“Energy Efficient Motor”

Department of Electrical Engineering

Index

Chapter 1

Introduction

In today’s power scenario we are facing a major power crunch. Day by day gap between demand and supply of electric energy is widening. Bridging this gap from supply side is very difficult and expensive proportion. The only viable way in handling these crises, in addition to capacity addition, is the efficient use of available energy sources.

            Electric motors are industry’s basic need. Industries consume about 50% of the power generated in the country and electric motors consume around 76% of the total electricity used in the industrial sector. Majority of the motive loads use squirrel cage induction motor as driving element. Most of the motors use in industry is oversized. Even when proper sized motors used, they are not fully loaded to their capacities. This result into poor efficiency which leads to more power consumption and energy cost .Therefore improvement of efficiency of the motor must be a part of any comprehensive energy conservation effort. This conservation is possible by using energy efficient motors in place of standard motors. As motors are the largest users of the electrical energy, even small efficiency improvements can produce very large saving across the country. Energy conservation measures taken by individual consumers in this direction will improve the national economy and benefit the environment on global scale.     

1.1             Motor Efficiency History:  

• Current Interest in Motor Efficiencies Began with the 1976 Energy Crisis.
• Premium Efficient Motors Introduced in 1980’s.
• The National Electrical Manufactures Association (NEMA) first made a definition between Standards and Energy Efficient motors in MG1-1987 with their September 1990 revision.
• These “Energy Efficiency” motors efficiencies later became the standards for the Energy Policy Act of 1994 (EPAct).
• In October 1997, the Energy Policy Act of 1994 too effect mandating minimum efficiency levels for general purpose TEFC and OPD 1 - 200Hp (0.75–150kW) 2, 4, 6 and 8 pole foot-mounted motors.
• This required that any EPAct motor sold in the United States comply with minimum nominal efficiency, testing and labeling standards.
• The consortium of Energy Efficiency (CEE) established “premium” efficiency guidelines used by many utilities for rebate programs in 1996.
• In mid-2001 NEMA and CEE harmonized their efficiency standards, establishing NEMA Premium efficiency standards for ODP and TEFC 1- 500Hp (0.75- 370kW) 2, 4, and 6 pole motors in low and medium voltage.
• The NEMA Premium standards first defined in NEMA MG1-1998, Rev 2 dose not differentiate between mountings configurations and all types of motors are covered.

1.2             Energy-efficient motors have been around for a long time  

     Typically, a standard off -the-shelf three-phase induction motor will have been designed not to maximize efficiency but to minimize manufacturing costs. But there are still a number of elements that can be designed differently to achieve appreciable savings (Fig. 5). In addition to a number of aspects that can be fine tuned for better performance, the main improvement comes from using more and / or better active materials, such as the die-cast copper squirrel cage rotors that have recently reached a commercial state of development.

     In 1994, the German Copper Institute (DKI) decided to become more actively involved with the markets in the electrical engineering sector and employed a specialist for this purpose – an understandable move given that these markets account for 60 % of all copper used. The DKI specialist looked into the question of motor efficiency and did some basic calculations. Having got over his initial astonishment, he then asked the manufacturers why higher efficiency motors and drives were not available. Siemens: ‘We’ve got them, but nobody wants them.’ ABB: ‘We have had them for ten years now. It’s just that no one buys them.’ Perhaps this is not really surprising given that 80% of all standard electric motors and drives are sold to original equipment manufacturers (OEMs) who have no real incentive to buy the more expensive high-efficiency motors (HEMs) as they only manufacture but don’t actually use the equipment into which the motors are built. What followed was a visit to see colleagues at the Copper Development Association in Great Britain . CDA UK is the only other copper association to have employed a specialist electrical engineer longer than the DKI and it offers software packages to help in the economic sizing of power cables, bus bars and motors.3 In response to a CDA UK initiative, the motor manufacturer Brook Hansen decided to restructure its product portfolio. Initially the company offered both low-price and energy-efficient models of its motors. Later on, the decision was taken to sell certain motor sizes and types only in the high-efficiency version – a move that was well received in both the national and international markets. In most cases, a high-efficiency motor can simply replace a more conventional low-price variant. While the use of more material certainly makes these motors heavier (Fig. 6), they are not necessarily larger in volume. In most cases only the stator and rotor laminations are a little longer and this can be compensated in part by using a smaller fan, as the thermal losses to be dissipated are lower. The high-efficiency motor is therefore not necessarily longer than a cheaper standard motor. Other dimensions are standardized and remain unchanged.

