Design of Power Supply and Distribution System in Residential Buildings

Li Caijuan

(School of Electrical Engineering,Lanzhou Institueof Technology,Lanzhou,Gansu 730050)

Abstract:This paper expounds the load classification and power supply measures in the residential area,and puts forward the solutions to the problems that are prone to errors in the design of residential power supply.

Key words:load classification;power supply measures;firepower equipment

In recent years,with the increase of residential building scale,people have higher and higher requirements on the power supply reliability of residential buildings.In addition,load classification and power supply requirements in the design of power supply and distribution system are mandatory standards,which makes the scrutiny very strict during electrical designs.In the electrical design,the power supply and distribution system mainly verifies the primary load and the power supply measures of the particularly important load in the primary load,relationship between backup power supply and emergency power supply,emergency power supply and normal power supply.Therefore,in the electrical design,first of all,load levels should be correctly classified,then according to the first,two,three different levels of load,take different power supply and distribution measures.

I. Load Classification of Residential Buildings

In the design of residential building power supply and distribution system,first of all,according to the construction scale,design positioning,using standard,fire classification,fire resistance grade requirements of residential area,accurately classify the load level according to the current design specification.

Combined with Civil Building Electrical Design Code(JGJ16-2008)the load classification of residential buildingsisshown in Table 1.

The primary and secondary electrical loads in high-rise residential buildings mostly are fire load and non-fire load.In the design specification of power supply and distribution system,the name and capacity of the electrical equipment corresponding to the loads at the first,second and third levels shallbe explained respectively.Because only making clear the first,second and third levels of load corresponding to the power equipment and load capacity at all levels,can determine the number of transformer installation and installation capacity;The reserve power supply capacity can be determined by defining the capacity of primary and secondary loads.The capacity of the particularly important load in the first level load determines the capacity of the self-provided generator set,EPSof the centralized emergency power supply device or UPS of the uninterruptible power supply,so the capacity of all levels of loads should be clarified in thedesign specification.

Table 1 Load Classification of Residential Buildings

II. Electricity Supply for Residential Buildings

The primary load in a residential building must be supplied by a dual power supply,which is independent of each other.Dual power can be supplied in oneof threeways:

(i)Fromtwodifferent power plants;

(ii)From two substations with voltages of 35kV and above;

(iii)One comes from a regional substation and theother hasitsown generatingequipment.

As the regional power grid is connected to the upper part of the main network,it is also difficult to meet the situation that the power plants directly deliver to the civil building users,the dual power supply isoften adopted in theaboveway(i)or(ii).

When two 10kV high-voltage power supplies from two regional substations can be introduced from the municipal power grid,according to the load characteristics, after technical and economic comparison,the following two wiring modes can be adopted:

(i)The two power supplies adopt single bus segment at the same time,and each of the two power supplies a part of the load,which is reserved for each other;

(ii)The two-way power supply adopts bus undivided,one for use and one for standby.If there is only one 10kV power supply in the municipal power grid,the self-provided diesel generator can be used as the backup power supply.The system wiring diagram as shown in figure 1 is adopted.In normal condition,the power is supplied by the transformer busbar.After the normal power is lost,thediesel generator isstarted(seefigure1).

Double circuit power supply is adopted for secondary load,and the two circuits are required to be independent of each other.Double circuit power supply can adopt the following one of three ways:

Figure 1 system wiring diagram asthe second power supply cannot be obtained dueto high load grade

(i)Power supplies fromtwo substations;

(ii)Power supply from different busbars of the samesubstation(or regional substation);

(ii)Two different circuits on the same bus from thesamesubstation(or regional substation).

The source of the power supply is not clearly specified in the specification,so the designer shall jointly determine the power supply situation of the project with the construction unit and the local power supply department at the preliminary design stage.

III.Design of Wiring Scheme of Low-Voltage Power Distribution System in Residential Buildings

In residential buildings,the 0.4kv low-voltage system is often operated by single bus section.Attention should be paid in electrical design:lighting load and power load should be supplied separately on the bus as far as possible,and normal load and emergency load should be supplied by different transformers.Fire and non-fire power supply shall be separated.

In order to ensure the reliability of power supply of equipment,the following loads shall be supplied from the low-voltage main distribution room to the final distribution box with a dedicated power supply circuit,which shall be strictly separated fromthegeneral distribution line:

(i)Fireelectrical equipment

(ii)Emergency lightingfor stairwells

(iii)elevator

In electrical design,fire fighting electrical equipment must use a separate power supply circuit[1],which cannot be shared with other power and lighting circuits.Only in this way,when the non-fire power supply is cut off due to fire,the fire power supply will not be affected.Specifically,when there is a 10/0.4kV substation in the building,the main power supply lines for fire fighting load and non-fire fighting load fed out from the low-voltage switchgear must be separated.When the building is equipped with a 0.4kV low-voltage distribution room,the main fire and non-fire power supply mains fed out from the distribution room should be separated.Meanwhile,it is necessary to note that the electrical fire equipment and emergency lighting should be set with double power automatic switching device at the distribution box at the last level accordingtothefireprevention division.

For super high-rise residential power supply should be set up with its own emergency diesel generator set. In view of the continuous improvement of municipal power supply quality and the low utilization rate of diesel generator set in actual projects,the diesel generator set should be optimized in the actual design and the capacity of diesel generator set should be reasonably selected.The low-voltage power distribution system wiring diagram of super-high-rise residential buildings can be adopted in figure 2 below.

Figure 2 wiring diagram of low-voltage distribution system for super-high-rise residential buildings

In the wiring diagram of the low-voltage distribution system in figure 2,the primary power supply of the emergency load is supplied by No.1 transformer,and the standby power supply is provided by the diesel generator.The power supply of the emergency load is switched between the diesel generator set and the No.1 transformer busbar.The emergency busbar III and IV are added to the system,which respectively are the emergency busbar for fire fighting and the bus for non-fire fighting essential load.The two busbars can be operated simultaneously without consideration to reduce the capacity of the diesel generator.In the design,it should also be noted that the starting command of the diesel generator of the emergency power supply should be issued by the auxiliary contact of the main switch AT of the normal power supply,that is,the delayed starting signal of the generator should be picked up from the automatic switching switch of the municipal power generator[2].It should be noticed that the starting signal of the generator cannot be sent by the contact of the relay,because the relay may misoperate to send the starting signal of the generator,thus causing the generator to run side-by-side with the normal power supply.

IV.Conclusion

In this paper,the problems that should be paid attention to in the design of power supply and distribution system in residential buildings are elaborated only in terms of the reliability of power supply.In the specific design,attention should be paid to the relevant regulations on power supply and distribution in residential buildings in combination with local power supply departments,so as to avoid the design rework caused by not meeting the local regulations.