Static electricity is the collection of electrical charges on the surface of a material, usually insulators. This electricity is therefore called static because there is no current flowing as usual - alternating or direct current. To understand static electricity, you need to understand the basics of atoms and magnetism. All physical objects are made up of atoms. Inside an atom are protons, electrons and neutrons. Protons are positively charged, electrons and neutral neutrons are negatively charged.
Typically, two materials are involved in static electricity, one having an excess of electrons or negative (-) charges on its surface and another material having an excess of positive (+) electrical charges. Atoms on the surface of a material that have lost one or more electrons will have a positive (+) electrical charge, gained a negative (-).
Causes of Static Electricity
Static electricity is usually generated when certain materials are rubbed against each other - like wool on plastic or shoe soles on carpet. This phenomenon also occurs if the materials are pressed against each other.
A material that loses electrons acquires an excess of positive (+) charges. A material that receives electrons gains an excess of negative (-) charges on its surface. Static electricity is generated much better when the air is dry or the humidity is low. When the air is humid, water molecules can collect on the surface of various materials. This can prevent the accumulation of electrical charges. It has to do with the shape of the water molecule and its own electrical forces. But when there is extreme turbulence between water droplets, such as in a thunderstorm cloud, static electric charges can accumulate on water droplets. Benjamin Franklin, using kites in a storm, showed that static electricity is also generated in a cloud during a thunderstorm.
Properties of static electricity
Static electricity can attract or repel materials from each other. It can also cause a spark when changing from one material to another.
A typical example of static electricity is a small electricity, which can be felt when touching a doorknob during dry weather.
Static electricity is generated when extra electrons (negatively charged particles) accumulate and are shed.
This type of electricity does not move through wires, but accumulates on the surface and transfers charges from one element to another. Popular demonstrations of this usually involve rubbing a balloon over a fabric such as corduroy trousers and then placing the balloon next to a wall where the balloon itself can stick.
Everyday 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, there is a redistribution of static charges that change 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.
At solids the distribution of charges occurs due to the movement of electrons, and in liquid and gaseous - 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 at school in 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.
Also known is the experience of deflecting a thin jet of water under the action 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:
dry indoor air;
reinforced concrete walls from which multi-storey buildings are made.
How is static charge created?
Usually the physical body contains equal amount 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 electric charge of a certain sign.
Static refers to the state of rest, when the body is not moving. Inside its substance, polarization can occur - the movement of charges from one part to another or their transfer from a nearby object.
The electrification of substances occurs due to the acquisition, removal or separation of charges when:
interaction of materials due to forces of friction or rotation;
a sharp temperature drop;
irradiation in various ways;
separation or cutting of physical bodies.
They are distributed over the surface of an object or at a distance from it at several interatomic distances. For ungrounded bodies, they spread over the area of the contact layer, and for those connected to the earth contour, they flow onto it.
The acquisition of static charges by the body and their flow occurs simultaneously. Electrification is provided when the body receives more energy potential than it expends in the external environment.
A practical conclusion follows from this provision: in order to protect the body from static electricity, it is necessary to divert the acquired charges from it to the earth circuit.
Methods for assessing static electricity
According to the ability to form electric charges of different signs when interacting with other bodies by friction, physical substances are characterized according to 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 woolen 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 you can see, the potential of static electricity reaches very large 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 significantly reduces the humidity of the air. Its effect on the amount of body stress in 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 humidifiers are used to combat it.
In nature, static electricity can reach enormous levels. When clouds move long distance significant potentials accumulate between them, which are manifested by lightning, the energy of which is enough to split a century-old tree along the trunk or burn a residential building.
When static electricity is discharged in everyday life, we feel “pinching” of fingers, we see sparks emanating from woolen things, we feel a decrease in vigor and efficiency. The current that our body is exposed to in everyday life adversely affects the well-being, condition nervous systems s, but it does not bring obvious, visible damage.
Manufacturers of measuring industrial equipment produce devices that allow you to accurately determine the magnitude of the voltage of accumulated static charges both on the equipment cases and on the human body.
How to protect yourself from static electricity in your home
Each of us must understand the processes that form static discharges that pose a threat to our body. They should be known and limited. To this end, various educational events are held, including popular TV shows for the population.
