UNIVERSITY OF NAIROBI FACULTY OF ENGINEERING DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING

Transcription

1 UNIVERSITY OF NAIROBI FACULTY OF ENGINEERING DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING LIGHTING AND DISTRIBUTION SYSTEM DESIGN FOR A PROPOSED RESIDENTIAL ESTATE IN FAHARI CITY PROJECT INDEX: PRJ 100 BY CHORE VICTOR F17/1975/2005 SUPERVISOR: DR. NICODEMUS ABUNGU EXAMINER: DR.CYRUS WEKESA PROJECT REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF BACHELOR OF SCIENCE IN ELECTRICAL AND INFORMATION ENGINEERING UNIVERSITY OF NAIROBI 2011 Submitted on: 18TH May, 2011

2 DEDICATION Tribute to my family who believed in me and encouraged me to come this far Thank you. ii

3 ACKNOWLEDGEMENTS Would like to thank Dr.Nicodemus Abungu for his technical support, guidance, and patience during the research and implementation of this project iii

4 DECLARATION AND CERTIFICATION This BSc. work is my original work and has not been presented for a degree award in this or any other university... CHORE VICTOR F17/1975/2005 This report has been submitted to the Dept. of Electrical and Information Engineering, University of Nairobi with the approval of my supervisor: Dr. Nicodemus Abungu Date... iv

5 TABLE OF CONTENTS Page DEDICATION... ii ACKNOWLEDGEMENTS... iii DECLARATION AND CERTIFICATION... iv TABLE OF CONTENTS... v TABLE OF FIGURES... viii ABSTRACT... ix CHAPTER INTRODUCTION PROBLEM STATEMENT... 2 CHAPTER LITERATURE REVIEW LIGHTING DESIGN INTERIOR LIGHTING EXTERIOR LIGHTING LIGHTING DESIGN... 5 LUMEN METHOD... 5 POINT-BY-POINT METHOD POWER DISTRIBUTION SYSTEMS IN BUILDINGS... 6 DISTRIBUTION IN DOMESTIC BUILDINGS... 6 DISTRIBUTION BETWEEN BUILDINGS GROUNDING AND EARTHING DIVERSITY LIGHTNING PROTECTION POWER FACTOR CORRECTION BACKUP GENERATOR CHAPTER INTERIOR LIGTHING DESIGN SCHEMES TYPE J MAISONNETE LOUNGE ROOM DINING ROOM KITCHEN v

6 3.2 TYPE A MAISONETTE TYPE B MAISONETTE TYPE C MAISONETTE CHAPTER LOAD CALCULATION FOR THE BUILDINGS TYPE J1 HOUSE TYPE C HOUSE TYPE B HOUSE TYPE A HOUSE LOAD BALANCING PER PHASE DISTRIBUTION OF LOADS BETWEEN THE CONSUMER UNITS CHAPTER EXTERIOR LIGHTING DESIGN SCHEMES STREET LIGHTING DESIGN OVERALL BALANCED LOADS CHAPTER CABLE SIZING TYPE A HOUSE CONSUMER UNIT CABLES SIZING OF CABLES FROM METER BOARD TO DISTRIBUTION BOARDS SIZING OF SUB DISTRIBUTION BOARD CABLES SIZING OF MAIN DB CABLES CHAPTER DISTRIBUTION OF POWER TYPE OF DELIVERY SYSTEM UNDERGROUND VERSUS OVERHEAD DISTRIBUTION SYSTEM POWER DISTRIBUTION WITHIN THE RESIDENTIAL ESTATE METRE LAYOUT DISTRIBUTION SYSTEM RETICULATION FAULT CURRENT LEVELS FAULT CURRENT LEVELS AT THE SERVICE MAIN FAULT CURRENT LEVELS AT BEGINNING OF FINAL CIRCUITS FAULT CURRENT LEVELS AT THE CONSUMER UNITS FAULT CURRENT LEVELS AT THE SUB DISTRIBUTION BOARDS CHAPTER DISCRIMINATION vi PROTECTION OF CABLES PROTECTION AGAINST OVER CURRENT PROTECTION AGAINST OVERLOAD CO-ORDINATING BETWEEN CONDUCTORS AND PROTECTIVE DEVICES 48 PROTECTION AGAINST SHORT CIRCUIT... 49

7 9.6 PROTECTION OF CABLES AND CONDUCTORS AGAINST SHORT-CIRCUIT DISCRIMINATION DISCRIMINATION BETWEEN CUS AND DBS DISCRIMINATION BETWEEN SUB DBS AND THE MAIN DBS CHAPTER POWER FACTOR CORRECTION BACKUP POWER CALCULATION CONCLUSSION RECOMMENDATIONS FOR FUTURE WORK REFERENCES APPENDICES Appendix Appendix Appendix Appendix Appendix vii

8 TABLE OF FIGURES FIGURE FIGURE FIGURE FIGURE FIGURE FIGURE FIGURE LIGHTING PROTECTION IN A RESIDENTIAL HOUSE...11 FIGURE viii

9 ABSTRACT The task at hand was lighting up a residential estate in Fahari city and designing a power distribution system for the estate which had four types of maisonettes A, B,C and J totalling to 111 units. A review of literature on the relevant areas was done systematically with the end in mind which was to make design that can be implemented. Interior lighting design scheme was tackled using set standards for the four housing units from room to room depending on their functionalities. Load analysis was done after circuiting and application of diversity to come up with a revised load of 123,121,125,132 Amps respectively. The no of C U were 2 for each unit with a load of 75A and 8 ways. The revised load for the whole estate was summed up and a resultant distributed over three phases to achieve balance among the loads of since for three phase systems balance is very important. The cables were sized cable used was 1.5mm2,,6mm2,16mm2, 50mm2,185mm2,300mm2 for lighting, power points, CU s metre board, sub DBs and main DB s respectively. Reference was made to the IEE tables for cables to check their relevant ampacity and voltage drop. The distribution system was designed A design was made within the available means and an underground radial system was utilised composed of 4 pad mounted transformers, 12 main distribution boards and 37 sub distribution boards, armoured and unarmoured cables. Faults in the system were analysed for the magnitudes of fault current at the various level which were around 2000 Amps at the CU level and for distribution board level A. A protection system was designed protective devices placed at various points in the installation such AS 80 A, 250A or 630AJ or K FRAME MCCB. Power factor correction was done where a 150Kvar capacitor bank was placed at the Main DB level back up power is also provided using a portable Honda generator rated at 40KW. ix

10 x

11 CHAPTER INTRODUCTION Lighting design is about the distribution of power in a given area of interest which can be a building open place like a stadium and many others. The design is usually initiated by taking into account the requirements of the end user and working backwards using the relevant theory, calculations and assumptions. Through this procedure the total load is determined for both lighting and power points and thus the sizing of cables, consumer units, miniature circuit breakers and moulded case circuit breakers can be done accurately, economically and efficiently. 1

12 1.2PROBLEM STATEMENT The objective of this project was to achieve lighting and distribution system design for a proposed residential estate in Fahari city under the IEE (Institution of Electrical Engineers) standards and regulations. This is an estate consisting of three and four bed maisonettes which come in four unique designs i.e. type A, B, C and J all with ground and first floor. This was tackled using lumen method of lighting which was able to achieve maximum visual performance. Backup generation was also incorporated to ensure the system maintains a continuous supply in case of interruptions in the main source in our case Kenya Power and Lighting Company Ltd. 2

13 CHAPTER 2 LITERATURE REVIEW 2.1 LIGHTING DESIGN The concept of efficient lighting has given rise to a set of standards or criteria for lighting different places. Lighting for a given area depends on the intended use of the place. The growing demand for quality lighting design has been accompanied by the demand for quality lighting equipment. Differentiated lighting requires specialized luminaires designed to cope with specific lighting tasks. We need completely different luminaires to achieve uniform wash light over a wall area, for example, than you do for accentuating one individual object or different ones again for the permanent lighting in a theatre foyer than for the variable lighting required in a multipurpose hall or exhibition space. 2.2 INTERIOR LIGHTING Lighting practitioners must evaluate the application and consider the important lighting design criteria such as including direct glare, surface luminances, and uniformity for different areas. Different types of fittings may be considered in three categories: General utility- designed to be effective, functional and economical e.g. the fluorescent lamps. Special- usually provided with optical arrangements such as lenses or reflectors to give directional lighting. Decorative- designed to be aesthetically pleasing or to provide a feature rather than to be functional. Lamp color, e.g. cool color of light may psychologically imply a cool relief from the hot exterior environment. Choice of lamp color has no effect on light levels or cost- it is basically an aesthetic choice. Direct lighting uses down lights to illuminate the reading tables, they are the most appropriate for libraries where down light are those light fittings that radiate downwards. They are usually mounted on the ceiling and illuminate the floor or other horizontal surfaces and are louvered to add protection against glare. Residential lighting is planned on the basis of activities, occupants' ages, and physical capabilities and limitations, not on the basis of room type. The designer should provide enough general lighting for a range of activities. Artificial Light Sources 3

