|Year : 2011 | Volume
| Issue : 2 | Page : 113-119
Electrical Energy Auditing and Harmonic Analysis of Industrial Units: A Case Study
Pankaj Oberoi1, SK Aggarwal2
1 Department of Electrical Engineering, Baddi University, Himachal Pradesh, India
2 Department of Electrical Engineering, MM University, Haryana, India
|Date of Web Publication||24-Oct-2011|
Department of Electrical Engineering, Baddi University, Himachal Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
In any industry, the three top operating expenses are often found to be on energy, labor and materials. If one were to find out the potential cost savings in each of the components, energy would invariably emerge at the top, and thus energy management function constitutes a strategic area for cost reduction. This paper discusses the common aspects of electrical energy management in small- and medium-sized industries. It contains the findings and the analysis of the results obtained from the electrical energy audit program employed in an industrial unit, Isolloyds Engineering Technologies Ltd. (Baddi, Himachal Pradesh). The electrical energy audit was carried out under four major heads: (i) lighting audit, (ii) Heating Ventilation Air Conditioning (HVAC) audit, (iii) power load audit (motors, melter, etc.), and (iv) harmonic analysis. Readings were taken under these heads and analyzed to find the scope of energy conservation opportunities in the selected test case industrial unit.
Keywords: Energy audit, energy conservation opportunities, harmonic analysis, industrial unit
|How to cite this article:|
Oberoi P, Aggarwal S K. Electrical Energy Auditing and Harmonic Analysis of Industrial Units: A Case Study. J Eng Technol 2011;1:113-9
|How to cite this URL:|
Oberoi P, Aggarwal S K. Electrical Energy Auditing and Harmonic Analysis of Industrial Units: A Case Study. J Eng Technol [serial online] 2011 [cited 2019 Nov 20];1:113-9. Available from: http://www.onlinejet.net/text.asp?2011/1/2/113/86645
| 1. Introduction|| |
Electrical energy is the most expensive and the most important form of purchased energy. For this reason, its use must be confined to a minimum for efficient and economic operation  . Because of its flexibility, electricity offers advantages over the conventional fossil fuels, and efforts to conserve electricity can result in significant cost savings  . Industries use a large amount of electrical energy, and that is why it is important to ensure a loss-free and energy-efficient system in industries  . In developing countries like India, where electrical energy resources are scarce and production of electricity is very costly, energy conservation studies are of great importance. Energy audit is the translation of conservation ideas into realities by blending technically feasible solutions with economic and other organizational considerations within a specified time frame  . An energy audit is a study of a plant or facility to determine how and where energy is used and to identify methods for energy savings. Energy audits can mean different things to different individuals. The scope of an energy audit, the complexity of calculations, and the level of economic evaluation are all issues that may be handled differently by each individual auditor and should be defined prior to the beginning of any audit activities , . If we can reduce the energy usage or improve the energy efficiency in air conditioning and other mechanical and electrical installations in a building, energy can be conserved and some of the resulting environmental problems, such as green house effect and ozone depletion, can be alleviated. The energy audit of a medium-sized industrial unit has been explored in this work. Energy conservation can be obtained by proper maintenance and operation. These activities include shutting off unused equipment, improving electricity demand management, reducing winter temperature settings, turning off the light, etc.  . An Energy Management System can be developed with the basic idea to store the cheaper electrical energy at night in an energy buffer and to use this stored energy during the day  .
| 2. Auditing Procedure|| |
Energy audit cannot be successfully carried out without the commitment from the top management. Management must be firstly convinced of the necessity of implementing energy management and hence energy audit  . Energy audit consists of several tasks, which can be carried out depending on the type of the audit and the size and the function of the audited facility  . Therefore, an energy audit is not a linear process and is rather iterative. The audit described in this paper has been carried out based on the following functional activities:
- Walk-through survey
- Motor load survey used in various processes
- Harmonics analysis
| 3. Field Visits and Measurement Work|| |
Isolloyds Engg. Tech. Ltd. is one of the oldest Indian companies in the field of fibrous high-temperature insulation, with widest marketing and contracting base in India and the Middle East. An exhaustive electrical energy audit was carried out and various data were collected related to the audit work, for further analysis.
3.1 Plant Electrical Energy Consumption
The energy consumption of the factory was identified in terms of the equipments and functional area wise. The results were obtained after measurements during the factory visits. Data loggers, power analyzers, clamp meters, etc. were used to measure the electrical energy consumption of the factory. The total load of the unit is approximately 816.5 kW [Table 1] and [Figure 1].
