Technical and Economic Evaluation of Efficiency Improvement after Rewinding in Low-Power Induction Motors: A Brazilian Case
Abstract
:1. Introduction
2. Rewinding of Squirrel Cage Induction Motors
2.1. Stator Resistance
2.2. Stator Leakage Inductance
- Concentric winding, single layer with full pitch coils: coil pitch (y/τ), which is given in function of the pole pitch (τ), is equal to 1;
- Imbricated winding, double layer with short pitch coils: coil pitch (y/τ) is equal to 0.917 (11/12);
- Imbricated winding, double layer with short pitch coils: coil pitch (y/τ) is equal to 0.833 (5/6) and;
- Imbricated winding, double layer with short pitch coils: coil pitch (y/τ) is equal to 0.75 (3/4).
2.3. Three-Phase Squirrel Cage Induction Motor (SCIM) Analysis
- δE very small (E1cos(δE) ≈ E1);
- the angle δV is a function of ωLls/Rs;
- as well as the factor of voltage drop (KΔV = [1 + (Rs/ωLls)2]1/2);
2.4. Efficiency Calculation
- 2 × Ø0.63 mm (Kfill = 40.2%), with y/τ = 0.833, double layer and 216 turns per phase. Reason: this is the largest efficiency achieved and it is in the borderline of the IE4/Super-Premium class (this work considers IE4 threshold 85.5%, i.e., 1.5 percentage points above IE3 threshold and 12% less losses than IE3).
- 2 × Ø0.55 mm (Kfill = 30.6%), with y/τ = 0.833, double layer and 216 turns per phase. Reason: the efficiency achieves IE3/Premium class with an intermediate slot filling (non-full), differently from the previous SCIM, but with the same coil pitch.
- 2 × Ø0.63 mm (Kfill = 40.2%), with y/τ = 1, single layer e 212 turns per phase. Reason: likewise the previous SCIM, the efficiency achieves IE3/Premium class, but with full slot filling. The advantage is to achieve this class without changing the concentric winding for an imbricated winding. The only change is the strand material (Cu instead of Al).
3. Experimental Tests and Technical Considerations
- Measuring stator resistance at ambient temperature [19]. In this paper, the ambient temperature is 25 °C.
- Carrying out no-load test as in [19]. For all tests are used a controlled power supply, model 3000 iL, 3 kVA, maximum current is 3.3 A/phase, manufactured by California Instruments® (San Diego, CA, USA).
- Measuring stator resistance after thermal stability at no-load test, in a time below 30 s after turn-off the SCIM [19]. Before this, the temperature must be measured to confirm thermal stability. In this work, a model SD InfraCAM thermal imaging camera, by FLIR Systems® (Wilsonville, OR, USA) it was used. Figure 2 shows the measurement locus in the end winding.
- Carrying out the load tests after the SCIMs achieve thermal stability. The stator resistance must be measured within 30 s after turning-off the motor, [19]. After this, the temperature of the end winding is measured, as previously presented. In sequence, the efficiency can be measured by method A [19]. This stage must be repeated for all previously listed loads (25%, 50%, 75%, 100%, 115% and 130%).
- After the measurement of stator resistances under several load levels, the average temperature of the stator winding is calculated and the efficiency is measured again, but using method B for each load level, as in [19].
3.1. Workbench to Measure Efficiency by Methods A and B IEEE 112/2017
3.2. Efficiency Measurements and Determination of Efficiency Class
4. Economic Analysis
4.1. Life Cycle Cost Analysis (LCC)
4.2. Cost-Effectiveness Test Methods
4.2.1. Net Savings Method (NS)
4.2.2. Saved Energy Cost (SE)
5. Methodology and Data
- IE3—Replacement of the existing SCIM IE2 by a new SCIM IE3/Premium of the same power.
- IE4—Replacement of the existing SCIM IE2 by a hypothetical SCIM IE4/Super-Premium of the same power. The SCIM IE4 has efficiency equal to the class threshold (85.5%) and the price is 15% above the IE3 price.
