KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY, KUMASI INSTITUTE OF DISTANTCE LEARNING BSc. (Electrical Engineering) FIRST SEMESTER Examination, 2017 EE 365: ELECTRICAL SERVICES DESIGN (Third Year) DECEMBER, 2017 THREE HOURS Lecturer: Emmanuel Addo Student Index: ____________________________________ INSTRUCTIONS TO THE CANDIDATE: 1. Answer ALL questions in SECTIONS A and B 2. Circle the letter corresponding to your answer to a given question on the question paper and shade the same letter on the scannable sheet provided 4. Indicate your INDEX NUMBER on top of the Answer booklet. 5. ALL the data that you will need for this paper have been provided in the tables 1 to11 CAUTION: DO NOT TAKE AWAY ANY EXAMINATION MATERIAL PROVIDED TO YOU, UNLESS YOU ARE TOLD TO DO SO. 1 SECTION A The figure below represents the characteristics of an incandescent lamp. The data on the operation of filaments A and B on a 240V supply are as given below i)Electricity cost per unit is 0.50 cedis ii)The maximum life span of any filament at any under voltage operation is 200% that of the rated voltage. Rated voltage Rated Power Rated lamp life Rated lamp lumens Cost of lamp Lamp replacement labour cost Lamp A Lamp B 240V 200W 1000hrs 2880 lm 5 cedis 1.50 cedis 200V 100W 1000hrs 1230 lm 6 cedis 1.60 cedis Use the above information to answer questions 1 to 7 2 1. Find the percentage operating voltage of filament A a)80% b) 100% c) 120% d) 140% 2. Find the percentage operating voltage of filament B a)80% b) 100% c) 120% d) 140% c) 35% d) 45% c) 150W d)250W c) 1500lm d)2500lm 3. Find the percentage life span of filament B a)25% b) 50% 4. Find the power output of filament B a)200W b) 300W 5. Find the lumens output of filament B a)2880lm b) 2460lm 6. Find the cost of lamp and labour per 1000hrs used of filament B a) GH¢30.4 b) GH¢32.25 c) GH¢45.50 d) GH¢38.80 7. Find the cost of lamp per 1000hrs per 1000 lumens of filament B a) GH¢17.730 b) GH¢13.325 c) GH¢12.360 d) GH¢14.480 A shop has the following single-phase loads, which are balanced as evenly as possible across the 415 V three-phase supply. 2 x 5 kW and 8 x 3kW thermostatically controlled water heaters 3 x 6 kW and 1 x 4 kW cookers 2 x 4 kW instantaneous water heaters 8 x 30 A ring circuits feeding 13 A sockets 12 kW of discharge lighting (Sum of tube ratings) Use the above information to answer questions 8 -12 below. 8. Calculate the total design current for the thermostatically controlled water heaters (a)137.54A ( b) 165.86A (c) 150.43A (d). 141.78A 9. Calculate the total design current for the instantaneous water heaters. (a) 37.84A ( b) 33.6A (c) 50.34A. (d) 41.87A 10. Calculate the total design current for the cookers. (a) 77.84A ( b) 73.87A (c) 88.97A 3 (d) 62.55A. 11. Calculate the total design current for the ring circuit of 1 3A socket outlets. (a) 130.89A ( b) 133.6A (c) 150.22A. (d) 135.00A 12. Calculate the total design current for the discharge lamps. (a) 90.85A ( b) 83.9A (c) 67.55A. (d) 135.00A A lamp of 100 candle-power is placed at the centre of a room 10 m× 6m× 4 m high. Use the above information to answer questions 13 and 14 below. 13. Calculate the illumination in each corner of the floor a) 0.36 lx b) 0.21 lx c) 1.13 lx d) 3.54 lx 14. Calculate the illumination at a point in the middle of the 6 m wall at a height of 2 m from the floor. a)1.28 lx b)0.76 lx c)1.52 lx d) 9.28 lx 15. Light is produced in electric discharge lamps by a) heating effect of current b) magnetic effect of current c) carbon electrodes. d) ionization in a gas or vapour 16. The output of a tungsten filament lamp depends on a)size of lamp b)size of shell c) temperature of filament d) all of the above. 17. Wavelength of green color is nearly a)4000 Ao b)4500 Ao c) 5000 Ao d)5500 Ao. 18. The purpose of providing a choke in a tube light is a)to eliminate corona effects b)to avoid radio interference c) to improve power factor d)to limit current to appropriate value. 