They show with accessible means ways to create static voltage, the principles of its measurement and methods for implementing preventive measures.
For example, given the triboelectric effect, it is best to comb your hair with natural wood combs, 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 body of the car when it is moving on a dry road, special tapes with antistatic agent are used, which are attached to the bottom. Their various types are widely presented on sale.
If there is no such protection on the car, then the voltage potential can be removed by briefly grounding the case 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 clothes made of synthetic materials, it can be removed by treating vapors from a special spray can with the Antistatic composition. In general, it is better to use less such fabrics and wear natural materials made of 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, as the harmful effects on the body will be reduced.
The influence of dry air, typical for urban apartments in winter time, has already been discussed. Special humidifiers or even small pieces of moistened cloth placed on the bytarii improve the situation and reduce the formation of static electricity. And here is the regular execution wet cleaning indoors allows you to remove electrified particles and dust in a timely manner. This is one of better ways protection.
Household electrical appliances also accumulate static charges on the case during operation. The potential equalization system connected to the common ground 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 subject to static and needs to be protected 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 electrical characteristics devices or disable them altogether.
Under production conditions, the discharge can be random and depend on a number of different factors:
the values 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 body of the operator is shown in the picture.
The magnitude of the current is influenced by: the capacity of the charge accumulated by a person, the resistance of his body and contact pads.
In the production of electrical equipment, a static discharge can be created without the participation of the operator 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 case and the resistance of the contact pads formed. In this case, the semiconductor at the initial moment is simultaneously affected by the induced high voltage potential and the discharge current.
Due to such a complex impact, damage can be:
1. explicit, when the performance of the elements is reduced to such an extent that they become unusable;
2. hidden - by reducing the output parameters, sometimes even falling within the established factory specifications.
The second type of malfunctions is difficult to detect: they most often affect the loss of performance during operation.
An example of such damage from the action of high static voltage is shown by the deviation graphs of the current-voltage characteristics in relation to the KD522D diode and the integrated circuit BIS KR1005VI1.
The brown line under number 1 shows the parameters of semiconductor devices before testing with increased voltage, and curves with numbers 2 and 3 show their decrease under the action of an increased induced potential. In case #3, it has more impact.
Damage can be caused by:
overestimated induced voltage, which breaks through the dielectric layer of semiconductor devices or violates the structure of the crystal;
high flowing current density, causing a high temperature, leading to the melting of materials and burning of the oxide layer;
tests, electrical thermal training.
Hidden damage may not affect performance immediately, but after several months or even years of operation.
Methods for performing 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. exclusion of the formation of electrostatic charges;
2. blocking their entry into the workplace;
3. Increasing the resistance of devices and accessories to the action of discharges.
Methods No. 1 and No. 2 allow you to protect a large group of various devices in a complex, and No. 3 is used for individual devices.
The high efficiency of maintaining the operability of the equipment is achieved by placing it inside the Faraday cage - a space fenced on all sides with a fine-mesh metal mesh connected to the ground loop. External electric fields do not penetrate inside it, and static magnetic fields are present.
Shielded cables work according to 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 flow. The third technique protects devices from the effects of charges, but it does not affect their drain.
You can improve the stacking of discharges by:
creating a coronation;
increasing the conductivity of materials on which charges accumulate.
Solve these questions:
air ionization;
increase in working surfaces;
selection of materials with the best bulk conductivity.
Due to their implementation, pre-prepared lines are created for draining static charges to the ground loop, preventing them from getting on the working elements of the devices. It takes into account that the general electrical resistance created path should not exceed 10 ohms.
If the 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 a comprehensive electrostatic protection of the workplace for an operator involved in the maintenance and adjustment of electronic devices is shown in the picture.
The surface of the table is connected to the ground loop through a connecting conductor and a conductive mat using special terminals. The operator works in special clothes, wears shoes with conductive soles and sits on a chair with a special seat. All these measures allow high-quality removal of accumulated charges to the ground.
Working air ionizers regulate humidity, reduce the potential of static electricity. When using them, it is taken into account that the increased content of water vapor in the air adversely affects human health. Therefore, they try to maintain it at a level of about 40%.