The following points can be observed from this survey:
- The major load in the plant is that of melter, which constitutes approximately 50% of the total load.
- Motor load constitutes approximately 38% of the total load.
- Total number of units consumed per month after taking average of 12 months is 3.5-4.0 lakhs.
3.2 Lighting Survey
A walk-through audit was conducted during visits to assess the illumination requirement of the plant and scope of improvement of illumination quality and illumination level, with an objective of cutting down the electrical energy consumption and cost of electricity. After the survey, it was observed that mercury vapor (MV) lamps were being used for plant lighting in the work area as well as for street lighting.
It had been observed that one MV lamp is used every 100 m 2 in the workshop area. Efficiency of an MV lamp is approximately equal to 45 lm/W. For a 250 W lamp, the total lumen output is 11,250 lm, which means 11,250 lm/100 m 2 area. Whereas the lumens required per m 2 are 120 lumens/m 2 , total lumens required per 100 m 2 are 12,000 lm approximately. In [Table 2], illumination assessment of the lighting survey has been provided.
The illumination requirement could be fulfilled by some other energy-efficient options as well. The light emitting diode (LED) panel is one such option, which is more energy efficient and has longer lifespan [Table 3]. The benefits of using LEDs vary depending on the application, but typical technology features include:
- Up to 90% energy cost savings
- A long life of more than 100,000 hours
- Minimized maintenance hassles and costs
- Excellent cold weather performance
The total number of LED panels needed to get the required lumen output is 57 and wattage of each panel will be 65 W [Table 4] and [Table 5]  .
|Table 5: Calculation of electrical energy cost and savings for LED panel|
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3.3 Payback Period
The calculations for payback period have been given in [Table 6].
3.4 Motor Survey
For most of the applications, three-phase, 4-pole, 1470- rpm induction motors of Kirloskar make have been used for various production processes in the plant. During survey and measurement process, it was observed that some of the motors are underloaded. Two blower motors being used (60 hp) with melter have been running at half of their rated load. One needling machine (25 hp) has been running at 60% of the rated capacity and one conveyor motor (20 hp) has been running at half of its rated capacity [Table 7].
3.5 Problems with Underloaded Motor
- An underloaded motor always runs at a low lagging power factor. If the motor is loaded around 50% of the rated load, power factor can be as low as 0.5 lagging. This means industry is utilizing only 50% of the power from the supply mains and paying for 100% if the billing is kVA based.
- Extra expenditure on installation of power factor improvement equipment to maintain the power factor within permissible limits set by the state electricity board needs to be done. Otherwise, penalty has to be paid.
- Efficiency of a standard induction motor is about 87-90% at the rated load and it reduces drastically at half of the rated load depending upon the size of the motor and loading (about 70-75% for 60 hp motor). This means motor will draw more current for the same mechanical output [Figure 2] and [Table 8].
| 4. Energy-Efficient Motors|| |
More and more industries are switching to energy-efficient motors (EEMs) because EEMs lower the production costs. Just a small increase in motor efficiency can significantly lower the production costs. A motor can cost thousands of rupees a year to operate, so savings of even a few percent add up quickly. An EEM generates savings whenever it is running and as long as it lasts, which may be 20 years or more.
EEMs cost more than the standard motors, but purchase price pales in comparison to a motor's operating costs. Since the annual operating cost of a motor is often 5-10 times its initial cost, the typical 3-5% higher efficiency of an EEM can more than offset its 15-20% higher initial cost over its life. In addition to costing less to operate, EEMs generally last longer, require less maintenance, and reduce system amperage draw. The efficiency curves of two EEMs are shown in [Figure 3] and [Figure 4].
|Figure 3: Efficiency of EEMs as per IS-12615 (Eff1 = 2-pole motor, Eff2 = 4-pole motor)|
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EEMs also offer other advantages, such as longer insulation life, longer lubrication interval, greater inertial acceleration, and higher service factors. In addition, they may be better equipped to handle heavy starting loads, large sustained loads, phase imbalances, voltage excursions, high ambient temperatures, and impaired ventilation. EEMs also do not add as much to air-conditioning loads as standard motors, since they do not give off as much heat.