Chapter 2

Basics

2.1      Electric Motor Efficiency:

 Electric Motor Efficiency is the measure of its ability to convert kilowatt of electric power supplied to the motor terminal and the horse power of mechanical energy taken out of the motor at the rotating shaft.

                                              Watts output

Efficiency (%) =       ----------------- × 100

                                               Watts input

                                                   746 × HP   

            =   ----------------- × 100

                                                    V × I × cos Φ

                                           Input - Losses

                                   =   ----------------- × 100

                                                 Input

2.2       Efficiency consideration  

An AC 3 phase induction motor has five components of energy losses, which are presented below :

Percentage Motor Component’s Loss:  

2.3 Description of Motor component’s Losses:

 Copper Loss:  

Depends on the effective resistance of motor winding:

·        Caused by the current flowing through it.

·        Is equal to I²R

·        Proportional to Load.

·        Is equal to I²R + Rotor I²R Loss.  

Iron Loss:

Depending on the magnetic structure of the core and results from a combination of hysterisis and eddy current effect due to changing magnetic fields in the motor’s core

·        Voltage Related.

·        Constant for any particular motor irrespective of load.  

Friction and Windage loss:  

·        Occurs due to the friction in the bearing of the motor.

·        The windage loss of the ventilation fan, other rotating element of the motor.

·        Depend on the bearing size, speed type of bearing, lubrication used and fan blade profile.

·        Constant for given speed irrespective of load.  

Stray Loss:

It is very complex and Load related.

·        Arises from harmonics and circulating current.

·        Manufacturing process variations can also add to stray losses arises from harmonics and circulating current.

·        Manufacturing process variations can also add to stray losses.

Chapter 3

Ways to Save on Motor Energy Costs

There are of course other means by which energy can be saved without the use of HEMs and/or variable-frequency drives (VFDs). The simplest method to save energy is the often forgotten option of just switching off drives or motors that are not being used. While this might appear a very trivial proposal, if it is to be implemented in an industrial production process it re quires the installation of appropriate logistics systems. Manual deactivation is unlikely to be a realistic option given how often we fail to turn off the lights in a room even though we can see that they are not needed – something that is certainly not the case when we are dealing with drives used in an industrial application. There are also drives that only have to operate at full power for short periods and spend the greatest part of their operational life running at very low loads or even idling. However, switching off these drives may not be worthwhile because the cycle time is too short and the motor’s moment inertia too great. A typical example is the saws that are used in steel mills to cut the steel to the right dimensions as it lengthens during the rolling process. This involves swinging the movable saw blade into position during a pause in the rolling process. From an operational point of view these intervals must be kept as short as possible and particular care is therefore given to establishing the right size, type and configuration of the saw drive. In view of the relatively large size of the motor used, it is worthwhile switching back to a star connection when the motor is running at low load or idling (the motor may well already have a star-delta configuration to assist start-up). Switching should be achieved preferentially using electronic load relays as this helps to lessen wear and reduce EMC problems. Switching to a star configuration is equivalent to reducing the operating voltage by a factor of v3, a substantial saving in this case given that the motor would spend a considerable portion of its operating life in idle mode. This is one of the reasons why the operating point for optimum efficiency (Fig. 9) is much higher than in a transformer. Because motor design can vary individually, and as motors with specific power ratings are not always available off the shelf, and are often dimensioned to include reserve capacity, catalogues now tend to specify not just efficiencies for full load operation, but also for 75 % and sometimes 50 % loads.

Another supplementary measure is installing a separately driven fan that only runs when cooling is essential. A wide range of these cooling fans has become available since the introduction of variable-frequency drives that can provide large torques at low motor speeds or even from a standing start and where self-cooling therefore no longer functions.

3.1                        Avoiding Idle or Redundant Runing of motors:

The Simplest and most obvious method of saving motor energy is simply to turn it off when its not needed. Motors often run unnoticed when they are not needed, increasing energy costs. Motors can be switched on and off manually and this is a fine solution for many applications, but there are also timers and sensors available that will turn them off automatically. Examples of motors that could be turned off at night include those for service hot water circulation, air compressors and ventilation fans.

