Section I. Overview of electrical safety
Electrical safety mainly includes personal safety and equipment safety in two aspects. Personal safety refers to the safety of people engaged in the work and the use of electrical equipment in the process of operation; equipment safety refers to the safety of electrical equipment and other related equipment, building.
I. Characteristics of electricity
(a) the special form of electricity, invisible, can not be seen. People can feel the daily electricity, only the conversion of electrical energy,
such as light, heat, magnetism and so on.
(ii) the transmission speed of electricity (300,000 kilometers per second).
(iii) Electricity is highly networked, with a number of lines linked into a whole." Generation, supply and use of electricity" is done simultaneously in an instant.
Localized faults may sometimes affect the entire grid.
(D) the possibility of accidents and the danger of large. Occurrence of personal electric shock, fire, damage to equipment, explosion and other electrical accidents, will affect the production, and even cause the whole enterprise production paralyzed, the consequences are very serious.
Two, current damage to the human body
(a) perceived current
In a certain probability, through the human body to cause any human feeling of the smallest current is called perceived current.
(ii) get rid of the current
Through the body of the current exceeds the perceived current, muscle contraction increases, tingling sensation increases, the sensory part of the expansion to the current increases to a certain extent, the person will be electrocuted due to muscle contraction, spasm and grasp the electrified body, can not get rid of the electrode by themselves. People can get rid of electrodes after electrocution of the maximum current is called to get rid of the current.
(C) minimum lethal current
Life-threatening current in a relatively short period of time is called lethal current. The causes of death by electric shock are complex. An industrial-frequency alternating current of tens of milliamperes or more passing through the body may cause both ventricular fibrillation, or the heart to stop beating, and respiratory arrest. However, since ventricular fibrillation occurs much earlier than respiratory arrest, causing ventricular fibrillation is the primary. If the current through the body is only 20 to 25 milliamps, it generally cannot directly cause ventricular fibrillation or cardiac arrest.
(D) electric shock and electric injury
Electric shock is an injury caused by the passage of electric current through the interior of the human body, which destroys the normal work of the human heart, nervous system, and lungs. Electric shock can result from the human body touching electrically charged wires, the casing of leaky equipment or other electrically charged bodies, as well as from lightning strikes or capacitive discharges.
Electrical injuries are localized injuries to the human body caused by the thermal, chemical, or mechanical effects of electric current, and include such different forms of injury as arc burns, scalds, electric branding, skin metallization, electromechanical injuries, and electroluminescence.
(E) five factors of the degree of injury to the human body of electricity
1, the size of the current through the human body
Through the human body of the industrial frequency 50 ~ 60 Hz AC current does not exceed 0.01 amperes, DC current does not exceed 0.05 amperes, the human body is basically safe. Current greater than the above values, will make people feel paralyzed or severe pain, breathing difficulties, and even their own inability to get rid of the power supply, life-threatening. The current through the human body, whether AC or DC, is greater than 0.l amperes, as long as a relatively short period of time will cause a person to suffocate, cardiac arrest, unconsciousness and death.
The size of the current through the human body depends on the applied voltage and the resistance of the human body. The human body resistance varies, generally 800 to 1000 ohms. In general places, for the human body only less than 36 volts is safe.
2, energized duration
Electrocution accidents, the longer the duration of the current, the more the human body resistance decreases, the more likely to cause ventricular fibrillation, that is, the greater the risk of electric shock. This is because the longer the current lasts, the more energy accumulates and the current that causes ventricular fibrillation decreases.
3, energized pathway
The current through the heart, will cause the heart to tremble or the heart stops beating, blood circulation is interrupted, resulting in death. Current through the spinal cord will paralyze a person's limbs. Therefore, the path of electric current through the human body is most dangerous from hand to foot, followed by from hand to hand, and again from foot to foot.
4, through the type of current
Through the frequency of the human body current, industrial frequency current is the most dangerous. 20 ~ 400 Hz AC current to get rid of the current value of the lowest (i.e., the danger is greater); lower or higher than this band, the danger is relatively small, but the high-frequency current is easier to cause burns through the skin than the industrial frequency current, therefore, we can not ignore the use of high-frequency current safety issues; direct current The danger of direct current is relatively smaller than that of alternating current.