19.The level of illumination on a surface least depends on a)candle power of the source b) distance of the source c)type of reflector used d) ambient temperature. 20.A lamp has a mean spherical candle power of 25, the total flux of light from the lamp is a) 25 lumens b) 25 π lumens c) 314 lumens d) 625 lumens. 21.Radio interference from a fluorescent lamp can be reduced by a)putting two lamps in parallel b) eliminating choke c)putting a capacitor across the lamp d) none of the above. 4 22.A lamp giving out 1200lm in all directions is suspended 8m above the working plane. Calculate the illumination at a point on the working plane 6m away from the foot of the lamp. a)0.764lm/m2 b) 9.6lm/m2 c) 0.489lm/m2 d) none of the above. 23. The direct lighting scheme is most efficient but is liable to cause i. Monotony a)i only ii. Glare b) i and ii only iii. Hard shadows c) ii and iii only d) i, ii, and iii 24. Floodlighting is NOT used for .................. purposes a) Reading b)Aesthetic c)Advertising d) Industrial 25. Desired illumination level on the working plane depends upon a)Age group of observers b)Whether the object is stationary or moving c)Size of the object to be seen and its distance from the observer d)All of the abo 26. On which of the following factors does the depreciation factor depend on ? i)Lamp cleaning schedule ii) Ageing of the lamp iii. Type of work carried out at the premises a)i only b) ii only c)i and ii only d) i, ii, and ii 27. The function of capacitor across the supply to a fluorescent tube is primarily to a) Stabilize the arc b) Reduce the starting current c)Improve the power factor of supply d) Reduce the noise 28. A small light source with intensity uniform in all directions is mounted at a height of 10m above a horizontal surface. Two points A and B both lie on the surface with point A directly beneath the source. How far is B from A if the illumination at B is only 1⁄10 as great as A a)19.1m b)12.3m c) 21.5m d)15.8m 29. A lamp of 100 candela is placed 1 m below a plane mirror which reflects 90% of light falling on it. The lamp is hung 4 m above ground. Find the illumination at a point on the ground 3 m away from the point vertically below the lamp. a)3.20 lux b) 4.99 lux c)1.78 lux d) 2.88 lux 30. A drawing office containing a number of boards and having a total effective area of 70m2 is lit by a number of 40W incandescent lamps giving 11lm/W. An illumination of 80lux is required on the drawing boards. Assuming that 60% of the total light emitted by the lamps is available for illuminating the drawing boards, estimate the number of lamps required. a. 13 b) 21 c) 4 5 d)5 31. Calculate the brightness (or luminance) of snow under an illumination of 44,000 lux. Assume that snow behaves like a perfect diffusor having a reflection factor of 85 per cent a) 16.5 × 103 cd⁄m2 b) 3.5 × 103 cd⁄m2 c)14.0 × 103 cd⁄m2 d) 11.9 × 103 cd⁄m2 32. Two lamps A and B are hung at a height of 9 m from the floor level. The distance between the lamps is one metre. Lamp one is of 500 candela. If the illumination on the floor vertically below this lamp is 20lux, find the candle power of the lamp number two. a)1140 candela b)1650 candela c) 1130 candela d)1620 candela 33. It is required to provide an illumination of 100 lux in a factory hall 30 m by 15 m. Assume that the depreciation factor is 0.8, coefficient of utilisation is 0.4 and efficiency of lamp is 14 lm/W. Calculate the number of lamps if sizes of the lamps available is 250W. a. 26 b) 40 c)6 d) 4 34. A room 8m by 12m is lit by 15 lamps to a fairly uniform illumination of 100lm/m2. Calculate the utilization coefficient of the room given that the output of each lamp is 1600 