Also effective way there may be regular ventilation of the room or the use of a ventilation system in it, when the air passes through the filters, ionizes and mixes, thus ensuring the neutralization of the resulting charges.
To reduce the potential accumulated by the human body, bracelets can be used to complement the set of antistatic clothing and shoes. They consist of a conductive strip that is attached to the arm with 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 can cause pain and electrical shock.
During the charge draining to the ground, it is important to ensure the rate of its departure in 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:
forced shunting of the outputs of electronic boards and blocks 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 supplied with metal cables, which, during landing, work as protection against static electricity.
The most dangerous form of electromagnetic interference (EMI). The human body can accumulate an electrostatic charge of up to 25,000 volts. This charge can be discharged very quickly through an electrically grounded object or device. Applying a voltage pulse of 25,000 V to any electronic device has the potential to damage it.
Detection and Prevention of Electrostatic Discharge
Static electricity can be discharged through the computer's digital components. Electronic devices used in the construction of digital equipment are particularly susceptible to damage from electrostatic discharge. In fact, electrostatic discharge is the most dangerous form of electrical interference for digital equipment.
The following are the most common causes of electrostatic discharge:
- Low humidity (high temperature and dry conditions environment)
- Incorrect grounding
- Unshielded cables
- Poor connection quality
- Moving mechanical parts
School teachers demonstrate the principle of creating a static charge by rubbing various materials against each other. When people move, pieces of clothing rub against each other and can create a significant electrostatic charge on the body. Walking on carpet can generate charges in excess of 1000 volts. Motors in electrical devices such as vacuum cleaners and refrigerators also generate high levels electrostatic charge.
Electrostatic discharge is most likely to occur in low humidity environments. If the relative humidity drops to less than 50%, static charges can build up very easily. In general, electrostatic discharge does not occur if the humidity exceeds 50%. As soon as the charge reaches a value approaching 10,000 V, the probability of its discharge through grounded metal parts becomes very high.
While electrostatic discharge does not affect humans, it does destroy certain electronic devices. A high voltage pulse can burn the input circuits of many microcircuits. Sometimes such damage does not appear immediately. They can build up over time and eventually lead to device failure. Electronic logic devices based on MOS structures are especially sensitive to electrostatic discharge.
High voltage, low risk to people
Readers may be somewhat surprised that a voltage of 25,000 V present in a monitor poses a lethal danger to humans, while an electrostatic charge of 10,000 V or 25,000 V does not pose such a danger. The reason for this is the amount of current that this voltage source creates. For example, the monitor and power supply circuits can generate a current of several amperes, while an electrostatic discharge generates a current that does not exceed one thousandth of an ampere. Therefore, an alternating current of 1 A, created by a voltage of 120 V of the power supply, is deadly, but a current of one microampere, created by an electrostatic discharge of 25,000 V is not.
It can occur on insulated conductors, on the surface or in the volume of dielectrics.
The friction that occurs when two substances of different kinds come into contact leads to the electrization of dielectrics. This is due to different molecular and atomic forces. We can say that static electricity is obtained when their balance is disturbed due to the acquisition or loss of an electron.
It is very easy to explain this process. The equilibrium state of an atom is achieved when there are the same number of protons and electrons. Moving from one atom to another, electrons form positive and negative ions. When they are out of balance, static electricity occurs.
Protons and electrons have the same electrical charge, but with different polarities. It is measured in coulombs and determines the amount of electricity that passes in 1 second. in the cross section of the conductor. The static charge is directly proportional to the number of unstable ions, that is, the deficit or excess of electrons.
Static electricity can be generated. This happens due to the absence of one electron from the positive ion, as a result of which it can accept a free electron from the negative particle. In turn, a negative ion can be an atom or a molecule with big amount electrons. In these cases, there is one electron that is able to neutralize the positive charge.
The main causes of static electricity are:
- separation or contact of two materials;
- rapid temperature changes;
- UV radiation, radiation, strong electric fields, ;
- operations performed by cutting (cutting machines or paper cutters);
- induction, that is, the emergence electric field caused by static charge.