Three, the human body electrocution
The human body electrocution, mainly divided into: single-phase electrocution: two-phase electrocution, step voltage electrocution three.
(a) single-phase electrocution
Single-phase electrocution, refers to people on the ground or other grounded body, a part of the human body touches a phase of the electrocution of the electrified body.
(B) two-phase electrocution
Two-phase electrocution, refers to the two parts of the human body at the same time touching the two-phase electrified body electrocution.
(C) step voltage electrocution
Stepping voltage electrocution, refers to the person enters the ground current dispersion field electrocution. Due to the uneven distribution of potential on the ground within the bulk current field, the potential between the two feet of the person is different. The difference between these two potentials is called the step voltage. The size of the step voltage is related to the distance between the person and the grounding body. When a person's foot across the grounding body, the maximum step voltage; people farther away from the grounding body. Step voltage is smaller; and the distance from the grounding body more than 20 meters, the step voltage is close to zero.
Section II electrical accidents
I. Classification of electrical accidents
(a) electrical accidents can be divided into personal accidents, equipment accidents, electrical fires and explosions according to the form of the disaster.
(b) the occurrence of accidents in the circuit conditions, can be divided into short-circuit accidents, broken wire accidents, grounding accidents, leakage accidents.
(c) according to the severity of the accident, can be divided into very large accidents, major accidents and general accidents.
(1) mega-accident, refers to the cause of three and more than three deaths; a large area of power outages, resulting in serious load shedding; major electrical equipment or production plant serious damage, resulting in a fire accident loss of more than 300,000 yuan; causing other users of the power outage, resulting in a serious political impact and economic losses.
(2) A major accident is one that causes one or two deaths or three or more serious injuries; a large area of power outage, resulting in load shedding; damage to major electrical equipment, resulting in a more serious political impact and economic loss due to power outage.
(3) general accidents, refers to other accidents in addition to major accidents and major accidents.
(4) according to the basic causes of accidents, electrical accidents can be divided into the following categories:
(1) electrocution accident. Personal contact with a charged body (or too close to the high-voltage charged body), due to the current flowing through the human body and the personal injury caused by the accident. Electrocution accident is caused by the current energy applied to the human body. Electrocution can be divided into single-phase electrocution, two-phase electrocution and step voltage electrocution.
(2) Lightning and electrostatic accidents. Localized temporary loss of balance of positive and negative charges, under certain conditions will be released from the energy of the charge, the human body caused by the injury or other accidents caused. Lightning can often destroy buildings, injuring people, animals, but also may cause fire; electrostatic discharge of the greatest threat is to cause fire or explosion accidents, may also cause injury to the human body.
(3) radio frequency injury. Electromagnetic field energy on the human body caused by the injury, also known as electromagnetic field injury. Under the action of high-frequency electromagnetic fields, the human body due to the absorption of radiation energy, the organs will be subject to varying degrees of injury, thus causing a variety of diseases. In addition to high-frequency electromagnetic fields, ultra-high voltage high-intensity industrial electromagnetic fields will also cause some damage to the human body.
(4) circuit failure. Electrical energy in the transmission, distribution, conversion process, due to the loss of control and caused by the accident. Circuit and equipment failures not only threaten personal safety, but can also seriously damage electrical equipment.
The above four types of electrical accidents, with electric shock accidents are the most common. But no matter which type of accident, it is caused by the improper release or transfer of energy from various types of currents, charges, and electromagnetic fields.
Two, electric shock accidents
1, the main causes of common electric shock accidents are:
Electrical lines, equipment maintenance in the measures are not implemented;
Electrical lines, equipment installation does not meet the safety requirements;
Non-electrical workers arbitrarily deal with electrical matters;
Wiring error;
Operation of leakage of electricity in the machine and equipment or Use of leaky power tools (including: equipment, tools without grounding, zero protection measures;
Equipment, tools have been interrupted by the protective wire;
With power to move the equipment due to damage to the power supply insulation;
Welding operators wearing undershirts, shorts, do not wear insulated shoes, sweating through the gloves, the pliers accidentally touching themselves, wet hands to operate the machine buttons, etc.;
Due to storms, lightning strikes and other natural disasters;
The poor management of temporary electricity on site.
