Here is a compilation of essays on ‘Energy-Efficient Motors’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Energy-Efficient Motors’ especially written for school and college students.
Essay on Energy-Efficient Motors
Essay Contents:
- Essay on the Introduction to Energy-Efficient Motors
- Essay on the Benefits of Energy-Efficient Motors
- Essay on the Purchase of Energy-Efficient Motors
- Essay on Motor Losses and Loss Reduction Techniques
- Essay on the Determining and Comparing Motor Efficiencies
- Essay on the Motor Efficiency Testing Standards
- Essay on Determining Annual Energy Savings
- Essay on Assessing Economic Feasibility
- Essay on the BIS Specifications for Energy Efficient Motors
- Essay on Efficiency as Function of Load
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1.
Essay on the Introduction to Energy-Efficient Motors:
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The electric motor has a long history of development since its invention in 1887, with most early effort aimed at improving power and torque and reducing cost. The need for higher efficiency became apparent during the late 1970’s.
Now the trend is towards marketing all motors with improved efficiency at little or no premium. However, because improved efficiency requires more careful manufacture, only the higher quality manufacturers are supplying high-efficiency units.
Most motors operate at less than their design loading. Safety margin, selection of preferred sizes and starting torque requirements mean that most motors are operating at between 60% and 80% of full load and many will run at very low load for a substantial part of their working life. It is important that high-efficiency motors retain their energy efficiency at these typical load factors and the leading manufacturers typically optimize efficiency at about 75% full load.
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An electric motor can consume electricity to the equivalent of its capital cost within the first 500 hours of operation – a mere three weeks of continuous use or three months of single shift working. Every year, the running cost of the motor will be from four to sixteen times its capital cost.
Over its working life, an average of thirteen years, it may consume over 200 times its capital cost in energy. Clearly, the lowest overall cost will not be achieved unless both capital and running costs are considered together.
Growing cost of energy calls for power saving at each possible step of manufacturing. Electric motor driven systems used in industrial processes consume more than 70 percent of electricity used in industry, hence best possible technology is being applied for achieving highest possible efficiency values.
The efficiency of an electric motor is determined by the amount of useful power it produces compared to the amount of energy required to operate it. Motor efficiency is commonly expressed as a percentage.
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Higher efficiencies are achieved by following special features:
i. Low loss special grade of thinner laminations. This reduces the Iron loss even at partial loads.
ii. Thicker conductors and more copper contents reduce copper loss due to lower resistance.
iii. Longer core length, reduced and uniform air gap between stator and rotor to reduce stray losses.
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iv. Special design of fan and fan cover to reduce wind age Losses.
2. Essay on the Benefits of Energy-Efficient Motors:
The efficiency curve of energy efficient motors is almost flat resulting in higher energy savings as in most of the cases the motor is not always fully loaded.
The special design features also result in lower operating temperatures, which enhance the life of motor and reduce the maintenance costs.
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These motors have inherently low noise and vibration and help in conservation of environment.
The energy efficient motors have high power factor. The higher power factor reduces the currents in the cables supplying power to motor and this reduces cable loss, improving the system efficiency sometimes by even 2%. Sometimes this allows even a lower cable size saving tremendously on capital costs. Reducing capacitors required improving power factor also makes saving.
The benefits of using these motors are maximum in continuous duty applications like Blowers, Compressors, Fans, and Exhausters Pumps, etc.
In many applications the load factor of the motor will range between 60 to 80%. The efficiency curve of standard motor is drooping in nature, i.e., there is a sharp fall in efficiency at partial loads. But the energy efficient motors have a flat efficiency curve and hence the fall in efficiency is marginal. Thus energy saving is significant even in part loads.
The efficiency curves of standard motor and an efficient motor can be represented as: 
Additional Benefits of Energy-Efficient Motors:
Energy-efficient motors are longer than standard-efficiency motors as the rotor and stator cores are lengthened to reduce losses associated with the magnetic flux density. However, they are mounted in the same frame as corresponding standard-efficiency T-frame motors. They fully conform with NEMA inrush current, starting and breakdown torque standards. Conventional NEMA controls and protection can be applied.
Energy-efficient motors typically operate cooler than their standard efficiency counterpart? Lower operating temperatures translate into increased motor, insulation and bearing life. The result is fewer winding failures, increased bearing life, longer periods between scheduled maintenance actions and fewer forced outages.
