UNIVERSITY OF NAIROBI FACULTY OF ENGINEERING DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING BUILDING ELECTRICAL SERVICES DESIGN FOR HOSTEL

Transcription

1 UNIVERSITY OF NAIROBI FACULTY OF ENGINEERING DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING BUILDING ELECTRICAL SERVICES DESIGN FOR HOSTEL ALONG NYERERE ROAD PROJECT NUMBER: PRJ 095 BY OELE O. COLLINS ERICK F17/1999/2005 SUPERVISOR: DR. N. O. ABUNGU EXAMINER: MR. DHARMADHIKARY PROJECT REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF BACHELOR OF SCIENCE IN ELECTRICAL AND ELECTRONIC ENGINEERING OF THE UNIVERSITY OF NAIROBI 2010 Submitted on: 18 th May, 2011

2 DEDICATION This project is dedicated to all my immediate family members. They have been my source of inspiration all my life. i

3 ACKNOWLEDGEMENTS I humbly do acknowledge the ALMIGHTY GOD for enabling me reach this far with this project. I gratefully acknowledge the support of Dr. Nicodemus Abungu, my project supervisor. He has been of immense help and motivation during this entire project process. I also acknowledge my fellow colleagues who challenged me with their input and constructive criticism. I do extend much sincere thanks and appreciation to all the aforementioned. ii

4 DECLARATION AND CERTIFICATION ND CERTI This BSc. work is my original work and has not been presented for a degree award in this or any other university... OELE O. COLLINS ERICK F17/1999/2005 This report has been submitted to the Department of Electrical and Information Engineering, University of Nairobi with my approval as supervisor: DR. NICODEMUS ODERO ABUNGU Date: 18th May 2011 iii

5 ABSTRACT The main objective of the project is to design the building electrical services for a hostel along Nyerere road and located in Nairobi, Kenya. The site plan has one building with a total of six, (6) floors. Due to the location, the most reliable source of electrical power is the mains national grid power. In order to achieve the main objective and to specify the size and number of back-up generators to be employed, the final circuits consisting of lighting and power sockets is designed first. The lighting design is done using the lumen method which takes into consideration the size and use of the room being lit. Power points layout design is done by considering the needs of the final user of the premises in every room; this ensures that the need for electrical power is fulfilled in the design. The final circuits are to be supplied by fifteen, (15) consumer units. These consumer units are then all distributed on one, (1) distribution board, ensuring that all the singlephase loads are balanced almost equally on each phase with amperes on red phase, amperes on the yellow phase and amperes on the blue phase. This guaranteed that cables and distribution equipment are utilized much more effectively due to small differences in current on each phase. The load of the entire building is kw or kva and so the power back-up systems design has one hooded diesel generator rated 450 kva. This is located at a convenient area and caged within the site compound. To ensure co-ordinated operation of the Miniature Circuit Breakers (MCB), and Moulded Case Circuit Breakers (MCCB) when safeguarding against the effects of overloads and short circuits, discrimination between the devices is observed. This has enabled the system to switch off only the breaker closest to the fault without disruption of supply to other areas. Finally lightning protection is done to safeguard against the effects of a lightning stroke. With this system the hostel will have safe, reliable and expandable power supply. iv

6 TABLE OF CONTENTS DEDICATION... i ACKNOWLEDGEMENTS... ii DECLARATION AND CERTIFICATION... iii ABSTRACT... iv CHAPTER INTRODUCTION Objectives Prelude Building Electrical Services Design Codes and Standards End User Accessories... 2 CHAPTER THEORY AND BACKGROUND Lighting Design Hostel Lighting Design Illuminance Recommendations Light Sources Lumen Method of Lighting Design Light Switches Electrical Power Circuits Socket Outlets Kitchen Unit Electrical Service Network Diversity Power Circuit Design Consumer Units Distribution Board Switch-Boards Commercial Back-Up Diesel Power Generators Wiring Cable Sizing v

7 2.4 Protection Systems Overload Protection Short Circuit Protection Protection System Equipment Discrimination and Protection System Co-ordination Lightning Protection CHAPTER PROJECT WORK AND IMPLEMENTATION Site Location Site Plan and Introduction Sample Lumen Method of Lighting Design Calculation for One Hostel Room Sample Power Points Layout Design for One Hostel Room Entire Hostel Lighting Fittings Design and Power Points Layout Designs CHAPTER DESIGN ANALYSIS AND DISCUSSIONS Design Analysis Based on Load Calculations and Circuits Arrangements Introduction Lower Floor Upper Ground Floor CHAPTER DISTRIBUTION SYSTEM TOPOLOGY Consumer Unit, (CU) Design and Specifications Consumer Unit, CU UGF Consumer Unit Total Single-Phase load calculations, Total Load Currents Drawn, Cable Length and Cable Size Selection from the Distribution Board, (DB) feeding the CU Distribution Board, (DB) Design and Specifications Single-Phase Loads Distribution Board Design and Specifications Three-Phase Loads Distribution Board Design and Specification Power Back-Up Generator Size of Back-Up Generator Sizing of Cable of the Back-Up Generator Electrical Distribution Reticulation vi

8 5.5 Electrical Distribution Protection System based on Fault Current Levels at Various Points in the Installation Fault Current Level at the Switch-Board Fault Current Levels at the Beginning of Final Circuits Discrimination between CUs and DBs Discrimination between DBs and the Switch-Board Discrimination between Moulded Case Circuit Breaker, (MCCB 1) and Switchboard Discrimination between Generator Moulded Case Circuit Breaker, (MCCB 2) and Switch- Board Lightning Protection Design Power Factor Correction CHAPTER CONCLUSIONS CHAPTER RECOMMENDATION FOR FUTURE WORK Software for Building Electrical Services Design Bill of Quantities Earth Faults CHAPTER REFERENCES CHAPTER APPENDICES Appendix A-1: Auto Computer Aided Designs, (AUTOCAD) for Lighting Design and Power Points Layout Design Appendix A-2: Lightning Protection Design Appendix B: Consumer Units Designs and Specifications Appendix C: IEE tables Appendix D: MEM Catalogue Extracts Appendix E: Power Back-Up Generator Data Sheet and Performance Appendix F: Utilization Factors vii

9 CHAPTER INTRODUCTION 1.1 Objectives The main objective of the project is to do a building electrical services design for a hostel along Nyerere road. In order to achieve the main objective, the project work is split into other smaller but related sections and scopes with specific targets to be met. The areas of utmost interest and covered exhaustively and in detail in this project are thus: Lighting design Power points layout design Cables sizing Power back-up system Protection system design Discrimination and co-ordination system Power factor correction 1.2 Prelude Engineering specialization consists of various fields. One of these fields is the building design and construction which has six different categories: civil, structural, mechanical, electrical, environmental and materials engineering. 1 This project will focus on the electrical category of building design and construction from the electrical services design engineer s perspective rather than that of the installation electrician or architect. The main focus is to ensure that the electrical system meets the following criteria: Reliability Durability Maintainability 1 Sidney M. Levy, Construction Process Planning and Management, An Owners Guide to Successful Projects 2007, Page 47 1

10 Efficiency Economy Building Electrical Services Design Any electrical requirements are greatly influenced by the needs of the client or end-user of the building. The end-user is more interested in the appearance and the function of the various appliances whereas the design engineer is interested in the complete electrical design and installation Codes and Standards Every building must follow the laid down local, national or international codes and standards that it is associated with its location and the acceptable codes and standards for that region. The international codes and standards are developed by international standardization organizations such as the Institute of Electrical and Electronics Engineers (IEEE). They prepare standards that are adoptable and acceptable on a global scale. National codes and standards are developed by associations within a particular country or region which are then applied within local or national legislation in order to be enforceable by law. 3 Such codes and standards have to be considered by the design engineer in order for the final work to be acceptable to the client and the local authorities End User Accessories These are the various electrical equipments which are utilized by the end user in controlling the function of the electrical installations made within the living or working space. They are called accessories because they are accessory to the wiring. 4 These accessories include switches, socket outlets, fused connection units, and the kitchen units. 2 U.S. Army Corps of Engineers, Electrical Power Supply and Distribution Technical Manual No , Page Barrie Rigby, Design of Electrical Services for Buildings 4 th Edition, Page 1 2

