, they try to maintain it at a level of about 40%.
Another effective way can be to regularly ventilate the room or use a ventilation system in it, when the air passes through filters, is ionized and mixed, thus neutralizing the resulting charges.
To reduce the potential accumulated by the human body, bracelets can be used to complement a set of antistatic clothing and shoes. They consist of a conductive strip that is attached to the arm using a buckle. The latter is connected to the ground wire.
With this method, the current flowing through the human body is limited. Its value should not exceed one milliamp. Larger values may cause pain and electrical injuries.
As the charge flows to the ground, it is important to ensure that it leaves at a rate of one second. For this purpose, floor coverings with low electrical resistance are used.
When working with semiconductor boards and electronic components, protection against damage by static electricity is also provided by:
forced shunting of the terminals of electronic boards and units during checks;
using tools and soldering irons with grounded working heads.
Containers with flammable liquids located on vehicles are grounded using a metal circuit. Even the fuselage of the aircraft is equipped with metal cables, which act as protection against static electricity during landing.
The world consists of atoms. These are tiny particles from which our body is built, the jeans on our legs, the seat in the car under the butt and the smartphone with Lifehacker on the screen.
Inside atoms there are smaller elements: a nucleus of protons and neutrons, and electrons that orbit around it. Protons are charged with a plus sign, electrons - with a minus sign.
Usually an atom has the same number of such pluses and minuses, so it has zero charge. But sometimes electrons leave their orbits and are attracted to other atoms. Most often this occurs as a result of friction.
The movement of electrons from one atom to another creates energy, which is called electricity. If you direct it through a wire or other conductor, you get . You can clearly see its work when you charge your smartphone via cable.
With static electricity it's different. It is “lazy”, does not flow and seems to rest on the surface. An object has a positive charge when it lacks electrons, and a negative charge when it has an excess of electrons.
How does static electricity manifest itself?
1. Electric discharge
If you put clean, dry wool socks on your feet and rub them on a nylon carpet, you can get an electric shock.
During friction, electrons will jump from the socks to the carpet and vice versa. They will end up with opposite charges and will want to balance the number of electrons.
If the difference is large enough, you will get a visible spark as soon as you touch your toes to the carpet again.
2. Attracting objects
Lightning strikes tall buildings, trees and the ground and causes equipment failures.
How to avoid static electricity
1. Increase humidity
Dry indoor air is static electricity's best friend. But it practically does not appear if the humidity exceeds 85%.
To increase this indicator, regularly carry out wet cleaning and use air humidifiers.
When the heating is on, you can put a wet cloth on the radiator so that the water evaporates and makes air.
2. Use natural materials
Most natural materials retain moisture, synthetic ones do not. Therefore, the former are less susceptible to static electricity than the latter.
If you comb your hair with a plastic comb, they will receive a static charge and begin to fly away from each other, ruining your hairstyle. This can be avoided by using wooden accessories.
It's the same story with rubber-soled shoes. It provokes the creation of static electricity on the body. But insoles made of natural materials neutralize its effect.
Cotton T-shirts and clothes made from other natural fabrics do not create static electricity. An artificial sweater is the opposite.
3. Use grounding
With its help, static electricity can be discharged into the ground. This applies not only to lightning rods, which redirect the lightning charge, but also to working with electrical equipment.
When a professional technician opens a laptop to remove dust, he always uses a special grounding cord attached to his hand - an antistatic bracelet.
Antistatic wrist strap / aliexpress.com It is needed to avoid static electricity from reaching the microcircuits from your hands. Otherwise, it will damage them, and after a while the computer may fail.
What is static electricity. Static voltage is
Types of static electricity. Appearance and removal of static
An imbalance between electrical charges inside a material or on its surface is the occurrence of static electricity. The charge remains until it is removed by electrical current or discharge. Static electricity is caused when two surfaces come into contact and separate, and at least one of the surfaces is a dielectric - a material that does not conduct electrical current. Most people are familiar with static electricity because they have seen sparks when an excess charge is neutralized, felt the discharge and heard the accompanying crackling sound.
Causes of Static Electricity
Substances consist of atoms that are normally electrically neutral because they contain an equal number of positive charges (protons of the nucleus) and negative charges (electrons of the atomic shells). Static electricity involves the separation of positive and negative charges. When two materials come into contact, electrons can transfer from one material to the other, resulting in an excess of positive charges on one material, and an equal excess of negative charge on the other material. When materials are separated, the resulting charge imbalance is maintained.
Upon contact, materials can exchange electrons; materials that hold electrons weakly tend to lose them, while materials in which the outer shells of the atoms are not completely filled tend to capture electrons. This effect is called triboelectric, and causes one material to become positively charged and the other negatively charged. The polarity and magnitude of the charge when separating materials depends on the relative position of the material in the triboelectric series.
The materials are arranged in a row, one end of which is positive and the other negative. When a pair of materials rubs, the material closest to the positive end of the row becomes positively charged, while the other becomes negatively charged. There is no single triboelectric series (similar to the voltage series of metals), just as there is no single theory of electrification. Typically, materials with a higher dielectric constant are located closer to the positive end of the row.
The order of materials in the triboelectric series may be disrupted. So in a silk-steel pair, glass is negative, in a glass-zinc pair, zinc is negative, and in a zinc-silk pair, it is not the zinc that is negatively charged, as one would expect, but the silk. This lack of order is called a triboelectric ring.
The triboelectric effect is the main cause of static electricity in everyday life, when various materials rub against each other. For example, if you rub a balloon against your hair, it becomes negatively charged and can be attracted to the positively charged sources of a wall, sticking to it and defying the laws of gravity.
