Is your motor taking a toll on your pocket?

Is your motor taking a toll on your pocket?

Energy efficiency has always been blessed with several technologies; the focus has been on utilities such as compressors, pumps, chillers, boilers, Ovens, furnaces, and many others to achieve significant savings. However, motors being prime mover to most of these types of equipment, have seen an exuberant growth in technology, be it Eff, Eff1 & Eff2 era or transition from IE1 to IE2 or IE3, which have rarely demonstrated average savings in double digits for a group of motors. As all energy efficiency projects compete with each other on the commonality of rupees saved per rupee invested, double-digit percentage savings and recovery of investment in less than two years; energy efficiency delivered through motors also need to qualify in this matrix which is, in general, followed for go or no-go decisions in the implementation of energy efficiency projects. It’s here that IE4 and IE5 class motors qualify both of these criteria and leave their predecessors IE2 and IE3 way behind. This was repeated observation while implementing the SEE-Tech Solutions energy-efficient motors program.

Let’s evaluate the rationale behind such a result and the approach needed to ensure double-digit savings. We intend to share our learning in this blog while implementing our Energy Efficient Motor Program with IE4 and IE5 Motors. Accordingly, the following seven issues have been the key aspects in getting the best results so far:

1. What is the Application?

This is the beginning point in the IE4 or IE5 motor selection for a given application and is very important. Aspects like load RPM Vs Motor RPM, the drive is already provided or not, compatibility of existing drive with IE4 & IE5 motor, power rating & duty cycle, load torque requirement, the environment of motor usage, nature of the application and several other aspects are essential for the proper selection of IE4 & IE5 motor.

It has been found that the same IE4 or IE 5 motor retrofits have resulted in additional savings with changing applications. For example, in SEE Tech’s Energy Efficient Motors Implementation program, the savings arrived with the same IE5 motor (1.5 KW, 3000 RPM), all other conditions remained the same, savings achieved in a pump application has been 25%, agitator application 29% and for elevator application 39%. However, it must not be assumed that a pump application gives the least and an elevator application gives the highest savings. These numbers are applicable just for those machines. But, yes, it can be interpreted that savings through IE5 motors are significantly higher.

2. Nameplate or Full load Motor Efficiency: What does it convey and doesn’t?

The motor nameplate represents total load efficiency, and that’s what remains in our mind for a particular size or efficiency class of a motor, and we tend to compare the motors based on these nameplate efficiencies. However, the fact is that motor efficiency is different at different loading. At 0% loading, efficiency is also zero, and it improves to 40% to 70% at 50% loading and finally to 80% to 90% or even 95% plus at full load for different sizes and efficiency classes of the motors. Therefore, our first learning has been that comparing efficiency at full load does not serve any purpose and often misleads the otherwise obtainable results.

3. Right-Sizing of the Motor: How important is this, and how does it affect operating efficiency?

As seen in the above graph, motor efficiency drops with underloading of the motors (more in IE1 & lesser in IE5); this implies that for the same load if a higher size motor is installed, it will draw more power. In the field also, the same has been observed. Interestingly, on a load drawing 4.1 KW on an IE2 class 7.5 KW motor (88.7% efficiency), an IE2 class 5.5 kW motor (87.7% efficiency) was installed, and it was ensured that the motor RPM and the load remained the same, the input power reduced to 3.94 KW. The reason was that loading improved from 48.52% to 62.83%, causing operating efficiency to improve from 83.41% to 86.51% (The loading & efficiency numbers are obtained by using SEE-Tech’s software: (SEE-UtiSave).

4. IE1 to IE5 Motor Efficiency at Various Loading – how much flatter is the curve?

For the same size of the motor, the first graph shows us how the efficiency curve gets flattened as we move from IE1 to IE5 and onwards; therefore, at a variable or part load, the difference in efficiency from IE1 to IE5 is very high as compared to that towards the full load. The other two graphs indicate variation in motor efficiency (in the form of losses & % slip) for motor loading for IE 1 to IE 4 motors.

Here the takeaway is that as we move from IE1 to IE5, the curve becomes flattened (2nd & 3rd graph), implying that the part-load efficiency of IE4 & IE5 is far better than their counterparts from IE1 to IE3. Many applications operate at lower loading or variable loading; in such cases, it is better to achieve higher efficiency and flatter the curve (2nd & 3rd graph).

5. Motor & load connection (Direct/Belt/Gear): How does this impact?

Belt & gear drives effectively add to the input power by 4% to 6% in the case of belts and as high as 8 to 12% in gear drives. So when the transition takes place from IE1-IE3 to IE4 or IE5, there is an opportunity to install the motor directly on the load as VFD will be there (mandatorily in the case of PMSM IE5 motors as these cannot be used without a PMSM enabled drive. Or for reducing the RPM to bring it equal to the earlier motor RPM so that the load (pump/blower/other) rotates at the same RPM to deliver the same flow/head/additional load side parameters). As we move from IE1 to IE5 motors, operating RPM move towards synchronous RPM, and in the case of IE4 & IE5 motors, the motor runs at synchronous RPM. So, if the load RPM (with IE4 & IE5) is not brought back to the earlier RPM (with IE1-IE3 motors), the load will rotate faster, and output will increase, and we may not get the desired savings. While adopting IE4 or IE5 motors, the use of drives becomes almost mandatory except in a few cases where getting to the previous RPM by changing pully size is more feasible than installing a motor directly onto the load shaft.

6. The difference between Motor Nameplate & Synchronous RPM

Another observation at the nameplate level is that apart from a rise in nameplate efficiency as we move from IE1 to IE5, the motor nameplate RPM is the same as its synchronous RPM. PF levels have also improved towards IE4 & IE5. It is also observed that IE4 and IE5 can take comparatively higher starting torque than their counterparts, IE1-IE3. Due to many such reasons, we have observed that lower size motors (appropriate size motors) can be opted for while transiting to IE4 & IE5.

7. Opportunity to enhance savings through automation

As the drive is in place while moving from IE1-IE3 to IE4 or IE5, the opportunity for automation must be looked upon, evaluated, designed, installed, and commissioned. This could be done as a second step but must not be left without an honest attempt. This aspect can add a substantial number to the savings while investment will not increase proportionately as the investment for the drive is already there.

So, to conclude, all seven aspects collectively play an important role in getting the best possible savings, and that’s why all the seven aspects must be considered simultaneously for the selection of the motor. It’s not about just getting the savings by moving from IE1 to IE5; it’s about getting the maximum outcome from the investments made.

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