Contents of electrical safety blackboard

As an energy source, electricity, like sunlight, water and air, is an indispensable partner of human beings. If the operation is illegal, it may cause accidents such as fire and explosion, equipment damage and personal injury, which will cause immeasurable losses to our life and property safety. What information does the electrical safety blackboard newspaper have?

Electrical risk factors and accident types

First, get an electric shock

1, divided into electric shock and electric injury.

2. Shock current value: sensing current (average male 1. 1ma, female 0.7ma), escape current (average male 16ma, female 10.5ma), ventricular fibrillation current (about 50ma, related to duration). Human body impedance: it is about1000 ~ 3000Ω when dry, and about 500 ~ 800Ω when wet.

3. Type of electric shock:

According to whether the charged body contacted by the electric shock person is in normal charged state, it can be divided into direct contact electric shock and indirect contact electric shock;

According to the way the human body contacts the charged body, it can be divided into three types: single-phase electric shock, two-phase electric shock and step voltage electric shock. Single-phase electric shock accidents account for more than 70% of all electric shock accidents.

4. Electric injury is the harm to human body caused by thermal effect, chemical effect and mechanical effect of current. Electrical injuries include electrical burns, electrical burns, skin metallization, mechanical injuries, electro-optic ophthalmia and other injuries. Electric burns. This is the most common electric injury. Most electric shock accidents include electric burns. Electrical burns can be divided into current burns and arc burns.

Second, the electrical fire and explosion

1, electrical fires and explosions are caused by electrical ignition sources. Dangerous temperature, electric spark and arc generated by electrical equipment in operation are the main forms of electrical ignition sources.

(1) Dangerous temperature: short circuit, overload, electric leakage, poor contact, overheating of iron core, poor heat dissipation, mechanical failure, abnormal voltage, electric heating appliances and lighting appliances, and electromagnetic radiation energy.

(2) Spark and arc: Spark is a breakdown discharge between electrodes, and arc is a collection of a large number of sparks. Divided into working sparks and arcs, accident sparks and arcs.

2, electrical devices and electrical lines deflagration.

Including oil-immersed transformer fire and explosion, motor fire and cable fire and explosion.

Third, lightning damage.

1, lightning type, hazard form and accident consequences

(1) lightning types: direct lightning (each discharge process of direct lightning includes three stages: pilot discharge, main discharge and residual light), lightning induction (including lightning electrostatic induction and lightning electromagnetic induction) and spherical lightning.

(2) the form of lightning disaster

It has the characteristics of large lightning current amplitude, steep lightning current, strong impact force and high impact overvoltage.

It has destructive effects on electrical, thermal and mechanical properties.

(3) The consequences of lightning accidents: fire and explosion, electric shock, damage to equipment and facilities, and large-scale power failure.

2. Lightning parameters: thunderstorm days, lightning current amplitude, lightning current steepness and lightning surge overvoltage.

Fourth, electrostatic hazards

1, electrostatic hazards and accident consequences

Cause explosion and fire accidents, may cause secondary accidents and hinder production.

2, the characteristics of static electricity

(1) generates static electricity.

Charging methods (contact-separation charging, open circuit charging, induced charging and charge transfer), solid static electricity, human static electricity (up to 10000 V or more), powder static electricity, liquid static electricity, steam static electricity and gas static electricity.

(2) Dissipation of static electricity: neutralization and leakage.

(3) Influencing factors of static electricity: materials and impurities, industrial equipment and industrial parameters.

Five, radio frequency electromagnetic field hazards

Generally, it refers to electromagnetic waves with frequency above 100khz. Danger:

1. The radiation energy absorbed by human body is damaged to varying degrees.

2. Induction discharge in production leads to accidental detonation of the detonating device.

Six, the harm of electrical equipment failure

Category: open circuit, short circuit, abnormal grounding, electric leakage, misoperation, damage to electrical equipment or components, etc.

Hazards: lead to fire and explosion, abnormal power supply, abnormal power failure and safety-related system failure.