11 CHAPTER THEORY AND BACKGROUND 2.1 Lighting Design This area covers all the literature reviewed for purposes of lighting design covered in the scope of the project Hostel Lighting Design The scope of lighting considered for this project is known as artificial lighting or more intrinsically electrical light sources. This is the use of electric energy to produce illuminance levels similar to those of daylight and could technically now be produced in interior living and working spaces or in exterior spaces, for example the lighting of streets and public spaces, or for the floodlighting of buildings 5 Definition of terms used in lighting design is important in order to avoid ambiguity: Luminous Intensity represents the force that generates the light that we see. 6 The SI Unit is the candela (candle power) abbreviated cd. Luminous Flux is a quantity of light with an SI unit lumen abbreviated lm. Luminance is the density of luminous power, expressed in terms of lumens per unit area and is abbreviated E. Maintenance Factor is used in order to allow for the collection of dirt on a lamp and also ageing, both of which cause loss of light. It has no unit and is abbreviated M.F Utilization Factor is the ratio of the lumens received on the working plane to the total flux output of lamps in the scheme. It has no unit and is abbreviated U.F Luminous Efficacy describes the luminous flux of a lamp in relation to its power consumption and is therefore expressed in lumen per watt (lm/w). 5 Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page 22 6 Walter T. Grondzik, Alison G. Kwok, Benjamin Stein, John S. Reynolds, Mechanical and Electrical Equipment for Buildings, 11 th Edition, Page 471 3

12 2.1.2 Illuminance Recommendations There are general recommendations arising from visual task studies which indicate that assuming good contrast, the required luminance, categorized by type of task are shown in table Furthermore, the chartered institute of building service engineers has published standards for luminance recommendations in the Code for Lighting, Table 2.1: General Luminance Recommendations Category of Visual Task Required Luminance (cd/m 2 ) Casual Ordinary Moderate Difficult Severe 400 and above. They have used a method to determine the recommended average luminance level known as the standard maintained luminance Light Sources Discharge lamps produce light by a process where gases are heated within a controlled enviroment in the lamp. This is done by applying voltage between two electrodes located in a discharge tube filled with inert gases or metal vapors. A current is produced between the two electrodes. Electrons in the discharge collide with gas atoms, which are in turn excited to radiate light, when the electrons are travelling at a sufficiently high speed. For every type of gas there is 7 Walter T. Grondzik, Alison G. Kwok, Benjamin Stein, John S. Reynolds, Mechanical and Electrical Equipment for Buildings, 11 th Edition, Page 492 4

13 a certain wavelength i.e. light, is produced from one or several narrow frequency ranges. These lamps include fluorescent lamps and opal spheres enclosed diffusing fluorescent luminaires which have wide applications due to low power consumption and availability. Fluorescent lamps are usually tubular in shape, whereby the length of the lamp is dependent on the wattage and have a high luminous efficacy. They have a long lamp life, but this reduces considerably with the higher the switching rate. Both igniters and ballasts are required for the operation of fluorescent lamps. Fluorescent lamps ignite immediately and attain full power within a short period of time. Instant reigniting is possible after an interruption of current. Fluorescent lamps can be dimmed. There are no restrictions with regard to burning position. For purposes of this report, the different types of fluorescent fittings utilized have the following general specifications: 2 58 Watts HPF Surface Mounted Fluorescent Batten with Mirror Brite Lovres 2800 lumens (type 5 light fitting), 2 58 Watts HPF Dust Proof Jet Proof and Corrosion Resistant Fluorescent with Acrylic Differ 2800 lumens (type D light fitting), 1 36 Watts HPF Fluorescent Batten 2800 lumens (type 4 light fitting) 8 The different types of opal spheres enclosed diffusing fluorescent luminaires utilized in this project have the following general specifications: 100 Watts Ball Fitting 2800 lumens (type 2 light fitting), 23 Watts Single Angular Wall Bracket with PL lamp 2800 lumens (type W light fitting), Watts Pendant set 2800 lumens (type B light fitting) Lumen Method of Lighting Design The lumen method of lighting design is used to determine a lighting layout that will provide a design maintained luminance. The method uses the formula: N = Where the letters carry the following meanings: E A F UF MF Equation Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page 62 9 Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page 62 5

14 N Number of luminaires E Average luminance on the working plane in lux A Area of the working plane in m 2 F Flux from one lamp in lumens UF Utilization Factor MF Maintenance Factor Light Switches Light switches are used to make or interrupt a circuit. There is a maximum current which the contacts of any particular switch can make or break, and a maximum voltage that the contact gap can withstand. A switch must not be put in a circuit which carries a current greater than that which the switch can break. It is sometimes necessary to fully isolate power equipment such as heaters or fans. This means disconnection of both the live and neutral contacts from the circuit. This is done with the use of double pole switches. 2.2 Electrical Power Circuits Electricity power circuits in a building consist of light switches, sockets, kitchen units and similar outlets connected in a safe and balanced manner in order to ensure continuity of supply and user satisfaction Socket Outlets Socket outlets are electrical devices that allow the safe connection of appliances to the power source. They typically have three pins. Two of the three pins are for the line and neutral cables, and the third one is for a separate circuit protective conductor, earth cable. The standard employed in this project is to connect a maximum of six, (6) twin sockets in a ring circuit. This allows for a maximum load power of 1000W 240V on each twin socket within the circuit if the diversity factor chosen is one, (1).Hence adequate protection can be applied using the current drawn as: = 1000W 6 240V = 25 Amps 6

15 Equation 2.2 The ring circuit consists of live, neutral conductors and an exposed earth looped into each socket outlet. This allows for supply from either direction hence ensuring continuity of supply even when one of the sockets fails to operate Kitchen Unit Kitchen appliances such as microwaves and electric kettles draw higher electric current than most other appliances. They therefore, require more durable and resistant sockets known as the kitchen unit. The kitchen unit switch is double pole thus providing complete isolation of the appliance to the wiring. 2.3 Electrical Service Network Diversity Diversity occurs in an operating system because not all loads connected are operating simultaneously or are not simultaneously operating at their maximum rating 11 For commercial buildings such as the hostel in this project, the diversity was assumed to be 100% for all the lighting loads. This ensures that the system is able to handle maximum load at any given time in order to improve on the reliability of the system. A diversity factor of 67 % is applied for the twin socket outlets in the hostel rooms and a diversity factor of 50% for the high level twin socket outlets. A diversity factor of 100% is also applied for the kitchen unit Power Circuit Design In order to design the power circuits, it is important to take note of the miniature circuit breaker, (MCB) standard ratings that are available. The MCBs utilized for the purpose of this project are 6Amps, 10Amps, and 20Amps size ratings talogue.pdf Page

16 The lighting fittings are assigned to circuits such that they do not exceed the 5Amp switch rating for each circuit. This would enable the use of the 6Amps MCB to protect the individual lighting circuits. Similarly, the socket outlets are assigned to circuits such that they can be assigned to the standard MCB ratings. The 20 Amps MCB rating is found appropriate to protect a single ring socket outlet Consumer Units They are also known as consumer control units. These are single phase boards which are utilized to house the miniature circuit breakers protecting all the power circuits within a given area. The maximum rating of the consumer units, (CUs) utilized for this project is 100Amps and is operated by the two-pole switch as shown in Figure 2.1 Figure 2.1: Consumer Unit, (CU) The CU has ways which are the individual circuits within the area served by it. This ensures that each circuit or way is protected by its individual miniature circuit breaker. It also provides a simple way of balancing the loads equally amongst all the three phases of a three phase supply system because each consumer unit is assigned one phase. The CUs are designed to have a certain number of ways such as 12-way CU and 13-way CU for this project. Each way is a circuit consisting of either lighting fittings or socket outlets or a kitchen unit. 8

