The Design of Lighting Systems, Electrical Energy Management and Tariffs - Essay Example

Abhudhay Dev www.academia-research.com Order 155031 28 February, 2007 Investigate the design of Lighting Systems, ElectricalEnergy Management and Tariffs Abstract While designing an electrical circuitry for any house, building, hospitals, factory it is kept in mind that cost should be less and purpose should be fulfilled. This is the job of an electrical engineer to balance the cost and resources available. The lighting system of any building or factory should be designed in such a way that operating cost be as low as possible. Thus such resources should be used which consumes less energy. Distribution should be in a way that the generated energy should be supplied to maximum number of consumers. This is done when the consumption is less and proper and no wastage of energy is there. The lamps and other devices should be of proper rating and proper standard. The design should be such that required illumination is obtained in a least possible cost. Investigation of Lighting System 1) Construction, operation of some lamps:- a) Fluorescent Lamp :- The basic construction of this type of lamp is that it has a discharge tube made up of glass. There are two electrodes at both the ends. This tube contains gases at certain pressure which on ionization emits light. The fluorescent powder is coated at both inside and outside the tube. The electrodes at both the ends are coated with some electron emitting material. A choke coil is connected in series with the lamp to stabilize current. One capacitor is also connected to compensate the power factor. This lamp emits white colour and widely used in homes, offices and shops. b) Electric Discharge Lamp :- These were the first type of lamps that were used. In these type of lamps there is a discharge tube in which two electrodes are connected to both ends and excited by electric source. The gas inside the tube gets ionized and emits light. There are various types of electric discharge lamps namely sodium vapour lamp and mercury vapour lamp. c) Filament Lamp :- In this lamp a fine filament is connected to the electrodes and excited which emits light. The construction of these kinds of lamps is very simple. Earlier fine carbon was used as element in these lamps later on tungsten was preferred in place of carbon. Principle of good lighting While designing lighting system following considerations should be done. 1) Proper illumination level :- This is the major factor because for proper vision the brightness of the object should be proper which depends on illumination level. Degree of illumination depends upon some factors like size of the object, distance from the observer, object background contrast. There are some standards made by ISI for illumination level in various parts of he building. For street lighting also some standards are made. Table below shows some average value of illumination level. Places Illumination level Heavy Traffic routes 30 Average traffic routes 15 Secondary roads with local traffic 8 Secondary roads with light traffic 4 2) Uniform Illusion :- The vision of eye depends on the brightness of the object. If the uniformity of light is there the eye has to adjust more. This will cause fatigue. The method to achieve uniform illumination Generalized light should also be employed with local light. 3) Colour of light :- The brightness of any object basically depends on colour of light falling on it. The composition of light should be such that appearance is natural. Thus the use of fluorescent light is increased for indoor purpose. For outdoor applications sodium vapour lamps are preferred. 4) Shadow and Glare :- Shadow at work place also causes fatigue. Thus hard shadows are avoided. This does not means that where should be no shadows. Shadows provide shape to the objects thus light shadows should be present but hard and long shadows should be avoided. Glare is the reflection of light from various objects. Glare can be direct or indirect. Indirect glare is from desk top, parts of object, calendars, mirror and other objects. Direct glare is from the source of light. The solution to this is to mount the source of light to a certain height to a considerable level. 5) Space between sources :- For proper illumination it is necessary to have sufficient distance between the sources of light. To overcome the dark areas the light sources should be placed such that no shadows are formed. The spacing between sources depends upon the light source and height of the roof from ground. The ratio of distance between the horizontal and vertical layer should also be proper. 