lumens. a)16% 35. b) 40% c)62.5% d)25% The illumination in a drawing office 30m by 10m is to have a value of 250 lux and is to be provided by a number of 300-W filament lamps. If the coefficient of utilization is 0.4 and the depreciation factor 0.9, determine the number of lamps required. The luminous efficiency of each lamp is 14 lm/W. a)8 36. b)40 c) 50 d) 6 A room 30m x 15m is to be illuminated by 15 lamps to give an average illumination of 40lm/m2. The utilization factor is 0.24 and the depreciation factor is 1.4. Find the M.S.C.P. of each lamp. a)284 cd b)557 cd c) 32 cd d)1114 c SECTION B A floor plan of a block of rooms of a hostel building has been provided at figure 1. The ceiling height is 3.2 meters above the floor. Assume the heights of the working planes in the master bed 6 rooms, living and dining rooms and the common hall are 0.65m, 0.85m and 0.80m respectively. The initial reflectance of the ceiling, wall and floor should be taken as 80%, 50% and 20% respectively. The average light output of a 4ft 40W fluorescent tube is 3300 lumens. The required utilisation factors to be used for calculating the number of lamps in the master bed rooms, living and dining rooms and the common halls should be obtained by means of the zonal cavity method. The assumed maintenance factor for the design is 1.25. The Main Switch that supplies the DBs is situated at the main entrance. The ambient temperature of the rooms may be taken as 45oC. HRC fuses are to be employed for the installation. The DB voltage is 240V, single phase . The dimensions shown on the floor plan are those of the rooms. Use the above information to achieve following: 1) To provide on the floor plan: a) 4ft (1200mm), 40 watts bare fluorescent fittings, showing their circuits and switching arrangements. Twin fittings may be used where appropriate. The “recommended wattage” method may be used for the lighting at all other places. b) The required number of 80 watts ceiling fans in the living and dining rooms, the bed rooms and the common halls. c) 13 amperes flush socket outlets at the appropriate places, showing their circuit arrangements. d) One 20 amperes air conditioner outlet in each of the master bedrooms. Show their circuits. e) One cooker control unit for a 6.5 kW cooker in each kitchen. The cooker control units incorporate 13 amperes socket-outlets. f) Eight 40-W security lights appropriately distributed around the building. g) Required number of additional distribution boards. State the ratings and number of ways of the distribution board (s). h) Legend of the symbols you will use. Standard symbols should be used throughout. i) Simple installation instructions or notes. j) Justify assumptions that may be necessary. Table 1 Standard Fuse Ratings 7 250 AMP 150 AMP 100 AMP 60 AMP 45 AMP For circuits of more than 13kW (13000 W) 30 AMP For socket ring mains, some cooker and shower circuits up to 7kw (7000 W) 20 AMP For storage and water heater circuits 15 AMP For single appliance circuits up to 3kw (3000 W) 13 AMP For appliances between 700 and 3000w (3kW) 5 AMP For lighting circuits. The maximum permissible load of a lighting circuit is 1200W or 12* 100 watt lamps Table 2 Minimum number of socket outlets allowable for various rooms in a building Room Number of outlets Kitchen 3 Living room /Common Hall /Passage 4 Dining room 2 Double/Master bedroom 3 Single bedroom 2 Study bedroom 2 Study 2 Garage 1 Store 1 8 Table 3 Percentage effective ceiling or floor cavity reflectance (𝜌CC,𝜌fc) for various reflectance combinations 𝜌c,𝜌f 80 𝜌w 80 70 50 30 65 50 30 10 50 30 10 0 80 80 80 80 30 30 30 30 10 10 10 0.2 79 78 77 76 30 30 30 30 10 10 10 0.4 78 76 74 72 30 29 27 26 11 10 9 0.6 77 75 71 68 29 28 26 25 11 10 9 0.8 75 73 69 65 29 27 25 23 11 10 8 1.0 74 71 66 61 29 27 24 22 11 9 8 1.2 73 70 64 