BUILDING ELECTRICAL SERVICES DESIGN FOR A PROPOSED COLLEGE ADMINISTRATION BLOCK

Transcription

1 BUILDING ELECTRICAL SERVICES DESIGN FOR A PROPOSED COLLEGE ADMINISTRATION BLOCK PROJECT INDEX: PRJ 107 BY ONSONGO KEVIN NYAKUNDI F17/1770/2006 SUPERVISOR: DR. N. O. ABUNGU EXAMINER: DR. WEKESA DATE: 27 TH MAY 2011.

2 OBJECTIVES Design of a Lighting System Design of power points layout Load assessment Load Balance realization Design of Electrical Power Distribution System Design of back-up power system Power Factor correction Protection

3 INTRODUCTION The College is located in an area where solar and wind are the main sources of energy Total load = = 1000 Number of floors =4 266kVA The design of the distribution system was in compliance with the IEE regulations for electrical installations.

4 A section of the college map.

5 LIGHTING DESIGN Two methods commonly used for design: 1. Lumen method (Zonal cavity method). 2. Point by point method. Lumen method: Uses horizontal illuminance criteria to establish a uniform luminaire layout in a space. Considered for uniform lighting. Point by Point method: Suitable for outdoor schemes and indoor schemes where reflectances are negligible. Lumen method was used in this project.

6 SAMPLE CALCACULATION:REGISTRAR S OFFICE Recommended illuminance = 500lux Floor dimension : L = 4.8m, W = 3.5m Ceiling height = 3m Mounting height, H m = = 2.15m K = = ( ) UF = Lighting design lumens(ldl) = 3600lumens Required Flux = = 8400lumens 8400 Flux to be installed = = 29577lumens Number of Luminaires =

7 Registrar s office on ground floor Luminaire Quattro lamps

8 Fittings arrangement on first floor

9 LIGHTING CIRCUITS Radial circuits are used. Worst case of 100W per lamp. 10 lighting points assigned to each lighting circuit. MCB rating of 6A is used to protect each lighting circuit.

10 DESIGN OF THE POWERING POINTS Sockets (BS 1363) Radial circuit Ring circuit Ring circuits were used each protected by a 32A MCB. Maximum of 4 twin sockets per ring circuit. Kitchen Units: Used to connect power to the cooker. They also have an attached socket. Single Phase Isolators: Used to power the hand driers and single phase air conditioners.

11 Power and data points on Mezzanine Floor.

12 LOAD ASSESSMENT This was to facilitate the determination of the design current I b. The main loads in the installation were: Lighting circuits. Ring circuits. Single phase isolators. Design current I b = V P η Cos φ I b for a single lighting point = = 0.538Amps Each lighting circuit had 10 lighting points, thus 5.38A. Total load for light circuit = = Watts

13 MAXIMUM DEMAND ASSESSMENT Evaluated for each of the final circuit. This was done to facilitate load balancing. Maximum demand was calculated as follow; Maximum demand (A) = Connected load diversity Maximum demand : the highest rate at which power is consumed. Connected load : the sum of all loads in the installation. Diversity : accounts for the fact that some of the connected loads will not be running at the same time instant as other loads. Example: Each lighting circuit: Total load = Watts Diversity factor = 0.9 Maximum demand= = Watts

14 LOAD BALANCING Equally distributing the single-phase loads across the three-phase supply is known as balancing the load. Was achieved by distributing the various loads on the different phases. Load balancing in the building Floor Red phase Yellow Phase Blue Phase Ground Mezzanine First Second Total Load(W) Current(A)

15 POWER DISTRIBUTION Desirable principles in distribution schemes in buildings are: The circuit should be reliable. The circuit should be economical. It should be able to meet future expansions without large financial costs. Distribution system can be: The vertical supply system (rising mains). The horizontal supply (distribution at each floor level). The vertical supply system was used.

16 BACK-UP GENERATOR Used to provide critical loads with power in the case of mains failure. All the loads were to be backed up i.e. 266kVA A 340kVA Manlift hooded generator was used. The MFP intended for automatic operation of the generator was incorporated at the switch board.

17 SIZING OF CABLES The size of a cable to be used for an installation depends upon: the current rating of the cable under defined installation conditions. the maximum permitted drop in voltage as defined by Regulation 525. Was done with an allowance of 20% to cater for future growth. Conductor cross section area got from IEE standard Table 4D2A. Voltage drop per ampere per metre obtained from Table 4D1B. Volt drop = Where: V I b = = V Ib L 1000 voltage drop per ampere per metre in mv/a/m Total load CU load

18 Cable sizing for consumer units on ground floor

19 DISTRIBUTION SYSTEM RETICULATION Fig.7: Distribution system layout Fig 6: Distribution system reticulation layout

20 POWER FACTOR CORRECTION Is the relationship between active power and total power. Power factor correction helps in: Reducing copper losses. Enables economic use of conductors and switchgear Power factor before correction =0.7 Required power factor =0.9 Power factor triangle N/B: 150kVAr capacitor bank chosen

21 PROTECTION SYSTEM DESIGN Protection of cables (BS 7671). Protection against overcurrent; overload and short circuit achieved by use of MCBs and MCCBs. Discrimination: IEE Wiring Regulations

22 Summary of discrimination for the protective devices and protection of cables Consumer Unit(CU) GF.1 GF.2 GF.3 GF.4 GF.5 GF.6 CU Cable size (mm 2 ) Cable Rating (A) Cable current (Amps) Rating of largest MCB in CU(A) Fault current (Amps) Rating of MCCB upstream

23 CONCLUSIONS The design of lighting and distribution system was achieved under the IEE standards and regulations. The total load was assessed to be 266kVA. The distribution system was realized by use of one DB and 24 Cus. Back-up system designed with a 340kVA generator in place. Reactive power improved by a 150kVAr capacitor bank. Protection system was designed.

24 RECOMMENDATIONS FOR FUTURE WORK There is need for; Automation of the lighting system. Development of a program code to do calculation of earth faults and cable sizes.

25 THANK YOU