4.1 Energy-efficient Motor's Performance
The efficiency of a motor is the ratio of the mechanical power output to the electrical power input. Design changes, better materials, and manufacturing improvements reduce motor losses, making premium or EEMs more efficient than the standard motors [Figure 5]. Reduced losses mean that an EEM produces a given amount of work with less energy input than a standard motor. In 1989, the National Electrical Manufacturers Association (NEMA) developed a standard definition for EEMs  . The definition was designed to help users identify and compare electric motor efficiencies on an equal basis.
|Figure 5: Losses comparison among standard and high efficiency motors |
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4.2 Factors Responsible for Improving Efficiency
- Increase the amount of active material
- Use of double-layer windings
- Utilize high-performance lamination materials
- Optimize the air gap dimensions
- Improve the efficiency of fan assembly
- Increase the rate of heat transfer between active parts and frame
- Use high-efficiency bearings
- Optimize fabrication process
4.3 Payback Period ,
For the same rating, conventional motor (60 hp) consumes approximately 9 kW more on 75% load [Table 9].
|Table 9: Comparison between EEM and standard motor (60 hp) on the basis of number of kW h consumption per year|
Click here to view
| 5. Harmonic Analysis|| |
With the increased usage of non-linear electrical loads and automation in industrial units, poor power quality due to harmonic distortion has come up as a serious issue. To tackle the problem of increasing harmonic distortion in power distribution system, Himachal Pradesh State Electricity Board (HPSEB) has recently issued guidelines to various medium- and large-scale industrial units of the state to get voltage and current harmonic contents evaluated at their premises at the Point of Common Coupling (PCC) and undertake remedial filtering solutions, if required, for harmonic limits in excess of the limits stipulated by IEEE-519-1992 Standard.
The goal of harmonic studies is to quantify the distortion in voltage and current waveforms in the power system of industrial units. The results are useful for evaluating corrective measures and troubleshooting harmonic related problems.
5.1 Effects of Harmonics on Networks ,
- Overloading of neutral conductor
- Reduced efficiency of motors
- Malfunctioning of control equipment
- Poor power factor of the total system due to introduction of distortion power factor
- Overloading of power factor capacitors
- Increase in kVA demand of the plant due to increase in rms current drawn
5.2 Harmonic Measurements at the Case Unit
The harmonic spectrum of LT currents in three-phase distribution system of the plant recorded with the help of Power and Harmonic Analyzer is indicated in [Figure 6], [Figure 7] and [Figure 8] and [Table 10].
5.3 Verification of IEEE Limit Compliance
From the data provided by the Electrical Section of the Plant, per unit impedance of the transformer is 0.0514. The inductance of the transmission line (XL ) is 0.477 Ω Km. The maximum demand current (IL ) is 1100 A. The CT ratio is 1600/5. The short-circuit current (Isc ) calculated at PCC is 14955.8 A and short-circuit ratio is 13.6 [Table 11].
The industrial consumer under study falls in the category of short-circuit ratio lying in the range <20, for which the maximum allowable THD value is 4% (up to 11 th harmonics). It is clear that the measured THD value at the PCC of Isolloyds Engg. Tech. Ltd. is large as compared to its allowable limit of 4%. Further, total demand distortion (TDD) is within limits for Y phase only. Therefore, the consumer must install a harmonic filter to improve the power quality and save the penalty on harmonic emission.
| 6. Conclusion|| |
On the basis of electrical energy audit conducted, the following recommendations have been suggested to the consumer:
- MV lamps should be replaced by LED panels in a phased manner.
- Further, electric energy cost could also be saved in the office area where air conditioners are used, by using false ceiling and double door system.
- Proper size of motor should be used, as per the rated load. If possible, motor should be replaced with a proper size motor in a phased manner.
- In due course of time, if any motor gets damaged or some new motor is to be purchased, EEMs should be purchased.
- Harmonic components at PCC are greater than the permissible limits. Therefore, the consumer must install harmonic filter to improve the power quality and save the penalty on harmonic emission.
- Harmonic component across individual loads is much higher where variable frequency drives are used, which reflects at the PCC, so a more in-depth analysis is required and a harmonic filter can be designed.
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| Authors|| |
Pankaj Oberoi has completed his B.Tech in Electrical Engineering with first division from MMEC, Mullana in year 2004 and completed M.Tech from M.M. University, Mullana in year 2009. He has been working as faculty member in EED at IEET, Baddi University for the last six years. He has worked in the field of Electrical Energy Management especially in industrial sector. His other interest areas are Power Electronics and Electrical Drives.
S. K. Aggarwal obtained his B.E. from M.D. University and M.Tech and PhD from National Institute of Technology, Kurukshetra, Haryana, with honors. He has five years of work experience in power plant operation and maintenance and erection and commissioning with National Thermal Power Corporation. Presently, he is working as a Professor in EED at MMEC, Mullana. His research interests are load and price forecasting, AC-DC load flow analysis, neural networks and signal processing, renewable energy sources.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11]