Accelerated life testing, by subjecting the motor to repeated stalls and other abuse, indicates that energy-efficient motors should have a longer life expectancy than standard-efficiency designs. Besides this increased capacity to withstand stalling and overloads, energy-efficient motors should run quieter and operate with lower no-load losses.
Besides reducing operating costs and extending winding and bearing service lives, additional benefits typically associated with using energy-efficient motors include:
i. An extended warranty
ii. Extended lubrication cycles due to cooler operation
iii. Better tolerance to thermal stresses resulting from stalls or frequent starting
iv. The ability to operate in higher ambient temperatures
v. Increased ability to handle overload conditions due to cooler operation and a 1.15 service factor
vi. Fewer failures under conditions of impaired ventilation
vii. More resistance to abnormal operating conditions, such as under and over voltage or phase unbalance
viii. More tolerance to poorer voltage and current wave shapes
ix. A slightly higher power factor in the 100 hp and lower size range, which reduces distribution system losses and utility power factor penalty changes.
These benefits however, depend on many factors. Based on manufacturer design practices, energy-efficient motors may have higher or lower power factors than their standard-efficiency counterparts. Both energy-efficient and standard motors should be derated the same amount under conditions of voltage unbalance.
Generally, the perception exists that standard and energy-efficient motors operate at different temperatures and there is more temperature margin available in the energy-efficient motor before reaching NEMA operating temperature limits.
3. Essay on the Purchase of Energy-Efficient Motors:
Using readily available information such as motor nameplate capacity, operating hours and electricity price you can quickly determine the simple payback that would result from selecting and operating an energy-efficient motor.
Using energy-efficient motors can reduce your operating costs in several ways. Not only does saving energy reduce your monthly electrical bill, it can postpone or eliminate the need to expand the electrical supply system capacity within your facility. On a larger scale, installing energy conserving devices allows your electrical utility to defer building expensive new generating plants, resulting in lower costs for you, the consumer.
Energy-efficient motors are higher quality motors, with increased reliability and longer manufacturer’s warrantees, providing savings in reduced downtime, replacement and maintenance costs. Saving this energy and money requires the proper selection and use of energy-efficient motors.
There are three general opportunities for choosing energy-efficient motors:
(1) When purchasing a new motor,
(2) In place of rewinding failed motors, and
(3) To retrofit an operable but inefficient motor for energy conservation savings.
Energy-efficient motors should be considered in the following instances:
i. For all new installations,
ii. When major modifications are made to existing facilities or processes,
iii. For all new purchases of equipment packages that contain electric motors, such as an conditioners, compressors and filtration systems,
iv. When purchasing spares or replacing failed motors,
v. Instead of rewinding old, standard-efficiency motors,
vi. To replace grossly oversized and under-loaded motors,
vii. As part of an energy management or preventative maintenance program, and
viii. When utility conservation programs, rebates or incentives are offered that make energy-efficient motor retrofits cost-effective.
4. Essay on Motor Losses and Loss Reduction Techniques:
A motor’s function is to convert electrical energy to mechanical energy to perform useful work. The only way to improve motor efficiency is to reduce motor losses. Even though standard motors operate efficiently, with typical efficiencies ranging between 83 and 92 percent, energy-efficient motors perform significantly better.
An efficiency gain from only 92 to 94 percent results in a 25 percent reduction in losses. Since motors losses result in heat rejected into the atmosphere, reducing losses can significantly reduce cooling loads on an industrial facility’s air conditioning system.
Motor energy losses can be segregated into five major areas, each of which is influenced by design and construction decisions. One design consideration, for example, is the size of the air gap between the rotor and the stator. Large air gaps tend to maximize efficiency at the expense of power factor, while small air gaps slightly compromise efficiently while significantly improving power factor.
Motor losses may be categorized as those which are fixed, occurring whenever the motor is energized and remaining constant for a given voltage and speed and those which are variable and increase with motor load.
These losses are described below:
1. Core loss represents energy required to magnetize the core material (hysteresis) and includes losses due to creation of eddy currents that flow in the core. Core losses are decreased through the use of improved permeability electromagnetic (silicon) steel and by lengthening the core to reduce magnetic flux densities. Eddy current losses are decreased by using thinner steel laminations.