- Rew_IE3—Rewinding the existing SCIM IE2 in order to achieve the IE3/Premium class. The new winding has the following configuration: concentric winding with 2 × Ø0.63 mm, copper strands (Kfill = 40.2%), y/τ = 1, single layer, 212 turns per phase, 53 turns per slot and 53 turns per coil.
- Rew_IE4—Rewinding the existing SCIM IE2 in order to achieve the IE4/Super-Premium class. The new winding has the following configuration: imbricated winding with 2 × Ø0.63 mm, copper strands (Kfill = 40.2%), y/τ = 0.833, double layer, 216 turns per phase, 54 turns per slot and 27 turns per coil.
- Retrof_IE3—Replacement of the existing SCIM IE2 by a new SCIM IE2 that in the beginning of operation a rewinding was performed using this configuration: concentric winding with 2 × Ø0.63 mm, copper strands (Kfill = 40.2%), y/τ = 1, single layer, 212 turns per phase, 53 turns per slot and 53 turns per coil.
- Retrof_IE4—Replacement of the existing SCIM IE2 by a new SCIM IE2 that in the beginning of operation a rewinding was performed using this configuration: imbricated winding with 2 × Ø0.63 mm, copper strands (Kfill = 40.2%), y/τ = 0.833, double layer, 216 turns per phase, 54 turns per slot and 27 turns per coil.
5.1. Motors Prices
- Reconditioning/Stator Winding Redesign includes swap of bearings, V-ring seals, fixing ring and wave washer, if necessary, in addition to the frame painting as demanded by the manufacturer. If a repair in a non-failed motor is requested, the same price is charged.
- Generally, the rewinding workshop does not have expertise in recovery of a damaged squirrel cage rotor or damaged rotor shaft. However, in low-power motors, the squirrel cage rotor can be bought if the manufacturer provides it.
5.2. Input Data
- Discount rate (d) equal to 12% per year in the first analysis and 4% per year in the subsequent analysis which is composed of the national interest rate (6.9%) less inflation (2.95%) in December 2017. The second analysis presents how to measure the viability of an investment for a nationwide energy efficiency program.
- The energy escalation rate (ê) is equal 3.01% per year. This rate was established in the increase of the average industrial electricity tariff from 1996 to 2017, less inflation (see Figure 5).
- The industrial electricity tariff (C) is equal to 98.65 US$/MWh which is the average electricity tariff in Brazil (2017) [27]. In this tariff is discounted the possible variation of 18.05% [12]. This variation is due manifold tariffs of each electricity distribution companies in the country. As each electricity companies have its own tariffs, an average value is suitable. As the sensibility analysis performed in [12], the tariff is discounted by the variation because this action raises the viability threshold. The original tariff value was 120.38 US$/MWh.
- The average cost of the IE2, IE3/Premium, IE4/Super-Premium, Retrof_IE3, Retrof_IE4, Rew_IE3 and Rew_IE4 units are presented in Section 5.1.
- The technical motor data, e.g., efficiency and load, are presented in Section 2 and Section 3. The viability will be evaluated for 4000 and 8000 operation hours per year with 100% load. In sequence, only the two better cases will be evaluated at 75% load. If necessary, they will be evaluated at 50% load as well.
- The currency exchange rate used is US$1.00 = R$3.13 and US$1.00 = R$3.24 (year 2017) for the values presented in Section 2.
