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The working principle and types of explosion-proof motors

Date:2023-10-24   Author:XINDA MOTOR
Working principle of explosion-proof motor 
According to the explosion-proof principle, explosion-proof motors can be divided into explosion-proof motors, increased safety motors, positive pressure motors, non-sparking motors and dust explosion-proof motors.
Working principle of explosion-proof motor

It uses a flameproof enclosure to isolate the electrical parts that may produce sparks, arcs and dangerous temperatures from the surrounding explosive gas mixture. However, this kind of shell is not sealed, and the surrounding explosive gas mixture can enter the inside of the motor through the gaps between the joint surfaces of various parts of the shell. An explosion may occur when it comes into contact with ignition sources such as sparks, arcs, and dangerous high temperatures in the shell. At this time, the flameproof shell of the motor will not only not be damaged or deformed, but also when the explosion flame or hot gas spreads through the gap between the joint surfaces, Nor can it ignite the surrounding explosive gas mixture.
Working principle of increased safety motor
It is a motor structure that will not produce arcs, sparks or dangerous high temperatures under normal operating conditions, and then takes some mechanical , electrical and thermal protection measures to further avoid arcs, sparks or dangerous high temperatures under normal or recognized overload conditions. danger of high temperatures, thereby ensuring its explosion-proof safety.
Working principle of positive pressure motor
Equipped with a complete ventilation system, there are no structural dead spots inside the motor that may affect ventilation; the shell and pipes are made of non-combustible materials and have sufficient mechanical strength; the shell and main pipes maintain a sufficiently large positive pressure relative to the outside atmosphere; The motor must have safety protection devices (such as time relays and flow monitors) to ensure sufficient air exchange. It must also have automatic protection or alarm devices for under-pressure in the shell; the quick door or cover on the shell must be connected to the power supply Interlocking device. There is currently no unified series of positive pressure motor products in our country .
Working principle of non-sparking motor
This motor refers to a motor that will not ignite the surrounding explosive mixture under normal operating conditions, and generally does not cause ignition failure. Compared with the increased safety motor, in addition to the insulation dielectric strength test voltage, winding temperature rise, tE (AC winding after reaching the rated operating final temperature at the maximum ambient temperature, from the time when the starting current starts to rise to the limit Temperature time) and starting current ratio do not have special regulations like the increased safety type, other aspects are the same as the design requirements of the increased safety type motor.
Working principle of dust explosion-proof motor
This motor means that its casing is designed and manufactured according to specified conditions. It can prevent dust from entering the motor casing. Although it cannot completely prevent dust from entering, the amount of entry does not hinder the safe operation of the motor. The accumulation of internal dust is not likely to cause an ignition hazard and does not cause any risk of ignition during use. Motors that can cause explosions of surrounding explosive dust mixtures.

Basic explosion-proof types of explosion-proof motors

(1) Flameproof type "d"
Explosion-proof explosion-proof type is to enclose all parts of the equipment that may ignite explosive gas mixtures in a shell. The shell can withstand the internal explosion of the flammable mixture that penetrates into the shell through any joint surface or structural gap of the shell without being damaged. And it will not cause the ignition of an external explosive environment formed by one or more gases or vapors (see GB38362 standard). Put parts that may produce sparks, arcs and dangerous temperatures into a flameproof enclosure. The flameproof enclosure isolates the internal space of the equipment from the surrounding environment.

There are gaps in the explosion-proof shell. Due to the respiration and gas penetration of electrical equipment, there may be explosive gas mixtures inside. When it explodes, the shell can withstand the explosion pressure generated without being damaged. At the same time, the gaps in the shell structure can cool the flame and reduce the temperature. The flame propagation speed or the termination of the acceleration chain prevents the flame or dangerous flame products from passing through the explosion-proof gap to ignite the external explosive environment, thereby achieving the purpose of explosion-proof.
Flameproof type "d" is divided into Class I and Class IIA, IIB, and I IC according to the type of explosive gas environment in which it is allowed to be used This explosion-proof type equipment is suitable for areas 1 and 2.
(2) Increased safety type "e"
The increased safety explosion-proof type is a type of electrical equipment that does not produce arcs or sparks under normal operating conditions, taking some additional measures to improve its safety and prevent the possibility of dangerous temperatures, arcs, and sparks in its internal and external components. explosion-proof type. It does not include equipment that produces sparks or arcs under normal operating conditions.
On the structure of electrical equipment that does not produce sparks, arcs and dangerous temperatures during normal operation, measures should be taken to reduce or control the operating temperature, ensure the reliability of electrical connections, increase the insulation effect, and improve the protection level of the shell to reduce pollution caused by dirt. Possibility and moisture ingress and other measures can be taken to reduce the possibility of point failures and improve the safety and reliability of the equipment under normal operation and specified faults (for example: motor rotor stalling). This type of equipment is mainly used in Zone 2 hazardous locations, and some types can be used in Zone 1, such as increased safety low-voltage asynchronous motors, junction boxes, etc. with appropriate protection devices.
(3) Intrinsically safe “i”
Intrinsically safe explosion-proof type means that all circuits inside the equipment are made under standard specified conditions (including normal operation and specified fault conditions), and any spark or any thermal effect generated cannot ignite the specified explosive gas environment. circuit. 〖HTH〗 "iq" grade electrical equipment〖HT〗 is an intrinsically safe electrical equipment that cannot cause ignition under normal operation and under one fault or two fault conditions in any combination; 〖HTH〗 "スス" grade electrical equipment〖 HT〗 is an intrinsically safe electrical equipment that cannot cause ignition under normal operation and under the application of a fault condition.