14 i. Incandescent lamp. Until recently the most common electric light source was the incandescent lamp. This is still widely used, although its relatively low energy efficiency is leading to its replacement by other more efficient lamps such as the compact fluorescent lamp. Typical lamps for household use range from about 40 to 100 W, giving a light output of 420 to 1360lm at the typical lamp efficiency of about 12%. ii. Compact fluorescent lamp. The compact fluorescent lamp was designed as a more efficient replacement for incandescent lamp. It is supplied with screw or bayonet fixing system, and can be used in many light fittings designed for incandescent lamps. They are more commonly referred to as energy savers. Typical lamps for household use range from about 7 to 20W, giving a light output of 400 to 1200lm. iii. Fluorescent tube. Fluorescent tubes are the main form of lighting for offices and commercial buildings. They are a form of gas discharge lamp, and are formed in along thin glass cylinder with contacts at either end that secure them to the fitting and provide the electrical connection. The most efficient fluorescent tubes are the T5. With a smaller diameter (16mm) than earlier tubes, these can achieve a luminous efficacy of up to 104lm/W. iv. Discharge lamps. Discharge lamps work by striking an electrical arc between two electrodes, causing a filler gas to give off light. Different metals and filler gasses can be used to provide a range of colour and brightness. Discharge lamps provide high luminous efficacy combined with long life, resulting in the most economical light source available. v. Light Emitting Diode (LED). LEDs use semi-conductors to convert electrical energy directly into light. They are only recently becoming available as a light source for lighting purposes, and are highly efficient and long lasting making them very popular. Light Fittings The fitting into which a light source is installed is an important consideration in achieving energy efficiency. The fittings for fluorescent tubes are called luminaires and come in a variety of types, suitable for different applications. The important consideration in selecting a fitting is to achieve maximum efficiency without compromising the quality of light. 4

15 Common types of luminaire include the following: Channel luminaires; is the simplest form of luminaire is simply a tube holder with a white reflector. This has a high efficiency, but can result in glare problems since the lamp is visible. Prismatic diffuser; this uses an acrylic prismatic diffuser to conceal the lamps, resulting in low surface brightness, reducing glare problems. It is not very efficient due to light losses in the diffuser. Parabolic louvre; this provides excellent glare control without compromising efficiency, using reflective aluminum louvers to conceal the lamps from low viewing angles. Luminaire Typical total light output ratio(% of lamp flux) Channel Prismatic Diffuser Parabolic Louvre Up lighter 60 Figure 1 Performance characteristics of luminaires 2.4 EXTERIOR LIGHTING 2.5 LIGHTING DESIGN LUMEN METHOD When designing interior lighting schemes the method most frequently used depends upon a determination of the total flux required to provide a given value of illuminance at the working place. The method used is generally known as the lumen method which is implemented using the formula given below. N E A. F U M Where: N-number of light fittings, E-average illuminance on the working plane, A-area of the working plane in ( m2 ) F-lumen output of each luminaire (lumens 5

16 U-utilization factor: Ratio of lumens received on the working plane to the installed flux M maintenance factor: It is the ratio that takes into account of how the lighting conditions will deteriorate through use due to aging and dirt. Where; ( + ) K-room index: describes the influence of room geometry in lighting design Hm- height above working plane under direct luminary, L-length of the room W-width of the room U (utilization factor) is found for every value of K. Spacing to height ratio (SHR) is the centre to centre (s) distance between adjacent luminaries to their mounting height (Hm) above the working plane. Manufacturers catalogue can be consulted to determine maximum SHRs POINT-BY-POINT METHOD This is a lighting design procedure for predetermining the illuminance at various locations in lighting installations by use of luminaries photometric data. Two components come into play direct component of illuminance due to the luminaires and the interreflected component of illuminance due to the room surfaces which are both calculated and summed up.this method of calculation is particularly suitable for outdoor schemes. The inverse square law finds application in this method, the light intensity in a given direction is found from polar diagrams supplied by manufacturer. 2.6 POWER DISTRIBUTION SYSTEMS IN BUILDINGS DISTRIBUTION IN DOMESTIC BUILDINGS Lighting circuits Lighting circuits can incorporate various switching arrangements. In a one-way switch circuit the single-pole switch must be connected to the live conductor. To ensure that both live and neutral conductors are isolated from the supply a double-pole switch may be used, although these are generally limited to installations in larger buildings where the number and type of light fittings demand a relatively high current flow. Provided the voltage drop of 4% is not exceeded, two or more lamps may be controlled by a one-way single-pole switch. In principle, the two-way switch 6

17 is a single-pole changeover switch interconnected in pairs. Two switches provide control of one or more lamps from two positions, such as that found in stair/landing, bedroom and corridor situations. In large buildings, every access point should have its own lighting control switch. Any number of these may be incorporated into a two-way switch circuit. These additional controls are known as intermediate switches. [7] Figure Figure Figure Power points Ring circuits 7

18 A ring circuit is used for single-phase power supply to three-pin sockets. It consists of PVC sheathed cable containing live and neutral conductors in PVC insulation and an exposed earth looped into each socket outlet. In a domestic building a ring circuit may serve an unlimited number of sockets up to a maximum floor area of 100. A separate circuit is also provided solely for the kitchen, as this contains relatively high rated appliances. Plug connections to the ring have small cartridge fuses up to 13 amp rating to suit the appliance wire. [7] DISTRIBUTION BETWEEN BUILDINGS A simplified form of a distribution system from generation down to distribution can be represented by figure Figure For large developments containing several buildings, either radial or ring distribution systems may be used. Radial system Radial system separate underground cables are laid from the substation to each building. The system uses more cable than the ring system, but only one fused switch is required below the distribution boards in each building. 8

19 Figure2-0-5 Ring circuit system In this system an underground cable is laid from the substation to loop in to each building. To isolate the supply, two fused switches are required below the distribution boards in each building. Current flows in both directions from the intake, to provide a better balance than the radial system. If the cable on the ring is damaged at any point, it can be isolated for repair without loss of supply to any of the buildings. Figure2-0-6 Distribution of power is will be treated in detail later in chapter 7 9

20 2.7 GROUNDING AND EARTHING The object of earthing a consumer s installation is to ensure that all exposed conductive parts and extraneous conductive parts associated with electrical installations are at, or near, earth potential. Earthing conductors and protective conductors need to satisfy two main requirements, namely to be strong enough to withstand any mechanical damage which is likely to occur, and also to be of sufficiently low impedance to meet the need to carry any earth fault currents without danger.the most important safety system in any building or zone is the one protecting from the hazards of fault current this is normally achieved by use of an earthing or grounding circuit. This is achieved using any of these configurations: The TT system The TN-S System The TN-C-S 2.8 DIVERSITY Connected load is the sum of the ratings of all the electrical equipment at a consumer s premise that is connected to the supply system. Diversity in electrical installations permits specification of cables and overload protection devices with regard to a sensible assessment of the maximum likely demand on a circuit. For instance, a ring circuit is protected by a 30 amp fuse or 32 amp mcb, although every socket is rated at 13 amps. Therefore if only three sockets were used at full rating, the fuse/mcb would be overloaded. In practice this does not occur, so some diversity can be incorporated into calculations. Diversity can be described as the likely current demand on a circuit, taking into account the fact that, in the worst possible case, less than the total load on that circuit will be applied at any one time. Additional information is given in the table containing diversity factors as per IEE requirements in Appendix 3[9, 7]. 2.9 LIGHTNING PROTECTION Lightning protection systems are used to prevent or lessen damage to structures done by lightning strikes. Lightning protection systems mitigate the fire hazard which lightning strikes pose to structures. A lightning protection system function is to provide a low-impedance path for the lightning current to lessen the heating effect of current flowing through flammable structural materials. 10

21 Due of the high energy and current levels associated with lightning, no lightning protection system can guarantee absolute safety from lightning. Lightning current will divide to follow every conductive path to ground, and even the divided current can cause damage. However, the benefits of basic lightning protection systems have been evident. A complete lightning protection system is as shown in fig Figure Lighting protection in a residential house 2.10 POWER FACTOR CORRECTION In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. The higher currents increase the energy lost in the distribution system, and require larger wires and other equipment. Because of the costs of larger equipment and wasted energy, electrical utilities will usually charge a higher cost to industrial or commercial customers where there is a low power factor. An automatic power factor correction unit is used to improve power factor. A power factor correction unit usually consists of a number of capacitors that are switched by means of contactors. Capacitors may be connected across the main busbars of industrial loads in order to provide power factor improvement. The capacitor only corrects the power factor between the point at which it is inserted and the supply undertaking s generating plant, and therefore from a 11

22 commercial point of view so long as it is fitted on the consumer s side of the kilovolt-amperes meter its purpose is served.[9] 2.11 BACKUP GENERATOR Generators are used for the generation of electricity and they ensure that most of the essential appliances can be run whenever there is a power outage. Diesel and natural gas generators are reliable, require minimal maintenance and offer an additional or backup power source. Generators of different wattage capacities can be used according to the needs of the individual. The choice of buying the right type of generator depends upon a number of factors like the wattage capacity, voltage ratings, fuel type, fuel efficiency, noise level, portability and price. Standby generators provide backup power in homes and offices and are permanently installed outside the house or office building they are plugged into the electric circuits or home wiring. They can automatically detect disruption in the usual electric supply and begin supplying power within a given duration after which it is switches off again when normal power resumes. 12