2. Windings and friction losses occur due to bearing friction and air resistance. Improved bearing selection, air-flow and fan design are employed to reduce these losses. Inan energy-efficient motor, loss minimization results in reduced cooling requirements so a smaller fan can be used. Both core losses and windage and friction losses are independent of motor load.
3. Stator losses appear as heating due to current flow (I) through the resistance (R) of the stator winding. This is commonly referred to as an I2 R loss. I2 R losses can be decreased by modifying the stator slot design or by decreasing insulation thickness to increase the volume of wire in the stator.
4. Rotor losses appear as I2 R heating in the rotor winding. Rotor losses can be reduced by increasing the size of the conductive bars and end rings to produce a lower resistance or by reducing the electrical current.
5. Stray load losses are the result of leakage fluxes induced by load currents. Both stray load losses and stator and rotor 12 R losses increase with motor load. Motor loss components are summarized in Table. Loss distributions as a function of motor horsepower are given in Table while variations in losses due to motor loading are shown in Fig. 6.3.
Table:
Typical distributions of motor losses, % (1800 RPM open drip-proof enclosure):
5. Essay on the Determining and Comparing Motor Efficiencies:
When evaluating motors on the basis of efficiency improvements or energy savings, it is essential that a uniform efficiency definition be used. It is often difficult to accurately compare manufacturers published, quoted or tested efficiencies as various values are used in categories and vendor literature.
Common definitions include:
i. Average or nominal efficiency:
These terms are identical and refer to the average full-load efficiency value obtained through testing a simple population of the same motor model. These are the most common standards used to compare motors.
ii. Guaranteed minimum or expected minimum efficiency:
All motors purchased or a stated percentage of the motors purchased are guaranteed to have efficiencies that equal or exceed this full-load value. (Based on NEMA Table).
iii. Apparent efficiency:
‘Apparent efficiency’ is the product of motor power factor and minimum efficiency. With this definition energy consumption can vary considerably as the power factor can be high while the efficiency is low. Specifications should not be based on ‘apparent’ efficiency values.
iv. Calculated efficiency:
This term refers to an average expected efficiency based upon a relationship between design parameters and test results. Specifications should not be based on ‘calculated’ efficiency values.
6. Essay on the Motor Efficiency Testing Standards:
It is critical that motor efficiency comparisons be made using a uniform product testing methodology. There is no single standard efficiency testing method that is used throughout the industry.
The most common standards are:
i. IEEE 112 -1984 (United States).
ii. IEC 34-2 (International electro technical commission).
iii. JEC – 37 (Japanese electro technical committee).
iv. BS – 269 (British).
v. C – 390 (Canadian standards association).
vi. ANSI C50.20 same as IEEE 112 (United states).
IEEE standard 112 – 1984, Standard test procedure for polyphase induction motors and generators, is the common method for testing induction motors in the united states. Five methods for determining motor efficiency are recognized.
The common practice for motors in the 1 to 125-hp size range is to measure the motor power output directly with a dynamometer while the motor is operating under load. Motor efficiency is then determined by carefully measuring the electrical input and the mechanical power output.
The motor efficiency testing standards differ primarily in their treatment of stray load losses. The Canadian Standards Association (CSA) methodology and IEEE 112 – Test method B determine the stray load loss through an indirect process.
The IEC standard assumes stray load losses to be fixed at 0.5 percent of input, while the JEC standard assumes there are no stray load losses. As indicated in Table, the efficiency of a motor, when tested under the different standard conventions, can vary by several percentage points.
In India national standard for energy efficient motors as given by BIS is IS: 12615 (2004) for three phase squired cage induction motor.
7. Essay on Determining Annual Energy Savings:
Before you can determine the annual savings, you need to estimate the annual energy savings. Energy-efficient motors require fewer input kilowatts to provide the same output as a standard-efficiency motor.
The difference in efficiency between the high-efficiency motor and a comparable standard motor determines the demand or kilowatt savings. For two similar motors operating at the same load, but having different efficiencies, the following equation is used to calculate the kW reduction.
where
hp – Motor nameplate rating
L – Load factor or percentage of full operating load
Estd – Standard motor efficiency under actual load conditions
Eef – Energy-efficiency motor efficiency under actual load conditions
The kW savings are the demand savings. The annual energy savings are calculated as follows:
kwhsavings = kWsaved × Annual operating hours
You can now use the demand savings and annual energy savings with utility rate schedule information to estimate your annual reduction in operating costs. Be sure to apply the appropriate seasonal and declining block energy charges.
