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Opportunities and challenges in EE motors

     
 

Energy efficient motors are available in two versions- Eff2 (efficiency level 2) and Eff1 (high efficiency level 1), from almost all major manufacturers in India. The Indian standard for efficiencies is listed as per IS: 12615- Rev Nov, 2004, from 63 frame size (0.37 kW) to 315L frame size (160 kW) at full load and with negative tolerance as given in IS: 325. The tolerance is 15% on (1-) up to 37 kW and 10% on (1-) >37 kW motors.

Opportunity 1- Using name plate efficiency

Part load efficiencies are also important, as the average load factor for induction motors, in our country, is <50%. Please see some examples, from published values of some manufacturers

Rated Sync. Make A Make B Make C
kW Rpm 100% 75% 50% 100% 75% 50% 100% 75% 50%
5.5 1500 89.5 89.5 88.5 89.2 88.7 84.5 89.2 88.7 87.2
7.5 1500 90.3 90.5 89.3 90.1 90.1 86.0 90.1 90.1 88.1
15 1500 92.5 92.5 91.5 92.5 92.2 84.2 91.8 91.8 89.8
30 1500 93.2 93.2 92.5 93.2 93.2 89.5 93.2 93.2 91.2
45 1500 94.2 94.2 93 93.9 93.9 90.5 93.9 93.9 91.9
75 1500 94.7 94.7 93.7 94.7 94.7 92.8 94.7 94.7 92.7
110 1500 95.2 95.2 94.2 95.2 95.2 93.3 95.2 95.2 93.2

Make A, not only has higher part load efficiencies but also uses lower tolerance to efficiency through the use of superior design, quality input materials and manufacturing practices.

How to calculate energy saving from higher efficiency?

The first step is to calculate the Load factor: The ratio of actual output to rated output gives the Load Factor (%) = Calculated output x 100 / Rated output Or the ratio of measured input to rated input Load Factor (%) = measured input x Rated Eff% / Rated Output The next step is to understand the motor Efficiency: The ratio of output to input, in percentage, is the motor operating efficiency Calculated output x 100 = Efficiency (%) Measured Input The third step is to calculate the annual energy saving from: The net saving potential can be arrived at by the following equation Rated output (kW) x LF x {1 /present Eff – 1/ proposed eff} x hours/year x tariff The fourth step is to calculate simple pay back in months: (Purchase cost of EE motor / Annual energy saving)*12 = Simple pay back(months)

Challenges

  • Many manufacturers do not punch Efficiency or PF on the name plate
  • If the PF is punched, then, (1.732 x V x I x PF)/1000 = Input power in kW
  • If the efficiency is punched, then, rated output / efficiency = input in kW
  • To determine the operating point efficiency, “Field efficiency audit” has to be carried out. BEE has drafted the code of practice for this audit

Opportunity 2 -Motors from 0.37 kW to 7.5 kW (small motor group)

When compared with the older version of motors, in this group, the increment in efficiency values are as high as 5% in some cases. However this gain in efficiency is difficult to be measured and established because of the inaccuracies in measurement, metering resolution and any process change that may occur between two studies. For example, a saving of 5% over 2kW input load is 0.1units/hour, which may be lost, if study on individual motor is made.

Therefore if a group of motors is taken as opportunity area, then, with the full cooperation of the process, we can establish the energy reduction from pre and post supply study for the cumulative load of the process.

For this load mapping, we need to measure the following parameters:

  • Measurement of input power of all individual motors in the group
  • Measurement of the motor shaft speeds of all the motors
  • Measurement of the driven load speeds
  • Measurement of the cumulative energy across the DB incomer and
  • Record of the process throughput per shift, for a given product mix.

After the replacement of these small group motors is made with Eff1 or Eff2 motors, the same study may be repeated and the net saving can be established, for the identical process.

 

Follow good rewinding practices

  • Rewind the motors as per the original winding data.
  • Do not allow rewinders to use open flame or heat the stators above 350°C for extracting the old, burned out winding. This can increase core losses.
  • Sand blasting of the core and/or grinding of laminations can create shorts in the core, leading to higher core losses.
  • Keep data on no load inputs (current, power at a measured voltage) for all new motors, including motors returning after rewinding.
  • Measure motor winding resistance after each rewinding