17 2.3.4 Distribution Board A distribution board, (DB) is a component utilized in a power supply system to divide the 3- phase power into balanced loads while providing protection to each consumer unit connected to it. The protection is provided using moulded case circuit breakers, (MCCB) for each way. A typical DB is shown in figure 2.2 Figure 2.2: Distribution Board, (DB) Switch-Boards The main reason for using cubicle switch boards is to ensure that if there is any future load growth the bus-bars within the cubicle would enable easy expansion of the distribution network. They also provide a safe enclosure for all connections to meters and power isolators as well. A typical cubicle switch board is shown in figure Dr C. R. Bayliss and B. J. Hardy, Transmission and Distribution Electrical Engineering 3 rd Edition, Page 139 9

18 Figure 2.3: Cubicle Switch Board Commercial Back-Up Diesel Power Generators Diesel engines are more suited to continuous running for lengthy periods at higher load ratings and are therefore used more widely for stationary applications. The use of hooded diesel generators as shown in figure 2.4 is becoming increasingly important in industries. These generators provide for low noise levels which reduce noise pollution. The hood also ensures that the generator may be placed outdoors which lowers the cost of installation by eliminating the need to build a generator room. Figure 2.4: Diesel Generator 10

19 2.3.7 Wiring External wiring is done depending on the location of various consumer units. This is achieved using underground or overhead cables. Underground cables are usually armoured poly vinyl chloride, (PVC) insulated cables. They provide extra protection against mechanical damage due to the armour that is wound over the insulated cables along its entire length. The armored cable is run in a high-impact grade heavy gauge PVC conduit which is buried at least 600mm 13 below ground level and 750mm under a road. Cable entries into a building have to be through a hole in the wall which has to be tight round the cable. It has to be sealed to prevent dirt, vermin and moisture entering. This may be done using a draw box above the ground level or using a duct built through the wall below ground level. Internal wiring is done using PVC insulated copper wires which run in a PVC conduit fixed into the concrete during construction or in a false ceiling for lighting Cable Sizing The size of the cable is determined by the amount of current it has to carry as well as the length which the cable has to be laid. This is done using recommended ampacity and voltage drop values provided in the IEEE standard power cable ampacity tables which were used for purposes of this project. Other recommended standards can be found in the Appendix C of this document. 2.4 Protection Systems No matter how well designed a power system is, there is always a likelihood of faults occurring. These fault currents can cause a great deal of damage even over a very short period of time, tens or hundreds of milliseconds. It is therefore essential to provide adequate protection to detect and disconnect elements of the power system before irrepairable damage occurs. Overcurrent 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. 13 Barrie Rigby, Design of Electrical Services for Buildings 4 th Edition, Page 65 11

20 2.4.1 Overload Protection An overload is an overcurrent in a circuit that is electrically sound. This may be due to 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. The IEE Wiring Regulations specify the following current levels for coordinating overload protection between cables and protective devices. I I I I I 1.45 I Equation 2.3 Where the symbols carry the following meanings: I = design current of circuit I = nominal current of protective device I = current-carrying capacity of the cable I = minimum operating current of protective device Short Circuit Protection 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. Protection of cables against short circuit can be done by utilizing the adiabatic equation. The time t in which a given short circuit current will raise the temperature of the conductors to the limiting temperature, can be calculated from the formula 12

21 t = k s I Equation 2.4 Where the symbols carry the following meanings: t = duration in seconds s = cable cross section (mm 2 ) I = effective short circuit current (Amps) k = a factor taking into account various criteria of the conductor Therefore, if the circuit breaker protecting the cable operates in less time than that required for the cable to reach its temperature limit, the cable is protected Protection System Equipment Moulded case circuit breaker, (MCCB) is a power switch with built-in protective functions used on circuits requiring high current ratings. They operate as switches for normal load current opening and closing functions. They also automatically disconnect excessive overloads and interrupt short circuit currents as quickly as possible. They as well as provide indication status of the MCCB if it is open, closed or tripped. They are normally utilized in distribution boards, (DB) and switch boards. Miniature circuit breakers, (MCBs) are similar to moulded case circuit breakers but as their name implies, these are smaller in size and are mostly used for current ratings below 100 A. They are mainly used to protect the final circuits and are housed in the consumer unit, (CU) Discrimination and Protection System Co-ordination Discrimination in power systems describes a hierarchy of circuit devices that are arranged such that a single upstream circuit breaker can fan out to several downstream protective devices to act in a co-ordinated fashion should a fault occur. Under fault conditions, only the upstream protective device closest to the fault should operate to clear the fault, leaving all other healthy circuits operational. In this project current discrimination and time discrimination will be employed. 13

22 2.4.5 Lightning Protection In lightning protection design, the goal is to dissipate static charges around a given structure at a rate sufficient to maintain the charge below the value at which a lightning flash will occur. The typical duration of a lightning flash is approximately 0.5 seconds. A single flash is made up of various discharge components, among which are typically three or four high-current pulses called strokes. Each stroke lasts about one 1ms; the separation between strokes is typically several tens of milliseconds. Application of the point discharge theory is widely utilized in lightning protection. The theory holds that discharge from the point of an electrode to a surrounding medium will follow predictable rules of behavior. It has been proven that the sharper the point of the air conductor then the greater the discharge. The greater the number of discharge points, the more efficient the dissipation system. The air terminal provides a zone of protection which can be described as a cone. This is shown in figure 2.5.The air terminal at the highest point offers the greatest protection zone. Figure 2.5: Lightning Protection Zones and Cones Air termination is provided to intercept a lightning strike and no part of a roof should exceed 5 m from part of a termination conductor, unless it is a lower level projection which falls within the zone of protection. The air terminations are horizontal conductors running along the ridge of a pitched roof or around the periphery of a flat roof 14

23 The down conductor is that part of the external lighting protection system that conducts lightning current from the air terminal system to the earth termination system. They provide a low impedance route from the air terminations to the earth terminals. The down conductor must be installed straight and vertically in order to provide the shortest and most direct path to earth thus the formation of bends must be avoided. The earth termination system is the part of the external lightning protection system that conducts and disperses lightning current to earth and it is required to give the lightning discharge current a low resistance path to earth. 15

24 CHAPTER PROJECT WORK AND IMPLEMENTATION This chapter covers the scope of work carried out for the building electrical services design for a hostel along Nyerere road located in Nairobi, Kenya. 3.1 Site Location The site of the hostel is in Nairobi, the capital city of Kenya. Therefore, no issues are raised about national power grid and mains connectivity and reliability of power supply. 3.2 Site Plan and Introduction The project site plan has one building with a total of six floors. It is a proposed hostel along Nyerere road with a total of six floors. These are lower floor, upper ground floor, first floor, second floor, third floor and the attic floor as shown with the architectural floor plans drawings attached in appendix A-1. The architectural floor plans drawings are then used to come up with an appropriate lighting scheme through a lighting fittings design and power points layout design on each hostel floor plan. A schedule of symbols and lighting luminaires settled for in the lighting fittings design and power points layout design has been attached as drawing number E01 in appendix A-1 as an aid to understanding this project work Sample Lumen Method of Lighting Design Calculation for One Hostel Room Lounge Area in One Hostel Room Located at the Upper Ground Floor Illuminance = 150 lux (IES Code recommendation for such an area). The position of measurement was the desktop. Floor area dimensions: Length = 5.8metres, Width = 2.821metres Ceiling height = 2.5metres Mounting height (floor): Hm 2.5 m 0.85 m = 1.65 metres LW Room index K H L W m 16