Prevention and removal of static charges
Preventing static buildup is as simple as opening a window or turning on a humidifier. An increase in moisture content in the air will lead to an increase in its electrical conductivity; a similar effect can be achieved by ionization of air.
Objects that are particularly sensitive to static discharges can be protected by applying an antistatic agent, forming a conductive layer on the surface of the object.
Semiconductor components of electronic devices are especially sensitive to static electricity discharges. Conductive antistatic bags are typically used to protect these devices. People who work with semiconductor circuits often ground themselves with antistatic wrist straps. You can avoid the formation of static charges when in contact with the floor (for example, in hospitals) by wearing antistatic shoes with conductive soles.
Discharge
A spark is a discharge of static electricity when excess charge is neutralized by the flow of charges from or to the surroundings. An electric shock is caused by irritation of nerves when a neutralizing current flows through the human body. The stored static energy depends on the size of the object, the electrical capacitance, the voltage to which it is charged, and the dielectric constant of the surrounding environment.
To model the effect of static discharge on sensitive electronic devices, the human body is represented as a 100 pF electrical capacitance charged to a voltage of 4 to 35 kV. When touching an object, this energy is discharged in less than a microsecond. Although the total discharge energy is low, on the order of millijoules, it can damage sensitive electronic devices. Large objects store more energy, which poses a danger to people if they come into contact, or spark ignite flammable gas or dust.
Lightning
Lightning is an example of a static discharge of atmospheric electricity resulting from the contact of ice particles in thunderclouds. Typically, significant discharges can only accumulate in areas of low electrical conductivity. The discharge usually occurs at a field voltage of the order of 10 kV/cm, depending on humidity. The discharge superheats the surrounding air, producing a bright flash and a cracking sound. Lightning is just a large-scale version of a static electricity spark. A flash occurs due to the heating of the air in the discharge channel to such a high temperature that it begins to emit light, like any hot body. A thunderclap is the consequence of the explosive expansion of air.
Electronic components
Many semiconductors in electronic devices are very sensitive to the presence of static and can be damaged by discharge. When handling nanodevices, be sure to wear an antistatic wrist strap. Another precaution is to remove shoes with thick rubber soles and stand on a grounded metal base at all times.
Generation of electricity in flows of flammable and combustible materials
Static discharge is a hazard in industries that use flammable materials, where small electrical sparks can cause an explosion. The movement of tiny particles of dust or liquids with low electrical conductivity in pipelines or their mechanical mixing can cause the formation of static. Static discharge in a cloud of dust or vapor may cause an explosion.
Grain elevators, paint factories, fiberglass production sites, and fuel pumps can explode. Charge accumulation in a medium occurs when its electrical conductivity is less than 50 pS/m; at higher conductivity, the resulting charges recombine (recombination is the reverse process of ionization), and accumulation does not occur.
Filling large transformers with transformer oil requires precautions because electrostatic discharges within the liquid can damage the transformer insulation.
Since the intensity of charge formation is higher, the higher the liquid flow speed and the diameter of the pipeline, in pipelines with a diameter of more than 200 mm, the liquid flow speed is limited by the standard. Thus, the flow rate of hydrocarbons containing water is usually limited to 1 m/s.
The formation of charges is limited by grounding. When the conductivity of the liquid is below 10 pS/m, this measure is not enough, and antistatic additives are added to the liquid.
Fuel transfer
Pumping flammable liquids such as gasoline through pipelines can create static, and discharge can ignite fuel vapors.
Similar incidents occurred at gas stations and at airports when refueling aircraft with kerosene. Grounding and antistatic additives are also effective here. The flow of gas in pipelines is dangerous only if there are solid particles or liquid droplets in the gas.
On spacecraft, static electricity poses a great danger due to the low humidity of the environment, and this danger will have to be taken into account during planned flights to the Moon and Mars. Walking on dry surfaces can create huge charges that can damage electronic devices.
Ozone cracking
Static discharges in the presence of air or oxygen cause the formation of ozone. Ozone damages rubber parts, in particular, leading to cracking of seals.
Static discharge energy
The energy released during static discharges varies widely. Discharges with an energy of more than 5000 mJ pose a danger to humans. One of the standards suggests that consumer items should not create a discharge with an energy exceeding 350 mJ per person. The maximum voltage is limited to 35-40 kV due to the limiting factor - corona discharge. Potentials below 3000V are usually not felt by humans. Walking 6 meters on PVC linoleum at an air humidity of 15% causes the formation of a potential of 12 kV, while at 80% humidity the potential does not exceed 1.5 kV.
A spark occurs when the spark energy is above 0.2 mJ, but a person usually does not see or hear a spark of such energy. For an explosion to occur in hydrogen, a spark with an energy of 0.017 mJ is sufficient, and up to 2 mJ for hydrocarbon vapors. Electronic components are damaged at spark energies between 2 and 1000 nJ.
Application of statics
Static electricity is widely used in xerographs, air filters, automobile painting, photocopiers, paint sprayers, printers, and aircraft fueling.
Related topics:
electrosam.ru
Occurs when the intraatomic or intramolecular equilibrium associated with the acquisition or loss of an electron is disturbed. With the same number of protons and electrons, the atom is in a state of equilibrium. Electrons move between atoms very easily, forming positive ions when an electron is missing, or negative ions when an extra electron is present. When this imbalance occurs, static electricity occurs. Why does static electricity occur?