A phenomenon called static electricity is found everywhere in everyday life. Electrostatic discharge occurs at very high voltages but at low currents. In this case, there is no danger to humans.
Despite this, protection against static electricity is necessary, as it can be dangerous for many elements of electrical appliances. Transistors, microprocessors, circuits, etc. very often suffer from it. When working with electronic components, it is necessary to take measures to prevent the accumulation of static charge.
A direct danger exists with lightning that occurs during the formation of thunderclouds. Clouds due to the movement of air currents that are saturated with water vapor can also form. Such discharges often occur between charged clouds and the ground. In this case, you need protection from static electricity in the form of lightning rods. They are able to conduct a discharge straight into the ground. In addition to lightning, a thundercloud creates dangerous electrical potentials on insulated metal objects due to the process
Lungs, obtained as a result of various manifestations of static electricity, are harmless at first glance, but this is far from being the case. This phenomenon can hide a great danger, since the resulting spark can cause a fire. Static electricity and protection against it are two concepts that everyone should be aware of, because sometimes serious troubles happen due to ignorance.
In everyday life and at work, it is necessary to prevent the occurrence of this kind of electricity. To do this, you should carry out regularly Flammable liquids - this is another serious threat. They must be used in well-ventilated areas, which partially prevent static electricity (and protection against it in this case, you are almost guaranteed). When handling such liquids, use natural clothing, earthing rotating machinery, and only metal containers for storing liquids that can quickly ignite.
The concept of static electricity is familiar to everyone from school course physics. Static electricity arises in the process of the appearance of charges on conductors, surfaces of various objects. They appear as a result of friction that occurs when objects come into contact.
What is static electricity
All substances are made up of atoms. An atom has a nucleus surrounded by equal numbers of electrons and protons. They are able to move from one atom to another. When moving, negative and positive ions are formed. Their imbalance leads to the fact that static occurs. The static charge of protons and electrons in an atom is the same, but has a different polarity.
Statics appears in everyday life. Static discharge can occur at low currents but high voltages. In this case, there is no danger to people, but the discharge is dangerous for electrical appliances. During the discharge, microprocessors, transistors and other circuit elements suffer.
Causes of static electricity
Static occurs under the following conditions:
- contact or separation of two different materials;
- sudden changes in temperature;
- radiation, UV radiation, x-rays;
- operation of the paper cutting machine and cutting machines.
Static often occurs during or before a thunderstorm. Thunderclouds, when moving through air saturated with moisture, form static electricity. The discharge occurs between the cloud and the ground, between individual clouds. The device of lightning rods helps to conduct a charge to the ground. Thunderclouds create an electrical potential on metal objects that cause light shocks when touched. For a person, a blow is not dangerous, but a powerful spark can cause some objects to ignite.
Each resident has repeatedly heard a crack that is heard when removing clothes, a blow from touching the car. This is a consequence of the appearance of static. An electric discharge is felt when cutting paper, combing hair, and pouring gasoline. Free charges accompany a person everywhere. The use of various electrical devices increases their appearance. They occur when pouring and grinding solid products, pumping or pouring flammable liquids, when transporting them in tanks, when winding paper, fabrics and films.
The charge appears as a result electrical induction. Large electric charges are created on the metal bodies of cars in the dry season. The TV screen or computer monitor is capable of being charged by exposure to a beam created in a cathode ray tube.
The harm and benefits of static electricity
Many scientists and inventors have tried to use a static charge. Bulky units were created, the benefits of which were low. The discovery by scientists was useful corona discharge. It is widely used in industry. With the help of an electrostatic charge, complex surfaces are painted, gases are cleaned of impurities. All this is good, but there are numerous problems. Electric shocks are of great power. They can sometimes hit a person. This happens both at home and in the workplace.
The harm of static electricity is manifested in shocks of different power when removing a synthetic sweater, when leaving the car, turning on and off the food processor and vacuum cleaner, laptop and microwave oven. These strikes can be harmful.
There is static electricity, which affects the work of the cardiovascular and nervous systems. It should be protected from it. The person himself is also often a carrier of charges. When in contact with the surfaces of electrical appliances, they become electrified. If this is a control and measuring device, the case may end in its breakdown.
