Application of electrical fire protection measures and electrical fire restrictive protectors in cotton textile mills

Abstract: Cotton textile mills are fire hazard sites, and certain fire prevention measures
should be considered and taken when carrying out electrical design.

This paper introduces some measures
for electrical fire protection from the problems of wiring, the selection of fuses, the selection of neutral point grounding methods and grounding.

In addition, the application
of electrical fire restrictive protector is introduced on the problem of short-circuit fault of the line that causes the fire.

Keywords: cotton textile mill; Electrical fire protection; Flow restriction protector to raw cotton as the main production of raw materials of cotton textile factory, in the production process to produce a large number of flammable substances such as flying flowers, cotton wool, cotton wool, dust, etc.
, once the fire source, it is easier to cause fire, especially prone to electrical fire accidents
.

If an electrical fire accident is to be avoided, some corresponding measures
should be taken.

1, motor wiring distribution pipeline problems 1.
1 motor outlet junction box, is the key point
of electrical circuit failure.

Operation experience shows that more than two-thirds of the faults of the motor line occur in
the junction box.

The reason is that most of the cases are due to the tightening screw is not pressed tightly, the motor vibration is too large, the lead wire is artificially touched and bent, the repulsive force generated between the wires when the motor is started, etc.
The terminal is loose or the lead wire is broken, and the joint is overheated, the insulation is aging, which causes short-circuit failure
.

If the junction box is not well sealed, a large amount of flying flowers, dust, and ignited by the sparks generated by the failure, it will spew out of Mars and cause a fire accident
.

In order to meet the fire protection requirements, the universal open or open junction box should be converted into a closed junction box
.

When refraining the junction box, it is necessary to pay attention to the adoption of sealing measures, but also to make the junction box have a certain space margin, to prevent the insulation once aged or damaged, because the wire heads are too tight with each other and the interphase short circuit
occurs.

1.
2 The protective tube of the power cord is converted to tetrafluoroethylene hose
.

Buried in the ground to protect the motor power line of the steel pipe, the exposed ground height does not exceed 150 mm, and the junction box is connected, commonly used metal snakeskin hose, susceptible to external touch and bruising, causing short circuit electrical spark
.

In order to eliminate this hidden danger of accidents, the metal snakeskin hose equipped with the original machine can be replaced by a tetrafluoroethylene hose
.

When pairing with the exposed steel pipe, it is necessary to pay attention to the handling of the connection, which can be bonded with No.
634 epoxy resin glue, and can also be tightened
with ethylene tape.

1.
3 When selecting the motor power line, the strength and toughness of the wire should be considered
.

Most of the cotton textile mills use motors with small capacity, and the power cord generally only considers the allowable working current of the wire, and does not consider the strength and toughness
of the wire.

For example: the motor capacity on the loom is generally 0.
8 kilowatts or less, the use of single-stranded wire (especially single-stranded aluminum core wire) in the junction box for hard connection, because the weaving machine vibration is relatively strong, it is easy to loosen the connection or break the wire, resulting in single-phase operation or short circuit of
the motor.

The prevention measure is that all motors threatened by vibration, regardless of capacity, the power cord connected to the motor is switched to multi-stranded copper core wires to avoid wire breakage accidents
.

2.
The selection and use of fuses Some fires are caused by
the selection and improper use of fuses to cause the fuse to burst out of the electric spark.

Therefore, the reasonable selection and use of fuses in cotton textile mills is an important link
that cannot be ignored.

In general, for a single directly starting squirrel cage motor, the fuse is selected according to the following formula
.

Le.
r≥ Lg.
d/(2-2.
5) or Ie.
r≥ Le.
dx 2.
5 type: rated current of le.
r fuse; starting current of Ig.
d motor; The rated current
of the Le.
d motor.

The fuse selected according to the above formula is determined only according to the size of the fuse current, and does not consider the fuse time
of the other of the two factors that mark the fuse amperisecond characteristics.