23 CHAPTER 3 INTERIOR LIGTHING DESIGN SCHEMES 3.1 TYPE J MAISONNETE The maisonette was composed of a number of unique areas each of which had its own recommended luminaires e.g. lounge, bedroom and kitchen and study as given in the Interior Lighting Design published jointly by the Lighting Industry Federation Limited and The Electricity Council, Fifth Edition. The design method used was the lumen method as it was previously decided that it would find application in the lighting design of the interiors in the housing units. LOUNGE ROOM The area in question is rectangular in shape although the dimensions are close to that of a square. The lounge is the largest room in the maisonette Illuminance200 lux(ies recommendation for such an area) Position of measurement-table top Floor area dimensions: Length6m Width5.2m Ceiling height3m Mounting height (above working plane table top) H M 3m-0.85m2.15m The maximum spacing between luminaires Thus the lowest number is 2 rows of 2 ( + ) (6 5.2) ( ) To get the utilization factor (UF) after getting the room index use is made of the table of utilization factors versus room index for shallow ceiling mounted diffusing panel with a DLOR of 47.5%(Appendix 3).For a room of K1.11 and ceiling and wall reflectance of 0.7 and 0.5 respectively, the utilization factor by interpolation is 13

24 (1.11 1) ( ) (1.25 1) The fluorescent tube to be used is the low energy square flush ceiling with clear edged acid glass covering grey metallic finish with acid glass panels to allow further illumination from the side s power rating of the lamp is 2 24watts with a Lighting Design Lumen (LDL) output of 2300lm 2 2 2( ) This is not sufficient since the code recommends 200lux.It is proposed to increase the number of luminaires To ensure adequate illumination 6 are used in a configuration of 2 rows of 3 which is shown in the attached AutoCAD diagram This new arrangement will result in the an illuminance of; 2 3 2( ( ) ) 0.8( ) Thus the required illuminance from the tables of 200 is satisfied as 233 is adequate although it s slightly higher. DINING ROOM This is situated next to the Lounge room it is also rectangular in shape and its recommended service illuminance of 200 lux The position of measurement is the dining table top Floor area dimensions Length4.0m Width3.6m Ceiling height3m Mounting height (above working plane), H m 3m-0.85m2.15m 14 Hm ( + ) ( ) ( )

25 To get the utilization factor(uf) after getting the room index use is made of the table of utilization factors versus room index for shallow ceiling mounted diffusing panel with a DLOR of 47.5%(Appendix 3).For a room of K0.88 and ceiling and wall reflectance of 0.7 and 0.5 respectively, the utilization factor by interpolation is ( ) ( ) ( ) The fluorescent tube to be used is the low energy square flush ceiling with clear edged acid glass covering grey metallic finish with acid glass panels to allow further illumination from the sides power rating of the lamp is 2 24watts with a Lighting Design Lumen (LDL) output of 2300lm To check whether the illuminance is adequate ) ( ( ) 0.8( ) Thus the illumination is now sufficient as per recommendation This fitting can be arranged as No.1 (2)24Watts ceiling mounted located at the centre of the room and the other two wall mounted luminaire conveniently placed on the walls. KITCHEN This is a work area with tasks such as cooking, washing and they require more illumination than the areas we have seen above. The IES code recommendation for such an area is 300lux and the room is rectangular. Floor area dimensions L4.2m Width3.6m Position of measurement is the working surface. Ceiling height is 3m Mounting height (above working plane) H m 3m-0.85m2.15m 15 Hm ( + )

26 ( ) ( ) To get the utilization factor(uf) after getting the room index use is made of the table of utilization factors versus room index for shallow ceiling mounted diffusing panel with a DLOR of 47.5%.For a room of K0.97 and ceiling and wall reflectance s of 0.7 and 0.5 respectively, the utilization factor by interpolation is ( ) ( ) ( ) The fluorescent tube to be used is the twin batten illumination from the sides power rating of the lamp is 2 100watts with a Lighting Design Lumen (LDL) output of 2750lm each To check whether the illuminance is adequate 1 2( ( ) ) 0.8( ) Thus the illumination is now sufficient as per recommendation This fitting can be arranged as 1 (2)100Watts The procedure above was followed in the remaining rooms until they were all assigned light fittings as per requirements and some decorative elements were also put into consideration. 3.2 TYPE A MAISONETTE The procedure followed for the previous sections was also applied at to this housing unit. 3.3 TYPE B MAISONETTE The procedure outlined in the previous section was also applied to this housing unit. 16

27 3.4 TYPE C MAISONETTE The procedure outlined in the previous section was also applied to this housing unit. CHAPTER 4 LOAD CALCULATION FOR THE BUILDINGS 4.1 TYPE J1 HOUSE The various fittings that have been put in the house were noted down as shown in the table 4.1 this was done according to the floors i.e. basement, ground and first floor. ROOM NAME Room 1 Room 2 Garage Kitchen yard Open court Lobby(1) Store Kitchen Entrance Porch Lobby(2) Powder room Dressing room Dining room Bathroom Lounge Stairs Guest bedroom TOTALS Security lights TYPE OF LIGHT FITTING C1 C1 C2 A1 A1 A1 A1 C2 A1 A1 A1 D1 D1 A1 and B1(2) D1 A1(4) and B1(2) B2(2) A1 and B1(2) 28 F8 POWER POINTS Single socket Single socket Twin socket None None None Single socket Twin socket and cooker unit None None None 1ø isolator and shaver unit None Single socket Shaver unit Twin socket None Single socket 12 None Table4. 1 Ground floor house type J ROOM NAME Covered terrace Stairs Landing TOTALS TYPE OF LIGHT FITTING A1(3) B2(2) None 5 Table4.2 Lower ground floor house type J 17 POWER POINTS Twin socket None None 1

28 ROOM NAME Porch below Entrance below Bedroom 4 Bedroom 3 Bedroom 2 Bedroom 1 Wardrobe Balcony Lobby Master bathroom Bathroom Cloak Dressing room TOTALS TYPE OF LIGHT FITTING A2 A2 A1 and B1(2) A1 and B1(2) A1 and B1(2) A1 and B1(3) A2 A1 B2(2) D1 D1 D1 D1 23 POWER POINTS None None Single socket Single socket Single socket Single socket None None None Shaver unit Shaver unit and Water heater None None 7 Table 4.3 First floor house type J The light fittings shown in table and the various power appliances that have been tabulated above were further classified as shown below so as to be able to determine the exact separate load for the lighting circuits and power points. A worst case power of 100W was taken for the single lamps type A1 thus the net power of lamp type A1 was calculated as follows; Similarly a worst case power of 200w was taken for the twin lamps type A the lamps were22 in number giving This procedure was repeated for the rest of the lamps and the table below is a summary of the results. 18

29 Lighting circuits LIGHT FITTING A A1 B1 B2 A2 A3 D E F(security light) TOTAL NO WATTAGE PER UNIT 200W 100W 200W 100W 200W 100W 100W 100W 200W TOTAL W Table 4.4 Complete lighting circuit The lighting circuit total load excluding diversity was as shown in table 4.4. The power ratings of the appliances used in a residential house revealed that most are rated between 150 and 1500watts. For a single socket we would approximate a power of 750 watts and for a twin socket power of 1500watts. TYPE OF FITTING Single socket Twin socket Shaver unit Single ø isolator Cooker unit Water heater TOTAL NO WATTAGE PER UNIT 750W 1500W 1000W 1500W 6000W 3000W TOTAL W Table 4.5 Complete power point circuit The complete lighting loads and power point loads for house type J is was as shown in table 4.4 and 4.5. The separation of circuits as shown below was done so as to enable us to incorporate diversity into our work since not all the bulbs or power points can all be in use at a specific time. 19

30 Revised load table CIRCUIT POWER DEMAND CURRENT DEMAND Lighting Ring circuit 1 Ring circuit 2 Ring circuit 3 Cooker Water heater Hand dryer TOTAL 10000W A 32A 32A 32A 25A 12.5A 6.25A DIVERSITY ALLOWANCE % % % % A % % A Table 4.6 Complete revised load table Accounting for future load growth The integral switch of a consumer unit is rated at 100A as stated previously in the first section. Our load is more than this so we need to use more than one consumer unit so two consumer units were used to meet design requirements and also minimise costs. Load per consumer unit should not exceed 75A actual load per cu is 66A and future load per CU is 79 A. 4.2TYPE C HOUSE The various fittings in the house type C were assigned using the relevant calculations from the previous section LIGHT FITTING A A1 B1 B2 A2 A3 D E F(security light) TOTAL NO WATTAGE PER UNIT 200W 100W 200W 100W 200W 100W 100W 100W 200W TOTAL W Table4. 7 complete lighting circuit The lighting circuit total load excluding diversity was as shown above. 20