Material separation and surface contact are the most common causes of static electricity, especially in manufacturing processes involving the handling, winding or unwinding of various roll materials. Electrical breakdown occurs in the gap between adjacent materials. When the film leaves the contact zone, a slight crackling sound is heard and a slight spark is observed. In this case, the static charge gains a value quite sufficient to penetrate the surrounding air. The synthetic film is electrically neutral before contact with the shaft. But when the film comes into contact with the roller, a stream of electrons is directed at it and creates a negative charge. A positive charge dissipates very quickly along a grounded metal shaft. If an object is capable of accumulating a large charge and high voltage is present, static electricity can result in sparking, electrostatic attraction or repulsion, and electric shock to personnel. Several problems associated with static electricity
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electric-220.ru
Protection against static electricity. Origin, days
Static electricity occurs due to the retention of charges in an electrostatic field on dielectric materials. It negatively affects human life and the operation of electrical devices. The formation of sparks from static electricity contributes to fires and explosions. The energy power is quite enough to ignite gas-air mixtures and dust.
A charge of static electricity can accumulate on a person's body if he is wearing clothing made of wool or chemical fibers. A potential value of about 7 Joules is not dangerous to humans, but can cause cramps and muscle contractions. And this, in turn, can create conditions for injury at work, falling from a height, etc.
Static electricity negatively affects the functioning of precision instruments, radio communications, and causes malfunctions. Workers who are constantly exposed to static electricity are more likely to suffer from cardiovascular diseases and diseases of the nervous system.
Only protection against static electricity can reduce to zero or completely prevent the occurrence of this negative phenomenon.
Sources of static electricity
- Action of various radiations.
- Sudden change in temperature.
- The interaction of bodies with each other during movement.
This phenomenon has a negative impact and poses a danger. Protection against static electricity allows you to completely prevent or significantly reduce its effect.
In everyday conditions, a static field often occurs on animal fur, when removing synthetic clothing, combing hair, wearing rubber shoes, walking on a carpet in wool socks, or using plastic products.
The electrostatic field does not threaten human life; the discharge produces a weak current that is not capable of causing too much harm to the human body. It can only create some discomfort. To prevent this effect, you only need to follow a few simple rules: in frosty and dry weather, do not pet animals, take off woolen clothes more slowly, or treat them with a special compound, and use a wooden or metal comb when combing your hair.
The accumulation of electrostatic energy is facilitated by:
- Reinforced concrete walls of the building.
- The air is too dry.
For electronic devices, electrostatic charge is the worst enemy. Some elements of electronic devices are not able to withstand the high voltages that occur during discharge. Sensitive elements may fail or degrade their performance.
If flammable liquids are exposed to an electric field, this will create conditions for their ignition. These liquids may accumulate a static charge when transported in tanks. Also, a charge arises from a mechanism or a person who comes close to it. Therefore, in industrial production, where there are flammable liquids, much attention is paid to the grounding of movable structures and mechanisms. For sewing shoes and special clothing, production also uses special fabrics that are not capable of accumulating an electric charge.
Operating principle
Let's figure out how a static charge is formed. In a normal state, physical bodies have the same number of negative and positive particles. Due to this balance, a neutral state of the body is created. When the neutral state is violated, the body receives an electric charge of one pole.
Statics is the state of a body at rest, when it is without movement. In the substance of the body, polarization can occur, which is expressed in the movement of charges between parts of the body, or from a nearby object.
Substances become electrified due to the separation of bodies, changes in charges during friction, sudden changes in temperature, and irradiation. The electric field charges are located on the surface of the body or are removed from the surface at a distance equal to the interatomic distance. If the bodies are not grounded, then the charges are concentrated on the contact area, and if there is grounding, the charge goes into the ground loop.
The processes of charge accumulation and their drainage occur at the same time. The body becomes electrified if it receives a greater charge of energy compared to the charge consumed. As a result, it becomes clear that protection against static electricity must discharge accumulated charges to the ground loop.
Amount of static electricity
All physical substances have their own characteristic on the triboelectric scale, depending on their ability to create electrical charges of different poles when rubbed. The main such substances are shown in the figure.
To have an idea of the size of the resulting static charges, consider several examples:
- The rotating pulley with the drive belt can charge up to 25,000 volts.
- The body of a car moving on a dry road can receive a charge of up to 10,000 volts.
- A person wearing wool socks walking on a dry carpet can accumulate a charge on the body of up to 6000 volts.
As a result, it becomes clear that the voltage of the electrostatic field can reach significant levels even in everyday life. This charge does not cause significant harm to a person due to its low power. The discharge flows through a large resistance and is calculated in several fractions of a milliampere.
Air humidity also reduces electrostatic charge. It affects the value of the body's potential during contact with different materials. Therefore, protection against static electricity may involve the use of air humidifiers.
In the natural environment, static electricity exists, reaching enormous values. For example, when clouds move between them, large energy potentials arise, which are expressed in lightning discharges. The power of these discharges is quite enough to burn down a wooden house or split the trunk of a perennial tree.
In everyday conditions, during discharges of an electrostatic field, a person feels small tingling sensations in his fingers, sparks are visible from the friction of woolen clothing, and a person’s performance decreases. The electrostatic field negatively affects the human condition, but does not cause obvious damage.
There are measuring instruments that can accurately measure the value of the static potential of the accumulated charge on the human body and on the body of any device.
Anti-static electricity
There are various methods of protection against electrostatic field discharges, both in everyday life and in industrial conditions. They have their differences. Let's take a closer look at each of them.
Protection at home
Every person must present the danger that static discharges pose to the body. You need to know them and be able to limit them. To solve this problem, various events are organized to train people in protection methods, including television programs.