In fact, the amperiosecond characteristics of fuses vary greatly from model to model
.

For example, RC fuses with larger heat capacity and RL fuses with smaller heat capacity have a difference
of nearly 2 times the amperiosecond characteristics.

If different types of fuses are selected according to the same formula, it is bound to refuse or malfunction in actual operation, which not only does not play its due protective role, but also causes adverse consequences
.

According to the characteristics of the operation of cotton textile machines, most of the screw fuses are selected as the short-circuit protection device of the motor, and the selection formula: Le.
r≥Lg.
d/ (1-2) or le.
r≥le.
dx 3.
5-5 The specific selection method is: For motors below 10 kilowatts, available: Le.
r≥le.
dx5 For motors above 10 kilowatts and less than 28 kilowatts, available: When selecting a fuse for Le.
r≥le.
dx3.
5, the break-off capacity
of the fuse should also be considered.

Because when the fuse is fused, it is generally in two possibilities, one is fused under the allowable current, and the other is fused when the current is broken, which kind of fuse belongs to in actual operation, which can only be judged
by operating experience in actual operation.

Where the sound is particularly loud when fused, sparks appear, the fuse in the tube is fused into many small dots, the inner wall of the melt pipe has fuse steam adherence, the inner wall of the pipe has a scorching phenomenon or even bursts, most of which are fused when the breaking current is broken, and it belongs to the general overload current when it is fused
.

When the short circuit current exceeds the fuse breaking capacity, the fuse can not be reasonably disconnected, at this time the fuse often bursts, burns, and then leads to a two-phase or three-phase short circuit
.

In the selection of fuses, the requirements of the current break should be given sufficient attention, when using, we must pay attention to the following three points; 1) The rated current of the fuse cannot be greater than the rated current
of the melting pipe.

2) Pay attention to the rated voltage value of the fuse, do not use it in circuits higher than the working voltage of the fuse
.

3) The number of times
the fuse is cut off cannot be ignored.

According to the technical conditions, RC series fuses ensure safe disconnection of the rated current breaking capacity 1-3 times, RM, series of fuses must be replaced after disconnecting the rated current capacity of 3 times, cotton textile mills widely used RL series fuses safely disconnect and cut off the number of times 3-5 times
.

These regulations must be carefully observed
in daily maintenance work.

3.
According to the analysis of electrical fire accidents in the past few years, the selection of the neutral point working system accounts for 70% of the fire accidents caused by a single relative short circuit, 25% of the two-phase short circuit and two relative short circuits, and 5%
of the three-phase short circuit.

The above situation shows that solving the electric spark or arc generated by a single relative short circuit is the key
to reducing and avoiding electrical fire accidents.

Our factory uses two power transformers for the whole plant to use electricity, the original design of the neutral point direct grounding system of the three-phase four-wire system power supply mode
.

In this way, although the power and lighting power supply in the same workshop can use the same power transformer, due to the wide distribution of power distribution lines and more electrical equipment, it is mixed with flammable production raw materials such as raw cotton and tampon, and once a single relative short circuit occurs, there is a large short circuit current
.

Later, according to the actual situation of each workshop, the neutral point of the power transformer that supplies the power supply to the power of the spinning mill that is prone to electrical fire is changed from direct grounding to non-grounding, and the lighting power supply
is taken separately.

In this way, if a single relative ground short circuit occurs, the relative ground voltage of the fault is close to zero, so there will be no more large electric sparks
.

In the past two years, our factory has had more than 50 single relative short circuit phenomenon, each time accurately issued a grounding sound and light signal, the duty staff quickly eliminated, to avoid the occurrence of electrical fire accidents
.

4.
Grounding problems The design and construction of grounding and zeroing of electrical equipment should not only consider the normal operation and personal safety of electrical systems and electrical equipment, but also avoid the disconnection or connection of the grounding line as much as possiblePoor touch, so as not to produce sparks and cause fire
.

