Indoor electrical installation

Transcription

1 Indoor electrical installation Standard scheme of electrical installation TP CC MB LB LB LB SR TP transformation plant (electrical power in the grid system) 400 kv (national grid system) transformers 33 kv (industrial consumers)... local transformation plants 415 V (residential building supply) CC case of electrical power connection - placed in front of building (pillar in a fence, building facade) - min. 0.6 m above the ground - include main building fuses - may contain main electrical measurement and transformation MB main distribution board - placed inside the building - split electrical installation to subsidiary boards - fuses and circuit-breakers for each line - electrical measurement + circuit-breaker and transformer for protection subsidiary distribution board - split electrical installation to local (flat, office) boards - separate for: - recommended for each floor - lighting system of corridors - boiler room - elevator engine room - air-handling unit room - cooling machine room - laundry - other individual units (shops, copy centers, laboratories, large-scale-kitchen etc.) LB local (flat, office) distribution board - before FB is flat electrical measurement - required for each flat - split into flat electrical installation - includes flat fuses and circuit-breakers 1

2 Electrical installation conductors and cables placed in wall grooves, electricity moulding etc. 1 st floor a) Workshop Copy centre LB3 LB2 1 LB4 MB LB1 Flat CC Shop 1 st floor b) Workshop Copy centre LB3 LB2 LB4 MB+ LB1 Flat CC Shop 2

3 2 nd - 4 th floor Copy Office LB Office Office Office 5 th floor Boiler room elevator Boiler room 3

4 Design of electric conductor Initial parameters: Design electric load P p b.sp i [kw] P i electric input of each single electrical appliance in the building β coefficient of demand, simultaneity (fig. 1) Fig.1 Coefficient of demand β Number of Number of Number of β β flats flats flats β

5 Fig.2a Ultimate simultaneous electric input of a flat (CSN ) Level of electricity use Electric input P [kw] A lighting, 7 B lighting, cooking 11 C - heating not defined (see el. input of heating plant) Tab.2b Ultimate electric input for other services in building except flats Room Electric input P [kw] Boiler room (non electric heating) 2 Air-handling unit room 6 Elevator engine room 8 Laundry 4 Copy centre 7 Small workshop 5 Fig.3 Coefficient of demand β for various buildings (Informative only) Building type β School 0.75 Kindergarten 0.75 Large shops 0.9 Bakery, confectionery, cafe 0.85 Restaurant, bar 0.6 Other small shops 0.75 Theatre, cinema 0.65 Public buildings (town hall, court...) 0.65 Public lighting 1.0 Design electric current Three-phase current I p P p 3 U cosϕ [ A] Single-phase current I p Pp U cosϕ [ A] 5

6 P p design electric load [W] U three-phase system 400 V, single-phase system 230 V cos ϕ power factor (0,95-1,0) ϕ lag angle between peak voltage U [V] and peak current I [A] means that instantaneous available power P [W] is less than the product of two peaks. P U. I. cos ϕ... for single-phase P U. I. 3. cos ϕ... for three-phase real power ( todoa work) power factor apparent power kw kva Design of electric conductor allowed voltage drop allowed conductor s core warming Allowed voltage drop - maximum voltage drop U for main building source conductor is 5% - maximum voltage drop U for conductors from distribution board to electric appliances is 3% l 1 l 2 l 3 l 4 Transforma tion plant I P1 I P2 I P3 I P4 Building 4 Building 1 Building 2 Building 3 n 3 I l cos i 1 pi i U s ϕ [ V ] γ S l the distance of certain buildings from transformation and switching plant [m] I p design electric current in particular conductor s segment [A] S area of conductor s cross-section [mm 2 ] γ specific conductivity of conductor s core Aluminum core: 35 S.m.mm -2, 6

7 Copper core : 56 S.m.mm -2 If the voltage drop is higher than allowed than area of conductor s cross-section is: n 3 2 I l cos i 1 pi i S ϕ [ mm γ U s Allowed conductor s core warming As the voltage drop is lower, the electric current I n >I p, where I n is allowable conductor s current related to conductor s cross-section area S. While this condition is satisfied, than the core temperature doesn t exceed its limit. Conductor s and cable s core temperature has to be lower during any circumstances such as overload or short-circuit. I Z k 1.k 2.k 3 k n. I N I P [A] ] I Z nominal electric current [A] I N allowable conductor s current [A] (Fig. 4) I P design electric current [A] k 1.k 2.k 3 k n coefficients representing different conditions than those used for estimation of I N in Fig.4 I Z < I P undisposed conditions k 1.k 2.k 3 k n < 1 larger S I P < I Z < I N satisfactory conditions k 1.k 2.k 3 k n < 1 keep S I N < I Z possitive conditions k 1.k 2.k 3 k n > 1 keep S I P k<1 I N k>1 Fig. 4 Maximum conductor s (cable) current. Core temperature 70 C, surrounding air temperature 30 C, soil temperature 20 C Copper condutor s core Aluminum conductor s core Area of D x D section x [mm 2 A B C ] A B C KmW -1 KmW -1 KmW -1 KmW

8 x 0.7 and 2.5 WmK -1 are values of soil thermal resistance A insulated conductors in wall, wall groove, B insulated conductors on wall surface, open wall grooves C multicore cables on wall surface, inside wall, in open wall grooves, in floor D multicore cables inserted in tube in soil Example: Design electric load: 10 flats in a residential building, total electric input of appliances in the flat 7 kw 10 flats... β 0.45, P i 7*10 70 kw > P p 70*0,45 31,5 kw Design electric current: ,5 I p [ A] 47, ,95 A Design of electric conductor: l 1 15 m, l 2 30 m, l 3 45 m, l 4 60 m I p1 I p2 I p3 I p4 47,8 A U s 400 V U s 20 V (max. 5%), γ 56 S.m.mm ( ) 0.95 S mm Allowed conductor s core warming: soil thermal resistance 2.5 WmK -1 I n 63 A I p 47,8 A 2 I n > I p OK 8