The total annual cost savings is equal to:
Total savings =
(kWsaved × 12 × monthly demand charge) +(kWhSavings × energy charge)
The above equations apply to motors operating at a specified constant load. For varying loads, you can apply the energy savings equation to each portion of the cycle where the load is relatively constant for an appreciable period of time.
The total energy savings is then the sum of the savings for each load period. Determine the demand savings at the peak load point. The equations are not applicable to motors operating with pulsating loads or for loads that cycle at rapidly repeating intervals.
Example 1:
3, 7 kW 4 pole motor running at full load.
Let
Std motor efficiency = 85%
Energy efficient motor efficiency of same rating = 88.3 %
Let the Price of standard motor: Rs 7215/-
And price of energy efficient motor is = Rs 9380/
Consider Working hours = 16 per day, and working days 300 in a year and power rate Rs 4.50 per kWH
The value of X calculated as per given formula above
X = 0.1626
Savings = 0.1626 × 16 × 300 × 4.5 = Rupees 3514/- per year
Extra investment Rs 2615/-
Payback period = 9 months
Relevance of Life time cost as compared to initial investment:
Example:
Energy cost for a 15 years usage at Rs 4.50 / kWH is staggering 14.10 lacs as compared to buying cost of Rs 7215/-. Also the energy kWH rate is likely to only go up in future. If we compare initial purchase price of the motor with the cost of energy it uses over it working lifetime, the initial cost represents less than two percent of its lifetime cost in most of the cases.
So.it makes a great deal of sense to choose an eff1 level motor whenever a motor is needed to drive any applications.
Example 2:
The following analysis for a 75 hp TEFC motor operating at 75 percent of full rated load illustrates how to determine the cost effectiveness of obtaining an energy-efficient versus a standard-efficiently motor for the initial purchase case.
Kilowatts Saved:
where Estd and Eef are the efficiencies of the standard motor and the alternative energy-efficient unit.
This is the amount of energy conserved by the energy-efficient motor during each hour of use. Annual energy savings are obtained by multiplying by the number of operating hours at the indicated load.
Energy Saved:
kwhsaving = Hours of operation × kWsaved
= 8,000 hours × 1.21
= 9,680 kWh/year
Annual cost savings:
Total cost savings
= (kWsaved × 12 × Monthly demand charge) + (kWhsaving × Energy charge)
= 1.21 × 12 × $5.35 / kW + 9,680 × $0.03 / kWh (say)
= $368
In this example, installing an energy-efficient motor reduces your utility billing by $368 per year. The simple payback for the incremental cost associated with a energy-efficient motor purchase is the ratio of the discounted list price premium or incremental cost to the total annual cost savings.
Take price discount as 75%, the cost effectiveness is:
Thus, the additional investment required to buy this energy-efficient motor would be recovered within 1.5 years. Energy-efficient motors can rapidly “pay for themselves” through reduced energy consumption. After this initial payback period, the annual savings will continue to be reflected in lower operating costs and will add to your firm’s profits.
8. Essay on Assessing Economic Feasibility:
Because of better design and use of higher quality materials, energy-efficient motors cost 15 to 30 percent more than their standard efficiency counterparts. In many cases, however, this price premium is quickly recovered through energy cost savings. To determine the economic feasibility of installing energy-efficient motors, assess the total annual energy savings in relation to the price premium.
Common methods of assessing the economic feasibility of investment alternatives include:
i. Simple payback
ii. Life cycle costing methodologies
a. Net present value (NPV)
b. Benefit to cost ratio
c. Internal rate of return (ROR)
Most industrial plant managers require that investments be recovered through energy savings within 1 to 3 years based on a simple payback analysis. The simple payback is defined as the period of time required for the savings from an investment to equal the initial or incremental cost of the investment.
For initial motor purchases or the replacement of burned-out and un-rewindable motors, the simple payback period for the extra investment associated with an energy-efficient motor purchase is the ratio of the price premium less any available utility rebate to the value of the total annual electrical savings.
For replacements of operational motors, the simple payback is the ratio of the full cost of purchasing and installing a new energy-efficient motor relative to the total annual electrical savings.