25 K = ( ) = The utilization factor, (UF) is obtained from the table of utilization factors versus the room index for a opal sphere enclosed diffusing single angular wall bracket and having a down light output ratio, (DLOR) of 45%.This UF table is attached in appendix F of this project document. For a room of K = 1.15 and ceiling and wall reflectances of 0.7 and 0.5 respectively, the utilization factor, (UF) is by use of interpolation: UF = ( ) = The opal sphere enclosed diffusing single angular wall brackets complete with 23 W PL lamp (type W light fitting) luminaires and the opal sphere enclosed diffusing pendant set complete with 100 W lamp (type B light fitting) luminaire are used. Each luminaire has a known lighting design lumen, (LDL) output of 2800 lumens. The lumen method of lighting design, equation 2.1, in section is now applied for the lounge area in one hostel room in upper ground floor plan as shown in Table 3.1 From the previous analysis and discussions for the lounge area, the following parameters have been achieved: E = 150 lux A = (5.8m 2.821m) = 16.36m 2 F = 2800 lumens UF = 0.39 MF = 0.8 Number of light fittings for the lounge area = = 2. 8 light fittings This is approximated to three, (3) light fittings for lighting the lounge area or region in the hostel room as shown in figure 3.1 The same lumen method of lighting design is done and repeated for the other regions or areas within the hostel room. The results are summarized in table

26 Table 3.1: Summary of Lumen Method of Lighting Design for a Single Hostel Room Region/area in a Single Hostel Room Illuminance, E (Lux) Area, A (M 2 ) Maintenance Factor, MF Utilization factor, UF Flux of one light fitting, F (Lumens) No. of light fittings, N Lounge Bedroom Bath Kitchen These details and results for the lumen method of lighting design for one hostel room are now shown fully in figure

27 Figure 3.1: Small Section of Upper Ground Floor Plan Comprising of One Hostel Room illustrating the Lumen Method of Lighting Design Similar calculations were applied to all the other rooms and the other regions or areas of the entire project site plan Sample Power Points Layout Design for One Hostel Room In domestic power socket design an unlimited number 14 of sockets can be connected in a ring circuit for a floor area of up to 100m 2. This design problem is for a commercial hostel and thus ring circuiting for the socket outlets is used to allow for supply from either direction hence ensuring continuity of supply even when one of the sockets fails to operate. Therefore, the design incorporated two, (2) normal-level twin sockets estimated to draw a power of 1000W each. These are shown in the turquoise (faded blue) color located in the lounge and bedroom areas. 14 Building Services Handbook, 4 th Edition, Page

28 Power points layout design also has one, (1) high-level twin socket estimated to draw a power of 1000W also shown in turquoise color and located in the kitchen area. The same kitchen area has one, (1) kitchen unit shown in red color. These are all illustrated in figure 3.2 Figure 3.2: Small Section of Upper Ground Floor Plan Comprising of One Hostel Room illustrating Power Points Design Layout. 3.3 Entire Hostel Lighting Fittings Design and Power Points Layout Designs An appropriate lighting scheme and power points layout as with factors discussed in section 3.2 is now adopted and applied to the entire hostel regions. The entire and complete lighting fittings and power points layout designs on architectural A3 paper size drawings are attached in appendix A-1 and labeled as appropriate. 20

29 CHAPTER DESIGN ANALYSIS AND DISCUSSIONS 4.1 Design Analysis Based on Load Calculations and Circuits Arrangements Introduction A count is done from the lighting and power points designs drawings on A3 paper sizes attached in appendix A-1, to establish the number of light fittings and power points on each hostel floor. The total load is then calculated to facilitate determination of the number of consumer units, (CUs) and distribution boards, (DBs) to be used in supplying each hostel floor. The CUs and DBs are located for safety, convenience of supplying the loads (that is, good spartial spread) and so as to be near the centre of gravity of the loads they are to supply. Their distances from the DBs supplying them are measured and so is the distance of the various DBs from the switchboard determined. The fittings are then assigned to be supplied by the various CUs (that is, circuiting is done). The factors taken into account when assigning fittings are: 1. Total current for a group of lights switched on by a single switch must not exceed 5 Amperes, this been the limiting value current that an ordinary switch s contacts can repeatedly make or break without risking excessive burning that would shorten the service life of the switch. Putting a worst case that is the upper limit of 100W on each light fitting supplied at 240 V implies: Current drawn = 100 W Amps / 240V fitting Maximum number of fittings per switch = fittings 2. In this work the maximum load assigned per CU should not draw current more than 100 amperes. For the hostel floors with heavy loads a CU load of 70Amps- 76Amps is adopted, while the hostel floors with light loads a CU load of 40Amps- 55Amps is adopted. 21

30 A sample calculation on the lower floor plan loads being considered as the hostel floor with light load is documented in section From the architectural drawings provided the upper ground floor, first floor, second floor and third floor plans depicted the same architectural design and upper ground floor is settled for consideration as the hostel floor with heavy load and its sample load calculations documented as shown in section Lower Floor From the lighting fittings design in drawing number E02 in the appendix A-1, a count is done to establish the number of lighting fittings on this floor and the results summarized in table 4.1 as: Table 4.1: Summary for Lighting Fittings Loads on Lower Floor. Fitting type No. of fittings Diversity factor Assumed rate (Watts) Total load (watts) Type W Type Type Type N Type B Type D Type Type 2D Total (watts) 5100 The assumption made here is this been a hostel all lights are likely to be on at the same time hence a diversity factor of 1 From the power points layout design in drawing number E03 in appendix A-1, the same procedure is repeated and the results are summarized in table

31 Table 4.2: Summary for Power Points Loads on the Lower Floor. Fitting type No. of fittings Diversity factor Assumed rate(watts) Total load(watts) Twin sockets Hand drier Fan Total(watts) The assumption made in the power points design analysis is not all sockets, toilet hand driers and toilet fans are likely to go on at the same time hence a diversity factor of 2 3 is assumed. Therefore, total load for lower floor = 5100 W W = Watts Applying 20% future load growth the total load for lower floor is: = = Watts 100 Therefore the total current drawn by lower floor loads is: = W 240 V = Amps A standard consumer unit settled for in this project has a 100 Amps integral isolator and thus allows a maximum load current of 100Amps.For a load current of Amps, logically 2 consumer units (CUs) are required with each consumer unit drawing current of around = Amps/ Cu. Hence a CU load of 40A-55A is adopted for hostel floors with light loads that is the lower floor and the attic floor Upper Ground Floor There are a total of twelve, (12) rooms on this floor. Therefore, for phase balance at the distribution board, (DB) a working formula is: 23

32 = 12 rooms 3 phases = 4 rooms/phase Looking at one hostel room and doing a load analysis of the overall lighting fittings as in table 4.3: Table 4.3: Summary for Lighting Fittings Loads Design on One Hostel Room on Upper Ground Floor. Fitting type No. of fittings Diversity factor Assumed rate(watts) Total load(watts) Type B Type W Type N Type 2D Type Type Total(Watts) 900 Power points design Looking at one hostel room and doing a load analysis of the overall power points as in table 4.4: Table 4.4: Summary for Power Points Loads Design on One Hostel Room on Upper Ground Floor. Fitting type No. of Diversity Assumed rate Total load fittings factor (watts) (watts) Twin sockets High level twin 1 1 sockets Kitchen unit

33 Total (Watts) Therefore total load per room = 900 W W = Watts Current drawn per room is: = W 240 V = Amps Therefore, total current for 4 rooms is: = = Amps. Hence a CU load of 70 Amps-76 Amps is adopted for hostel floors with heavy loads. That is upper ground floor, first floor, second floor and third floor. Applying 20% future load growth the total current for 4 rooms is: = = Amps Amps is less than 100 Amps where 100 Amps is the maximum load current of a standard CU with a 100 Amps integral isolator which is chosen in this project. Therefore a load current of Amps will be comfortably handled with 1 CU, implying 1 CU will supply 4 hostel rooms on the upper ground floor. Therefore, 12 rooms on the entire upper ground floor will be supplied by: = 12 rooms 4 rooms 1 CU = 3 CUs The 3 CUs will thus be arranged and distributed on the upper ground floor as: Consumer Unit upper ground floor 1 (CU UGF1), Consumer Unit upper ground floor 2 (CU UGF2), and Consumer Unit upper ground floor 3 (CU UGF3). However, there are corridor and balcony light fittings with a load analysis of: 25