 3.2                         Use Variable speed Drives (VSD) for Variable Loads:

Some loads driven by motors don’t need to operate at the same speed all the time. For example, pumps and fans often don’t need to produce the same flow all the time. These types of loads offer big opportunities for saving by moderating their speed according to their load. For example , reducing a fan’s average speed by 20 percent with a VSD can reduce energy consumption by more than 40 percent.  

3.3   Properly size Motors:

                           Many motor systems are oversized, and a significantly oversized motor will run at low efficiency increasing energy costs. An oversized motor also costs more to buy. The efficiency of most motors peaks around 75 to 80 percent of full load and drops off sharply below 40 to 50 percent of full load, although these ranges vary by design and manufacturer. High – Efficiency motors tend to maintain their efficiency over a wider range of loads than standard motors. Motors loaded below 50 percent are almost always attractive candidates for replacement.

3.4     High Efficiency motors:

When replacing an existing motor or when specifying new equipment, consider using a high-efficiency motor. High-efficiency motors use better quality materials and are manufactured to higher quality specifications than standard efficiency motors. They are five to 10 percent more efficient on average than standard motors in the smaller sizes (25 horsepower or less)

As discussed above, increasing fan or pump speed can actually result in an increase in energy use. So, it’s important to specify that the new motor has a full load speed no greater than that of the motor it’s replacing.

 3.5                        Reduce the Load:

 Often it’s possible to reduce the load on a motor and save energy by reducing pressure losses losses in pipe duct runs with low-pressure loss elbows and fittings. Duct and pipe systems with lower pressure losses (usually expressed as “static pressure”) can often use a slower speed fan or pump to deliver the same amount of flow. This can result in big saving. Other way to reduce the load on a motor systems include aligning the motor drive, replacing inefficient drive trains such as belts, chains, and gears with direct drive systems.

Chapter 4

Efficiency Measuring techniques

      Quantifying what has been said so far requires the exact measurement of the losses that occur in a motor, and that is something easier said than done. A transformer takes up electrical energy and releases electrical energy and the Measurement of losses is in this case relatively simple. The secondary windings are shorted and the short-circuit voltage is applied to the primary side. The short-circuit voltage is the voltage required to produce the rated (i.e. full load) current in the shorted secondary winding. The copper loss in watts is then measured on the primary side at this voltage. The iron loss is then determined by measuring the power at the rated voltage of the transformer when operating under no load (open circuit) conditions. With a motor, the situation is not as simple. A motor transforms electrical energy into mechanical energy and measuring the mechanical energy means measuring the torque and speed of the motor when running under load. That, roughly speaking, is the approach taken in the direct method of measurement specified in IEC standard 60034-2 (or in modified form in IEC 61972 CDV, method 1) and in IEEE 112B.

      Even when the measurement is performed with the greatest possible care and high-precision instruments are used, the efficiency can be determined only to ± 0.5 of a percentage point. If a machine has an efficiency of 95%, this imprecision means that the efficiency can fluctuate between 94.5% and 95.5%; expressed relative to the size of the overall losses, this represents an uncertainty of ± 10%. That is unsatisfactory and achieving a higher level of precision is both difficult and costly. Instead of measuring the difference between the (electrical) input and (mechanical) Output power, power losses can be measured directly using the so-called calorimetric method. The motor is run in an adiabatic chamber and the ensuing heat losses are then determined. However, the complexity of the calorimetric technique has led to another method, the so-called loss-summation method, being used in practice. This approach is similar to that used in transformers and involves separate determination of the open-circuit and load losses, which are then summed and added to an estimate of the stray loss that depends only on the size of the motor and the frequency. This method is considered to be sufficiently exact by many manufacturers in continental Europe, but is criticized in the USA , where unsurprisingly they favour their own method, and by the British. The USA and UK believe that motors tested using the European / German method end up with significantly better energy efficiency ratings (see Fig. 9). This controversy was the reason why selecting the right measuring technique was the central topic under discussion at the triennial EEMODS conference (Energy Efficiency in Motor-Driven Systems) in London in September 1999. At the EEMODS conference held in Treviso in September 2002, the subject seemed to have run its course. At the Treviso meeting, speakers were invited to a special session on ‘Pumps and Fan Systems’ aimed at improving the efficiency of the overall system. So progress is being made. A view supported by the fact that after the EEMODS 2005 in Heidelberg , the conference will be held every two rather than every three years. The latest one took place in Beijing in June 2007. One topic not on the agenda is the influence of poor power quality (under voltage, over voltage, voltage asymmetry, harmonics) on motor performance. The effects of power quality on performance characteristics such as starting torque and especially motor efficiency are far greater than initially thought. Poor power quality can more than wipeout the beneficial effects of deploying a HEM; on the other hand, the difference between motors in the three energy efficiency classes become even more apparent as the quality of the power supply voltage deteriorates.

