Different techniques for energy conservation and cost reduction are described below. II. SELECTION OF CHEAP AVAILABLE SOURCE

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1 2010), 29th November 2nd December, 2010, pp Management and Conservation of Electrical Energy in Industrial Units Rehan Liaqat, Lecturer, Electrical Engg. Deptt. GC University Faisalabad, Abdul Rauf Bhatti, Assistant Professor, Electrical Engg. Deptt. GC University Faisalabad, H.T.Hassan, Associate Professor,Electrical Engg. Deptt. UET Lahore, International Conference on Power Generation and Renewable Energy Technologies, 29th November to 2nd December 2010 at International Islamic University Islamabad, Pakistan Abstract Proper management of electrical energy system is very significant due to energy crisis and high energy costs. It can enhance system efficiency and hence result in significant energy savings and cost benefits. This paper explores different practices which can be adopted for proper management and conservation of electrical energy. Index Terms electrical energy conservation, variable frequency drives, electrical energy management, load management I. INTRODUCTION Electricity is usually generated at areas far away from consumers. This energy reaches the consumers after a lot of stages shown in Figure 1. The cascade efficiency of all these stages including driven load is about 50-60% [1]. It means 1 kwh saved at the utilization side is approximately equivalent to 2 kwh generated by the utility company at the far end. Conservation can be regarded as virtual generation. Moreover market is highly competitive these days. It is very difficult to sustain in the market with high energy costs of production. Similarly alarming amount of green house gases makes us think for ways of energy conservation. Different techniques for energy conservation and cost reduction are described below. II. SELECTION OF CHEAP AVAILABLE SOURCE Whenever a selection decision is to be made among different alternatives, choose the cheapest reliable source. Always consider the life cycle costs of different electrical energy sources while making the decisions. Sometimes people neglect the running cost by just looking at the low initial cost. An alternative with the lowest initial cost might be most expensive one due to its high running cost. Sometimes different sources are available in industry. For example an industry contains three sources of electrical energy. Gas generator is the prime source of energy whereas diesel generator and electric utility company connection are standby sources. Each source can supply 1 MW of electrical power. Standby sources are only used when gas fired generator is not operative. Rates of electricity from these sources are given in TABLE I. Source Unit Rate (Rs./kWh) TABLE I Electricity rates from different sources Gas Fired Generator Utility Company Diesel Generator Maximum demand charges of Rs.335/kW/month are also applicable in utility connection. Moreover there would be minimum charge of Rs.50,000 per month if consumer does not use any electricity from the utility connection. Figure 1. Efficiency of electrical system Assume that maintenance of the gas generator is due. During shutdown of gas fired generator, electricity is to be supplied from one of the sources. If one just considers the unit rate, one would consider utility connection as the second best option. But deep analysis shows that it might not be the true story; because in case of utility connection, maximum demand

2 charges (MDI charges) or fixed charges of Rs.335/kW/month would also be involved besides variable charges of Rs.6.24/kWh. If 1000 kw load is supplied by the utility connection for 1 hour, 1000 kwh would be consumed. There would be fixed charges of Rs.335, 000 and variable charges of Rs.6,240 comprising total charges of Rs. 341,240 as shown in TABLE II. If further electricity is consumed from this connection, only variable charges would be charged. Amount of fixed charges depends upon the maximum demand irrespective of the utilization time from connection. TABLE IV Feasibility analysis of standby sources with respect to time TABLE II Cost of electricity ( C U) from utility connection kwh Load=1000 kw Variable Charges Fixed Charges C U 1 1,000 6, , , ,000 62, , , , , , , , , , , , , , , , , , ,000 In case of diesel generator, no MDI charges are involved. Therefore it might be more feasible than utility connection for a certain period of time. TABLE III shows the comparison between charges of diesel generator (C D ) and utility connection. TABLE III Cost Comparison of diesel generator and utility connection C U - C D Minimum Utility Bill Cost Difference 1 321,240 50, , ,400 50, , ,800 50,000 9, ,040 50,000-3, ,760 50,000-45, ,000 50,000-59,000 III. LOAD MANAGEMENT Consumers using the electric utility connection as a prime source can save money by proper load management. Utility company charges maximum demand charges or fixed charges on the basis of MDI. MDI is the maximum of the demand obtained over a successive period of time; say 30 minutes, during a month. To reduce fix charges in the utility bill manage the load in such a way that load curve is as flat as possible as shown in Figure 2. kwh Load=1000 kw C D C U C U - C D 1 1,000 20, , , , , , , , , ,800 59, , , ,040 46, , , ,760 4, , , ,000-9,000 Table III indicates that diesel generator is more feasible than utility connection up to 24 hours. But one point is still to be addressed. If consumer does not use any electricity from utility connection even then he/she is bound to pay a minimum charge of Rs.50, 000. If this amount is also considered, it can be seen that diesel generator is more feasible than utility supply if duration of gas generator maintenance is about 20 hours. But if duration of shutdown is more than 20.7 hours, use of utility connection is more feasible during the shutdown period. This value of time can be found by the equation formulated below. Figure 2. Load curve For example, an industry consumes 450,000 kwh during a month with 900 kw MDI. The kwh consumed during the whole month indicates that the average load of the industry is 625 kw. And industry is paying 44% more charges due to high MDI. By proper scheduling of machines and production management, industry should try to maintain a uniform load near 625 kw in order to reduce the MDI charges in the utility bill. Cost comparison is given in Table IV by assuming Rs.335/kW/month as MDI charges rate.