34 Table 4.5: Summary for Corridor and Balcony Light Fittings Loads on Upper Ground Floor Type of fitting No. of fittings Diversity factor Assumed rate(watts ) Total load (watts) Type N Total (watts ) 1400 The load current drawn by balcony and corridor light fittings is: = 1400 W 240 V = Amps This current will be supplied by one of the three CUs arrived at in the design load analysis earlier and consumer unit, CU UGF 2 is chosen for this supply. Therefore, now evaluating the total single-phase load for upper ground floor with a total of 12 rooms is: = ( )W W = Watts The same analysis is done for the other hostel floors and the single-phase loads results summarized in the table

35 Table: 4.6: Summary for All Single-Phase Hostel Loads. Floor Total load(watts) 20% future load growth factored in Total Current drawn(amps) No. of CUs Arrangement total load(watts) CUs Lower CU LF1, CU LF2 Upper ground CU UGF1, CU UGF2, CU UGF3 First CU FF1, CU FF2, CU FF3 Second CU SF1, CU SF2, CU SF3 Third CU TF1, CU TF2, CU TF3 Attic CU AF1 TOTAL CUs From the summary table 4.6 the overall single-phase loads for the entire hostel will be supplied by 15 CUs. The lifts and hose reel pumps are three-phase loads and will be supplied directly from one distribution board, (DB) way. 27

36 CHAPTER DISTRIBUTION SYSTEM TOPOLOGY 5.1 Consumer Unit, (CU) Design and Specifications Consumer Unit Design based On: Circuits Arrangement, Load Calculations, Miniature Circuit Breaker, (MCB) size and Cables Selection. From table 4.6, it is apparent that all the single-phase loads will be supplied with fifteen, (15) CUs. In order to avoid redundancy, the first consumer unit at upper ground floor, (CU UGF1) is chosen in this project document to explain the concept of consumer unit design and specifications in details. The results for the other consumer units are then summarized. Referring to the upper ground floor circuits arrangements design drawing number E04 and E05 attached in appendix A-1 where circuiting has been done; the various assignments of singlephase loads are analyzed as follows: Circuit CIR UGF 1.1 CIR UGF 1.1 means that the single-phase loads are assigned to consumer unit, CU UGF 1 and the way assigned to them on this CU is also way 1.Thus the assignment of fittings on this CU way is summarized in table 5.1 Table 5.1: Summary for Assignment of Fittings on Circuit CIR UGF 1.1 Fitting type No. of fitting Diversity factor Assumed rate(watts) Total load(watts) Type W Type B Type 2D Type N Type Type Total(watts)

37 Therefore, current drawn by the assignment of fittings on circuit CIR UGF 1.1 is: = 900 W 240 V = 3.75 Amps The standard sizes for miniature circuit breakers, (MCBs) by MEM catalogue are 6A, 10A, 16A, 20A, 32A, 40A, 50A, 63A. Therefore, a 6 A MCB is used to protect the circuit UGF 1.1. From the IEE tables attached in the appendix C for one twin cable single phase, 1mm cable which carries up to 14 Amps is appropriate. However, 1.5mm cable which carries up to 18 Amps is settled for supplying this circuit. Circuit CIR UGF 1.2 CIR UGF 1.2 means that the single-phase loads are assigned to consumer unit, CU UGF 1 and the way assigned to them on this CU is way 2. Thus the assignment of fittings on this CU way is summarized in table 5.2 Table 5.2: Summary for Assignment of Fittings on Circuit CIR UGF 1.2 Fitting type No. of fitting Diversity factor Assumed rate(watts) Total load(watts) Type W Type B Type 2D Type N Type Type Total(watts) 900 Therefore current drawn by the assignment of fittings on circuit CIR UGF 1.2 is: = 900 W 240 V = 3.75 Amps Therefore, a 6 A MCB is used to protect the circuit UGF 1.2. Again, a 1.5mm cable which carries up to 18 Amps is settled for supplying this circuit. 29

38 The same design and specifications analysis is done for circuits CIR UGF 1.3, CIR UGF 1.4, CIR UGF 1.5, CIR UGF 1.6, CIR UGF 1.7, CIR UGF 1.8, CIR UGF 1.9 and CIR UGF The overall consumer unit, CU UGF 1 design results and specifications are now summarized as in section Consumer Unit, CU UGF 1 Circuit and way on CU Total load(watts) Total current (amps) UGF UGF UGF UGF UGF UGF UGF UGF UGF UGF MCB size 6A 6A 6A 6A 20A 20A 10A 10A 10A 10A Cable size(mm 2 ) From section specifications, the consumer unit, CU UGF 1 is now designed and specified while incorporating the ten protected circuit ways and allowing for a minimum of two blank spare ways for future use as shown in figure 5.1. The design and specification details for CU UGF 1 are: 30

39 Figure 5.1: 12-way Single-Phase and Neutral Consumer Unit, CU UGF1 on Upper Ground Floor The same design analysis is done for consumer unit, CU UGF 2 and consumer unit, CU UGF 3 located at the same upper ground floor. This is also done for all the other consumer units located at the other hostel floors, which are CUs at the lower floor, CUs at first floor, CUs at second floor, CUs at the third floor and a CU at the attic floor. The further design results for these CUs and their specifications are attached in appendix B of this project document Consumer Unit Total Single-Phase load calculations, Total Load Currents Drawn, Cable Length and Cable Size Selection from the Distribution Board, (DB) feeding the CU Consumer Unit, CU UGF1 From section 5.1.1, CU UGF1 will have a total overall single-phase load of: 31

40 = Watts Therefore, current drawn by these single-phase loads is: = W 240 V = Amps Length of cable to feed this CU from the Distribution board, (DB A) located at the lower ground floor is = 18m From IEE tables for non-armoured one twin cable single-phase enclosed type, attached at the appendix C, a 25mm cable which carries up to 79 Amps is chosen. Its appropriateness is chosen through a voltage drop calculation. Allowing up to a maximum of 1.5% voltage drop (which is the maximum voltage drop allowed for in this design between a DB and CU) on this cable chosen to supply this CU from the DB. %voltage drop 70.98A18m1.8 mv / A / m 1 100% 0.958% % is less than the maximum 1.5% design voltage drop allowed for. A 25mm, nonarmoured one twin cable single-phase chosen from the enclosed category is hence very appropriate and settled for. The same analysis is done for all the other CUs on the same upper ground floor (CU UGF2 and CU UGF3) and also the other floors. The results are then summarized are in section Summary for All the 15 Consumer Units within the Hostel Consumer unit Total load (watts) Total current (Amps) Cable length (Metres) Cable size(mm 2 ) Voltage drop (%) CU UGF CU UGF CU UGF CU LF CU LF

41 CU FF CU FF CU FF CU SF CU SF CU SF CU TF CU TF CU TF CU AF Distribution Board, (DB) Design and Specifications From the proposed hostel architectural drawings in Appendix A-1, the light fittings and power points layouts were single-phase loads. The proposed hostel design also allowed for two passenger lifts and two hose reels pumps as a fire fighting measure. The proposed hostel thus had both single-phase loads and three-phase loads. The distribution board system design settled for is to treat the single-phase loads separately and also the three-phase loads separately. Thus: Single-Phase Loads Distribution Board Design and Specifications From the 15 consumer units, (CUs) summary in section and settling on a single or one distribution board, (DB) to feed all of them. This is designated as DB A and placed at the lower floor within the hostel premises for safety as shown in drawing number E03, in the auto computer aided designs in appendix A-1. The distribution system topology in figure 5.2 is then adopted to feed all the 15 CUs with singlephase loads of the proposed hostel. 33

42 Fig 5.2: Distribution Topology to feed all the 15 CUs Supplying Single-Phase Loads Load Balancing at the Supply Phases of Distribution Board, (DB) A The 15 CUs are then distributed amongst the red, yellow and blue phases of the DB A so as to result in as close balance as possible at the supply phases. The results are summarized in table 5.3 Table 5.3: Summary for Load Balancing at the DB A Supply Phases Floor Phase load Consumer Red phase (Watts) Yellow phase (watts ) Blue phase (watts ) unit Lower ground CU LF1 34