31 TYPE OF FITTING Single socket Twin socket Shaver unit Single ø isolator Cooker unit Water heater TOTAL NO WATTAGE PER UNIT 500W 1000W 1000W 1500W 6000W 3000W TOTAL W Table4. 8 Complete power point circuits The complete lighting loads and power point loads for house type C was as shown above. The separation of circuits as shown below was done so as to enable us to incorporate diversity into our work since not all the bulbs or power points can all be in use at a specific time. Revised load table CIRCUIT POWER DEMAND CURRENT DEMAND Lighting Ring circuit 1 Ring circuit 2 Ring circuit 3 Cooker Water heater Hand dryer TOTAL 7200W A 32A 32A 32A 25A 12.5A 6.25A DIVERSITY ALLOWANCE 30 66% % % % A % % A Table4. 9 complete diversity table Accounting for future growth Thus the load per CU 62.5 A The integral switch of a consumer unit is rated at 100A as stated previously in the first section. Our load is more than this so we need to use more than one consumer unit so two were used to meet design requirements and also minimise costs. Load per consumer unit should not exceed 75A, the actual load per cu is 63A and future load per CU is 70 A 21

32 4.3 TYPE B HOUSE CIRCUIT POWER DEMAND CURRENT DEMAND Lighting Ring circuit 1 Ring circuit 2 Ring circuit 3 Cooker Water heater Hand dryer TOTAL 5760W A 32A 32A 32A 25A 12.5A 6.25A DIVERSITY ALLOWANCE 24 66% % % % A % % A Table 4.10 Revised load table house type B 4.4 TYPE A HOUSE The distribution of lighting and power point circuits for this type of house was summarised in this table CIRCUIT POWER DEMAND CURRENT DEMAND Lighting Ring circuit 1 Ring circuit 2 Ring circuit 3 Cooker Water heater Hand dryer TOTAL 6240W A 32A 32A 32A 25A 12.5A 6.25A DIVERSITY ALLOWANCE 26 66% % % % A % % A Table4.11Revised load table house type A Accounting for future load growth The complete loads of the various types of houses was summarised as shown in table 4.12 TYPE OF HOUSE NUMBER OF HOUSES REVISED LOAD House A House B House C House J A 121A 125A 132A Table LOAD WITH FUTURE GROWTH 147A 145A 150A 158A POWER IN WATTS 35.28KW 34.8KW 36KW 37.92KW

33 The numbers of houses of each type were as follows A 37, B 30, C 24 and J LOAD BALANCING PER PHASE The estate was supplied by 3 phase 415V and it was required that the whole estate load be divided equally over the three phases so that the load per phase is balanced. The load was balanced among the housing units as shown in table Type of House House A House B House C House J No Red phase Current No Yellow phase Current Total Distribution of houses among the phases Table 4.13 Distribution of houses among the phases No Blue phase Current No It is observed from the table that balance is approximately attained between the three phases. An attempt will be made in the following sections to bridge this discrepancy. 4.6 DISTRIBUTION OF LOADS BETWEEN THE CONSUMER UNITS Loads in each of them were allocated to the two consumer units as shown; the lighting load was divided among some of the ways so that in case of a fault in the whole house does not go dark. The ground and lower ground lighting was subdivided into three ways, way 1,2 and 3 while first floor lighting was allocated way 1 of the second consumer unit. The power points which were grouped into ring circuits were also allocated individual ways per ring circuit. This procedure was followed for the rest of the circuits and details are as shown in the consumer unit schematic fig 1. 23

34 House type J 100A 8A CIR R1.1 3 x 1.5 mm2 PVC SC CU Cables - Lighting 8A CIR R1.2 3 x 1.5 mm2 PVC SC CU Cables - Lighting 40A CIR R1.3 3 x 2.5 mm2 PVC SC CU Cables - Sockets 40A 40A CIR R1.4 3 x 6 mm2 PVC SC CU Cables - Sockets CIR R1.5 3 x 6 mm2 PVC SC CU Cables - Sockets CIR R1.6 Spare CIR R1.7 Spare CIR R1.8 Spare 100A 8A CIR R2.1 3 x 1.5 mm2 PVC SC CU Cables Lighting first floor 8A CIR R2.2 3 x 1.5 mm2 PVC SC CU Cables Lighting security 32A CIR R2.3 3 x 6.0 mm2 PVC SC CU Cables - Cooker 16A 40A CIR R2.4 3 x 4.0 mm2 PVC SC CU Cables Water heater CIR R2.5 3 x 6 mm2 PVC SC CU Cables Sockets first floor CIR R2.6 Spare CIR R2.7 Spare CIR R2.8 Spare Fig 4.1 The same procedure was followed for the rest of housing units and the layout of the consumer unit is shown in the appendix [1]. 24

35 CHAPTER 5 EXTERIOR LIGHTING DESIGN SCHEMES 5.0 STREET LIGHTING DESIGN The lighting design of the residential estate requires that the streets and roads connecting the various sections of the site be lighted to aid motorists and facilitate movement at night. Criteria to be used in this estate were the size of adjacent road and the required illuminance for the different areas. The main road that leads into the estate is wider than the rest of the roads thus it is bound to handle more traffic thus requiring more illumination. Lighting was implemented using the vale lantern from Candela Company of United Kingdom picture attached. Its height varies from 6 to 12 metres. For the street next to the main road 12 m height was used and for the feeder roads 8 m. Spacing between the lamps was desired to be 30m with the exemption of junctions and corners where smaller spacing would be acceptable since more illumination is required. The positioning of the street lights is as shown in the AutoCAD diagram code E. The lamp used for the street lighting was of two types: Type S1 fitting was used with a lamp whose wattage was 200 watts mounted on a mast of height 8 metres. This was placed mainly along the feeder roads within the estate. Number of lamps used was 92. Type S2 fitting was used with a lamp whose wattage was 350 watts mounted on a mast of 12 metres. This was placed on the perimeter of the residential estate and on the main road leading into the estate. Number of lamps used was 73. The fitting recommended for lamp type S1 was 200 watts thus the total power that was to be consumed by these lamps was The fitting for lamp type S2 was 350 watts thus the total power that was to be consumed by these lamps was The distribution of power was done using a control pillar/external consumer unit whose number of ways was allocated to be four. 25

36 Power is supplied to the estate through a three phase 415 Volts which is dropped at the external distribution board placed in a convenient position to supply power to the houses and street lighting. Power for street lighting was tapped from phases of the distribution board and supplied to various sections after dividing the area into three regions each fed by its individual control pillar. The on and off switching was done at the control pillar using a photocell for convenience and reliability. The street lighting could be implemented using a series or a parallel connection the latter was used in the implementation so as to avoid a situation where areas that are downstream going without power in case of a burnt bulb. The voltage drop along each stream was monitored so that it would not reduce the voltage to an unacceptable level. 5.1 OVERALL BALANCED LOADS As we recall from the previous breakdown of the housing unit loads into phases we can note there is a discrepancy to be filled up in the yellow and blue phase. Deficit in the red phase is 11A Deficit in the yellow phase is 8A Balance among the phases must be achieved thus the deficits were to be filled up as follows 13 lamps put on the red phase,10 lamps put on the yellow phase. Type of House House A House B House C House J Subtotal Street Lighting Type S1 Type S2 Grand total No Red phase Amps No Yellow phase Amps A 5512 No Blue phase Amps A 5520 No A A A Table 5.2 Final balanced load A

37 The table shows how the design was done to achieve overall balance over the whole residential estate. As an aid to understanding the table an explanation of the entries in the red phase column is made as follows; i. 13 houses of type A were allocated on this phase whose total current was 1911 Amps ii. 10 houses of type B were allocated on this phase iii. 8 houses of type C were allocated on this phase iv. 6 houses of type J were allocated on this phase v lamps type S1 put on this phase vi. 25 lamps type S2 vii. Total load on this phase is 5574 A CHAPTER 6 CABLE SIZING After the loads were allocated to the various consumer units it was desired to size the cables appropriately as per the current flowing in the circuit. Cable size would be chosen according to the following parameters; Amount of current flowing in the circuit. Size of protective device upstream Length of cable from the circuit to the consumer unit. Voltage drop along the circuit should not exceed an allocated percentage. 6.1 TYPE A HOUSE LIGHTING CIRCUITS A typical single way of the consumer unit holding a lighting circuit accommodates approximately 14 single lighting points each with a power output of approx 100 watts thus total power flowing in the circuit excluding diversity is The current flowing in a single way of a lighting circuit is as shown 27