At these events, people are explained where and how the static field comes from, methods for measuring it, and methods for performing preventive work. For example, to avoid the unpleasant sensations of a static field, it is advisable to use wooden combs instead of plastic ones to comb your hair. Wood has neutral characteristics and does not create electrostatic field charges during friction. In stores you can easily purchase a wooden comb of any shape and type.
To prevent the formation of static potential on the car body when driving on a dry road surface, special antistatic tapes are used, which are fixed at the rear of the car on the bottom of the body. In the retail chain you can easily choose any version of such a tape.
If the car is not protected in any way from a possible discharge of the accumulated potential charge, then the voltage can be removed by temporarily grounding the car body by connecting it to the ground through a metal part. To do this, you can use the ignition key. It is imperative to relieve tension before refueling the car with gasoline.
When a static charge forms on clothing made from chemical fibers, it is recommended to use Antistatic. This is a special aerosol can that is sold in stores. It removes static electricity from clothing, fabrics, and synthetic car seat covers, especially in winter when the air is dry. But, in order not to use various spray cans and chemicals, it is recommended to wear clothes made from natural materials: cotton and linen.
If shoes have rubberized soles, this creates conditions for the accumulation of stress potential. To prevent this from happening, it is enough to put special antistatic insoles in your shoes, which are made from natural materials. As a result, the negative impact on a person will decrease.
Too dry air in city apartments in winter contributes to the accumulation of electrostatic charge. There are special devices for this – air humidifiers. If there is no such device, then a large wet wipe that needs to be placed on the battery will do. As a result, the charge accumulation process will decrease and the situation in the apartment will improve. It is also recommended to carry out wet cleaning regularly. This will allow you to remove dust and electrified areas in a timely manner. This method is the best.
Electrical devices in everyday life also accumulate a static charge on the housing during operation. To reduce the effect of static charge, a potential equalization system is installed. It is connected to the ground loop of the entire house. An acrylic bathtub is susceptible to the accumulation of static charge on it, and it must be protected by a potential equalization system. Even a cast iron bathtub with an acrylic liner is also susceptible to this negative phenomenon.
Protection against static electricity in production
In industrial production, several methods are used to maintain the functionality of equipment:
- Increasing the resistance of devices and equipment to electrostatic discharge.
- Blocking the penetration of charge into the workplace.
- Preventing the occurrence of electrostatic charges.
The last two methods make it possible to protect many devices, while the first method is used only for certain types of equipment.
High protection against static field discharges and maintaining the functionality of the device is provided by a Faraday cage. This is a metal cage in the form of a mesh with a fine mesh. The cage encloses the equipment on all sides. It is connected to the ground loop. Electric fields do not pass inside the cage, and at the same time, the Faraday cage does not interfere with the magnetic static field. Cables are protected using the same principle by equipping them with a metal shield.
Protection against static electricity is divided according to implementation methods:
- Structural and technological.
- Chemical.
- Physico-mechanical.
The last two methods make it possible to reduce the formation of charges and increase the speed of their sinking into the ground. The first method protects devices from charges, but does not divert them to ground.
You can optimize electrostatic charge reduction as follows:
- Increasing the conductivity of materials.
- Creation of coronation.
Such problems are solved using:
- Selecting materials with good volumetric conductivity.
- Increasing working surfaces.
- Ionization of airspace.
To implement these tasks, highways are created for the flow of static charges to the ground, bypassing the working components of the devices. If materials have high resistance, then other methods are used.
Related topics:
electrosam.ru
Static electricity is... What is Static electricity?
Static electricity is a set of phenomena associated with the emergence, conservation and relaxation of a free electric charge on the surface or in the volume of dielectrics or on insulated conductors.
The girl's hair became electrified from friction.
Origin
Electrification of dielectrics by friction can occur when two dissimilar substances come into contact due to differences in atomic and molecular forces (due to differences in the electron work function of the materials). In this case, a redistribution of electrons (in liquids and gases, also ions) occurs with the formation of electric layers with opposite signs of electric charges on the contacting surfaces. In fact, atoms and molecules of one substance, which have a stronger attraction, remove electrons from another substance.
The resulting potential difference between the contacting surfaces depends on a number of factors - the dielectric properties of the materials, the value of their mutual pressure upon contact, the humidity and temperature of the surfaces of these bodies, and climatic conditions. With the subsequent separation of these bodies, each of them retains its electric charge, and with an increase in the distance between them due to the work done to separate the charges, the potential difference increases and can reach tens and hundreds of kilovolts.
Electrical discharges can be mutually neutralized due to some electrical conductivity of moist air. When air humidity is more than 85%, static electricity practically does not occur.
Static electricity in everyday life
Static electricity is widespread in everyday life. If, for example, there is a wool carpet on the floor, then when rubbing against it, the human body can receive a minus electrical charge, and the carpet will receive a plus charge. Another example is the electrification of a plastic comb, which, after combing, receives a minus charge, and the hair receives a plus charge. The negative charge accumulator is often plastic bags or polystyrene foam. The plus charge accumulator is often dry polyurethane foam, if you squeeze it by hand.
When a person whose body is electrified touches a metal object, such as a heating pipe or refrigerator, the accumulated charge will instantly discharge and the person will receive a mild electric shock.
Electrostatic discharge occurs at very high voltages and extremely low currents. Even simply brushing your hair on a dry day can build up a static charge of tens of thousands of volts, but the current released is so small that it often cannot even be felt. It is the low current values that prevent the static charge from causing harm to a person when an instantaneous discharge occurs.