The discharge current brought by a person destroys connections with its heat, breaks the tracks of microcircuits, destroys the film field effect transistors. As a result, the circuit becomes unusable. Most often, this does not happen immediately, but at any stage during the operation of the tool.
In factories processing paper, plastics, textiles, materials often behave incorrectly. They stick to each other, stick to various types equipment, repel, collect a lot of dust on themselves, are wound incorrectly on spools or bobbins. This is due to static electricity. Two charges of the same polarity repel each other. Others, one of which is positively charged and the other negatively, attract. Charged materials behave in the same way.
In printing plants and other places where flammable solvents are used, fire may occur. This occurs when the operator is wearing shoes with non-conductive soles and the equipment is not properly grounded. The flammability depends on the following factors:
- discharge type;
- discharge power;
- source of static discharge;
- energy;
- presence of solvents or other flammable liquids nearby.
Discharges are spark, carpal, sliding carpal. A spark discharge emanates from a person. Carpal occurs on the pointed parts of the equipment. Its energy is so small that it practically does not cause a fire hazard. A sliding brush discharge occurs on synthetic sheets, as well as on roll materials with different charges on each side of the web. It poses the same danger as a spark discharge.
Damage ability - main question for safety professionals. If a person holds on to the bobbin and is himself in a zone of tension, his body will also be charged. Always touch ground or grounded equipment to discharge the charge. Only then will the charge go to the ground. But a person will receive a strong or weak electric shock. As a result, reflex movements occur, which sometimes lead to injury.
A long stay in a charged zone leads to irritability of a person, to a decrease in appetite, and worsening of sleep.
Dust from the production area is removed by ventilation. It accumulates in pipes and can be ignited by a static spark.
How to remove static electricity from a person
The simplest means of protection against it is equipment grounding. In production conditions, screens and other devices are used for this purpose. In liquid substances, special solvents and additives are used. Antistatic solutions are actively used. These are substances with low molecular weight. The molecules in an antistatic agent move easily and react with moisture in the air. Due to this characteristic, static is removed from a person.
If the operator's shoes have non-conductive soles, he must necessarily touch the ground. Then the escape of static current into the ground cannot be stopped, but the person will receive a strong or weak blow. We feel the effect of static current after walking on carpets and rugs. Drivers getting out of the car receive electric shocks. It is easy to get rid of this problem: just touch the door with your hand while sitting still. The charge will drain to the ground.
Ionization helps a lot. This is done using an antistatic bar. It has many needles made of special alloys. Under the action of a current of 4-7 kV, the air around decomposes into ions. Air knives are also used. They are an antistatic bar through which air is blown and cleans the surface. Static charges are actively formed when liquids with dielectric properties are sprayed. Therefore, to reduce the action of electrons, a falling jet should not be allowed.
It is advisable to use antistatic linoleum on the floor and clean more often with household chemicals. At enterprises associated with the processing of fabrics or paper, the problem of getting rid of static is solved by wetting materials. Increased humidity prevents harmful electricity from accumulating.
To remove static, you must:
- humidify the air in the room;
- treat carpets and rugs with antistatic agents;
- wipe the seats in the car and in the rooms with antistatic wipes;
- Moisturize your skin more often
- refuse synthetic clothing;
- wear shoes with leather soles;
- prevent the appearance of static on the laundry after washing.
Indoor flowers, a boiling kettle, and special devices moisturize the atmosphere well. Antistatic compounds are sold in household chemical stores. They are sprayed over the carpet surface. You can make your own antistatic. To do this, take a fabric softener (1 cap), pour into a bottle. Then the container is filled with clean water, which is sprayed over the surface of the carpet. Wipes moistened with antistatic agent neutralize the charges on the seat upholstery.
Moisturizing the skin is done with lotion after a shower. Hands are rubbed several times a day. You should change clothes for natural. If it is charging, treat it with antistatic agents. It is recommended to wear shoes with leather soles or walk barefoot around the house. Before washing, it is advisable to pour ¼ cup of soda (food) on clothes. It removes the discharges of electricity and softens the fabric. When rinsing clothes, you can add vinegar (¼ cup) to the machine. It is better to dry clothes in the fresh air.
All of these measures help to neutralize static problems.