6) Mounting of light :- The height of the light source should not be very high. This reduces the amount of light falling on the work plane. Also while mounting the light source the illumination level of light source should be considered. Tariff Structure Cost is the major factor that is to be considered in the distribution of electricity. The engineer has to make choice between the equipments of high cost with high efficiency and low cost with low efficiency. In the former case the initial cost is high but operating cost is low and in the later case initial cost may be low but running cost is high. The economic consideration is done in three categories. Fixed cost, semi fixed cost and operating cost. Fixed cost :- The initial cost of machines, electrical accessories, fitting cost all the other cost which are at the time of setting up an electrical system is considered in fixed cost. These do not vary with any other factor. Semi fixed cost :- The depreciation cost of machine, interest on machine, salary of maintenance staff and other employers all comes in the semi fixed cost. Operating cost :- The running cost of machine and other devices is considered in this point. The tariff is fixed by the government for a single unit thus bills are made according to the consumption of energy by consumer. The fixed and semi fixed costs cannot be reduced. So to reduce the energy cost operating cost should be reduced. For this purpose the machines and other electrical equipments should be of high efficiency and proper rating. Factors affecting the consumption 1) The consumption is affected by the seasonal variation like in summer season consumption is more than in winter season. 2) Low power factor equipments is use by the consumers. 3) Consumption of energy at off peak periods. 4) Inefficient devices and machines. 5) Use of local and false rated machines by consumers. Various Types of Tariffs 1) Flat demand rate 2) Straight meter rate 3) Step rate tariff or step meter rate 4) Block rate tariff or Block meter rate 5) Two part tariff 6) Power tariff factor 7) Three part tariff or Doherty rate Types of Domestic tariff 1) Monthly tariff 2) Tariff on single connection 3) Tariff on two phase connection Types of Industrial Tariff 1) Small scale industry tariffs 2) Medium industrial tariffs 3) Large industry tariffs Incandescent lamp This is a very simple kind of lamp that consist of a fine filament inside a glass globe. The glass globe is evacuated to prevent from temperature rise. Any general filament cannot be used in this lamp there are certain properties for the filament material. It should have high melting point, low vapuor pressure, high resistivity, low temperature coefficient and sufficient mechanical strength. The materials that are used for this kind of filament is carbon, osmium, tantalum and tungsten. Material Melting point Efficiency 1) Carbon 3500 c 3.5 lumens/watt 2) Osmium 2600 c 5 lumens/watt 3) Tantalum 2800 c 5 lumens/watt 4) Tungsten 3400 c 10 lumens/watt Advantage of Incandescent lamp :- 1) Operates at unity power factor 2) Independent of other supporting devices. 3) Available in various ratings, shape. 4) Good illumination level. Discharge Lamp :- This lamp has two advantages over incandescent lamp that it has high efficiency and white light. The basic principle of discharge lamp is very simple. It has a glass tube in which gas is filled. This gas is ionized and emits light. The two ends have electrodes. Argon, sodium and mercury gases are used in discharge lamp. It consumes high current. The choke coil is used in series with the lamp so that high current is compensated. Major application of this kind of lamp is in homes, streets, factory area, parking areas. The larger loads are connected in series in three phase supply with choke coil to reduce high current. Thus large lighting loads are balanced and required illumination. These loads do not require rotating magnetic field thus can be easily connected and make proper use of power level. Flickering is also reduced in three phase connected loads. Various Lighting effects 1) Glare :- When light enters directly from the source to the eyes, it produces glare. The eyes adjust itself according to the light source. This results in improper illumination of object. Methods to reduce glare :- a) Lamp should be mounted at certain height more than normal. b) Use of reflectors. When the height is less use of pearl glasses reduces glare. The polished surfaces should be avoided. When light enters from source to eyes it produces direct glare and when light enters through reflection of light from any surface it produces indirect glare. Stroboscopic Effect This effect is related to the illumination of moving parts. When light falls on any moving part or moving object it appears to be moving slower or in opposite direction than actual. This effect can be removed by using three lamps each of which is connected to three phases or by two lamps connected 90 degree out of phase of each other. This