On the other hand, such voltages can be dangerous for elements of various electronic devices - microprocessors, transistors, etc. Therefore, when working with radio-electronic components, it is recommended to take measures to prevent the accumulation of static charge.
Lightning
As a result of the movement of air currents saturated with water vapor, thunderclouds are formed, which are carriers of static electricity. Electrical discharges are formed between differently charged clouds or, more often, between a charged cloud and the ground. When a certain potential difference is reached, a lightning discharge occurs between clouds or on the ground. To protect against lightning, lightning rods are installed that conduct the discharge directly into the ground.
In addition to lightning, thunderclouds can cause dangerous electrical potentials on insulated metal objects due to electrostatic induction.
Notes
see also
Links
dic.academic.ru
Static electricity
The phenomenon of static electricity has been known for a long time, and each of us encounters its manifestations almost daily. When putting on or taking off clothes made of synthetic material, or contact with a TV or computer screen, a noticeable electrical discharge often occurs. In the modern world, the effect of static electricity has received wide practical application (printing and copying machines, painting). However, a discharge of static electricity can also lead to tragic consequences.
The ability of static electricity to cause explosions and fires was first discovered in 1893 by the American Richter, who was trying to improve the process of dry dry cleaning clothes and tried to introduce magnesium powder into benzene used in the cleaning process to increase its conductivity.
In the fuel and chemical industries, the problem of the occurrence of static electricity charges began to be deeply studied in the early 30s, after several explosions at SHELL factories. In maritime transport, the study of this problem began a little later, in the mid-60s, again after a series of explosions on tankers that transported crude oil. Fundamental research was carried out in the field of the occurrence of static electricity charges on tankers during various technological operations and international requirements for the prevention of the formation of electrostatic discharges were determined.
Let's consider the nature of the formation of electrostatic charge.
Causes of static electricity charges. There are three stages that sequentially lead to the risk of ignition of flammable mixtures when exposed to static electricity, namely:
Charge separation;
Charge accumulation;
Static electricity discharge.
It is known that atoms consist of a positively charged nucleus, around which negatively charged particles - electrons - rotate. The sum of all negative charges in a body is equal in absolute value to the sum of all positive charges in it, therefore, as a whole, the body is electrically neutral and has no charge.
Electrons located in the peripheral orbits of an atom can relatively easily leave their place and move to the orbits of atoms of another body or substance. The atom that loses electrons will lack them and gain a positive charge. The atom into whose orbits the detached electron will move will have an excess of electrons, and its charge will become negative. In other words, when electrons move from the orbit of one atom to the orbit of another, a redistribution of charges occurs, and at the same time one atom receives a positive charge and the other a negative one. Such charged atoms are called ions.
When bodies are electrified, charges are not created, but only separated: part of the negative charges passes from one body to another.
For example, when an ebonite stick is rubbed against wool, the ebonite receives a negative charge, and the wool becomes positively charged.
The flow of electrons occurs only in the case of interaction of atoms with different electron densities.
Whenever two dissimilar materials come into contact, charge separation occurs at the surface separating the materials. This surface can separate two solids, a solid and a liquid, or two immiscible liquids. At the interface, a charge of the same sign, for example positive, moves from material A to material B in such a way that these materials become positively and negatively charged, respectively. While materials A and B are stationary and in contact with each other, the charges are extremely close to each other. In this case, a slight potential difference between charges of opposite sign does not pose any threat.
Intensive charge separation occurs as a result of actions such as:
Passage of fluid flow through pipes or fine mesh filters,
Sedimentation of particles of a solid or immiscible liquid through another liquid,
Emission of small droplets or particles from the nozzle,
Splashing or agitation of a liquid when it comes into contact with a hard surface,
Strong friction of some materials against each other.
When charges are separated, a large potential difference is created between them. At the same time, a distribution of potential difference also occurs in the surrounding space, in other words, an electric field is formed (i.e., when washing a tank when liquid is sprayed, an electrostatic field arises throughout the entire volume of the tank).
If an uncharged conductor is placed in an electrostatic field, it will receive approximately the same potential as the field in which it is located. Moreover, the field sets charges inside the conductor in motion, a charge of one sign is attracted by the field to one end of the conductor, and an equal charge of the opposite sign is formed at the other end of the conductor. Charges separated in this way are called induced; they accumulate in an electrostatic field.
A charge can also arise where there is no direct contact between charged bodies, as well as when the material is exposed to another charged body, which causes the formation of positive and negative ions. For example, when a thundercloud passes over a tall building or ship, positive and negative ions are formed in the latter, although there was no direct contact between the materials or charges. This leads to the fact that the same substance or body can carry opposite charges.
An electric field is formed around a charged body, a kind of mapping of the space around the charged body. At two opposite points of the electric field, the potential difference in volts is determined. Electrical voltage is expressed in volts per meter (V/m).
In a uniform electric field, field strength is defined as the potential difference per meter. The magnitude of the field strength determines the possibility of a discharge occurring. In dry air, a spark electric discharge can occur at an electric field strength of about 3,000,000 V/m. However, if you place a grounded conductor in the field, then even with a weak field strength you can get a significant electrical discharge.
Charge accumulation. Previously separated charges tend to reconnect with each other and neutralize each other. This process is known as charge relaxation. If one or both of the materials carrying an electrostatic charge have low current conductivity, then the reconnection of charges is difficult and this material accumulates (accumulates) the charge on itself.
The time during which the charge is retained is characterized by the relaxation time
of a given material, which correlates with its conductivity. The lower the conductivity
material, the longer the charge relaxation period.