38 The cable for the lighting circuits was chosen using the highest current in the ways of the consumer unit which was 6 Amps with a 20% allowance for future load growth gives 7.2 amps. Thus the protective device utilized is the 8 A MCB Referring to the IEE tables of single phase twin cable the 1 mm2 cable has a current capacity of 13.5A which is higher than the max current that can be allowed to flow which is 8 A. The approximate length of the cable connecting the lighting circuit to the way of the consumer unit is 11.6 with a 20% allowance to give metres. It is desired to compute the voltage drop along the cable so as to know whether it is within the desired limits or so as to find out a desirable length that shouldn t be exceeded this is shown Case 1 the 1 square mm % ℎ % Total voltage drop from the distribution transformer all the way should not exceed 6% allocating each section a 1.5% drop would give a max allowable drop of this section. It is observed that the drop is more than the maximum allowable thus it is wise to choose the next cable i.e. 1.5 mm2 with a capacity of 17.5A. Similar calculations give a result as shown % % At this stage it was observed that the voltage drop is within the required limit thus it may work for all the lighting circuits. It was desired to find out the maximum length of cable that could work with the given parameters. Maximum length of cable is given by the formula below 28

39 ℎ( ) (100 / / ) ℎ % metres Thus the lighting circuits can all use the following cables as long as the circuit connecting them is less than 17.8 metres RING CIRCUIT CABLE ALLOCATION These circuits were designed to carry a max of four twin circuits or eight single sockets or less. Thus the maximum load on each ring circuit could vary over a range shown below of 750w to 24kw but the average power is as shown below The current would be an amount varying about this value or less since the possibility of all the sockets being in use and drawing a large current is small for a residential house. Providing for a 20% allowance would result in a current of Approximate length of a ring circuit was 15 metres. The protective device used is the 40A MCB. Referring to the IEE tables of single phase twin cable the 2.5 mm2cable has a current capacity of 24 A which is lower than the actual current of 40A thus we check the next available cable which is the 6 mm2 cable % Maximum length of cable is given by %

40 ℎ % metres Thus this cable was used for the all the ways feeding the ring circuits in all the consumer units. Thus the ring circuits can all use the following cables as long as the circuit connecting them is less than 17.8 metres. COOKER UNIT The cooker unit was located in the kitchen which is 9 m including a 20% allowance gives 10.8m from the consumer unit it was desired to appropriately size its cable. From the previous sections it was noted that the current of the cooker is 22.5A.The protective device is 40A MCB thus the maximum current that can be allowed through is 40A Referring to the IEE tables of single phase twin cable the 4 mm2 cable has a current capacity of 32 A which does not satisfy the current requirements for the circuit % % At this stage it is observed that the voltage percentage voltage drop is close to the maximum value thus we check for the next available cable which is the 6 mm2 mm squared cable with a current carrying capacity of 41 amps and voltage drop of 7.3 % % It was observed at this point that this cable would be the best suited for this circuit WATER HEATER The water heater was located in the first floor for ease of water circulation and the distance from the consumer unit was found to be 13 metres adding an allowance of 20% was added to give 15.6m. The current flowing in the cable is 12.5Amps allowing for a 20% increase yields a current of 15Amps.The protective device is a 16A MCB. Referring to the IEE tables of single phase twin cable the 4 mm2 cable has a current capacity of 32 A which is higher than the max current of 16A thus we check for suitable voltage drop

41 % % The voltage drop was observed to be high due to the length of the circuit despite this the cable was still chosen for this circuit. 6.2 CONSUMER UNIT CABLES Consumer unit 1 had the following loads on its ways two lighting circuits and three ring circuits the total load on it is Consumer unit 2 had the following loads on its ways two lighting circuits, one ring circuit, cooker unit and water heater its total load is This load is lower than the other load thus sizing of cable is done using the higher current i.e. of the first consumer unit. Referring to the IEE tables of single phase twin cable the 16 mm2 cable has a current capacity of 76 A which is higher than the actual current of 74.4 as per current this cable is satisfactory so a check was performed to confirm whether the second condition is also met. The actual cable length to the meter board is 5.5 m plus 20% to give 6.6 m % % This voltage drop is within the required limit which is 1.5% thus it was chosen for use in the cable feeding all the consumer units. Maximum length of cable is given by ℎ % metres Thus this cable was used for all the cables feeding the consumer units as long as the circuit connecting them is less than metres. 6.3 SIZING OF CABLES FROM METER BOARD TO DISTRIBUTION BOARDS The highest current from an individual meter board of a house will come from the house type J and is 158 A. Thus the cable for this section is the 50 mm2 31

42 Protective device is the 160 A 2F MCCB. 6.4 SIZING OF SUB DISTRIBUTION BOARD CABLES DB S1, this distribution board supplies the housing units directly, allocated units for each vary from 4 to 6. max highest phase ℎ ℎ ℎ Length of cable connecting DB S1 to the individual houses 45m Cable size arrived at is the 185 Protective device settled on is the 320A MCCB. 6.5 SIZING OF MAIN DB CABLES DB 1 This distribution board supplies sub distribution boards 1 and 2 each of which support four housing units type B. On the Red Phase there are 6 CUs, for the blue 6 and yellow phase 4 thus we use the red or yellow phase to size the cable and protective device. Current used for sizing the cable max highest phase ℎ ℎ ℎ The size of cable for this circuit was calculated following the same procedure for the other circuits. Allowing for a 1.5% voltage drop on this cable means 300 appropriate. Protective device settled on is the 630A K FRAME MCCB. The other main distribution boards have either a lower load since than the one being used although the difference is not large enough to warrant a change in cable size. Thus the same cable was used for the other main distribution boards. 32

43 CHAPTER 7 DISTRIBUTION OF POWER In determining the design of distribution systems, three broad classifications of choices need to be considered: 1. The type of electric system: dc or ac, and if ac, single-phase or three phase. 2. The type of delivery system: radial, loop, or network. Radial systems include duplicate and throw over systems. 3. The type of construction: overhead or underground. The three-phase four-wire system is perhaps the most widely used. It is equivalent to three single-phase two-wire systems supplied from the same generator. The voltage of each phase is 120 out of phase with the voltages of the other two phases, but one conductor is used as a common conductor for all of the system. The current in that common or neutral conductor is equal to the vector sum of the currents in the three phases, but opposite in phase. as shown in fig 8. Figure TYPE OF DELIVERY SYSTEM Primary Distribution Primary distribution systems include three basic types: 1. Radial systems, including duplicate and throw over systems 2. Loop systems, including both open and closed loops 3. Primary network systems 33

44 Radial Systems The radial-type system is the simplest and the one most commonly used. It comprises separate feeders or circuits radiating out of the sub-station or source, each feeder usually serving a given area. The feeder may be considered as consisting of a main or trunk portion from which we have spurs or laterals radiating to which distribution transformers are connected. The spurs or laterals are usually connected to the primary main. The spurs or laterals are usually connected to the primary main through fuses, so that a fault on the lateral will not cause an interruption to the entire feeder. Should the fuse fail to clear the line, or should a fault develop on the feeder main, the circuit breaker back at the substation or source will open and the entire feeder will be de-energized. Loop Systems Another means of restricting the duration of interruption employs feeders designed as loops, which essentially provide a two-way primary feed for critical consumers. Here, should the supply from one direction fail, the entire load of the feeder may be carried from the other end, but sufficient spare capacity must be provided in the feeder. This type of system may be operated with the loop normally open or with the loop normally closed. Primary Network Systems Although economic studies indicated that under some conditions the primary network may be less expensive and more reliable than some variations of the radial system, relatively few primary network systems have been put into actual operation and only a few still remain in service. This system is formed by tying together primary mains ordinarily found in radial systems to form a mesh or grid. The grid is supplied by a number of power transformers supplied in turn from sub transmission and transmission lines at higher voltages. A circuit breaker is placed between the transformer and grid. Faults on sections of the primaries constituting the grid are isolated by circuit breakers and fuses. Secondary Distribution Secondary distribution systems operate at relatively low utilization voltages and, like primary systems, involve considerations of service reliability and voltage regulation. The secondary system may be of four general types: 1. An individual transformer for each consumer; i.e., a single service from each transformer. 34

45 2. A common secondary main associated with one transformer from which a group of consumers is supplied. 3. A continuous secondary main associated with two or more transformers, connected to the same primary feeder, from which a group of consumers is supplied. This is sometimes known as banking of transformer secondaries. 4. A continuous secondary main or grid fed by a number of transformers, connected to two or more primary feeders, from which a large group of consumers is supplied. This is known as a low-voltage or secondary network. Individual Transformer Single Service Individual-transformer service is applicable to certain loads that are more or less isolated, such as in rural areas where consumers are far apart and long secondary mains are impractical, or where a particular consumer has an extraordinarily large or unusual load even though situated among a number of ordinary consumers. In this type of system, the cost of the several transformers and the sum of power losses in the units may be greater (for comparative purposes) than those for one transformer supplying a group of consumers from its associated secondary main. The diversity among consumers loads and demands permits a transformer of smaller capacity than the capacity of the sum of the individual transformers to be installed. On the other hand, the cost and losses in the secondary main are obviated, as is also the voltage drop in the main. Where low voltage may be undesirable for a particular consumer, it may be well to apply this type of service to the one consumer. Common Secondary Main Perhaps the most common type of secondary system in use employs a common secondary main. It takes advantage of diversity between consumers loads and demands, as indicated above. Moreover, the larger transformer can accommodate starting currents of motors with less resulting voltage dip than would be the case with small individual transformers. In many instances, the secondary mains installed are more or less continuous, but cut into sections insulated from each other as conditions require. As loads change or increase, the position of these division points may be readily changed, sometimes holding off the need to install additional transformer capacity. Also, additional separate sections can be created and a new transformer installed to serve as load or voltage conditions require. Banked Secondaries 35