9. Essay on BIS Specifications for Energy Efficient Motors:
National Standard for Energy Efficient Motors:
i. IS 12615: 2004 (First revision) energy efficient induction motors — Three phase squirrel cage.
ii. IS 12615 covers energy efficient motors from 0.37 kW to 160 kW (up to Fr. 315 L)
iii. IS 12615 specifies two efficiency levels eff-2 and eff-1.
IS 12615: 2004 (First revision) – superior to existing Std. IS 8789:
i. To be considered as energy efficient, a motor must conform to one of the following efficiency levels specified in IS 12615:
a. Improved efficiency (eff 2)
b. High efficiency (eff 1)
ii. Eff1 efficiency levels are higher than those of eff2.
Both eff1 and eff2 are higher than the nominal values specified in IS 8789:1996.
Reason for IS 12615 specify two efficiency levels:
i. User has the option to go for eff1 motor and save energy but at higher initial cost. It is strongly recommended to go for eff1 motor when utilization is high.
ii. The standard is hence user friendly since it has provided two levels of efficiency. This in line with other international standards like CEMEP.
Payback period of eff1 motor is 3.4 months for a 15% price difference over IS 8789 motor.
Eff1 motor gives further savings over an eff2 motor:
Note:
The prices taken in the example are assumed and not the actual price of motor. These are taken just for example illustration.
Replacement Vs Rewinding:
Replace old eff2 motor with eff1 motor and get payback in 15 months.
Replace old IS8989 motor with eff2 motor and get payback in 9 months.
10. Essay on Efficiency as Function of Load:
The amount of loading on any electrical equipment or system has direct impact on its efficiency. The motors are the integral part in industries and these consume considerable amount of electrical energy. Improper loading of motors affects their efficiency. Far too often motors are mismatched—or oversized—for the load they are intended to serve or have been rewound multiple times.
To compare the operating costs of an existing standard motor with an appropriately-sized energy-efficient replacement, you need to determine operating hours, efficiency improvement values and load. Part-load is a term used to describe the actual load served by the motor as compared to the rated full-load capability of the motor. Motor part-loads may be estimated through using input power amperage or speed measurements.
Need for Calculating Motor Loading:
Most electric motors are designed to run at 50 to 100% of rated load. Maximum efficiency is usually near 75% of rated load. Thus, a 10-horsepower (hp) motor has an acceptable load range of 5 to 10 hp; peak efficiency is at 7.5 hp. A motor’s efficiency tends to decrease dramatically below about 50% load.
However, the range of good efficiency varies with individual motors and tends to extend over a broader range for larger motors. A motor is considered under loaded when it is in the range where efficiency drops significantly with decreasing load. However, the power factor tends to drop off sooner, but less steeply than efficiency as load decreases.
Overloaded motors can overheat and lose efficiency. Many motors are designed with a service factor that allows occasional overloading. Service factor is a multiplier that indicates how much a motor can be overloaded under ideal ambient conditions. For example, a 10-hp motor with a 1.15 service factor can handle an 11.5-hp load for short periods of time without incurring significant damage.
Although many motors have service factors of 1.15, running the motor continuously above rated load reduces efficiency and motor life. Never operate over-loaded when voltage is below nominal or when cooling is impaired by altitude, high ambient temperature or dirty motor surfaces.
If your operation uses equipment with motors that operate for extended periods under 50% load, consider making modifications. Sometimes motors are oversized because they must accommodate peak conditions, such as when a pumping system must satisfy occasionally high demands. Options available to meet variable loads include two-speed motors, adjustable speed drives and load management strategies that maintain loads within an acceptable range.
Determining if your motors are properly loaded enables you to make informed decisions about when to replace motors and which replacements to choose.
Following measures are recommended for efficient use of electric motors:
i. Motors that are significantly oversized and under-loaded replace with more efficient, properly sized models at the next opportunity, such as scheduled plant downtime.
ii. Motors that are moderately oversized and under-loaded replace with more efficient, properly sized models when they fail.
iii. Motors that are properly sized but standard efficiency replace most of these with energy-efficient models when they fail. The cost effectiveness of an energy-efficient motor purchase depends on the number of hours the motor is used, the price of electricity and the price premium of buying an energy-efficient motor.