The grounding wire of the metal shell of the electrical equipment of our factory was originally designed to be buried directly into the ground
with the outer skin of the metal protective pipe or the outer skin or grounding wire of the metal snakeskin pipe.

In actual operation, there have been many times due to metal snakeskin pipe breakage or underground grounding conductor decay or even rot, resulting in sparks caused by poor contact of the motor grounding wire
.

In order to eliminate the hidden danger of accidents, we will produce the grounding wire of the metal shell of all electrical equipment in the car smell, and all of them will be laid together with the phase line in the same protective tube (when the cable is used, the four-core is selected), and the insulation requirements are the same as the
phase wire.

All motor and electrical appliances are equipped with special grounding screws in the junction box, and the wires or cable cores for grounding must be connected to
this special screw.

The size of the grounding screw has a great relationship with whether the ground wire is safe and reliable, and it cannot be ignored
.

Grounding screws and grounding wires are generally sufficient to meet grounding requirements
when the data listed in Table 1 is not small.

Table 1 The cross-section of the specification grounding wire of the grounding screw and the grounding wire of the electrical equipment is selected according to the following formula, which can ensure that the short current
of the grounding is cut off reliably and quickly.

Ig= U/Zn≥ in the KIF type: Id—short-circuit current U—system phase voltage, Zn—impedance in phase-ground loops, including transformer impedance; K - coefficient of action, when using a fuse for protection, the K value is at least 4, when using an automatic switch for protection, the K value is at least 2; IH - the rated current of the fuse or the setting current
of the automatic switch tripper.

5, the choice of electrical fireproof current-limiting protector is a line short-circuit protection product, which can reasonably overcome the shortcomings of traditional circuit breakers, air switches and monitoring equipment, the short circuit current is long, the arc spark generated when the short circuit is short, and the service life is short, when a short circuit fault occurs, the short circuit current can be quickly limited at a microsecond speed to achieve arc extinguishing protection, which can significantly reduce electrical fire accidents.
Ensure the safety
of power supply in such a flammable place as a cotton spinning mill.

Taking the products of the Acquay brand as an example, the functional characteristics and selection of its ASCP series electrical fire restrictive protector are shown in the following table: Electrical fire restrictive protection as a short-circuit arc extinguishing protection product of the end line, usually set at the back end of the circuit breaker of the protected line, the series line is protected in the line, and the current limit protector of each line uploads the monitoring data to the Acquaris electrical fire monitoring host or the safe power cloud platform through wired networking or wireless means.
Implement remote monitoring function
.

The networking topology diagram is shown in the following figure
.

Electrical fire host networking topology map Safe power management cloud platform topology map Users can view the operating status and operating parameters of each electrical fire restrictive protector by monitoring the host, Web browser or mobile phone APP, and can remotely set the parameters of the protector, flow restriction control, as well as sound suppression, reset and other operations
.

The software operation interface is shown in the following figure
.

Safe electricity management cloud platform interface Wisdom fire steward APP interface 6, summarizing the facts tells us that to do a good job in the electrical fire prevention work of cotton textile mills, not only to do a good job in daily maintenance and maintenance and other basic work, but more importantly, to reform those process design, construction plans, equipment selection and equipment layout that have been verified by practice to be unreasonable, imperfect or inapplicable, etc.
, to fundamentally improve the reliability of the operation of each set of production and control devices to achieve a long cycle.
Full load operation, to achieve the purpose of
safe, stable and continuous production.

In addition, with the continuous maturity of modern electrical fire prevention technology and products, the use of new electrical fire protection solutions can not only improve the safety of power supply, but also realize remote monitoring, unattended, reduce manpower at the same time, improve management efficiency
.

References:[1].
Acqua Enterprise Microgrid Design and Application Handbook.
Version 2022.
05[2].
ZHANG Jingkui.
Cotton textile mill electrical fire prevention measures.
Labor Protection.
1981-10-28