Electric shock protection technology

A, direct contact with electric shock protection measures

1. insulation: the resistivity of insulation materials used in engineering is generally not lower than107 Ω m. The resistance of insulation materials is usually measured by shaking table. In any case, the insulation resistance per volt of working voltage shall not be lower than1000Ω.

2, screen protection and spacing:

1) The screen protector should be large enough and keep a necessary distance from the charged body.

2) The height of the fence should not be less than 1.7m, and the lower edge should not be more than 0. 1 m from the ground. The height of fences should not be less than 1.2m indoors and 1.5m outdoors, and the distance between fences should not be greater than 0.2m；: ; For low-voltage equipment, the distance between the barrier and the exposed conductor should not be less than 0.8m.. The fence height of outdoor distribution equipment should generally not be less than 2. 5 meters. On screen protection devices such as fences and fences, there should be "Stop, high voltage danger!" Wait for the signal.

3) Distance between electrical equipment: The height of the bottom of the low-voltage distribution box in the open workshop can be 1.2 m from the ground, and the height of the bottom of the low-voltage distribution box in the dark workshop can be1.4 m. The height of the bottom opening of the surface-mounted watt-hour meter board can be 1.8 m from the ground. The installation height of ordinary switchgear is 1. 3— 1。 5 meters; ; There should be a distance of 150mm between the switch handle and the building for easy operation. The height of the wall switch from the ground can be1.4m.. The height of the exposed socket from the ground can be 1. 3- 1。 8 meters, concealed socket can be 0. 2-0。 3 meters .. Indoor lamps and lanterns height should be greater than 2.5 m; ; If it cannot be realized due to actual conditions, it can be reduced to 2.2m；; ; When it is lower than 2.2 m, appropriate safety measures should be taken. When the lamp is above the desktop and cannot be reached by others, the height can be reduced to1.5m. ..

The height of outdoor lamps should be greater than 3m; ; When installed on the wall, it can be reduced to 2.5 meters. For cranes below 1 kV and below 1 kV, the minimum distance between the crane and the line conductor shall not be less than 1. 5 meters, for cranes below 10kV, not less than 2 meters.

4) Maintenance distance: During low-voltage operation, the distance between the human body and the tools it carries and the charged body should not be less than 0.1m..

High-voltage operation, 10 kv operation without shielding, and the distance between the human body and the tools it carries and the charged body should not be less than 0.7m；; Line operation:1.0m.

Second, indirect contact electric shock protection measures

1, IT system (protective grounding)

The metal parts of electrical equipment that may have dangerous voltage under fault conditions are closely connected with the earth through grounding wires and grounding bodies. Through low resistance grounding, the fault voltage is limited to a safe range; In the 380V ungrounded low-voltage system, it is generally required to protect the grounding resistance Re ≤ 4 Ω; Used in various ungrounded distribution networks.

2.TT system: the distribution network is directly grounded, and the shell of electrical equipment is grounded.

The fault voltage on the leakage equipment is greatly reduced, but it is necessary to install residual current action protection device or overcurrent protection device. Working grounding is not safe voltage. Mainly used for low-voltage users, that is, small users who are not equipped with distribution transformers and introduce low-voltage power from outside.

3, TN system (protection by zero)

Under normal circumstances, the uncharged metal part of electrical equipment is directly connected with the neutral point of distribution network. Equivalent to the traditional protection zero system. Its first safety function is to quickly cut off the power supply.

It can be divided into three types: TN-S, TN-C-S and TN-C. TN-S systems have the best safety performance and can be used in places with explosion danger, high fire danger and other high safety requirements. TN-C-S system should be used in low-voltage distribution places and civil buildings in the factory; TN-C system can be used in situations with low risk of electric shock and simple electrical equipment. 220/380 V three-phase four-wire distribution network adopts protective neutral connection, and the distribution transformer and its low-voltage neutral point are directly grounded.

Application security requirements:

1) In the same neutral point system, it is generally not allowed that some or individual devices are only grounded to neutral point;

2) Repeated grounding is qualified.