3 TABLE V VI. ENERGY EFFICIENT ELECTRIC MOTORS Reduction in MDI charges due to load management kwh MDI MDI Charges Unmanaged 450, ,500 Managed 450, ,375 MDI can also be controlled by applying MDI controllers. These controllers continuously monitor the status of running load. If load increases beyond a desired value preset by the consumer, a buzzer is sound for some time. If the consumer does not take any action, this controller automatically disconnects some loads in a sequenced manner preset set by the consumer and load is reduced [1]. This sequence can also be changed by the consumer according to requirement. In this way one can force the load below a certain value and can cut down the MDI charges. IV. POWER FACTOR IMPROVEMENT Due to inductive loads such as induction motors, power factor becomes low. Due to low power factor, more current is drawn from the system. Therefore line losses are increased, voltage level at the load end is decreased. kva loading on the transformers and generators is increased and hence system capacity is not fully utilized. Efficiency of the generators is also lowered at low power factor. Low power factor penalty charges are charged in the utility bill if power factor falls below a particular value usually 0.9. Automatic power factor relays can be employed for automatic switching of power factor improvement capacitors. Maximum benefit of the power factor improvement is obtained if improved at the load. Local power factor improvement should be done at feeders and large induction motors to get more benefits. V. MAINTAIN VOLTAGE LEVELS Voltage drops and phase imbalance should be avoided in a well managed system. A 10% reduction in motor terminal voltage from the rated can reduce its full load efficiency by 2% [2].Possible steps for maintaining proper voltages are proper settings of transformer taps, elimination of loose connections, proper sizing of cables, power factor improvement etc. Voltage imbalance has two impacts. It reduces motor efficiency and cause de-rating of motor. A voltage imbalance of 5% can increase the motor losses by 5% and reduce its rating by 25% [3]. Loose contact of some phase, unevenly distributed single phase loads, unbalanced three phase loads and faulty power factor equipment are the probable causes of voltage imbalance [2]. For a well maintained electrical system, voltage variations should be less than ±5% and voltage imbalance should be less than 1% [1]. Electric motors are the major consumer of electrical energy. About 70% of the total electrical energy consumption in industrial units is due to electric motors. If life cycle cost of an electric motor is considered, it is revealed that its initial cost is about 1% and the energy cost is near 90%. Remaining costs include down time and maintenance costs. It means saving in initial cost will not save in the long run. One should try to save in energy costs. For that purpose energy efficient motors should be preferred. These motor are more 2-6% more efficient than standard motors due to improved materials and manufacturing techniques [2]. Very old motor and motors rewound many times should be replaced with energy efficient electric motors. VII. PROPER SIZING OF MOTORS Motors operate with maximum efficiency near 75% loading. If loading of a motor (especially for fractional hp) falls below 40%, its efficiency is drastically affected. Therefore proper loading of motors should be ensured. Motor which consistently operate at loads below 40 % of rated capacity, a cost effective measure might be to operate in star mode by reconfiguring the wiring of the three phases of power input at the terminal box. Operating in the star mode leads to a voltage reduction by a factor of ' 3'and motor is electrically downsized. Now full-load operation in star mode gives higher efficiency and power factor than partial load operation in the delta mode [1]. VIII. USE OF VARIABLE FREQUENCY DRIVES Variable frequency drives can be to conserve electrical energy. These are more efficient than conventional methods of control [4]. Major advantages of variable frequency drives are given below. 1. These provide soft start hence avoiding the voltage dips and reducing the maintenance cost by avoiding sudden jerks in mechanical parts. 2. These provide better process control and hence improve product quality 3. These can be utilized for energy conservation especially in case of variable torque loads such as centrifugal pumps, centrifugal fans, centrifugal blowers, centrifugal compressors, propeller and turbine pumps, agitators etc. In variable torque loads, power varies with the speed cubed i.e. by reducing speed half, power requirement will become one eight. Significant energy savings are possible in applications involving variable torque loads by speed control. In flow control applications, significant energy reductions are possible by using variable speed drives.