2, to prevent electrocution, both technical measures and organizational and management measures, summarized in the following aspects:
(1) to prevent contact with electrically charged parts: common safety measures are insulated, screen protection and safety spacing.
Insulation: that is, the use of non-conductive insulating materials to close the charged body, which is to prevent direct electric shock of the basic protection measures.
Screening: that is, the use of cover, shroud, cover, box gate, etc. to isolate the charged body from the outside world.
Spacing: in order to prevent the body from touching or approaching the charged body, to prevent vehicles and other objects collision or excessive proximity to the charged body, in the charged body and the charged body, the charged body and the ground, the charged body and other equipment, facilities, should maintain a certain safety distance between.
(2) to prevent electrical equipment leakage injury: protective grounding and protective zero, is to prevent indirect electric shock of the basic technical measures.
Protective grounding: that is, the normal operation of electrical equipment is not charged metal parts and the earth closely connected. The principle is that through the grounding of the leakage equipment to the ground voltage is limited to a safe range, to prevent electric shock accidents. Protective grounding applies to the neutral point is not grounded in the power grid, the voltage higher than 1KV high-voltage power grid in the shell of the electrical device, should also be taken to protect the grounding.
Protection zero: in the 380/220V three-phase four-wire power supply system, the electrical equipment in normal circumstances is not electrically charged metal casing and the grid in the zero line closely connected.
(3) the use of safe voltage
According to the characteristics of the production and workplace, the use of the appropriate level of safe voltage, is to prevent the occurrence of electrocution casualties fundamental measures. The national standard "safe voltage" (GB3805--83) stipulates that the rating of our safe voltage is 42V, 36V, 24V, 12V and 6V, which should be selected according to the workplace, operator conditions, mode of use, mode of power supply, line conditions and other factors.
(4) leakage protection device
Leakage protection device, also known as the electric shock guard, in the low-voltage grid in the occurrence of electrical equipment and line leakage or electric shock, it can immediately send an alarm signal and quickly cut off the power supply automatically, thereby protecting personal safety.
(5) the rational use of protective gear
In the electrical work, the rational matching and use of insulating protective gear, to prevent electrocution accidents, to protect the operator in the production process of safety and health is of great significance. Insulation protective equipment can be divided into two categories, one is the basic safety protective equipment, such as insulating rod, insulated pliers, high voltage tester pen, etc.; the other is the auxiliary safety protective equipment, such as insulated gloves, insulated (boots) shoes, rubber mats, insulated table, etc..
(6) safe use of electricity organizational measures
Prevention of electric accidents, technical measures are very important, organizational and management measures are essential. Including the development of safety measures and regulations, safety measures and regulations, safety inspection, education and training, organization and analysis of accidents, the establishment of safety data files.
(D) elements of electrical safety
1, electrical insulation
Keep electrical equipment and power supply and distribution lines insulated in good condition, to ensure personal safety and accident-free operation of electrical equipment is the most basic elements.
Electrical insulation can be measured by determining its insulation resistance, compressive strength, leakage current and dielectric loss tax and other parameters to be measured.
2, safety distance
Electrical safety distance refers to the human body, objects, etc. close to the charged body without danger of safe and reliable distance, such as between the charged body and the ground, the charged body and the charged body, the charged body and the human body, the charged body and other facilities and equipment, should be maintained at a certain distance, this distance is called the safety distance.
3, safety current-carrying capacity
The safety current-carrying capacity of a conductor is a guide to the safe amount of sustained current through the body.
4, sign
Clear, accurate, uniform sign is an important factor to ensure the safety of electricity.
Section III safety distance of electrical equipment and facilities
I. Distribution line safety distance
(I) distribution line
Distribution line refers to the connecting wires from the power supply equipment to the electricity equipment.
