20 17 power supply and distribution knowledge of electrical engineers: explosive dust

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20 17 power supply and distribution knowledge of electrical engineers: explosive dust

1. Provisions on explosive dust environment:

(1) When it is used in the environment where explosive dust, combustible conductive dust, combustible non-conductive dust and explosive dust mixture formed by combustible fiber and air appear or may appear during production, processing, treatment, transportation or storage, the dynamic design of explosive dust environment should be carried out.

(2) The dust in the explosive dust environment shall be grouped according to the ignition temperature and shall comply with the provisions in the table below.

(3) In engineering design, the following measures should be taken to eliminate or reduce the generation and accumulation of explosive dust mixture:

(1) To improve the automation level, necessary safety interlock can be adopted;

② Dangerous temperature and sparks, especially overheating and sparks generated by electrical equipment or lines, should be limited, and explosion-proof or other protective electrical equipment and lines should be selected;

(4) The explosive dust environment should be partitioned according to the frequency and duration of explosive dust mixing and the following provisions.

① Area 10: explosive dust environment appears continuously or for a long time;

② Area 1 1: the environment where accumulated dust sometimes rises and explosive dust mixture occasionally appears.

(5) The division of explosion danger area should be determined according to the explosive dust quantity, explosion limit and ventilation conditions.

(6) If one of the following conditions is met, it can be classified as a non-explosive dangerous area:

(1) is equipped with a dust removal device with good dust removal effect. When the dust removal device stops, the process device can be interlocked and stopped;

(2) There is a blower room serving the explosive dust environment, which is isolated by a wall, and the air duct leading to the explosive dust environment has a safety device to prevent the explosive dust mixture from invading;

(3) The amount of explosive dust used in the area is not large, and it is operated in a fume hood or under a hood.

(7) The exhaust room serving the explosive dust environment should have the same grade as the explosion danger zone in the exhaust area.

2. The power supply design in explosive dust environment shall meet the following requirements:

(1) For power supply design in explosive dust environment, it is suggested that electrical equipment and circuits, especially those that can generate sparks during normal operation, be arranged outside the explosive dust environment. When it needs to be located in an explosive dust environment, it should be arranged in a place with less explosion risk. Portable electrical equipment should not be used in explosive dust environment.

(2) The electrical equipment and wiring in explosive dust environment should meet the requirements of different environmental conditions such as chemistry, machinery, heat, mold and sandstorm in the surrounding environment.

(3) In the explosive dust environment, the maximum allowable surface temperature of electrical equipment shall comply with the provisions in the table below.

(4) When non-explosion-proof electrical equipment is used for mechanical transmission of partition walls in explosive dust environment, it shall meet the following requirements:

1) The room where the electrical equipment is installed should be separated from the explosive dust environment by a solid wall with non-combustible body;

2) The transmission shaft shall be sealed by a stuffing box through a partition wall or with the same effect;

3) The exit of the room where electrical equipment is installed should lead to a non-explosive and fire-risk environment; When the room where electrical equipment is installed must be connected to the explosive dust environment, the relative positive pressure of the explosive dust environment should be maintained.

(5) Reliable overload protection shall be installed for electrical equipment that may be overloaded in explosive dust environment.

(6) For the motor used for emergency exhaust in explosive dust environment, control equipment such as emergency start button shall be set at the place convenient for operation when an accident occurs in production.

(7) In explosive dust environment, sockets and local lighting should be installed less. When necessary, sockets should be arranged in places where explosive dust is not easy to accumulate, and local lighting should be arranged in places where airflow is not easy to impact in the event of an accident.

3. The design and installation of electrical circuits in explosive dust environment shall meet the following requirements:

(1) The wires shall be laid in an environment with less explosion risk.

(2) When the channels, cables or steel pipes for laying electrical lines pass through the holes in the wall or floor between different areas, they shall be tightly sealed with incombustible materials.

(3) When laying electrical lines, avoid places that may be subject to mechanical damage, vibration, corrosion and possible heating. If it is unavoidable, preventive measures should be taken.

(4) Copper-core insulated wires or cables shall be used in explosive dust environment area 10 and explosive dust environment area 1 1 lines with strong vibration and voltage below1000 V..

(5) The selection of insulated wires and cables in the explosive dust environment area 10 shall meet the following requirements:

(1) The allowable current carrying capacity of insulated wires and cables shall not be less than 1.25 times of the rated current of fuse melt and 1.25 times of the setting current of automatic switch long-delay overcurrent release;

(2) The long-term allowable current carrying capacity of the branch line of squirrel-cage induction motor with lead voltage below 1000V should not be less than 1.25 times of the rated current of the motor;

(3) The wires and cables with voltage lower than 1000V shall be checked for thermal stability according to short-circuit current.

(6) In explosive dust environment, the rated voltage of insulated wires and cables of low-voltage power and lighting lines shall not be lower than the rated voltage of the network, and shall not be lower than 500V V V. The rated voltage of working neutral wire insulation shall be equal to the rated voltage of phase wire and shall be laid in the same sheath or tube.

(7) In the explosive dust environment 10 area, the phase line and zero line in the single-phase network should be equipped with short-circuit protection, and the phase line and zero line should be cut off at the same time with a bipolar switch.

(8) Cable lines in explosive dust environment in10 and 1 1 areas should not have intermediate joints.

(9) When selecting cables, environmental corrosion, rodent and termite hazards, environmental temperature and the way of electrical equipment entering the box should be considered. Flame retardant cables should be used when laying overhead.

(10)3 ~ 10kV cable lines shall be equipped with zero sequence current protection; The protection device installed in the explosive dust environment area 10 should act on tripping and should act on the signal of the explosive dust environment area 1 1.

4. (Mandatory Provisions) In explosive dust environment, it is forbidden to use insulated wires or plastic pipes.

5. The grounding design of explosive dust environment shall meet the following requirements:

(1) According to the Technical Specification for Grounding Design of Electric Power Equipment, the following parts that do not need grounding should still be grounded in explosive dust environment;

(1) Normal uncharged metal shell of electrical equipment with rated AC voltage of 380 volts and below and rated DC voltage of 440 volts and below in poor conductive grounding;

(2) In a dry environment, electrical equipment with rated AC voltage 127V and rated DC voltage 1 10V and below is normally not charged;

③ Electrical equipment installed on grounded metal structure.

(2) The metal shell of electrical equipment in explosive dust environment should be reliably grounded.

(3) In order to improve the reliability of grounding, the grounding trunk line should be connected to the grounding body in different directions and at least two places in the explosion danger zone.

(4) The grounding device of electrical equipment should be set separately from the grounding device of independent lightning rod for preventing direct lightning, and can be combined with the grounding device of lightning rod for preventing direct lightning installed on buildings; It can also be used in combination with grounding device to prevent lightning induction. The grounding resistance should be the lowest value.