Intrinsic safety starts from limiting the energy in the circuit, and reduces the potential spark energy to below the energy that can ignite the specified gas mixture through reliable control of circuit parameters. The heating temperature of the surface of the wires and components is limited to the ignition temperature of the specified gas mixture Down. This explosion-proof type can only be used in weak current equipment. This type of equipment is suitable for zones 0, 1, and 2 (Exiɑ) or zones 1 and 2 (Exib).
(4) Positive pressure type "p"
A type of explosion protection for electrical equipment. It is an electrical equipment that achieves safety by keeping the pressure of the protective gas inside the equipment enclosure higher than the pressure of the surrounding explosive environment. Different methods of protection are available for positive pressure equipment. One method is to protect the static positive pressure inside the system, while the other method is to maintain a continuous flow of air or inert gas to limit the entry of flammable mixtures into the interior of the enclosure. Both methods need to flush the shell with protective gas before starting the equipment to take away the flammable gas that enters the shell when the internal pressure of the device is not positive and prevent the formation of flammable mixtures in the shell. The key points of these methods are to monitor the system and perform regular air changes to ensure system reliability.
This type of equipment can be used in Zone 1 or Zone 2 hazardous locations according to the protection method.
(5) Oil-immersed type "o"
The oil-immersed explosion-proof type immerses the entire equipment or parts of the equipment in oil (protective fluid) so that it cannot ignite the explosive gas environment above the oil level or outside the shell. This is an old explosion-proof technical method mainly used in switchgear. The arc and spark formed are immersed in oil.
This type of equipment is suitable for use in Zone 1 or Zone 2 hazardous locations.
(6) Sand-filled type “q”
Sand-filled explosion-proof type is a type of electrical equipment protection that fills the shell with sand or other powder materials with specified characteristics so that under specified conditions of use, arcs or high temperatures generated in the shell cannot ignite the surrounding explosive gas environment.
This explosion-proof type fixes and completely buries conductive parts that can ignite an explosive gas environment into sand-filled materials, thereby preventing the spread of sparks, arcs and dangerous temperatures and preventing them from igniting external explosive gas environments. Typically it is used for components within Ex "e" or Ex "n" equipment and heavy duty traction battery packs. This type of equipment is suitable for use in Zone 1 or Zone 2 hazardous locations.
(7) "n" type explosion-proof electrical equipment
During normal operation, this type of electrical equipment cannot ignite the surrounding explosive gas environment, and it is unlikely that a fault causing ignition will occur (see GB38368 standard).
When "n" type electrical equipment operates normally, it means that the equipment electrically and mechanically complies with the design specifications and is used within the scope specified by the manufacturer. It is impossible to generate sparks, arcs and dangerous temperatures. This type of electrical equipment is only suitable for use in Zone 2 hazardous locations.
(8) Pouring type "m"
The encapsulated explosion-proof type is to encapsulate the electrical components in the encapsulating agent (compound) that may produce sparks, arcs or dangerous temperature parts that may cause the explosion of explosive mixtures, so that they cannot ignite the surrounding explosive mixtures.
The use of pouring and sealing measures can prevent short circuits of electrical components, solidify electrical insulation, avoid sparks on the circuit and the generation of ignition sources such as arcs and dangerous temperatures, prevent the intrusion of explosive mixtures, and control the surface temperature under normal and fault conditions. This type of equipment is suitable for hazardous locations in Zones 1 and 2.
(9) Airtight type "h"
This type of explosion-proof equipment adopts an airtight enclosure. That is, explosive gas mixtures in the environment cannot enter the inside of the equipment shell. Airtight shells are sealed by melting, extruding or gluing. Most of these shells are non-removable to ensure permanent airtightness.