43 10300 CU LF CU UGF1 Upper ground CU UGF CU UGF3 First CU FF CU FF CU FF3 Second CU SF CU SF CUSF3 Third CU TF CU TF CU TF2 Attic CU AF1 Phase totals (watts) (Red phase) (Yellow phase) (Blue phase) Thus distribution board, DB A, distribution system topology to supply the various CUs and its supply phases balanced as closely as possible is shown in figure

44 Figure 5.3: Distribution Board, DB A at the Lower Floor to Supply the 15 CUs at Various Floors Sizing of Cable Feeding Distribution Board A DB A supplies consumer units; CU LF1, CU LF2, CU UGF1, CU UGF2, CU UGF3, CU FF1, CU FF2, CU FF3, CU SF1, CU SF2, CU SF3, CU TF1, CU TF2, CU TF3 and CU AF1. Consumer units; CU UGF1, CU UGF2, CU UGF3, CU TF1 and CU AF1 have a total load of W and are on the red phase as seen in section W Therefore, DB current on red phase Amps 240V 36

45 CUs SF1, SF2, SF3, TF3 and LF1 have a total load of W and are on the yellow phase as seen in section W Therefore, DB current on yellow phase Amps 240V CUs SFF1, FF2, FF3, TF2 and LF2 have a total load of W and are on the blue phase as seen in section W Therefore, DB current on blue phase Amps 240V Length of cable connecting DB A to the switchboard = 4m Current used for sizing the cable = Amps (the largest of , and ) Allowing for a max of 1.5% voltage drop on this cable A 4m 0.2 mv / A / m 1 % voltagedrop 100% % % Voltage drop is less than the maximum 1.5% design voltage drop allowed. This means the 240mm 2, non-armoured one 3 or 4 core cable three-phase is appropriate Three-Phase Loads Distribution Board Design and Specification The three-phase loads within the proposed hostel are the two passenger lifts and two hose reel pumps for fire-fighting measures that are allowed for.the power ratings settled for these threephase loads in the design are summarized as in table 5.4 Table 5.4: Power Ratings for the Three-Phase Loads Three-phase load Power rating (watts) Passenger lift Passenger lift Fire fighting hose reel pump

46 Fire fighting hose reel pump Total three-phase load (watts) Another distribution board, (DB) is settled for in the design to supply these three-phase loads only. The reason is to avoid overloading DB A already settled for in section for supplying the hostel single-phase loads. This is designated as distribution board, DB B and it is placed at the attic floor within the hostel premises for safety as shown in drawing number E13 in the auto computer aided designs in appendix A-1. The distribution system topology in figure 5.4 is then adopted to directly feed all the three-phase loads for the proposed hostel. Fig 5.4: Distribution Topology to Supply all the Hostel Three-Phase Loads Directly. Thus in the next sections we proceed with three-phase loads power supply designs Lift Power Supply Design The lift is intended to take a power of 22kW, 3-phase at a power factor of

47 V I 3 p. f 22kW L L Where: VL 415 Lift line voltage IL Line current drawn by the lift p. f Lift power factor 22kW IL Amps V p. f L Thus, a 60 Amps isolator is chosen for one passenger lift.therefore, the two passenger lifts are to be supplied with two 60 Amps isolators Hose Reel Pump Power Supply Design The hose reel pump is intended to take a power of 11kW, 3-phase at a power factor of 0.8. V I 3 p. f 11kW L L Where: VL 415 Hose reel pump line voltage IL Line current drawn by the hose reel pump p. f Hose reel pump power factor 11kW IL Amps V p. f L Thus, a 30 Amps isolator is chosen for one hose reel pump. Therefore, the two hose reel pumps are to be supplied with two 30 Amps isolators. 39

48 These been three-phase loads they will balance equally at the DB supply phases; that is red, yellow and blue phases. Thus distribution board, DB B and its distribution system topology to supply three-phase power directly to all the three-phase loads is shown in figure 5.5 Figure 5.5: Distribution Board, DB B at the Attic Floor to Supply all the Hostel Three-Phase Loads Sizing of Cable Feeding Distribution Board B DB B supplies two, three-phase lift isolators each of rating 60Amps and two, three-phase hose reel pump isolators each of rating 30 Amps. Therefore DB B current (2 60) (230) 180Amps on every phase Length of cable connecting DB B at the attic floor to the switchboard = 20m Current used for sizing the cable = 180 Amps. Allowing for a maximum of 1.5% design voltage drop on this cable 180A 20m 0.42 mv / A / m 1 % voltagedrop 100% % % Voltage drop is less than 1.5% design voltage drop, meaning the 95mm 2 nonarmoured one 3 or 4 core cable three-phase is appropriate. 40

49 5.3 Power Back-Up Generator During the distribution design a standby generator for the entire establishment is also settled for as part of the project objective. This been a commercial building the back-up generator is to be able to ensure continuous power supply to the hostel incase of absence of Kenya Power and Lighting Company, (KPLC) grid power. A proposed generator room or necessarily a cage for this back-up generator is seen in drawing number E03 in the computer aided designs for lower floor plan in appendix A Size of Back-Up Generator From section , a summary for the hostel total single-phase loads is inferred. Section also gives a summary for the total three-phase loads for the proposed hostel. The total load capacity for the hostel is therefore summarized in table 5.5 Table 5.5: Summary for the Hostel Total Load Capacity Floor/three-phase load Total load(watts) Lower floor Upper ground floor First floor Second floor Third floor Attic floor lifts hose reel pumps Total hostel load (watts) Applying 15% future load growth for the possibility of an addition of another floor within the establishment or air-conditioning of the hostel premises; The total hostel load watts kW 41

50 Total hostel load in kw kva kVA powerfactor 0.8 Going by generator capacities currently available in Kenyan markets, a standard 450 kva, Volvo 50 Hz, hooded back-up generator is chosen. Its datasheet is attached in the appendix E of this project document. Other alternatives settled for are the John- Deere and Caterpillar types hooded diesel back-up generators of the same rating Sizing of Cable of the Back-Up Generator The backup generator will supply 450 kvaat 50Hz frequency thus: V I 3 450kVA L L Where: VL 415 Generator line voltage IL Line current drawn by the generator 450kVA IL Amps V L Length of generator cable (from the generator to switchboard) = 20m. Current used for sizing the cable = Amps since no cable size exists for a line 2 current of Amps. Thus we use two cable conductors in parallel, sized to accommodate Amps each. Allowing for a max of 3% voltage drop on this cable: A 20m 0.24 mv / A / m 1 % voltagedrop 100% % % Voltage drop is less than the 3% maximum value allowed. This means the two 185mm 2 armoured, one 3 or 4-core cable three-phase connected in parallel are appropriate. 42

51 5.4 Electrical Distribution Reticulation Combining all the distribution system topology discussions in section 5.0, section 5.1, section 5.2 and section 5.3, the comprehensive electrical distribution reticulation in figure 5.6 is arrived at for the proposed hostel as: Figure 5.6: Electrical Distribution Reticulation for the Hostel 43

52 5.5 Electrical Distribution Protection System based on Fault Current Levels at Various Points in the Installation Fault Current Level at the Switch-Board Base kva = transformer kva = kva B = 1,000 kva (KPLC provided) Base kv = transformer secondary voltage = 415V, therefore kvb = kv Per unit reactance of transformer = j0.04 p.u Length of feeder (from transformer at gate to Switch-board room) = 300 m = 0.3km Series impedance of feeder =( j0.48) / phase / km Therefore actual feeder impedance = j j0.144 / phase. Therefore p.u. reactance of feeder = Actual Impedance B kv 2 1,000 B kva 1, j , 000 = 2 = j0.836 p. u 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 Switch-board essential bus-bars, p.u. fault current = = p. u. voltage transformer p. u. voltage p. u. impedance p. u. impedance transformer feeder j0.836 j