4 per annum. These losses can be saved by employing VFD control which would change the speed of compressor motor according to air demand. For example boilers are widely used in process industries and power plants for steam generation. Since steam demand is varying, boiler operates different firings. Usually dampers are used to control the flow of combustion air. Variable frequency drive (VFD) is the most efficient method of flow control because in such type of control speed of force draft fan is actually changed by controlling the speed of motor. In case of discharge damper, motor operates at the same speed and thus not giving significant reduction in power consumption. Comparison of damper control and VFD air flow control methods is presented in Figure 3 [4]. TABLE VII Load /unload status of compressor Load State Unload State % of Time 75% 25 % kw Running hours 5,850 1,950 kwh 380,250 37,050 IX. LIGHTING Few suggestions for energy conservation in lighting are given below. Figure3. Comparison of air flow control methods A 30 TPH boiler usually operates at 66% firing. A comparison of damper control and VFD control of combustion air flow is presented In TABLE VI considering 7,800 hours of annual operation and unit cost of Rs.6.24/kWh. About Rs.1,265,472 can be saved per annum by using VFD control instead of damper control. TABLE VI. Comparison for 30 TPH Boilers Damper Control VFD Control kw Annual kwh 365, ,240 Energy Cost 2,277,850 1,012,378 Screw compressors are constant torque loads. Usually start/stop or load/unload techniques are used to maintain the desired pressure of compressed air. Both these methods are inefficient.in case of start/stop; repeated starts will cause the motor to overheat and other compressor components to require more frequent maintenance. Whereas in case of load/unload technique, an unloaded rotary screw compressor consumes about 15 to 35 percent of full-load horsepower while delivering no useful work [5]. Example of a screw compressor presented in TABLE VII indicates that the compressor could waste 37,050 kwh during 7,800 hours of annual operation causing a financial loss of worth Rs.231, Try the use of day light by using fiber glass sheets in ceiling. 2. Use timers to switch the lights on during night time 3. Switch off unnecessary lights 4. Reduce number of fixtures by task lighting 5. Apply distributed control of lights 6. Interlock major lighting with main driven load of machine where lighting load is intensive 7. Improve efficiency of lighting equipment. About watts can be saved per light by using electronic chokes instead of magnetic ballasts. 8. Use occupancy sensors where appropriate X. MEASUREMENTS AND RECORD KEEPING Proper measurement and record keeping can indirectly affect the reliability and efficiency of electrical system. If one cannot measure something, one cannot save that thing. Sometimes people just rely on running currents to compare the efficiency of two machines which is not appropriate. A machine drawing more current might be consuming less power due to its low power factor. So efficiency comparison might be wrong by just looking at the currents. Always consider the kw for correct comparison. So power analyzers should be procured for this purpose. Measurements of voltages, currents, kw, motor body temperature etc. should be taken regularly and these should be recorded. From those records, one can have a better estimate of a motor performance regarding its energy consumption and electricity cost. It would also help in preventive maintenance of machines and other equipment. XI. PROPER MAINTENANCE Preventive maintenance can enhance system reliability and system efficiency. It can also rise profits by reducing system down times. Preventive maintenance should be prepared as per recommendation of the equipment manufacturer and should be followed strictly. As far as maintenance of motor is concerned, some items to be checked during maintenance are

5 lubrication, ventilation, load sizing and alignment, bearing performance, wiring connections and terminal box etc. Suppose bearing of a motor is defective. If it is not changed, motor would burn. Now two costs are involved; rewinding cost and bearing cost. But if bearing were timely replaced, rewinding cost could be saved. Rewinding also reduce the efficiency of electric motor. Rewinding if not done properly can reduce the efficiency by 5 8% [1].Impact of rewinding can be accessed from the previous records of the motor. Using wires of greater cross section, slot size permitting, improved winding design etc. can preserve and in some cases increase the motors efficiency. XII. ENERGY AUDITS Energy studies should be performed in industrial units at periodic interval for assessment of electrical energy consumed by different machines. These studies would be supportive to trace different methods of energy conservation. The major hindrance in such studies is the lack of technical information and unavailability of technical equipment. Trainings should be arranged for industrial personnel and measuring equipment should be procured. XIII. REFERENCES [1] P. Dharmalingam, J. Nagesh Kumar, R.Suryanarayanan, S. Sathis Kumar, Energy efficiency in electrical utilities, 2 nd edition, 2005, BEE India [2] Gilbert A. McCoy, Todd Litman, John G. Douglass, Energy efficient Electric motor selection handbook Washington State Energy Office Olympia Washington, Revision 3 January [3] Gilbert A. McCoy, John G. Douglass Energy management for motor driven systems, Washington State University Cooperative Extension Energy Program Olympia, Washington, Revision 2 March 2000 [4] Wayne C. Turner, Energy management handbook, School of Industrial Engineering and Management, Oklahoma State University & Steve Doty, Colorado Springs Utilities, Colorado Springs, Colorado, 6th edition [5] Lawrence Berkeley, Vienna, VA, Improving compressed air system performance National Laboratory Washington, DC Resource Dynamics Corporation.