also improves the power factor. D.C. operation of fluorescent lamp does not produce stroboscopic effect and also ignore the problem of power factor. Utilization Factor Utilization factor is the ratio of total lumens reaching the working plane to the amount of total lumens produced. As whole light from the source does not reaches the working plane this factor evaluates the total light used. The value of utilization factor depends upon the height of lamp and area of working plane. The utilization factor is indirectly proportional to height of mounting and directly proportional to area of working plane. It also depends upon colour of light and type of lamp used. Maintenance Factor The regular use of lamps causes depreciation in the light output of lamp. The major cause of this is irregular cleaning of lamps especially in factories. Technically this is called soiling of lamp. Mathematically maintenance factor is the ratio of illumination level of old installed lamp to the illumination level of newly installed lamp. Improvement of Power Factor of Lagging Lighting Load There are various methods to improve power factor. 1) By phase advancers 2) By phase compensated motors 3) By static capacitor 4) By phase compensator Design and Planning aspect of emergency lighting system During the time of emergency the exit lamp should be viewed. The backup of emergency light during power failure should be instantaneous. The required illumination level should not be less than 6.5 lux. Generally high intensity lamps are used in emergency lighting system. D.C. supply is used for emergency lighting system. Customer prefers for quick backup of power and low concumption of energy. Diversity Factor The ratio of sum of all individual power consumption to the maximum demand of the power system is known as diversity factor. Increase in diversity factor increases the tariff. Load Factor The ratio of average load during fixed period of time to the load during peak time is known as load factor. Power Factor The ratio of real power to the apparent power is known as power factor. For proper working and high efficiency power factor of the system should be unity. Decrease in the power factor increases the tariff. 1) An open area of 30m *25m dimensions and 4m height, requires an average emergency luminance of 10 lux at floor level using single fluorescent luminaries. Calculate the total number of luminaries required if the photometric data for the used luminaries are: Maintenance factor =0.75 Emergency lighting design lumens LDL =400lm Factor to allow for battery discharge BF =0.8 Room index R I =2.0 Ceiling C =0.5 Walls W =0.5 Floor F =0.2 Solution :- Area to be illuminated = 30*25 = 750 m^2 Illumination required = 10 lux Total illumination required = 750*10 = 7500 lumens Utilization factor = 0.8 Depreciation factor = 0.75 Gross lumens required = A*E/ UF*DF =12500 According to the space height ratio the vertical luminaries required are 7 and horizontal luminaries required are 6. 2) A load of 200 kw at 0.8 pf lagging, describe with the aid of circuit diagram, how to improve the power factor to 0.95, and determine the added component and its value in terms of reactive power. Solution :- Load = 200 kw Power factor before improving = 0.8 Power Factor after improvement = 0.95 KVA rating of required capacitor bank = 200*(tan @1 -tan @2) =84 The power factor is improved by connecting a condenser bank of 84 KVA. 3)If the charge of maximum demand of a commercial consumer is 10 / kw or 10 / kVA per annum whose: 1. Total plant load is 30000 kw and only a maximum load of 4000 kw is used at any given time. Determine his maximum demand charges. 2. Maximum demand is 1200 kw and uses 12000 units a day, what will be his annual savings if the load factor is improved to 0.85 and what will be the annual savings 3. Maximum demand of 4000kVA operating at 0.75 power factor lagging, what will be his annual savings if pf correction is installed improving his power factor to 0.95 lagging Solution :- 1) Maximum demand charges = 10 / kw or 10 / kVA per annum =30000/4000 =7.5 Maximum demand charges are = 7.5*10 =75 per annum 2) Annual cost =1200*10*365*24 =105120000 Annual cost after power factor improvement =12000*365*24*10*0.85 = 893520000 Annual saving is = 893520000-105120000 = 578160000 3)Maximum demand = 400 KVA At 0.75 pf = 4000*0.75 = 3000 kw At 0.95 pf = 4000*0.95 = 3800 kw Total savings = (3800-3000)*10 = 8000 References :- 1) "Art and science of Utilization of Electrical Energy" by H. Partab, second edition, published by pritam Surat And Brothers. 2) "Utilization of Electrical energy" by J. B. Gupta. 3) "Utilization of Electrical Energy" by E. Openshaw Taylor, fifth edition, published by Orient Longman. 4) http://en.wikipedia.org/wiki/Glare_(material) 5) http://www.atis.org/tg2k/_diversity_factor.html Read More