6. Results and Discussion
6.1. Cost-Effectiveness with Discount Rate 12%
6.2. Cost Effectiveness with Discount Rate 4% in Brazil
6.3. Saved Energy Cost
7. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
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y/τ | 1 | 0.917 | 0.833 | 0.75 |
---|---|---|---|---|
Type | Conc. 1/S.L. 2 | Imbric. 3/D.L. 4 | Imbric./D.L. | Imbric./D.L. |
σ0 (%) | 0.89 | 0.74 | 0.62 | 0.69 |
KW1 (%) | 95.8 | 94.9 | 92.5 | 88.5 |
KW5 (%) | 20.5 | 16.3 | 5.3 | 7.9 |
KW7 (%) | 15.8 | 9.6 | 4.1 | 14.6 |
KW11 (%) | 12.6 | 1.6 | 12.2 | 4.8 |
KW13 (%) | 12.6 | 1.6 | 12.2 | 4.8 |
KW17 (%) | 15.8 | 9.6 | 4.1 | 14.6 |
KW19 (%) | 20.5 | 16.3 | 5.3 | 7.9 |
THD* (%) | 9.0 | 8.1 | 7.4 | 7.8 |
2 × Ø | Pitch | Rs (Ω) | Rs/ωLls | ωLls (Ω) | KΔV | I0 (A) | I1 (A) | η (%) |
---|---|---|---|---|---|---|---|---|
0.63 mm (Al) | Full | 5.7 | 0.940 | 6.1 | 1.372 | 1.25 | 2.42 | 81.9 |
0.55 mm (Cu) | Full | 4.4 | 0.733 | 6.0 | 1.240 | 1.30 | 2.44 | 83.7 |
0.917 | 4.2 | 0.838 | 5.0 | 1.305 | 1.53 | 2.57 | 83.8 | |
0.833 | 3.9 | 0.859 | 4.5 | 1.318 | 1.68 | 2.67 | 84.3 | |
0.63 mm (Cu) | Full | 3.3 | 0.550 | 6.0 | 1.141 | 1.34 | 2.46 | 84.9 |
0.917 | 3.2 | 0.639 | 5.0 | 1.187 | 1.58 | 2.60 | 84.9 | |
0.833 | 3.0 | 0.661 | 4.5 | 1.199 | 1.74 | 2.70 | 85.4 |
2 × Ø | Pitch | η (%) | η (%) Method B | η (%) Method A | I1 (A) | Meas. * I1 (A) | I0 (A) | Meas. I0 (A) |
---|---|---|---|---|---|---|---|---|
0.63 mm (Al) | Full | 81.9 | 81.2 | 81.8 | 2.42 | 2.42 | 1.25 | 1.25 |
0.55 mm (Cu) | 0.833 | 84.3 | 84.0 | 84.3 | 2.67 | 2.58 | 1.68 | 1.59 |
0.63 mm (Cu) | Full | 84.9 | 84.5 | 85.1 | 2.46 | 2.46 | 1.34 | 1.33 |
0.833 | 85.4 | 85.3 | 85.7 | 2.70 | 2.62 | 1.74 | 1.66 |
2 × Ø Pitch | η (%) 50% Method B | η (%) 50% Method A | η (%) 75% Method B | η (%) 75% Method A | η (%) 115% Method B | η (%) 115% Method A |
---|---|---|---|---|---|---|
0.63 mm (Al) Full | 77.7 | 78.3 | 80.8 | 81.6 | 80.9 | 81.2 |
0.55 mm (Cu) 0.833 | 79.4 | 79.6 | 83.0 | 83.5 | 84.2 | 84.0 |
0.63 mm (Cu) Full | 80.6 | 82.4 | 83.7 | 84.0 | 84.5 | 84.9 |
0.63 mm (Cu) 0.833 | 80.4 | 80.9 | 84.0 | 84.7 | 85.3 | 85.7 |
SCIM Type | IE1 | IE2 | IE3/Pemium |
---|---|---|---|
Price (US$) | 105.14 | 274.32 | 396.64 |
Power (HP) | Pair of Poles | Motor Price (US$) | SCIM Rewinding Cost (US$) | Relation (%) |
---|---|---|---|---|
1.5 | 1 | 274.32 | 60.73 | 22.1 |
1.5 | 2 | 309.11 | 71.28 | 23.1 |
2 | 1 | 338.44 | 85.34 | 25.2 |