46 The secondary system employing banked secondaries is not very commonly used, although such installations exist and are usually limited to overhead systems. This type of system may be viewed as a single-feeder low-voltage network, and the secondary may be a long section or grid to which the transformers are connected. Fuses or automatic circuit breakers located between the transformer and secondary main serve to clear the trans-former from the bank in case of failure of the transformer. Fuses may also be placed in the secondary main between transformer banks. Some advantages claimed for this type of system include uninterrupted service, though perhaps with a reduction in voltage, should a normal voltage conditions resulting from such load distribution; an ability to accommodate load increases by changing only one or some of the transformers, or by installing a new transformer at some intermediate location without disturbing the existing arrangement; the possibility that diversity between demands on adjacent transformers will reduce the total transformer load; more capacity available for inrush currents that may cause flicker; and more capacity as well to burn secondary faults clear. Some disadvantages associated with this type of system are as follows: should one transformer fail, the additional loads imposed on adjacent units may cause them to fail, and in turn their loads would cause still other transformers to fail (this is known as cascading); the transformers banked must have very nearly the same impedance and other characteristics, or the loads will not be distributed equitably among them; and sufficient reserve capacity must be provided to carry emergency loads safely, obviating the savings possible from the diversity of the demands on the several transformers. Banked secondaries, while providing for failure of transformers, do not provide against faults on the primary main or feeder. Further, a hazard on any transformer disconnected for any reason may result from a back feed if the secondary energizes the primary. Secondary Networks Secondary networks at present provide the highest degree of service reliability and serve areas of high load density, where revenues justify their cost and where this kind of reliability is imperative. In some instances, a single consumer may be supplied from this type of system by what are known as spot networks. In general, the secondary network is created by connecting together the secondary mains fed from transformers supplied by two or more primary feeders. Automatically operated circuit breakers in the secondary connection between the transformer and the secondary mains, known as network protectors, serve to disconnect the transformer 36

47 from the network when its primary feeder is de-energized; this prevents a back feed from the secondary into the primary feeder. This is especially important for safety when the primary feeder is de-energized from fault or other cause. The circuit breaker or protector is backed up by a fuse so that, should the protector fail to operate, the fuse will blow and disconnect the transformer from the secondary mains. The number of primary feeders supplying a network is very important. With only two feeders, only one feeder may be out of service at a time, and there must be sufficient spare transformer capacity available so as not to overload the units remaining in service; therefore this type of network is sometimes referred to as a single-contingency network. Most networks are supplied from three or more primary feeders, where the network can operate with the loss of two feeders and the spare transformer capacity can be proportionately less. These are referred to as second-contingency networks. Secondary mains not only should be so designed that they provide for an equitable division of load between transformers and for good voltage regulation with all transformers in service, but they also must do so when some of the transformers are no longer in service when their primary feeders are de-energized. They must also be able to divide fault current properly among the transformers, and must provide for burning faults clear at any point while interrupting service to a minimum number of consumers; this often limits the size of secondary mains, so that when additional secondary main capacity is required, two or more smaller size conductors have to be paralleled. Because these networks may represent very large loads, their size and capacity may have to be limited to such values as can be successfully handled by the generating or other power sources should they become entirely deenergized for any reason. When they are de-energized for any length of time, the inrush currents are very large, as diversity among consumers may be lost, and this may be the limiting factor in restricting the size and capacity of such networks. 7.2 UNDERGROUND VERSUS OVERHEAD DISTRIBUTION SYSTEM The distribution of power to the houses could be achieved using two methods: 37 Overhead distribution Underground distribution

48 Overhead distribution is the most common type of distribution due to its relatively lower cost of installation. It finds application mainly in rural areas where the electricity distribution is not organised although at times it is also used in organised residential areas that are self built. On the other hand underground distribution is used at times in some residential areas especially those built by real estate developers in bulk and later sold off to individuals although it is characterized by higher costs. It makes use of service turrets, underground armoured cabling networks and pad mounted transformers. 7.3 POWER DISTRIBUTION WITHIN THE RESIDENTIAL ESTATE The estate was fed from an 11kv line coming from the mains line supplying Fahari city. As it can be noted from the layout of the housing estate it is a high load centre due to the high concentration of houses. The system adopted for distribution of power was the radial system after weighing the points for it and against it a full description of this is as outlined in the previous sections. Layout of the cables an underground network was used for a number of reasons. The transformers used in the estate were desired to be four so as to reduce the distances of cables to the consumers. Thus the whole block was viewed as four independent sections and a transformer allocated to each section. The transformers stepped down the voltage from the 11kv to the 415 volts that was then fed to the main distribution boards and then to the sub distribution boards. Thus it was a requirement to size the transformers which is shown here: Highest phase current is 5520 A Load of the estate is calculated as shown Total load for the residential estate including street lighting This voltage was stepped down to 415 volts at the transformers located at various points then distributed to the houses within the area. The distribution was achieved using four transformers rated at 1.5MVA Low voltage transmission is characterized by a large current which result in heavy losses along the line thus it is required to minimise the distances covered by the stepped down voltages. 38

49 A design consisting of four pad mounted transformers and a basic grid of cables was laid consisting of 3 cables 11KV.This cable fed the transformers which fed the main distribution boards which were placed at convenient positions to power the sub distribution boards, which in turn fed the housing units minimum of 3 to a maximum of 6 per sub distribution boards. 7.4 METRE LAYOUT Each house was fed using two consumer units as shown in the previous circuits which in turn receive power from the metre box. A splitter circuit was added to connect the two consumer units to the metre. Layout showing the placement of consumer unit and the splitter used to connect the two consumer units to the meter board. CU A1 M CU A2 CU A3 M CU A4 39

50 7.5 DISTRIBUTION SYSTEM RETICULATION KPLC CU B1 CU B2 CU B3 CU B4 CU B5 CU B6 DISTRIBUTION BOARD 1 GFB11B2 CU B7 CU B8 B15,FB1 CU B9 CU B10 CU B11 6R3 CU B12 CU B13 CU B14 GFB11B2 CU B15 CU B16 B15,FB1 Figure 7.3 Layout of housing units from transformer 1 The distribution type in use was radial so from the transformer 1shown in figure 7.3 the main distribution boards fed were three and the figure above is a section of it highlighting one distribution board. Thus the number of outgoing set of lines i.e. 3 per set were 3 each heading out to its individual main distribution boards then branching out to the other sub distribution boards. The layouts of the other sub networks had similarities with the network shown here and some small 40 differences the layouts are as shown in the appendix [5]

51 CHAPTER 8 FAULT CURRENT LEVELS 8.1 FAULT CURRENT LEVELS AT THE SERVICE MAIN Base kva transformer kva 1,500 kva (KPLC provided) Base kv transformer secondary voltage 415V, kvb kv Per unit reactance of transformer j0.055 p.u Series impedance of feeder Ω/ ℎ per km The feeders to the various main distribution boards are of different lengths since the four transformers are located at different places and the main distribution boards are also spread over the area... ℎ ℎ ( ) ( ) (0.415) A three-phase fault is the most severe fault that can occur; so a breaker capable of clearing this magnitude of fault will have sufficient capacity to clear any other kind of fault occurring at the same point. For a three-phase short-circuit at the service mains bus bars [ ] The procedure outlined above was followed in the rest of the circuits and the results are summarised in the following section: 41

52 Transformer 1 Length of feeder Main DB1 Main DB Main DB Actual feeder impedance i Total Impedance i i o i P.U. Fault Current i o i o Table 8.1 Analysis from Transformer 1 Transformer 2 Length of feeder Main 0.02 DB4 Main DB Main DB Actual feeder impedance i Total Impedance i i o i P.U. Fault Current o i o Actual feeder impedance i Total Impedance i i i P.U. Fault Current o i i i Table 8.2 Analysis from Transformer 2 Transformer 3 Length of feeder km Main 0.05 DB7 Main DB Main DB Table 8.3 Analysis from Transformer o o

53 Transformer 4 Length of feeder km Main DB10 Main DB Main DB Actual feeder impedance i Total Impedance i P.U. Fault Current i o i i i o o Table8.4 Analysis from Transformer 4 At this stage we find the actual values using the base current and the p.u. values., Fault current (for three-phase fault at Service mains) The respective fault currents at the other main distribution boards were also determined using the procedure outlined above. Fault current at Main DB2 was DB DB , DB , DB DB DB , DB , DB ,, DB ,, DB ,,