Fig. shows Differences in the results of motor efficiency measurements using a range of measurement methods

Chapter 5

What is an energy efficient motor?  

·     An “Energy efficient” motor produces the same shaft output power (kW), but draws less input power (kW) than a standard (lower efficiency) motor.

·    Hence EEM consumes less electricity than comparable standard motor for any given load.

·    EEM are manufactured with higher quality materials and techniques; they usually have higher service factors and bearing lives, less waste heat output and less vibration.

5.1     Features of EEM:  

·  Highest efficiency.

·  Lower operating cost.

·  Has high overloading cost.

·  Suitable for operations at higher ambient temperature.

·  Fewer power factor correction.

·  Saving increases with time.

·  Confirmation with NEMA standards of protection and control.

·  Cooler and Quieter operation.

·  Longer insulation life : EEM’s winding run about 20˚C cooler which increases insulation life by 4 times.

·  Improved bearing life: EEM bearing run about 10˚C   cooler than standard motor bearing, which doubles the life.

·  Less Starting thermal stress.

·  Higher service factor.

·  Better suited for energy management systems.

·  EEM perform better under adverse conditions of abnormal voltage conditions like unbalanced voltages.

·  Efficiency of EEM remains almost constant from 50% to 100% of load.

5.2     Energy Efficient or High Efficiency Motor Design:

Efficiency is a measure of the effectiveness with which a motor converts electrical energy into mechanical energy, which is measured by watts input versus watts output. In the conversion process, watts are lost by transformation into heat, which is dissipated through the frame. To improve efficiency, watt losses must be reduced through optimized design, improved material selection and quality control

Watts Loss Area:

1. Iron.
2. Stator.
3. Rotor.
4. Friction and Windage Losses.
5. Stray Load Loss.

Chapter 6

Minimising losses in a motor

Improvements in motor efficiency can be achieved without compromising motor performance - at higher cost - within the limits of existing design and manufacturing technology.

From the Table 10.1, it can be seen that any improvement in motor efficiency must result from reducing the Watts losses. In terms of the existing state of electric motor technology, a reduction in watts losses can be achieved in various ways.

 All of these changes to reduce motor losses are possible with existing motor design and manufacturing technology. They would, however, require additional materials and/or the use of higher quality materials and improved manufacturing processes resulting in increased motor cost.

      Simply Stated: REDUCED LOSSES = IMPROVED EFFICIENCY    

Thus energy-efficient electric motors reduce energy losses through improved design, better materials, and improved manufacturing techniques. Replacing a motor may be justifiable solely on the electricity cost savings derived from an energy-efficient replacement. This is true if the motor runs continuously, power rates are high, the motor is oversized for the application, or its nominal efficiency has been reduced by damage or previous rewinds. Efficiency comparison for standard and high efficiency motors is shown in Figure 

All these measures reduce losses and result in the improvement of efficiency of a motor and hence in lower power consumption lower electricity bills. This means that the energy taken from the main supply is available to driven system with only very small losses. The reduction in the losses also results in conservation of power and thus more people can reap benefits of electricity.

Chapter 7

Expected Savings

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.

Assessing cost effectiveness of energy efficient motors:

Savings: Savings are calculated as follows :

kW - out put of motor in kW
E1 - efficiency of standard motor
E2 - efficiency of energy efficient motor

                kW   kW

 X=     

              E1     E2

Savings = X × (Working Hour's) × (Working Days) × (Tariff)

EXAMPLE:

3.7 kW 4 pole motor , Std. motor eff 2: 85 % ,Price eff2: Rs 7215/- and

EEM eff1: 88.3 %  EEM eff1: Rs 9380/ Working hours 16 per day, working days 300 in a year, power rate Rs 4.50 per kWH

X = 0.1626
RS Savings = 0.1626×16×300×4.5 = 3514/- RS per year
Extra investment RS 2615/-   Payback period = 9 months

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. Combining this with Usual Crompton greaves motors reliability, wide service network (over 180 service points all over India ), the wise choice is Crompton greaves Eff.1 Motor.

