The biggest advantage of this power supply mode is that the system does not need to use double switching device for power supply, but it also brings construction trouble and relatively more pipelines.
If there is no municipal dedicated overhead line and no double circuit, it is recommended to adopt the power supply mode of self provided power generation facilities as the second power supply, as shown in scheme III in Figure 1.
The author believes that the “single circuit power supply” mode in article 3.2.11, paragraph 3, of the civil standard can be used for non fire secondary loads.
According to the civil standard, when the load is small or the regional power supply conditions are difficult, the secondary load can be powered by one circuit of 35kV, 20kV or 10kV special overhead line, but article 3.2 Paragraph 1 of Article 11 specifies that the incoming line of external power supply for secondary load should adopt double circuit power supply, as shown in scheme 1 in Figure 1.
It is worth noting that after the urban network transformation is fully completed in many cities, the overhead lines are replaced with cables and laid in the underground tunnel.
article 4.4 of gb51251-2017 technical standard for building smoke control and smoke exhaust system Article 5 requirements: the smoke exhaust fan shall be set in the special machine room.
The author will analyze several problems collected for your reference.
If it is a secondary load for fire fighting, It is inconsistent with article 10.1.8 of gb50016-2014 code for fire protection design of buildings (2018 Edition).
The “Civil Code” does not specify the voltage level of the incoming power supply, and the “civil standard” is more rigorous.
The lighting in the fire fan room needs to be provided with normal lighting and standby lighting, and the illumination and working time of the standby lighting must meet the relevant requirements of article 10.3.3 of gb50016-2014 code for fire protection design of buildings (2018 Edition).
This problem can be further discussed, but there is no need to tangle, because there is another sentence “when the regional power supply conditions are difficult”, which can basically solve the above problem.
for power supply for secondary fire loads, the “one-way 10kV power supply” is still used in article 13.7.4, paragraph 4, of the civil standard The author believes that this is not rigorous and perfect enough.
Article 3.2 of civil standards According to paragraph 5 of Article 11, the lighting system with cross power supply can be rated as class II load.
Article 3.2 of civil standards In paragraph 3 of Article 11, “single circuit power supply” can be used for secondary load.
On the power supply of secondary load A.
Fire fighting facilities such as fire drainage pump and fire rolling shutter are placed on the site.
In the specific project design, the designers have no objection to placing the terminal distribution box for power supply such as fire drainage pump and fire rolling shutter in the distribution room of their respective fire compartment.
On the one hand, it can reduce the number of double cutting boxes, on the other hand, it also improves the power supply reliability and fire safety.
On the setting of fire terminal distribution box, article 13.7 of civil standard The location of the fire terminal distribution box has been specified in paragraph 6 of Article 4.
The author believes that, in general, it can be defined according to the scale of construction projects, that is, the power load of public buildings less than 20000 m2 and residential buildings less than 100000 m2 is defined as “small load”, that is, the installed capacity of transformer is about 2000kVA, not more than 3000kva, except under special circumstances.
Of course, the civil standard is in Section 3.4 It is proposed in Article 1 that when the total load capacity of electrical equipment is 250KW or the installed capacity of transformer is 160KVA and below, low-voltage 380V / 220V power supply can be used.
The author believes that the distribution box should be set in the exhaust fan room on site for the following reasons: A.
Therefore, it is a reasonable choice to set its end distribution box in a special distribution room.
Compared with the original jgj16-2008 code for electrical design of civil buildings (obsolete, hereinafter referred to as the civil code), although the civil standard is more detailed, more perfect, more rigorous and more operable, for the civil standard , designers still have some understanding deviation or confusion in specific engineering design.
When the power supply is led in by cable, the double circuit power supply mode should be adopted.
The newly compiled gb51348-2019 standard for electrical design of civil buildings (hereinafter referred to as the civil standard) has been implemented for some time.
The nature of the load is not described here.
Therefore, when considering the power supply scheme, the designer should fully understand the municipal power grid of the project location.
There are still some disputes about setting the terminal distribution box of smoke control fan in the distribution room.
Under what circumstances does it belong to “less load”? Indeed, there is some confusion and no convincing basis.
The power supply that can meet this requirement should be the fire fan distribution box set in the room, which can generally adopt the method shown in Figure 2..
The “lighting system” here should also refer to the general lighting system.
It can be seen from this requirement that the smoke exhaust fan itself is set in a relatively safe special machine room, and the distribution box of the smoke exhaust fan is set in this room, which is relatively safe and convenient for operation and maintenance.
The double circuit here should refer to the case of power supply by cable, that is, only when the load is small or the regional power supply conditions are difficult, the power supply mode of one circuit special overhead line can be adopted, as shown in scheme 2 in Figure 1.
for the introduction of external power supply, article 3.2 of the civil standard The voltage level introduced by external power supply has been specified in Article 11, that is, it should be 35kV, 20kV or 10kV.
For the problem of “small load”, there are no provisions in the civil standard, civil code and gb50052-2009 code for design of power supply and distribution system.
The author believes that this is not rigorous enough.