If the conductivity of the material is high, then the charges combine very quickly, thereby preventing the process of their separation, resulting in very little or no charge accumulation. A material with such conductivity can store or accumulate charge only if it is surrounded by a dielectric. In this case, the rate of charge loss will depend on the relaxation time of the dielectric.
It can be said that the most important factor determining the relaxation time of a material is its electrical conductivity.
All materials, according to the degree of their conductivity, can be divided into three main groups.
The first group is guides. Solid conductors include most metals, while liquid conductors include a range of aqueous solutions of salts, including sea water. The human body, which is more than 60% water, is also a conductor of electricity. Important properties of liquid conductors include not only their inability to hold an electrical charge unless they are insulated, but also their almost instantaneous discharge if they are insulated and the possibility of electrical discharge exists. In other words, the resulting charge spreads evenly throughout the material, and upon contact with grounding it instantly disappears.
Very often, discharges between two conductors occur in the form of a spark, in which case they are much more dangerous than discharges occurring between a conductor and a dielectric. When the charge relaxes between the conductor and the dielectric, it is not spark discharges that occur, but corona or brush discharges.
The second group is dielectrics or insulators. If a charge occurs only at the point of contact or separation of materials, then such materials are called dielectrics.
Charged dielectrics deliver charge to a location where direct contact of the charge with the conductor can occur. Highly charged dielectrics can directly initiate ignition sparks. Liquids are considered dielectrics if their conductivity is less than 50 pico-Siemens per meter (pS/m) with a relaxation period of no more than 0.35 s. Such liquids are often referred to as accumulating static electricity. These include pure oils and pure petroleum products (distillates), liquefied gases.
The third group is a series of liquids and solids with intermediate conductivity. A striking example is dark oils, crude oils, alcohols, acetone, etc.
When the electric field strength reaches a certain value, a field discharge can occur, which has various forms. To ignite the steam-air mixture, the electrostatic discharge must be powerful enough. It was found that to ignite a steam-air mixture of propane, it is enough for a discharge to occur between the electrodes with an energy release of 0.2 mJ, and to ignite a steam-air mixture of ammonia, a discharge 600 times more powerful will be required.
There are the following forms of electrostatic discharges.
Corona - bluish ion radiation. It can be seen on sharp corners or shrouds in some weather conditions. This glow is known as St. Elmo's Fire. Such radiation does not carry enough energy to create a flame.
The northern, or polar, lights are faint rays formed from very small sparks emitted by charged sharp corners or protrusions of structures in the direction of charged clouds or fog. Such a glow can occur in the tanks of supertankers; it also does not carry sufficient energy to cause a flame.
A spark occurs only if the electric field strength reaches a certain critical value. The ion beam increases with increasing field strength, and the end result of this increase is the production of a true spark. At high field strengths, a discharge is formed, better known as lightning. However, if we place a grounded conductor in an electric field, a spark discharge will occur that is sufficient to ignite the mixture even at low field strengths.
studfiles.net
Static electricity ESD and its consequences
What is the term “Static electricity” - a set of phenomena associated with the emergence, conservation and relaxation of a free electric charge on the surface or in the volume of dielectrics or on insulated conductors. Electrification occurs in the process of friction of two dielectrics, that is, electrons are actually separated from the substance with the formation of a potential difference on the contacting surfaces.
Why is static electricity dangerous?
But let's move on to practice, why does static in our work bother us so much? At first glance, we don’t see this, which means it doesn’t threaten us. This is an incorrect assumption, static is always present when we walk or come into contact with different objects and just on a hot sunny day in the air, the amount of static electricity can exceed all imaginable limits. A person begins to feel static voltage above 3000 volts and sparking can be seen from 5000 volts. Sometimes we can accumulate a charge of up to 10,000 volts on ourselves, despite the fact that radioelements can fail at currents arising at a voltage of already 5 volts. According to general statistics, more than 50 percent of all electronic components fail from electrostatic discharge, and the figure for already assembled and operated products exceeds 60 percent.
It is important to know that the amount of static electricity depends on many factors, the main one being relative air humidity:
So we don’t have to rub something on purpose to get a static discharge; this always happens without our desire.
How to deal with static electricity?
The first and most important rule is that working tools and devices must be grounded. When working with radioelements and assembled devices, a special antistatic bracelet is put on the person’s hand, which is connected to the grounding point through a 1 MΩ resistor.
The work table must also be grounded; there must be a coating on the work surface that can conduct electrical discharges as much as possible; it must have low resistance. It is also necessary to maintain cleanliness in the work area or workshop. Carry out wet cleaning as often as possible. In the room where repairs are being carried out, place a special conductive floor covering that ensures the removal of accumulated charge from the contacting surfaces to the grounding point.
This is only a small part of the information regarding antistatic safety; on the Internet there are a lot of sites dedicated to this particular topic, which contain many useful tips and rules, following which you can make your workplace as safe as possible. At the same time, thereby increasing the profitability and quality of all work performed.______________________ You are going to buy a house, there are a lot of profitable offers.
progulki.com.ua
Static voltage - Great Encyclopedia of Oil and Gas, article, page 1
Static voltage
Page 1
The static stresses in the blades of the first stages are relatively small. However, these blades operate in resonance with the frequency of the disturbing pulses, since their detuning from resonance is practically impossible; Therefore, increasing the damping capacity of the blades of the first stages of turbines is very powerful, and sometimes the only means of ensuring their reliability.
Static stresses should be found from the influence of centrifugal forces and from the stationary part of the hydrodynamic load.
Static voltage, within certain limits, is a work stimulant. It has been proven that preliminary static training, for example, of the forearm flexors, not only does not lead to subsequent dynamic work, but, on the contrary, it.