(B) overhead distribution lines
General overhead distribution lines are overhead distribution lines of 10 kV and below. 1 to 10 kV overhead distribution lines are high-voltage distribution lines, and overhead distribution lines of less than 1 kV are low-voltage distribution lines (high and low-voltage are categorized in the Electricity Safety Regulations with 1 kV as the boundary).
(C) the household line, into the house line
from the distribution line to the user into the line between the first support point of a section of overhead wires is called a household line; from the household line to lead people indoors a section of wire is called into the house line.
(D) cable lines
With the different working environment, cable lines can be divided into tunnels or trench cable lines, direct burial cable lines, cable lines under the bridge hanging and underwater cable lines.
(E) distribution line safety distance
is the distribution line in the laying of a certain range of quality to maintain the relative safety distance. Such as: overhead distribution lines, connecting lines, household low voltage wiring, cable lines, etc., in the process of new construction, reconstruction of post and telecommunications offices should be in line with the national electrical engineering installation standards.
Second, the electrician safe operation distance
Safety distance for maintenance operations: in the energized area of the non-electrical equipment for maintenance, the staff's normal range of activities and the safety of the energized equipment should be greater than the provisions shown in Table 20.
Table staff's normal range of activities and the safety distance from the energized equipment
Equipment voltage (kV) Distance (m) Equipment voltage (kV) Distance (m)
6 or less 0.35 154 2.00
10 ~ 35 0.60 220 3.00
44 0.90 330 4.00
60 to 110 1.50
Section IV Grounding
Electrical equipment, towers, or overvoltage protection devices, which will be connected to the grounding body with a grounding wire, is called grounding.
I. Grounding is classified according to its purpose
(a) In the power system, the grounding required for operation, such as neutral grounding, etc., known as the work of grounding.
(b) the metal casing of electrical equipment, reinforced concrete poles and metal towers, etc., due to insulation damage may be charged, in order to prevent this voltage jeopardizes the safety of the person and the grounding, known as protective grounding. Protective grounding is not grounded in the neutral point of the low-voltage distribution system and power high-voltage system, electrical equipment and electrical lines most used in a security measure.
(c) grounded voltage protection devices, such as lightning rods, lightning arrester and security gap, in order to eliminate the risk of over-voltage grounding, known as over-voltage protection grounding.
(d) easy fuel, natural gas storage tanks and pipelines, in order to prevent the effects of electrostatic hazards and grounding, known as anti-static grounding.
Two, grounding resistance
Earth or natural grounding body or the sum of the resistance to ground, known as the grounding of the grounding resistance. The value of the grounding resistance is equal to the grounding device to the ground voltage and through the grounding body into the ratio of the current in the ground.
Three, the role of grounding
1. Prevent electromagnetic coupling interference: such as digital equipment grounding; RF cable wiring shield grounding, etc.;
2. Prevent strong electricity and lightning strikes on communications equipment: such as columns of racks and general communications equipment chassis grounding, to prevent equipment, equipment, instrumentation, personal injury;
3. Communication system needs: such as the distant supply of the cable relay equipment. System using wire - earth system way.
Four, joint grounding
With the development of communications business, more types, decentralized grounding methods can not meet the requirements.
We work on communications equipment grounding, protective grounding (including grounding and building lightning protection grounding) *** with a group of grounding known as joint grounding.
The joint grounding is a mandatory provision of the new station must be done in accordance with this, in the machine room, the protective ground, the working ground to link them all together, and focus on trying to achieve a low grounding resistance.
Section V Electrical Safety Management
Technical measures for electrical safety
In the use of electricity, generally take: protective grounding, anti-high voltage tampering into the low-voltage protection, protection zero, repeated grounding protection; install fuses, disconnectors, thermal relays, earth leakage protection; the use of safe low-voltage and so on. At the same time must also strengthen the safety management of electrical operations, the serious implementation of the safety management system and safety regulations, as well as adhere to the regular education of safety thinking and safety knowledge.
The handover test of electrical equipment is generally the responsibility of the electrical department, and the requirements are in line with the "Electrical Equipment Handover Test Regulations".