3)pe line can quickly cut off the power supply when a single-phase short circuit occurs. Terminal circuit or socket circuit of 220 v TN system, short-circuit protection elements of hand-held electrical equipment and mobile electrical equipment shall ensure that the fault duration shall not exceed 0.4 s, and terminal circuit of distribution line or fixed electrical equipment shall ensure that the fault duration shall not exceed 5 s.

4) working grounding is qualified. The grounding resistance should generally not exceed 4 Ω, and should not exceed10 Ω in areas with high soil resistivity.

5) Monopole switches and fuses shall not be installed on 5)PE and PEN lines; PE wire and PEN wire should have measures to prevent mechanical damage and chemical corrosion; PE branch lines shall not be connected in series, that is, the exposed conductive parts of the equipment shall not be used as protective conductors.

6) The cross-sectional area of the protective conductor is qualified. The PE line with mechanical protection shall be not less than 2.5 mm2, and the PE line without mechanical protection shall be not less than 4mm2; the copper of the PEN line shall be not less than 10mm2; the aluminum shall be not less than 16 mm2; and the cable core shall be not less than 4mm2; SL≤ 16 is SL, 16 "SL ≤ 35 is16, SL" 35 is SL/2.

7) Equipotential bonding, including main equipotential bonding and auxiliary equipotential bonding.

Three, measures to prevent direct contact and indirect contact to get an electric shock

1, double insulation

(1) Classification of electric shock protection for electrical equipment: O, OI and I, II and III.

(2) Double insulation and strengthening insulation measures: working insulation, protective insulation, double insulation and strengthening insulation.

Equipment with double insulation and reinforced insulation belongs to Class II equipment, and the equipment is marked with "back". Working insulation is not less than 2m Ω, protective insulation is not less than 5m Ω, and reinforced insulation is not less than 7m Ω.

2. safe voltage: There are both direct contact electric shock protection and indirect contact electric shock protection safety measures.

(1) Limit and rating of ultra-low voltage: 42v, 36v, 24v, 12v and 6v; Equipment powered by ultra-low voltage belongs to three types of equipment; Selection of rating: 42V for hand-held tools in particularly dangerous environment, 36V or 24V for hand-held lighting in hazardous environment, 12V for hand-held lighting in metal containers and particularly humid hazardous environment, and 6V for underwater.

3, residual current action protection

Also known as leakage protection, its function is to prevent personal electric shock, prevent fire caused by grounding fault and monitor grounding fault.

(1) working principle. It consists of three basic links: detection element, intermediate link, actuator, auxiliary power supply and test device.

(2) Main technical parameters: rated residual operating current, rated residual non-operating current and breaking time.

The rated residual action current is divided into 13 grades, and below 0.03A is high sensitivity, which is mainly used to prevent various personal electric shock accidents; Above 0.03A to 1A belongs to medium sensitivity, which is used to prevent electric shock accidents and leakage fires; 1A or above is low sensitivity, which is used to prevent leakage fire and monitor ground accidents. The rated residual non-working current shall not be less than 65438+ 0/2 of the rated residual working current. The breaking time is divided into general type and delay type, and the delay type is only suitable for into indirect contact electric shock protection, with a delay time difference of 0.03A

(3) Protection requirements of residual current protection device. In TN system, TN-C system must be converted into TN-C-S, TN-S system or local TT system before it can be installed and used. In TN-C-S system, the residual current protection device is only allowed to be used in the part where N line and PE line are separated.

(4) Equipment and places where residual current protection devices must be installed. 1) terminal protection ① class I mobile electrical equipment; ② Electrical equipment for production; (3) Electrical and mechanical equipment on the construction site; ④ Electrical devices installed outdoors; ⑤ Electrical equipment for temporary electricity use; ⑥ Other power outlets or outlet circuits except wall-mounted air-conditioning power outlets in institutions, schools, hotels, restaurants, enterprises, institutions and houses; All landowners swimming pool, fountain, bath electrical equipment; (eight) electrical and medical equipment that may be in direct contact with the human body in the hospital; Pet-name ruby others. 2) Line protection ① Centralized installation of watt-hour meter boxes in rural areas; (2) distribution box of agricultural production equipment.

(5) Operation and management of residual current protection device. Working experience of 6 years, allowing power transmission 1 time.