53 = j1.08 = p. u Base current, I B Base kva 1,000 1, Amps 3 Base kv Fault current (for three-phase fault at Switch-board bus-bars) = p.u. fault current Base current, I B = , Amps â = Amps Fault Current Levels at the Beginning of Final Circuits KPLC incomer, length = 0.3km, impedance = 0.12+j0.48Ω/phase/km CU copper cable, r = 18µΩm final circuit conductor N Switchboard DB CU DB copper cable, transformer secondary, r = 18µΩm reactance = j0.04p.u, base kv = 0.415, Figure 5.7: Layout and parameters for fault current calculation The consumer unit, (CU) is placed in relation to the distribution board (DB) as shown in Figure 5.7. Largest MCB on consumer unit CU UGF 1 is of 20A, protecting a ring circuit of socket outlets. Total current drawn by CU UGF 1 is 70.98A. 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 45

54 must be determined. This would be the point at which the most severe fault the miniature circuit breaker (MCB) in the CU would have to clear, failing which the moulded case circuit breaker (MCCB) 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, X. 2. The phase and neutral of the KPLC incomer, Z3 3. The phase and neutral of the DB cable between the switchboard and the DB, Z2 4. The phase and neutral of the CU cable between the DB and the CU, Z1 From section 5.5.1: actual transformer impedance, X p. u. transf impedance kv 2 1,000 B KVA B j , 000 1,000 j The impedance of the KPLC incomer, Z j0.48 / phase / km 0.3km 2 = j0.288 Calculation of the impedances of the DB and CU cables can be done with via the use of the 8 resistivity of copper ( m at 20 C ), e.g. For the DB cable, the impedance of the KPLC incomer, Z j0.48 / phase / km 0.3km 2 = j

55 Calculation of the impedances of the DB and CU cables can be done via the use of the resistivity 8 of copper ( m at 20 C ), for example: For the DB cable, Z A 3510 m 8 copper l m 4m The factor of 2 been used to take into account the phase and neutral conductors. The factor 1.38 been used for PVC insulation. So that for the for the CU cable, Z A 1010 m 8 copper l m 18m The short circuit current, I SC 240 X Z Z Z V j j Amps A summary of results follow in sections , and Fault Current Levels at Consumer Units at the Upper Ground Floor, Lower Ground Floor and First Floor Consumer unit UGF1 UGF2 UGF3 LF1 LF2 FF1 FF2 FF3 CU cable size(mm 2 ) CU cable length(m) Impedance transfer up to CU (phaseneutral) (Ω) Fault current (Amps)

56 Fault Current Levels at Consumer Units at the Second Floor, Third Floor and the Attic Floor Consumer unit SF1 SF2 SF3 TF1 TF2 TF3 AF1 CU cable size(mm 2 ) CU cable length(m) Impedance transfer up to CU (phase-neutral) (Ω) Fault current (Amps) Fault Current Levels at the Distribution Boards Distribution board A B Distribution board cable size(mm 2 ) DB cable length(m) 4 20 Impedance transfer up to CU (phase-neutral) (Ω) Fault current (Amps) Discrimination between CUs and DBs Following results summarized under sections 5.5.2, 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 UGF 1 has been filled in table 5.6: a) 25 mm 2 cable size was arrived at in Section b) 79 Amps cable current capacity was arrived at in Section c) Amps cable current was arrived at in Section d) Amps fault current was arrived at in Section and also section e) 20 Amps MCB in CU was arrived at after considering ratings of protective devices for the various ways in the CU. f) 100 Amps SP/N G FRAME MCCB in DB for discrimination is arrived at from the MEM Catalogue Table in the Appendix D. 48

57 Table 5.6: Summary for Discrimination between CUs and DBs Consumer unit UGF1 UGF2 UGF3 LF1 LF2 FF1 FF2 FF3 CU cable size(mm 2 ) Cable current capacity(amps) Cable current(amps) Rating of largest MCB in CU(Amps) Fault current(amps) CU s DB A A A A A A A A Rating of SP/N G FRAME MCCB Upstream in DB(Amps) Table 5.7: Summary for Discrimination between CUs and DBs Consumer unit SF1 SF2 SF3 TF1 TF2 TF3 AF1 CU cable size((mm 2 ) Cable current capacity(amps) Cable current(amps) Rating of largest MCB in CU(Amps) Fault current(amps) CU s DB A A A A A A A Rating of SP/N G FRAME MCCB Upstream in DB(Amps) Discrimination between DBs and the Switch-Board Following results summarized under section , protective devices that would ensure discrimination between DBs and the switchboard are here tabulated. 49

58 As an aid to understanding the table 5.8, an explanation is given here of how column 2 under Distribution Board A has been filled: a) 240 mm 2 cable size was arrived at in Section b) 392 Amps cable current capacity is from IEE Tables. c) Amps cable current was arrived at in Section d) Amps fault current was arrived at in Section e) 100 Amps MCCB in DB was arrived at Section f) 200 Amps TP/N F FRAME MCCB in Switch-board for discrimination is arrived at from the MEM Catalogue Table in the Appendix D; the 160 Amps being ruled out as it offers discrimination up to 1600 Amps fault current which is considered to be too close to the Amps fault current expected at DB B1. Table 5.8: Summary for Discrimination between DBs and the Switch-Board (MCCB 3 and MCCB 4) Distribution Board A B DB cable size(mm 2 ) DB cable current capacity(amps) DB cable current (Amps) Largest MCCB in DB(Amps) Fault Current(Amps) Rating of TP/N F FRAME MCCB Upstream in Switchboard(Amps) 200 (MCCB 3) 200 (MCCB 4) Discrimination between Moulded Case Circuit Breaker, (MCCB 1) and Switchboard From section 5.4 using figure 5.6, the essential copper bus-bars are supplying all DBs (DB A and DB B ) when KPLC power is available. Therefore: Essential bus-bars, red phase current = Sum of red phase currents of DB A + Sum of red phase currents of DB B = Amps In a similar manner the essential bus-bars yellow and blue phase currents can be calculated. The results are summarized in table

59 Table 5.9: Summary for Switch-Board Essential Bus-Bar Phase Currents Item Red Phase (Amps) Yellow Phase (Amps) Blue Phase (Amps) DB A DB B Switchboard essential bus bar currents(amps) From section 5.5.4, considering the MCCB s feeding the DBs, the largest MCCB in the switchboard is of 200 Amps rating. In section 5.5.1, the prospective fault current at the switch-board bus-bars for a three-phase short circuit fault was found to be Amperes. At the essential bus-bars of the switch-board, the largest current has just been calculated above to be Amperes. Therefore, a moulded case circuit breaker, (MCCB) is required that is capable of passing through Amps normal load current and withstanding Amps fault current while discriminating the 200 Amps largest MCCB feeding the DBs. From the MEM catalogue in Appendix D, it is clear that the 250 Amps MCCB would be the most appropriate. Hence MCCB 1 breaker rating from the electrical distribution reticulation (in section 5.4) is 250 Amps Discrimination between Generator Moulded Case Circuit Breaker, (MCCB 2) and Switch-Board Since the entire proposed hostel establishment is on back-up, the generator phase currents are obtained as the sum of phase currents supplied to DB A and DB B. In summary we get: GENERATOR PHASE CURRENTS Item Red Phase Yellow Phase Blue Phase 51

60 (Amps) (Amps) (Amps) DB A DB B Generator phase currents(amps) Often, a 3-phase fault produces the largest short-circuit current magnitude; thus, this worst-case result is then used as the basis to select the short-circuit capabilities of switchgear from manufacturers' tables. So the requirement now becomes one of picking an MCCB that can let load current of Amps pass through, withstand a fault current of Amps, and discriminate a 200 Amps MCCB at the switchboard in case of fault at DB A. The appropriate MCCB is a 250 Amps TP/N MEM 2J FRAME MCCB. Therefore, MCCB 2 shown in the electrical distribution reticulation in section 5.4 has a breaker rating of 250 Amps 5.6 Lightning Protection Design The lightning protection is shown in drawing number E14, attached at the appendix A-1 The lightning protection is done and achieved using air terminals (shown in the blue color) which are mounted at the highest point of the roof thereby offering the greatest zone of protection and interception of lightning strikes. Earth rods (also shown in blue color) are sunk into the ground. The earth rods will conduct and disperse lightning current to the earth by giving the lightning discharge current a low resistance path to the earth. Copper tape or down conductors (shown in red color) are used to connect the air terminals to the earth rods thus conducting lightning current from the air terminal system to the earth termination system. Therefore, lightning strokes are discharged and directed to the ground as shown in figure

