Influence of fire power supply configuration and l

2022-09-19
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The influence of building fire power supply configuration and line voltage drop on linkage system

with the development of social economy in China, there are more and more large-scale buildings and high-rise buildings. In these buildings, automatic fire alarm and fire linkage system are essential facilities. During the construction and commissioning, it was found that when the building is large in scale, the floor is high, the line is long, and the power consumption of the fire fighting equipment is large, the fire fighting linkage power supply is not reasonably configured and the influence of the line voltage drop of the control line is easy to cause the terminal voltage to fail to start the fire fighting equipment. And these failed to attract the full attention of relevant personnel in the early stage of the project until the adjustment in the later stage of the project_ At the trial stage, the seriousness of the problem was found, and then we tried to take various remedial measures, which not only took time and labor, but also outweighed the gains. In the design of automatic fire alarm and fire linkage system, the rationality and reliability of the action power supply setting of fire linkage control equipment are very important. After the fire alarm is determined, the smoke control and exhaust facilities, fire doors, fire shutter doors, etc. in the fire area and adjacent areas shall be able to act quickly and accurately after receiving the action instructions. The operating power supply voltage shall be DC24V. Power supply configuration refers to the installation of a set of DC power supply equipment (including transformer, rectifier, battery pack, etc.) in the fire linkage cabinet. If the power supply DC24V passes, the compliance value will be lost (the reason has been clarified in point 2). The control will be sent from the fire control room to the fire end equipment in each area. Two aspects should be considered in the configuration of power supply in engineering practice: one is that the capacity of power supply should meet the requirements of simultaneous action of relevant fire-fighting equipment; The other is that the terminal voltage can meet the reliable action of the fire-fighting equipment, that is, to avoid the adverse effects of the voltage drop of the power supply line

1 influence of power supply configuration on the system

the fire linkage system requires that the operation of all fire-fighting equipment must be stable and reliable. In engineering practice, the quality of the power supply of the fire linkage system has an increasingly significant impact on the operation of its system equipment, which not only comes from whether the voltage, frequency, current and other basic elements of the system power supply meet the power demand of the fire equipment, but also from whether it matches the fire equipment. In the specific engineering design, the relevant fire-fighting equipment should include all positive pressure air supply outlets in the building staircase, smoke exhaust valves (openings) in the fire floor and the upper and lower adjacent floors, electric fire doors, fire shutter doors, etc. Taking a bank central building as an example, there are 4 fire doors on each floor, 2 smoke vents, 2 smoke proof stairs on the 18th floor, and 36 positive pressure air supply outlets in the stairwell. According to the fire code, The total current of the above fire-fighting equipment acting at the same time is:

itotal =3 (2i1+4i2) +36xi3

where: I1 smoke exhaust valve action current

I2 fire door action current

I3 air supply valve action current

according to: i1=0.8a

i2=0.4a

i3=0.8a

so:

how to select the construction engineering quality inspection center?Concrete pressure tester I total =3 (2 0.8+40 0.4) +36 0.8=38.7a

during the linkage test of the building, the fire control center gave a start-up instruction, the forced draft fan and smoke exhaust fan operated normally, but the forced draft valve and smoke exhaust valve did not move. After actual measurement, the power output is less than 24V. The reason is that the rated output current of this power supply is 36a. When the load current is greater than the rated current, the power protection circuit acts and reduces the output voltage, resulting in the low voltage at the air supply valve and smoke exhaust valve, which cannot be started

2 influence of line voltage drop on the system

the problem of line voltage drop is mainly caused by the internal resistance of conductor and contact resistance. The internal resistance of the conductor is the inherent resistance of the conductor itself. The resistance value is directly proportional to the length of the line, inversely proportional to the cross-sectional area of the conductor, and related to the quality of the conductor. Contact resistance refers to the contact resistance between the wire and the terminal, and between the wires in the line. When connecting the equipment, if the terminal is not crimped tightly, the resistance of G and LB contacts will increase. In addition, the wire head is not soldered and exposed to the air for a long time will produce an oxide layer, which will also increase the contact resistance. The more access devices, the greater the contact resistance

when controlling the electromagnetic tripping linkage equipment with large action current, the influence of line voltage drop is obvious. For example, the nominal working current of smoke control valve, positive pressure air supply valve and other equipment is generally 0.8A. Such a large action will cause a large voltage drop in the internal resistance of the line. Taking a commercial building as an example, there are 2 smoke vents on each floor, 2 smoke proof stairs on the 25th floor, and 50 positive pressure air supply outlets in the stairwell. During the linkage commissioning, it was found that the valves above 20 floors can sometimes act and sometimes cannot act, which is very unstable. Measured during linkage, the power supply voltage output terminal is 24V, and the output is normal. Measured at the valve, the voltage on the valve is only 16V. After inspection, it is found that the resistance of the control line is 0.32q. For each stair, the total current of the fire-fighting equipment acting at the same time is:

itotal =3 211+2513

the English Financial Times article said that

=3 20.8+25 0.8=24.8a

the line loss reached 8V, indicating that the DC24V starting voltage passed through the line voltage drop loss, and the terminal voltage was too low to link the fire-fighting equipment

3 measures to avoid the impact of voltage drop on the system

considering the impact of improper power supply configuration and line voltage drop, we can take the following measures to avoid such problems:

(1) correctly and reasonably configure the power source of fire linkage according to the fire protection regulations

(2) select high-quality copper core wires to reduce the internal resistance of the wires and minimize the joints of the wires, and the joints should be soldered

(3) on the basis of calculating the cross-sectional area of distribution conductors, appropriately increase the cross-sectional area of conductors

(4) lay more power buses according to the actual situation to reduce the contact resistance

(5) time sharing control the number of equipment to be controlled at the same time to reduce the instantaneous working current

to sum up, the power supply configuration of automatic fire alarm and fire linkage system is related to the building scale, power supply distance and the number of fire linkage equipment. While meeting the requirements of sufficient capacity, the impact of line voltage drop must not be ignored. Only by fully considering these factors and paying full attention to the process and quality in the construction stage, can the linkage function of the system be reliably guaranteed and its due role be brought into full play

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