CEE Oct-Dec 2002

. . ' SAVING ELECTRICAL ENERGY IN CEMENT PLANTS . . Rajnish Singla, Indo Rama Cement Ltd, Mumbai The author discusses the various energy losses commonly met with in operating electrical machinery and systems in cement plants, and suggests a series of modijicatiom for plugging these and thus conserve energy. The modifications are illustrated with respect to equipment like induction motors and industria/fan-drives used in large numbers, cable systems and even plant lighting, besides power-factor improvement. Minor and entailing little capital investment in most cases, they are essential(v strategic, e. g. planning ami selection of the equipment tailored to the plant's requirements, but capable nonetheless ofconserving substantial quantities of energy...... Ed Introduction As the gap between demand and production of electri cal energy keeps w idening, it becomes imperative to use machinery and equipment sys tem s in process industries w ith max imum efficiency, th ereby conser ving energy. Recent estimates indeed have shown that approximately 40 pe r cen t of the electrical energy produced in the country is wasted as losses, and if only we can avoid these by efticiently using machinery and equipment, we will not need to instal l more power plants in near future. The electrical system in cement plants is a vast distribution network which con. ists of motors. blowers, compressors, fans, panels, cables, bus ducts. transfo rmers and lighting. A ll these have their own lixed and variable losses. Cables, motors and dampers among these account for the major equipment losses because the motors ( inducti on) run almost all these equipment by conveyi ng power through cables. In this paper, an attempt has been made to discuss the energy losses in th ese equipment and the means of saving energy in them. Induction Motors ~lcctr i ca/motors account lor 80 per cent of th e total energy consumed by cement plants. Of these, 90 per cent are induction motors, thanks to thei r sturdiness and mai ntenance-free operati on. They are designed for 85-90 per cent efficiency at full load. In the pl ants these motors are onl y partially loaded, as a result of which their efficiency and power factor (pf) become poor. This is traceable to the fact that for a I 1-kW capacity required, the desi gne r keeps a safety factor of say 20 per cent, w hereby the rating becomes 13.2kW. This being not a standard rating. one chooses the next higher size, namely 15kW. Thus, against a requi rement of onl y ll kw, one installs a 15-kW motor. which leads to partial l oading and hence recurring losses. Even so, energy can be conserved in such si tuations by collecting li eld data and studying the loading pattern. Following are a few useful tips for conserving energy in induction motors. i) ll'hen louding is less than 30 per cent the rated capucil\' - Change the connection of motor from Delta to Star. T hisdecreases current, torque and max imum demand. and improves pf and effi ciency . It is a very effective method to conserve substan tial amo unt of energy without any investment. 8 ii) When loading is 30-6U per cent of the rated capacity - Replace the motor with the ·next lower size (internal reshuffl ing may be thebest option). This improves pf and effi ciency besides reducing line current. This again is an effective method to conser ve substanti al amount of energy w ithout any investment. iii) When loading is more than 70 per cent ofthe rated capacity- This comes under good load i ng of motors. Yet. ifthe motor is replaced w ith a higher-efficiency one, say 96-99 per cent, substantial amount of energy can be saved. Thi s however is a costly proposition as hi gh-effic iency motors are very expensive. T hrough proper planning. high -efficiency motors may be procured whi le orckring spare motors. Thus over a period, all motors can be rep laced w ith high-effi ciency ones. Th is yields good power saving. iv) 0l'er voltage- Over voltage of motors should be avoided. Motors are assoc iated with core losses which are directly proportional to voltage. So over voltage causes higher core losses. h~nce more power consumpt ion . T hus by reducing the voltage we can reduce the core losses . But torque is direct ly proportional to the square of the voltage. So any reduction in - .... \_ ,.t - -