Section VI Electromagnetic Protection
I, electromagnetic radiation
With the rapid development of electronic technology, the application of electronic equipment is more widely used throughout industry, agriculture, military, transportation, medical care, education and arts and many other fields, it can be said that all walks of life can not be separated from electronic equipment. Especially the use of high frequency communications, radar, television, radio, navigation and other equipment, in order to get a larger coverage, the need to radiate to the space of electromagnetic waves with strong energy. As a result, many electromagnetic radiation, broad radiation spectrum, so that we live in the environment of electromagnetic radiation steeply increased, and has reached a direct impact on the human ecological environment and the degree of human health.
Despite the potential hazards of electromagnetic radiation on the human body, especially when used improperly or without attention. But civilized society and modern mankind will not therefore reject or abandon those who can produce electromagnetic radiation, but with our life and work closely related electronic equipment, such as television stations, radio stations, radar stations, navigation stations, microwave relay stations and communication stations and other public **** service facilities, as well as televisions, microwave ovens, cell phones and other household or personal items. It can be said that we live in a space full of electromagnetic radiation!
Two, the harm of electromagnetic radiation
Radiation to the human body on the electromagnetic waves, part of the human body will be reflected or refracted out of the surface of the skin and clothing, the other part will be absorbed by the epidermis, and the human body's cellular tissues and the nervous system have an effect. Electromagnetic radiation can indeed produce adverse effects on the human body - one is to make the temperature of the body's cells and tissues increased and morphological changes; the second is the role of the human nervous system to produce functional changes.
The harm of electromagnetic radiation on the human body is mainly manifested in its adverse effects on the human nervous system, its main symptom is neurasthenia, specifically for dizziness, lethargy, insomnia, fatigue, as well as memory loss and frustration, and sometimes there is a headache and eye distension, limb pain, loss of appetite, hair loss, sweating, weight loss and other phenomena.
The adverse effects of electromagnetic radiation on human health is a reality, especially the higher frequency band. Our country is now in the form of laws or regulations have a safe dose of electromagnetic radiation health standards, in the equipment to take precautions to limit the intensity of electromagnetic radiation is not normal leakage at the same time, but also to engage in high-frequency electronic equipment related to electromagnetic radiation professionals a certain amount of special labor insurance and subsidies.
Three, electromagnetic shielding
Electromagnetic shielding is the main measure to prevent electromagnetic damage.
(a) electromagnetic shielding principle of operation
High-frequency electromagnetic shielding device made of copper, aluminum or steel, when the electromagnetic wave into the metal interior, resulting in energy loss, part of the electromagnetic energy into heat. As the depth into the conductor surface increases, the energy gradually decreases, the electromagnetic field gradually weakened. Obviously, the surface of the conductor field strength is the largest; the more into the interior, the field strength is smaller. These phenomena are the skin effect of electromagnetic radiation. Electromagnetic shielding is to work with this effect.
(B) shielding
1, active shielding
is the source of the field is placed in the shielding body, the electromagnetic field will be limited to a certain range, so that it does not shield the body outside the impact of the shielding of the staff or instrumentation shielding method.
2, passive field shielding
is the shielding room, personal protection and other shielding methods. This shielding is the field source outside the shielding body, so that the shielding body is not subject to electromagnetic field interference or pollution.
(C) shielding materials
For high-frequency protection of plate shielding and mesh shielding can be made of copper, aluminum or steel (iron). If necessary, double-layer shielding can be considered.
Four, high-frequency grounding
High-frequency grounding, including high-frequency equipment shell grounding and grounding to the shield. High-frequency grounding should be consistent with the general requirements of electrical equipment grounding, should also meet the special requirements of high-frequency grounding.
Shielding device with a good grounding, can improve the shielding effect, and to the middle wave band is more obvious.
High-frequency grounding line should not be too long, its length is best limited to 1/4 of the wavelength. If you can not meet this requirement, but also to avoid the wavelength of 1/4 of an odd number of times.
For shielded grounding, it is appropriate to connect only one point of the shield to the grounding body. If several points are connected to the grounding body at the same time, since the situation is not exactly the same at each point. Harmful unbalanced currents may arise.