54 8.2 FAULT CURRENT LEVELS AT BEGINNING OF FINAL CIRCUITS KPLC incomer, length 0.2km, Impedance 0.12+j0.48Ω/phase/km CU copper cable, Final circuit r 18μΩm conductor DB M Main DB N Transformer secondary, Reactance j0.055p.u, CU DB copper cable, CU KPLC meter, r 18μΩm Base kv 0.415, base kva 1,000 Figure 8.1: Layout and parameters for fault current calculation The consumer unit (CU) is placed in relation to the distribution board (DB) as shown in Figure A above. Largest MCB on consumer unit CU B1 is of 40A, protecting a ring circuit of socket outlets. Total current drawn by CU B1 is 60A. To be able to decide the ratings of the MCBs to use to provide discrimination, the fault current for a fault at a point just after the CU must be determined. This would be the point at which the most severe fault the MCB in the CU would have to clear, failing which the MCB at the DB would have to clear. The fault is a phase to neutral one and so that particular phase all the way back to the transformer plus the neutral would be involved. The transformer voltage would have to push current through the impedance of: 1. One phase/winding of the transformer, Ω 2. The phase and neutral of the KPLC incomer, 3. The phase and neutral of the DB cable between the main DB and the sub DB, 4. The phase and neutral of the cable between the sub DB and the KPLC meter, 5. The phase and neutral of the CU cable between the KPLC meter and consumer unit, 44. ( ) 1000

55 , (0.415) Ω ℎ ℎ, Ω ℎ Ω Calculation of the impedances of the DB and KPLC meter cables can be done with aid of the table in the Appendix, or alternatively via the use of the resistivity of copper ( Ω 20 ℎ, ) as shown Ω Ω Calculation of the impedances from the metre and CU cables is as shown in the equation and is done via the aid of a table and the results are summarised in table 8.5 ℎ, Ω Ω Calculation of the impedances from the metre and CU cables is as shown in the equation and is done via the aid of a table and results are summarized in the table 8.5. ℎ, ℎ ℎ , Ω A summary of results follow: Ω

56 8.3 FAULT CURRENT LEVELS AT THE CONSUMER UNITS Consumer unit CU cable size mm2 CU cable length(m) Impedance transfer up to cu phase-neutral Ω Fault current in Amps B B B B B B B B Table8.5 Analysis from Transformer 1 Consumer unit CU cable size mm2 CU cable length(m) Impedance transfer up to cu phase-neutral Ω Fault current in Amps B B B B B B B B Table8.6 Analysis from Transformer 1 The same procedure outlined above was used to find the respective fault currents at the other consumer units. 8.4 FAULT CURRENT LEVELS AT THE SUB DISTRIBUTION BOARDS Fault current levels at this stage were calculated using the similar procedure in the previous section and the results are summarised as shown: Distribution boards DB cable size mm2 DB cable length m KPLC incomer length in km Impedance transfer up to DB(phase-neutral Ω) Fault current Amps DB DB DB DB DB DB Table8.7 Analysis from Transformer 1 Distribution boards DB cable size mm2 DB cable length m KPLC incomer length in km Impedance transfer up to DB(phase-neutral Ω) Fault current Amps Table8.8 Analysis from Transformer 2 46 DB DB DB DB DB DB

57 A similar analysis was used to compute the respective fault currents at the other sub distribution board since here we have only tabulated those from transformer 1 and 2. 47

58 CHAPTER 9 DISCRIMINATION 9.1 PROTECTION OF CABLES Protection of cables is in accordance with the 16th Edition of the IEE Wiring Regulations (BS 7671). 9.2 PROTECTION AGAINST OVER CURRENT Over current is defined in the 16th Edition of the IEE Wiring Regulations as a current exceeding the rated value. For conductors the rated value is the current-carrying capacity. Overcurrent can be divided into two individual levels of fault these being overload current and short circuit current. These should be considered separately. 9.3 PROTECTION AGAINST OVERLOAD Overload is defined in the 16th Edition of the IEE Wiring Regulations as an over current occurring in a circuit which is electrically sound. This may be the result of too many appliances drawing current from a system, a faulty appliance, or a motor subjected to mechanical overload. Regulation of the 16th Edition of the IEE Wiring Regulations defines the basic requirement for overload protection, protective devices shall be provided to break an overload current flowing in the circuit conductors before such a current could cause a temperature rise detrimental to insulation, joints, terminations, or the surroundings of the conductors. Circuits shall be so designed that a small overload of long duration is unlikely to occur. 9.4 CO-ORDINATING BETWEEN CONDUCTORS AND PROTECTIVE DEVICES It is apparent that Regulation of the 16th Edition places emphasis on the surroundings of the conductor as well as the conductor itself. Regulation has laid down three conditions to meet this requirement: a) I b I n b) I n I z c) I I z Where I b design current of circuit I n nominal current of protective device 48

59 I z current-carrying capacity of the cable I 2 minimum operating current of protective device Miniature circuit breakers and moulded case circuit breakers normally have tripping factors of, or below this 1.45 figure so that if either of these devices is used in compliance with condition a) above will mean that condition b) is also met, thus providing overload protection to the conductors concerned. 9.5 PROTECTION AGAINST SHORT CIRCUIT Short circuit is defined in the 16th Edition of the IEE Wiring Regulations as: an overcurrent resulting from a fault of negligible impedance between live conductors having a difference in potential under normal operating conditions. IEE Wiring Regulation states that: provided an overload protective device complies with regulation 433 and also provides short circuit protection the regulations are satisfied without need for further proof. This is because if is satisfied then the cable and the overload rating of the device are compatible. However, where this condition is not met or in some doubt for example where a protective device is provided for fault current protection only, as in an MCCB backing up a motor overload relay then IEE Wiring Regulation must be satisfied where a protective device is provided for fault protection only, the clearance time of the device, under short circuit conditions, shall not result in the limiting temperature of any conductors being exceeded. 9.6 PROTECTION OF CABLES AND CONDUCTORS AGAINST SHORTCIRCUIT Regulation of the IEE Wiring Regulations takes account of the time by applying what is known as the adiabatic equation DISCRIMINATION The 16th Edition of the IEE Wiring Regulations (BS7671) requires that in an installation: The characteristics and settings of devices for overcurrent protection shall be such that any intended discrimination in their operation is achieved. Whether fuses or circuit breakers are utilised in a distribution system it is necessary to ensure that all the requirements of the 16th Edition of the IEE Wiring Regulations are complied with. 49

60 Discrimination, also called selectivity, is considered to be achieved when, under fault conditions the circuit breaker nearest the fault operates rather than any of the circuit breakers or fuses upstream of it. The discrimination of circuit breakers can be based on either magnitude of fault (current discrimination) or the duration of the time during which the circuit breaker sees the fault current (time discrimination). Current Discrimination in a distribution system requires a circuit breaker to have a lower continuous current rating and a lower instantaneous pick-up value than the next upstream circuit breaker. Current discrimination increases as the difference between continuous current ratings increases and as pick-up settings increase between the upstream and downstream breakers. Time Discrimination in a distribution system requires the use, upstream, of circuit breakers with adjustable time delay settings. The upstream breakers must be capable of withstanding the thermal and electrodynamics effects of the full prospective fault current during the time delay. The table included in the Appendix has been extracted from the MEM catalogue and has been used to aid the selection of the appropriate combination of MCBs to ensure discrimination between upstream and downstream protective devices. 9.8 DISCRIMINATION BETWEEN CUS AND DBS Following results summarized under previous sections, protective devices that would ensure discrimination between CUs and DBs are here tabulated. As an aid to understanding the tables, an explanation is here given of how column 2 under consumer unit B1 has been filled: a) 185 mm2 cable sizes was arrived at in Section 6 b) Amps cable current capacity was arrived at in IEE tables. c) 74.4 Amps cable current was arrived at in Section 6 d) Amps fault current was arrived at in Section 8 e) 40 Amps MCB in CU was arrived at after considering ratings of protective devices for the various ways in the CU. f) 80 Amps SP/N G FRAME MCCB in DB for discrimination is arrived at from the MEM Catalogue Table in the Appendix. 50

61 Consumer Unit CU cable 2 size(mm ) Cable current capacity(amps) Cable current(amps) Largest MCB in CU(Amps) Fault Current(Amps) CU s DB B1 B2 B3 B4 B5 B6 B7 B B9 B10 B11 B12 B13 B14 B15 B Rating of SP/N G FRAME MCCB Upstream in DB(Amps) Consumer Unit CU cable 2 size(mm ) Cable current capacity(amps) Cable current(amps) Largest MCB in CU(Amps) Fault Current(Amps) CU s DB Rating of SP/N G FRAME MCCB Upstream in DB(Amps) 9.9 DISCRIMINATION BETWEEN SUB DBS AND THE MAIN DBS Following results summarized under section 8 protective devices that would ensure discrimination between the sub DBs and the main DBs are here tabulated. 51