58 29 26 23 20 12 9 7 1.4 72 68 62 55 28 26 22 19 12 9 7 1.6 71 67 60 53 28 25 21 18 12 9 7 1.8 70 65 58 50 28 25 21 17 12 9 6 2.0 69 64 56 48 28 24 20 16 12 9 6 2.2 68 63 54 45 28 24 19 15 13 9 6 30 10 CCR or FCR Table 4 Ambient temperature correction factors Ambient temperature 250C 300C 350C 400C 450C 500C 550C 600C 650C 700C 750C PVC insulated 1.06 1.00 0.87 0.71 0.61 0.50 0.35 - - 0.94 0.79 9 Table 5. Utilisation factor of a typical luminaire Typical luminaire 𝜌cc 80 𝜌w 50 RCR Coefficients of utilization for 20% effective floor reflectance 𝜌fc = 20 Singe bare fluorescent 0 lamp 1 70 30 10 50 30 10 1.01 1.01 1.01 .96 .96 .96 .85 .81 .77 .81 .77 .73 2 .73 .66 .61 .69 .63 .58 3 .63 .56 .50 .60 .53 .48 4 .56 .47 .41 .53 .46 .40 5 .49 .40 .34 .46 .39 .33 6 .43 .35 .29 .41 .34 .28 7 .39 .31 .25 .37 .29 .24 8 .34 .27 .21 .33 .26 .21 9 .31 .23 .18 .30 .23 .18 10 .28 .21 .16 .27 .20 .16 10 ( RECOMMENDED WATTAGE METHOD) Table 6 Recommended lighting ratings of incandescent lamps for medium sized homes. Location Watts Living room 200 Passages 300 Stairs 60 Dining room 150 Kitchen 200 Bedrooms 150 Bathroom 60 Garage 150 Store 100 The above power values refer to tungsten filament lamps. If fluorescent lamps are to be used, multiply the above power values by factors from 1⁄3 to 1⁄2 . To prevent the risk of under designing, use the upper limit i.e. 1⁄2 of the above powers. Table 7. Illumination requirement of various parts of a building. Location Illumination level in lux Living room / Dining room 150 Common Hall 150 Bed room in general 100 Kitchen 200 11 Bathroom / store room 100 Table 8. Allowance for diversity factor for Guest House, Small Hotels, Boarding, Shops and, Offices Purpose Initial allowance remainder Lighting None 75% of total Motors (not lift) Full load largest motor +50% Standard socket outlets and cooker Full load of largest circuit + 50% circuits Water heaters (Instant type) Full load of largest and +25% second largest heaters Table 9 Grouping factors of cables Number of Circuits 1 2 3 4 5 6 7 Direct on walls 1.0 0.8 0.7 0.65 0.6 0.57 0.54 Closed together 1.0 0.85 0.79 0.75 0.73 0.72 0.72 . 12 Table 10. Current carrying capacities and associated voltage drops for twin and multicore PVC insulated cables non armoured ( copper conductors) Installation method (Clipped direct) Conductor cross One twin cable with or without protective One three core cable with or without protective conductor conductor Single phase three phase a.c or d.c a.c or d.c sectional area Current carrying Volt drop per Current carrying Volt drop capacity ampere per metre capacity metre A mV A mV 1.0 16 42 13 37 1.5 20 28 17 24 2.5 28 17 24 15 4.0 36 11 32 9.3 6.0 46 7.1 40 6.2 10.0 64 4.2 54 3.7 16.0 85 2.7 71 2.3 25.0 108 1.8 90 1.6 35.0 132 1.3 115 1.1 𝑚𝑚2 13 per ampere per 50.0 163 0.92 140 70.0 207 0.65 0.64 176 0.57 95.0 251 0.48 0.46 215 0.42 120.0 290 0.40 0.36 251 0.34 150.0 330 0.32 0.25 287 0.29 185.0 380 0.29 0.23 330 0.24 240.0 450 0.25 0.18 392 0.20 300.0 520 0.23 0.14 450 0.18 400.0 600 0.22 0.11 520 0.17 14 0.81 Table 11. Type of lamp Utilisation factor Maintenance Factor New condition Type illumination e.g. direct 𝜌c = 0.7 𝜌c=0.5 𝜌c=0.3 𝜌w=0.5,0.3 ,0.1 𝜌w=0.50.3 0.1 𝜌w=0.5,0.3 of Room 0.1 index Once every every A year 2 years 3years 1 .27 21 .17 26 21 .17 26 21 .17 Soiling rate normal 2 .46 .40 .36 .45 .40 .36 .44 .39 .36 1.35 4 .61. 56 .53 .60. 56 .53 .60. 55 .53 6 .67 .63 .61 .66 .63 .60 .66 .62 .60 10 .72 .70 .68 .71 .69 .67 .71 .69 .67 1.55 Soiling rate high 1.65 2.15 A typical table from which the utilisation factor and maintenance factor are found is in Table 1 where reflection factors of ceiling and wall are assigned values as 0.7(70%) for white and very light colours,0.5 (50%) for light colours; 0.3 (30%) for medium hues and 0.1 (10%) for dark colours 15 -