Chapter 8

Load Vs Losses Graph , Benefits & Application

8.1  Benefits of Energy Efficient Motors are as follows:-

1. Higher efficiencies at operating level and consequently, reduction in electricity bill.
2. Can take care of wider Supply variation and higher ambient.
3. Suitable for service factor loads.
4. Lower slip which enhances output of the end product.

8.2      Application:

Energy efficient motors are specially suited for industries which are power intensive and equipments which run on constant load for long duration.

For Examples :Ring Frames, Fans, Blowers, Mixers, Pumps, Compressors etc. are some of the driven equipment's and industries such as textile, paper, rubber, petrochemicals, cement, power generation etc are those that. are suited for such motors

Chapter 9

What Design Characteristics are Important?

9.1 Motor Size

Motors should be sized to operate with a load factor between 65% and 100%. The common practice of oversizing results in less efficient motor operation. For rare peak loads, use a pony motor.

9.2 Operating Speed

While the average speed of energy-efficient motors is slightly higher than the average speed of standard-efficiency motors for any given size, models of each type are available with a wide range of speeds. Installing a new motor with a higher speed can result in diminished energy savings. It is particularly important in centrifugal pump or fan applications to select replacement motors with a comparable full-load speed.

9.3  Inrush Current

Avoid overloading circuits. Energy-efficient motors feature low electrical resistance and thus exhibit higher inrush currents than standard models. The inrush current duration is too short to trip thermal protection devices, but energy-efficient motors equipped with magnetic circuit protectors can sometimes experience nuisance trips during start-up.

Chapter 10

 Energy Efficient (high efficiency) motors- what all can go wrong?

 After being made conscious of energy bills/ energy conservation, you wish to buy an energy efficient motor to replace an existing motor. What all go wrong and make you feel that the energy efficient motor that you bought did not give you the savings you expected out of it.

 10.1             Starting current restriction:

         The major chunk of a motor’s losses (more than 78%) comes from copper losses (in stator and rotor), to reduce these losses the resistance in the stator and rotor needs to be reduced. Reduced resistance results in the net impedance of the motor reducing, which causes an increased inrush (starting) current when the same rated voltage is impressed across motor terminals. Therefore all the premium/ high efficiency motors worldwide have a high starting current. We end up imposing a restriction on the starting current, which has the following adverse effects:

·  A motor with a lower rotor resistance has a lower starting torque by default. Further imposing a restriction on starting torque to go down Further. To ensure suitability of motors to start against the driven equipment, a higher rated motor needs to be selected (to ensure sufficient torque availability) and this causes the motor being under utilized. Efficiency will be adversely affected.

·  A motor with a lower rotor resistance has a higher rated speed. When such a motor replaces an earlier motor (which had a lower rated speed), it drives the driven equipment at a higher speed. This, in case of centrifugal pumps or blowers causes the load demand to increase in proportion to the cube of the speed (characteristic of pumps and blowers). Also the flow increases, which is interpreted as the motor not showing any saving. If we were to measure the increased flow, we would be able to see the saving.

 10.2  Reduced voltage starting suitability:

      As already indicated above, a premium/high efficiency motor has lower starting torque because of lower rotor resistance. When we impose reduced voltage starting suitability condition, to ensure that the motor does develop sufficient torque to overcome the load, a higher rated motor is selected. This results in the motor being under utilized during service and this under-utilization affects the efficiency adversely.

Chapter 11

When to buy energy-efficient motors  

            Using readily available information such as motor nameplate capacity, operating hours, and electricity price you can quickly determine the payback that would result from selecting and operating an energy efficient motor.

      Using energy-efficient motors can reduced 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 manufacture’s warranties, providing savings in reduced downtime, replacement and maintenance costs.

      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:

·        For all new installations.

·        When major modification are made to existing facilities or processes

·        For all new purchases of equipment packages that contain electric motors, such as air conditioners, compressors, and filtration systems.

·        When purchasing spares or replacing failed motors

·        Instead of rewinding old, standard efficiency motors

·        To replace grossly oversized and under loaded motors

·        As part of an energy management or preventative maintenance program.

When utility conservation programs, rebates, or incentives are offered that make energy efficient motor retrofits cost-effective.