Static stresses, determined by the formula O st t % / A, due to the same cross-section of the rods, coincide.
Static stress does not affect the scaling process of Kh18N10T steel to the same extent as carbon steel, apparently due to the formation of a thinner, more elastic and durable film on chromium-nickel steel.
Static stress does not affect the general corrosion of magnesium and its alloys; in the presence of chlorine ions they are prone to corrosion cracking. Sulfur dioxide and its aqueous solutions, as well as liquid and gaseous ammonia do not cause corrosion of magnesium. The best way to protect magnesium and its alloys is chemical treatment (immersion in a solution of chromic acid salts or anodic treatment in this solution) followed by priming the surface using ZnCrO4 and applying varnish or enamel.
The static shear stress E is less than the dynamic shear stress, which is associated with the physicochemical nature of the suspensions.
Static shear stress 0 is also determined on rotational (torsion) devices. Numerous studies have shown that to obtain stable results, measurements should be carried out at a low rotation speed of the device cylinder, but the measurement operation should take no more than 1 minute.
Static shear stress (SSS) of the drilling fluid Qt (Pa), where the subscript t indicates the time (min) the sample is at rest. The value characterizes the strength resistance of a drilling fluid that is at rest for a given time, and is determined using the SNS-2 device or VSN type rheometers as a tangential shear stress, which corresponds to the beginning of structure destruction.
The static shear stress (MPa) in the filter cake is determined by the value of 9K Kp.
Static shear stress characterizes the force that is required to bring a solution out of rest.
Static shear stress (SSS) 0, determined by the minimum tangential shear stress at which the destruction of the structure in a quiescent clay solution begins, Pa. SNS characterizes the strength of the thixotropic structure and the intensity of hardening over time.
Static shear stress (SSS) 6 (in dPa) characterizes the strength of the thixotropic structure of emulsions at rest. The presence of certain values of SNS in reverse emulsions gives them the ability to hold finely dispersed weighting agents in suspension, reduces the depth of penetration into the reservoir when the emulsion is located against the perforated thickness of the formation, or, conversely, leads to an increase in the pressure necessary to displace it from the reservoir. In this case, reverse emulsions can have SNS due to structuring of the entire volume of the dispersion medium with structure formers or due to the formation of a coagulation structure by combining globules of the dispersed phase into aggregates interconnected in the volume of the dispersion medium. The latter type of structure is easily destroyed when the system flows or the temperature rises.
How to check battery voltage with a multimeter
How to check battery voltage with a multimeter
When electric charges move freely through a conductor, it is called electric current. If they stop without moving and begin to accumulate on something, we should talk about static electricity. In accordance with GOST, statics is the totality of the occurrence, preservation and free accumulation of an electric charge on the outer surface of dielectrified materials or on insulators.
The occurrence of static electricity
When the physical body is in a normal neutral state, the balance of negatively and positively charged particles in it is maintained. If it is violated, an electric charge with one sign or another is formed in the body, polarization occurs - the charges begin to move.
Additional Information. Every physical object is capable of producing charges in either a positive or negative direction, which is how they are characterized on the triboelectric scale.
For example:
- positive: air, skin, asbestos, glass, leather, mica, wool, fur, lead;
- negative: ebonite, Teflon, selenium, polyethylene, polyester, brass, copper, nickel, latex, amber;
- neutral: paper, cotton, wood, steel.
Static electrification of objects can occur due to various reasons. The main ones are the following:
- direct contact between bodies with subsequent separation: friction (between dielectrics or dielectric and metal), winding, unwinding, moving layers of material relative to each other and other similar manipulations;
- instantaneous change in ambient temperature: sudden cooling, placing in an oven, etc.;
- radiation exposure, ultraviolet or x-ray irradiation, induction of strong electric fields;
- cutting processes - on machines for cutting or cutting paper sheets;
- special directional guidance with a statistical discharge.
At the molecular level, the occurrence of static electricity occurs as a result of complex processes when electrons and ions from colliding inhomogeneous surfaces with different atomic bonds of surface attraction begin to be redistributed. The faster materials or liquids move relative to each other, the lower their resistivity, the larger the areas that come into contact and the interaction forces, the higher the degree of electrification and electrical potential will be.
The sources of electrostatics, both in domestic and industrial conditions, are computer and office equipment, televisions and other units and devices powered by electric current. For example, the simplest computer has a pair of fans to cool the system unit. When the air accelerates, the dust particles contained in it become electrified and, retaining a charge, settle on surrounding objects, people’s skin and hair, and even penetrate into the lungs.
Also, static accumulates in large quantities on monitor screens. In homes and industrial premises, electrostatic charges are formed on floors covered with linoleum or PVC tiles, on people (in hair and on synthetic clothing).
In nature, static electricity is very powerful, arising when cloud masses move: huge potentials of electricity arise between them, which manifests itself in lightning discharges.
In industry, the formation of static charges is often encountered in the following cases:
- friction of conveyor belts on shafts, friction of wire belts on pulleys (especially in cases of slipping and jamming);
- when flammable liquids pass through pipelines;
- filling tanks with gasoline and other liquid petroleum fractions;
- entry and movement of dust particles in air ducts at high speed;
- during grinding, mixing and sifting dry substances;
- during mutual compression of dielectric materials of various types and consistencies;
- mechanical processing of plastics;
- the passage of liquefied gas (especially those containing suspensions or dust) through pipelines;
- moving carts with rubberized tires on insulating flooring.
