CEE Oct-Dec 2002

Cahlc Selection reduced. .An one-t ime measure, this Selection of cable size plays a is a permanent solution and a very criti cal rol e in controlli ng plant good power saving option. distribution losses. Improper cable size may lead to more line losses, Power Factor higher voltage drop, heating and clnmagc to cable which leads to production losses. Hence proper care should be taken in selecting the size of cab le. Cable is generally se lected on the basis of: (a) Voltage rnting. nnd (b) Current rating. n) l'ollage rating - Selection of cable i nsu lation is made on the basis or phase-to-phase voltage of the system in which the cable is applied and the genera l system category, i.e. whether the system is grounded or ungrounded. and the time in which a ground fault on the system i s c leared by protective equipment. b) Current ruling - Diameter of the conducto r is selec ted on th e following b<:~ses : (a) Continuous current carrying capacity , (b) Fault leve l criteria , (c) Voltage -drop limitati on criteria ( starting, and norma l ). and (d) l~ m e r gc n cy loading criteri a. The cable should be properly clermecl \\ ith due regnrd to ambi~nt ll.:mperaturc. maximum ri ~e in tcmpe ratur c. l oc atin11 underground or in air. number or cables in parallel. If the length is greater, then higher siLe of cnble may be se lected to ;woid voltage drop. If the current i ~ high, sny more than I 00 A or even hi gher. then rwo or more number of cables may be laid in parallel to avoid li ne losses and voltage drop. Fault-level criter ia must be taken care of. fail ing which during fault. short– circu it current w ill permanently damage cable in ~ ulation. To sum up. w i th prope r select ion of cable SiLe. piGnt Powe r facto r is key to the efficient use of electri cal energy by any plant. Industrial plants try to maintain a power factor of as high as 0 .99 or unity, since good power factor resul t s in: (a) Lowe r purchased-power costs if the uti lity enforces a power- factor clause, (b) Re l ease of system electri ca l capacity, (C) Voltage improvement, and (d) Lower system losses. What is power .fclctor and why is it poor? Power factor is the cosineof the angle between Jctive power and apparent power. Every equipment requires a magnetizing current known as nonworking curren t or reactive current to produce the flux necessary for the operation of electromagneti c devices. Without thi s magnet izing current. energy cdn not !low through the con.: of a transformer or across the gap or an induction motor. Power l~1c tor is genera lly poor in industry clue to partial lo<llling or motors. thy ri stor dri ves, electrical furnaces. lamps as the pe rcentage or the reactive current is hi gher rha:1 th e act ive cu tTCilt. Power fac tor can he improved by reducing the reacti ve po" cr component. which is usually done by installing capacito r ~ . Economi cs must be con sidered '' hile determining the capacitor locn tion. Fi gure I i llu strate s alternative schemes of install ation or capacitor vis-a-v is power source and motor. and the respect i ve reac ti ve current drawn . It i :. common pra ctice to connect capacitors just ahead or individual Figure so that cab les can al so be relieved or line losses. Capacitors should also be install ed in parallel to all motors ofca:)acity 55 kW and above. Capacitors of proper rating should be selected to maintain the desired power factor. Capacitor rating requi!·ed to improve the power factor can be calcu lated as below kYAr: kW X ( tan 0 1 -tan 8 2 where 8 1 is the actual powe r factor angle and 0 2 is the des i red or improved power factor angle Hence by main tain i ng good power factor. one can achieve a whole range of benefits. such as reduction of power system los~cs, voltage improvement, reduction of maximum demand, r el ease o f system capacity and earning pow(>r– factor in centi ves from stale electricity boards. etc. Liohtino "" !") Lighting load in cement plants va ries from 0.6 to I h. Whit o f cement. It can be reduced in many way s lik e sw it chin g. l ight<; otT durin g da) time . iso l ati ng the circuits or less visited areas and by using. energy erfic ielll lamps. Most or the lighting in cement plant s consists of gas discharge type, e.g. hi gh-power mercury vap0ur and sodium vapour. ll uorescent bmps. etc. Though these lamps require hi gh vo ltage for ' tart or the di scharge. once started . the) can maintain the discharge ~ven at IO\\ vo ltage. ' o much so. by operating such gas discharge lamps at less vo ltage. we can save sub..;tantial amount of energy. These lamps can be operated at :215 V wi thou t an: v isi ble fall in illuminat ion level. b) cli ;:;tribu tion losses can grentl y be mnturor equ ipmelll as shown in the install i ng energy co nserva ti o n 10 - t -