Chapter 12

Energy efficient motor replacement program

12.1 Divide your motors into the following categories:

·  Motors that are significantly oversized and under loaded- replace with more efficient, properly sized models at the next opportunity, such as scheduled plant downtime.

·  Motors that are moderately oversized and under loaded- replace with more efficient, properly sized models when they fail.

·  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.

 12.2 Determining motor loading:

         Operating efficiency and motor load values must be assumed or based on field measurements and motor nameplate information. The motor load is typically derived from a motors part- load input KW measurements as compared to its full load value. (When KW or voltage, ampere, and power factor readings are available.)

                         % Loading =       √3. Vav. Iav. Cosj/1000

                                                               KWrated /h

 Where,

Vav, Iav is the average line voltage and line current across the three phases,

KW rated is the nameplate rated KW and h is the declared rated efficiency.

Chapter 13

 Why Not High Motor Power Factor?

 As the diagram indicates, if the VAR vector is short, the power factor will be high. So it might see that motors with high power factor will help, because they will contribute less to the overall system VAR vector. But First: Motor load may not have much effect on system power factor. This is true when:

1.  Motor load is relatively small in comparison to resistance load (W) on the plant system, drawn by such equipment as plant lighting and resistance heating.

2.  Most of the induction motors load is represented by large, high-speed motors. Their power factor is inherently high, and the power factor of the fewer small motors won’t mean much.
3. The plant uses some synchronous motors. These don’t increase the VAR vector shown in the diagram, they tend to decrease it.
4. Motors are only part of the inductive load responsible for the length of the diagram’s VAR vector. Almost any plant has some power Transformers probably welding transformers, Possible solenoid-operated mechanisms, and induction heating equipment. Also there is “stray inductance”, in the plant’s wiring and in theory these wiring systems are pure resistance loads.
5. High motor power factor is wasted if the motor is oversized for the driven load, or runs much of the time at reduced load.

 In the above situation a high motor power factor won’t affect overall system power factor much. Probably not enough to justify the cost and other disadvantages of motors designed for maximum power factor.

 Second: You don’t get as good a motor design by concentrating on high power factor. The motor designer has to consider a number of parameters such as temperature rise, torque characteristics and efficiency, as well as power factor, and he can’t optimize them all. It’s costly to try to design both high power factor and high efficiency into a motor, and some of the design changes that improve power factor, such as reduced air gap, actually have the opposite effect on efficiency.

The Better Way

No matter what motors do to a plant system power factor, it can be corrected, and that’s the better way. The VAR vector in the diagram above represents inductive reactance. But there’s also capacitive reactance, which produces an opposite VAR vector. If a system is being affected by both kinds of reactance, they tend to cancel each other. In the system vector diagram below, capacitive VAR’s are almost as great as inductive VAR’s so W more nearly equals VA, and W/VA*100-the system power factor - is high.

 Chapter 14

   Conclusion

      As shows, the efficiency of three-phase induction motors can be improved through optimization of materials and operational parameters. If these improvements are realized, practically any motor that is operated more than just occasionally will, over the lifetime of the motor, yield savings equivalent to the purchase of several new motors. More detailed analyses are available from DKI13 and from the major motor manufacturers who also offer programs for selecting the best motors and drives for specific applications. Classifying motors into energy efficiency bands simplifies product selection and dispenses with the need for statutory control. The new labeling scheme is a major step forward as up until recently motor rating plates did not contain any information on power losses and efficiency. It would have been more expedient, however, to assign the label ‘EFF1’ to the lowest rather than the highest efficiency category, as this would have meant the ‘EFF’ series could be readily extended up ward as future efficiency improvements are introduced. Recent developments in the USA have seen the production of motors whose losses are now lower than those stipulated in statutory regulations. As a result, these new high-efficiency motors have received the rather ungainly moniker ‘NEMA Premium™’ and only time will tell what awkward lexical construction will be created to describe the next phase of motor efficiency improvements. And with motors be coming ever more efficient, there is clearly going to be little need to extend the existing classification system in the other direction beyond ‘EFF3’.

Fig. 23: Improvements across the board, if all the elements highlighted in Fig. 5 are optimized

Reference: -  

1.     Energy Efficient Motor System By Steven Nadel

2.     A Textbook  of Electrical Technology By B.L Theraja

3.     www.google.com

4.     www.ieee.org.in

5.     www.HEM.com