Danger of static electricity
Accumulated static electricity poses the greatest danger in industrial production. Unexpected ignition of flammable material by sparks from operator contact with grounded equipment may occur, followed by an explosion. The energy of electrostatic discharge is sometimes about 1.4 joules - this is more than enough to bring mixtures of dust, steam, gas and air present in any flammable substances to a state of combustion. According to GOST, the maximum energy of accumulated charges on the surface of an industrial facility should not be more than 40 percent of the minimum energy for ignition of the material.
During certain technological operations, for example:
- pouring and transporting sand in trucks;
- pumping fuel through pipelines;
- pouring alcohol, benzene, ether into ungrounded tanks at high speed;
- during conveyor work, etc., electrical potentials from 3 to 80 kilovolts are generated.
Note! In order for gasoline vapors to explode, 300 volts are enough, flammable gases - 3 kilovolts, and flammable dusts - about 5 kilovolts.
Statics also negatively affects the operation of all precision and ultra-precision instruments, radio communications equipment, and creates great problems in the functioning of automation and television mechanics. Many parts of complex electronic devices are simply not designed to withstand such high voltages generated by static discharge. It disables these parts, as a result of which the devices lose accuracy.
People can also accumulate charged particles if they wear shoes with non-conductive soles or wool, silk or synthetic clothing. Electrification occurs when moving (if the flooring does not conduct electricity) and interacting with dielectric objects.
The impact of static on the human body is carried out in the form of a long-flowing electric current of low voltage or an instantaneous discharge, which causes mild and not always pleasant tingling sensations on the skin (sometimes they are assessed as moderate or even strong pricks). In general, such exposure to a potential of no higher than 7 joules is considered harmless to health; however, even a weak current discharge can lead to reflexive muscle contraction, which is fraught with various industrial injuries (getting into the working areas of mechanisms, catching parts of the body or clothing by unfenced moving parts of machines, falling from height).
If we consider the effect of static electricity on the human body at the cellular level, then as a result of the activation of the neuroreflex mechanism, irritation of skin neurons and the smallest capillaries occurs. This leads to changes in the ionic composition of the tissues of our body, which manifests itself in increased fatigue during the day, a constant irritated mental state, disturbances in sleep rhythm and other problems in the functioning of the central nervous system. Overall performance decreases. Provoked by constant exposure to static electricity, spasms of blood vessels can cause bradycardia - a decrease in the frequency of contractions of the heart muscle and increased blood pressure.
Methods of protection against static in production
A set of protective measures is being developed and applied against the harmful and dangerous manifestations of accumulated static electric current in production conditions. They are based on the following methods:
- increasing the conductive properties of materials and the surrounding working environment, which leads to the dispersion of periodically appearing static electric charges in space;
- reduction in the speed of processing and movement of materials, which significantly reduces the possibility of generating static electric charges;
- full-scale use of well-designed grounding, which helps eliminate the accumulation of dangerous potentials;
- increasing the resistance of the machines and mechanisms themselves to the action of statistical discharges;
- preventing the penetration of electric current into the work area.
All methods used to prevent static electrical discharges are divided into structural, technological, chemical, physical and mechanical. The last three are aimed mainly at reducing the activity of generating electric charges and their rapid release into the soil. At the same time, the first of these methods are not related to grounding.
The so-called Faraday cage acts as a highly reliable means of protection against static electricity. It is made in the form of a fine-mesh mesh that encloses the machines over the entire area; it has a connection to the ground loop.
Thanks to this design, electrical fields do not penetrate inside the Faraday cage, and it does not affect the magnetic field in any way. Electrical cables previously covered with a metal sheet shield are protected according to the same principles.
Electrostatic charge can be optimally reduced by increasing the conductivity of industrial materials and by performing corona treatment (i.e., creating air plasma on the surface of materials with a corona discharge at room temperature). This is achieved through a special selection of materials with increased volumetric conductivity, increasing the working area and increasing the ionization of the air around the protected mechanisms. Special units - ionizers - generate positively and negatively charged ions, which are attracted to oppositely charged dielectrics and neutralize their charges.
Important! For substances with high electrical resistance, such methods of protection against static are not suitable.
Grounding is mandatory in the list of measures to protect against static electricity. The grounding device includes a ground electrode (conductive element) and a grounding conductor between the grounding point on the soil and the ground electrode. Grounding against electrostatics is considered sufficient if the resistance at any point of the equipment is not higher than 1 megaohm. Equipment often uses conductive films to cover the work surface.
Antistatic floors are laid in work areas; operators must work in antistatic clothing and shoes (the resistance of the sole material is not higher than 100 ohms).
Protection against static electricity at home
In everyday life, there is a set of measures and measures that help prevent the formation of electrostatic discharges:
- wet cleaning carried out every day reduces the amount of dust circulating in the air;
- preventing the air from drying out, ventilating the premises daily;
- use of antistatic brushes in cleaning;
- use of antistatic furniture;
- finishing the house with materials that remove static well: wood, antistatic linoleum and others;
- As for clothing, remove woolen clothes with slow movements, and to remove the sticking effect of silk items, use antistatic sprays;
- do not iron animal fur in cold and dry air;
- Comb your hair with wooden or metal combs instead of plastic combs.
Do not forget about protecting personal vehicles from the formation of static on the car body, especially before refueling it with gasoline. This is done using a simple antistatic strip under the underbody.
Static electricity is free electrical charges collected on various dielectrics. Both in industry and in everyday life, completely unhealthy static electricity accumulates, and protection from it is necessary, since such charges can harm both machines, mechanisms, industrial facilities and human health. Only reliable methods can nullify or completely prevent this negative phenomenon.
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