61 Figure 5.8: Lightning Protection for the Hostel 5.7 Power Factor Correction The total load for the building = KVA, and assuming a worst case power factor of 0.65 and trying to bring it to 0.9 as per the regulations. In practice penalties are charged to a consumer whenever the consumer s system has lesser power factor. To begin with, most loads are inductive in nature. Therefore, adding shunt capacitance can reduce the inductive reactance as the capacitive reactance opposes the inductive reactance of the load. Total building load: = V Amps 1000 = kva Assuming a power factor of 0.65 before correction to the value of 0.9 required by Kenya Power and Lighting Company, the analysis can be done using the power factor triangle as shown in figure

62 kva Cos = Cos = = kw kvar before p.f correction = sin = kvar Reactive Power after power factor correction = kW tan = kvar Capacitor Bank = = kvar Figure 5.9: Power Factor Triangle Hence the proposed Capacitor Bank Size = 150 kvar electronically switched in steps of 50, 50, and 50 kvar each. Cable length connecting capacitor bank to switchboard bus-bars = 4m Maximum current drawn by capacitor bank: = = Amps Appropriate 3 or 4-core three-phase, non-armoured PVC cable size = 120 mm 2 %voltage drop = A 4m 0.34mV/A/ m % = % < 3% 415 Therefore, the 120 mm 2, cable is appropriate. 54

63 CHAPTER CONCLUSIONS In this project, an attempt has been made to come up with an appropriate lighting scheme and distribution system layout for a proposed hostel. Various sizing of cables have also been discussed to supplying power to the entire hostel building. Overload, short-circuit and lightning protections have also been included in the building electrical services design. A power back-up generator capacity size of 450 kva has also been settled on for the entire establishment. These achievements are all in line with the main objectives of the project. Therefore, the laid down objectives at the start of the project were successfully met during the entire project process. Some challenges arose during the project process and appropriate solutions were considered. A challenge such as load balancing for the hostel was not an easy and smooth task. However, a solution was found by first assigning each of the overall loads of the first three similar hostel floors to a single independent supply phase. Topping-up of the three supply phases with the remaining deficit loads of the other hostel floors was done evenly and the end result was a close as possible load balancing. The other challenge was sizing the generator cable which has a line current of Amps. From the IEE tables no cable size exists for such a line current. This was solved as; Current used for sizing the cable = Amps. Therefore, the solution was to use two cable 2 conductors connected in parallel and sized to accommodate Amps each. As a result of appropriate solutions to the challenges faced and achievement of the project main objectives, the building electrical services design for a hostel along Nyerere road project was indeed a success. 55

64 CHAPTER RECOMMENDATION FOR FUTURE WORK 7.1 Software for Building Electrical Services Design Small computer programs and macros can be written and coded to be able to compute the load calculations, currents drawn by various load circuits and voltage drops across the cable conductors. The programs can further be developed to be able to pick appropriate cables from the IEE tables for cable and conductors databases depending on the calculation results. Hence it will do cable sizing for all the building electrical power systems. Further development of the computer programs to display and give all the building electrical services power systems parameters at strategic points is also necessary and recommended. These programs when integrated leads to development of a comprehensive software for the building electrical services. This will save the manual time and energy in this demanding project work due to its wider scope. This will also enable computational implementation of the project in future 7.2 Bill of Quantities A bill of quantities can be prepared to give an estimate of the financial cost of the building electrical services design for the hostel along Nyerere road. The bill of quantities will also help in contract administration procedures as part of engineering practice in the real practical world. 7.3 Earth Faults Because of time, I was not able to cover the scope of earth faults, its analysis and effects during the project process. I would therefore recommend a detailed study of earth faults along the aforementioned areas in the future. 56

65 CHAPTER REFERENCES 1. Sidney M. Levy, Construction Process Planning and Management, An Owners Guide to Successful Projects 2007, Page U.S. Army Corps of Engineers, Electrical Power Supply and Distribution Technical Manual No , Page Barrie Rigby, Design of Electrical Services for Buildings 4th Edition, Page 1 5. Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page Walter T. Grondzik, Alison G. Kwok, Benjamin Stein, John S. Reynolds, Mechanical and Electrical Equipment for Buildings, 11th Edition, Page Walter T. Grondzik, Alison G. Kwok, Benjamin Stein, John S. Reynolds, Mechanical and Electrical Equipment for Buildings, 11th Edition, Page Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page erswitch%20catalogue.pdf Page Dr C. R. Bayliss and B. J. Hardy, Transmission and Distribution Electrical Engineering 3rd Edition, Page Turan Goren, Guide to Electrical Power Distribution Systems, 6th Edition, Page Barrie Rigby, Design of Electrical Services for Buildings 4th Edition, Page Riang Yer Zuor, Building Services Handbook, 4th Edition, Page

66 EATON MEM, MEM Circuit Protection & Control, 2003 Issue, Page EATON MEM, MEM Circuit Protection & Control, 2003 Issue, Page EATON MEM, MEM Circuit Protection & Control, 2003 Issue, Page EATON MEM Memshield Air Circuit Breakers Specification, Page 1 58

67 CHAPTER APPENDICES Appendix A-1: Auto Computer Aided Designs, (AUTOCAD) for Lighting Design and Power Points Layout Design Table A.1: Guidance of AUTOCAD designs labeling Drawing No. Floor plan Design description E01 Schedule of symbols and lighting luminaires E02 Lower floor Lighting fittings design and circuit arrangements E03 Lower floor Power points layout design and circuit arrangements E04 Upper ground floor Lighting fittings design and circuit arrangements E05 Upper ground floor Power points layout design and circuit arrangements E06 First floor Lighting fittings design and circuit arrangements E07 First floor Power points layout design and circuit arrangements E08 Second floor Lighting fittings design and circuit arrangements E09 Second floor Power points layout design and circuit arrangements E10 Third floor Lighting fittings design and circuit arrangements E11 Third floor Power points layout design and circuit arrangements E12 Attic floor Lighting fittings design and circuit arrangements E13 Attic floor Power points layout design and circuit arrangements 59

68 Appendix A-2: Lightning Protection Design A detailed and clearer lightning protection design is shown in drawing number E14 attached in this appendix A-2 section. 60

69 Appendix B: Consumer Units Designs and Specifications This appendix B shows more consumer units detailed schematics, designs and specifications with the drawing number E15 attached here. 61

70 Appendix C: IEE tables NON-ARMOURED CABLE SIZES PVC INSULATED COPPER CABLES ENCLOSED One twin cable Single phase mm 2 A mv/a/m One 3 or 4 core cable three phase mm 2 A mv/a/m

71 ARMOURED CABLE SIZES PVC INSULATED COPPER CABLES One 3 or 4 core cable three phase mm 2 A mv/a/m

72 Appendix D: MEM Catalogue Extracts 64

73 65

74 Appendix E: Power Back-Up Generator Data Sheet and Performance 450KVA VOLVO DIESEL GENERATOR 360KW, SDMO V450KSA DIESEL GENERATOR SET 360Kw (450Kva) Standby, 320Kw (400Kva) Prime, 50Hz, 1500RPM, 3 Phase, 0.8PF VOLVO TAD1242GE, Turbocharged heavy duty diesel engine, 4 stroke, 1500rpm, Electronic governor LEROY SOMER LSA472VS3, 12lead Alternator. IP23 drip-proof protection, Insulation class H. Automatic voltage regulation. MERLIN GERIN, Main line circuit breaker, 3 pole, output rated, UL listed SDMO TELYS2, Advanced auto-start Digital control panel. All alarms, genset parameters, control functions and indicators. CE and UL listed 50 HERTZ, 3 PHASES, 0.8PF, 1500 RPM 66

75 Appendix F: Utilization Factors 67