62 As an aid to understanding the tables, an explanation is here given of how column 2 under Distribution Board B1 has been filled: a) 185 mm2 cable size was arrived at in Section 6 b) 390 Amps cable current capacity is from IEE Tables. c) 316 Amps cable current was arrived at in Section 6 d) Amps fault current was arrived at in Section 8 e) 80 Amps MCCB in DB was arrived at Section Amps TP/N J FRAME MCCB in Main DB for discrimination is arrived at from the MEM Catalogue Table in the Appendix; the 200 Amps being ruled out as it offers discrimination up to 2000 Amps fault current which is considered to be under the fault current for which it is supposed to discriminate. Distribution Board DB cable 2 size(mm ) S1 S2 S3 S4 S5 S6 S7 S M1 M1 M2 M2 M3 M3 M4 M DB Cable current capacity(amps) DB Cable current(amps) Largest MCB in DB(Amps) Fault Current(Amps) Main DB Rating of SP/N J/L FRAME MCCB Upstream in DB(Amps) 52

63 CHAPTER POWER FACTOR CORRECTION ℎ Assuming a power factor of 0.7 before correction to 0.9 required by the KPLC: Capacitor bank KVAr KVAr before 340.7kVA correction340.7 sin kvar Reactive power after Cos correction238.5 tan 25.84`115.5 kvar Cos KVA Cos KW In practice penalties are charged to a consumer whenever the consumer s system has lesser power factor, since it gives the idea of useless power being generated by the source (KPLC) and unnecessarily large currents flowing which result in increase in size of cables which result in extra costs. Obviously, if one can reduce the amount of useless power, power that is more useful will be available to the consumer, so it pays to improve the power factor wherever possible. As most loads are inductive in nature, adding shunt capacitance can reduce the inductive reactance as the capacitive reactance opposes the inductive reactance of the load. proposed capacitor bank size is 150kVAR and was used for the design and was split into 25, 50, 75 electronically switched. This capacitor bank was placed at the main distribution boards since this design does not have a switchboard. A similar capacitor bank was installed at similar points in the other distribution boards. Cable length connecting capacitor bank is 20m

64 10.2 BACKUP POWER CALCULATION The units at hand are for domestic purposes and most likely the houses will be owned by individuals so back up power would be designed at the individual unit level. The load current for the largest house is 132 Amps for the type J house so a backup generator was to be designed for this unit and a similar set was applicable to the other units since the difference in current is less than 10 Amps. The required KVA would be ℎ The generator to be used was a Honda generator models no ETU 650K rated AT 40 KW. 54

65 CONCLUSSION The design objective which was to design lighting and distribution system was achieved successfully. The lighting points were designed and allocated to each of the houses as per design criteria The overall load was calculated and phase current of 5574Amps was realised after balancing the load as much as possible over the three phases. The distribution system was designed and it was composed of 4 pad mounted transformers, 12 main distribution boards, 37 sub distribution boards and 222 consumer units. Fault analysis was done and a protective system made to ensure proper discrimination of protective devices upstream and downstream. Power factor correction was achieved successfully using a 150kvar capacitor bank switched electronically in steps of 25, 50, and 75. Backup power for the housing units was designed and a Honda generator with a rating of 40 kilowatts allocated to each of the housing units. 55

66 RECOMMENDATIONS FOR FUTURE WORK A bill of quantities could be made as per this design and appliances used to make it to be able to assist in sourcing of contractual services since these one eventually has to implement this design. A comprehensive analysis of earth faults would be included in the work to make the design more complete. Fault analysis could be implemented using programs instead of manual analysis and calculations so that background knowledge would not be a limiting factor in the quality and performance of the protective system designed. Automation would also be used in the design and placement of lighting points, power outlets and sizing of cables. An alternative distribution system design could be implemented to compare the effectiveness, cost and reliability of another design versus the one used here. The alternative design may involve use of overhead systems different transformer configurations and use of a loop or ring system. 56

67 REFERENCES [1] Harald Hofmann and Rudiger Ganslandt: Handbook of lighting design ERCO First edition 1992 [2] Section 9 lighting, Energy Efficient Building Design Guidelines [3] Gonen Turan, Electric Power Distribution System Engineering McGraw-Hill 1986 [4] IESNA Lighting Handbook, Ninth edition [5] [6] Zumtobel, The Lighting Handbook Second edition W.E. Steward and T.A. Stubbs, Modern Wiring Practice Revised and Updated 2005 [7] Fred Hall and Roger Greeno, Building services handbook 5th Edition Chapter 11 page [8] Antony J Pansini, Guide to Electrical Power Distribution Systems page [9] W. E. Steward and T.A. Stubbs, Modern Wiring Practice Revised edition [10] Trevor Linsley, Advanced Electrical Installation Work, Fourth Edition 57

68 APPENDICES Appendix 1 House type C Consumer units, C1 and C2 8A CIR R1.1 3 x 1.5 mm2 PVC SC CU Cables - Lighting 8A CIR R1.2 3 x 1.5 mm2 PVC SC CU Cables - Lighting 40A 100A 40A 40A CIR R1.3 3 x 2.5 mm2 PVC SC CU Cables - Sockets CIR R1.4 3 x 6 mm2 PVC SC CU Cables - Sockets CIR R1.5 3 x 6 mm2 PVC SC CU Cables - Sockets CIR R1.6 Spare CIR R1.7 Spare CIR R1.8 Spare 8A CIR R2.1 3 x 1.5 mm2 PVC SC CU Cables Lighting first floor 8A CIR R2.2 3 x 1.5 mm2 PVC SC CU Cables Lighting security 32A 100A 16A 40A CIR R2.3 3 x 6.0 mm2 PVC SC CU Cables - Cooker CIR R2.4 3 x 4.0 mm2 PVC SC CU Cables Water heater CIR R2.5 3 x 6 mm2 PVC SC CU Cables Sockets first floor CIR R2.6 Spare CIR R2.7 Spare CIR R2.8 Spare Fig

69 House type B Consumer units B1 and B2 8A CIR R1.1 3 x 1.5 mm2 PVC SC CU Cables - Lighting 8A CIR R1.2 3 x 1.5 mm2 PVC SC CU Cables - Lighting 40A 100A 40A 40A CIR R1.3 3 x 2.5 mm2 PVC SC CU Cables - Sockets CIR R1.4 3 x 6 mm2 PVC SC CU Cables - Sockets CIR R1.5 3 x 6 mm2 PVC SC CU Cables - Sockets CIR R1.6 Spare CIR R1.7 Spare CIR R1.8 Spare 8A CIR R2.1 3 x 1.5 mm2 PVC SC CU Cables Lighting first floor 8A CIR R2.2 3 x 1.5 mm2 PVC SC CU Cables Lighting security 32A 100A 16A 40A CIR R2.3 3 x 6.0 mm2 PVC SC CU Cables - Cooker CIR R2.4 3 x 4.0 mm2 PVC SC CU Cables Water heater CIR R2.5 3 x 6 mm2 PVC SC CU Cables Sockets first floor CIR R2.6 Spare CIR R2.7 Spare CIR R2.8 Spare Fig

70 House type A Consumer units A1 and A2. 8A CIR R1.1 3 x 1.5 mm2 PVC SC CU Cables - Lighting 8A CIR R1.2 3 x 1.5 mm2 PVC SC CU Cables - Lighting 40A 100A 40A 40A CIR R1.3 3 x 2.5 mm2 PVC SC CU Cables - Sockets CIR R1.4 3 x 6 mm2 PVC SC CU Cables - Sockets CIR R1.5 3 x 6 mm2 PVC SC CU Cables - Sockets CIR R1.6 Spare CIR R1.7 Spare CIR R1.8 Spare 8A CIR R2.1 3 x 1.5 mm2 PVC SC CU Cables Lighting first floor 8A CIR R2.2 3 x 1.5 mm2 PVC SC CU Cables Lighting security 32A 100A 16A 40A CIR R2.3 3 x 6.0 mm2 PVC SC CU Cables - Cooker CIR R2.4 3 x 4.0 mm2 PVC SC CU Cables Water heater CIR R2.5 3 x 6 mm2 PVC SC CU Cables Sockets first floor CIR R2.6 Spare CIR R2.7 Spare CIR R2.8 Spare Fig

71 Appendix 2 NON ARMOURED CABLES USED FOR INDOORS 2 cables- Single phase mm2 61 A 3 or 4 cables three phase mv/a/m A mv/a/m

72 ARMOURED CABLES USED FOR OUTDOOR AREAS One 3 or 4 core cable three phase One twin cable Single phase mm2 62 A mv/a/m A mv/a/m

73 Appendix 3 The following table has been extracted from Modern Wiring Practice, by W.E Steward and T.A. Stubbs, 12th Edition, page 97. Cross-sectional area Resistance(ohms per 1,000 metres) Bare conductors at 20 C (mm2) Copper Aluminium NOTE: For live conductor resistance under short circuit fault conditions, the values given above must be multiplied by the following factors: For PVC insulation 1.38 For 85 C rubber insulation 1.53 For mineral insulation 1.55 For protective conductor resistance under short circuit fault conditions, the values given above must be multiplied by the following factors: For PVC insulation 1.30 For 85 C rubber insulation

74 Appendix 4 TABLE OF TYPICAL ALLOWANCES FOR DIVERSITY 64

75 Appendix 5 MEM CATALOGUE FOR DISCRIMINATION 65

76 66

77 67

78 68