3 | 1 | 412.39 | 98.13 | 23.8 |
5 | 1 | 572.43 | 144.80 | 25.3 |
5 | 2 | 586.97 | 144.80 | 24.7 |
10 | 2 | 1025.30 | 195.30 | 19.0 |
100% Load | |||
---|---|---|---|
8000 Operating h/year | 4000 Operating h/year | ||
Method B | NS 1 (US$) | Method B | NS (US$) |
(1) Rew_IE4 | 555.10 | (1) Rew_IE4 | 380.40 |
(2) Rew_IE3 | 489.60 | (2) Rew_IE3 | 347.70 |
(3) Retrof_IE4 | 360.90 | (3) Retrof_IE4 | 146.10 |
(4) Retrof_IE3 | 296.90 | (4) Retrof_IE3 | 114.20 |
(5) IE4 | 263.40 | (5) IE3 | 64.50 |
(6) IE3 | 251.20 | (6) IE4 | 40.80 |
Method A | NS (US$) | Method A | NS (US$) |
(1) Rew_IE4 | 534.00 | (1) Rew_IE4 | 369.90 |
(2) Rew_IE3 | 485.50 | (2) Rew_IE3 | 345.60 |
(3) Retrof_IE4 | 339.00 | (3) Retrof_IE4 | 135.20 |
(4) Retrof_IE3 | 291.70 | (4) Retrof_IE3 | 111.50 |
(5) IE4 | 210.10 | (5) IE3 | 37.80 |
(6) IE3 | 197.90 | (6) IE4 | 14.10 |
75% Load | |||
---|---|---|---|
8000 Operating h/year | 4000 Operating h/year | ||
Method B | NS (US$) | Method B | NS (US$) |
(1) Rew_IE4 | 414.50 | (1) Rew_IE4 | 310.10 |
(2) Rew_IE3 | 395.60 | (2) Rew_IE3 | 300.70 |
(3) Retrof_IE4 | 202.10 | (3) Retrof_IE4 | 66.80 |
(4) Retrof_IE3 | 183.70 | (4) Retrof_IE3 | 57.60 |
(5) IE3 | 136.10 | (5) IE3 | 6.90 |
Method A | NS (US$) | Method A | NS (US$) |
(1) Rew_IE4 | 404.30 | (1) Rew_IE4 | 305.00 |
(2) Rew_IE3 | 360.70 | (2) Rew_IE3 | 283.20 |
(3) Retrof_IE4 | 190.90 | (3) Retrof_IE4 | 61.20 |
(4) Retrof_IE3 | 148.40 | (4) Retrof_IE3 | 39.90 |
(5) IE3 | 82.40 | (5) IE3 | −20.00 |
100% Load | |||
---|---|---|---|
8000 Operating h/year | 4000 Operating h/year | ||
Method B | NS (US$) | Method B | NS (US$) |
(1) Rew_IE4 | 716.40 | (1) Rew_IE4 | 461.10 |
(2) Rew_IE3 | 620.70 | (2) Rew_IE3 | 413.20 |
(3) Retrof_IE4 | 559.20 | (3) Retrof_IE4 | 245.30 |
(4) IE4 | 469.10 | (4) Retrof_IE3 | 198.60 |
(5) Retrof_IE3 | 465.80 | (5) IE3 | 150.70 |
(6) IE3 | 423.80 | (6) IE4 | 143.60 |
Method A | NS (US$) | Method A | NS (US$) |
(1) Rew_IE4 | 685.70 | (1) Rew_IE4 | 445.70 |
(2) Rew_IE3 | 614.70 | (2) Rew_IE3 | 410.20 |
(3) Retrof_IE4 | 527.40 | (3) Retrof_IE4 | 229.40 |
(4) Retrof_IE3 | 458.10 | (4) Retrof_IE3 | 194.70 |
(5) IE4 | 391.10 | (5) IE3 | 111.80 |
(6) IE3 | 345.80 | (6) IE4 | 104.70 |
75% Load | |||
---|---|---|---|
8000 Operation h/year | 4000 Operation h/year | ||
Method B | NS (US$) | Method B | NS (US$) |
(1) Rew_IE4 | 510.90 | (1) Rew_IE4 | 358.30 |
(2) Rew_IE3 | 483.30 | (2) Rew_IE3 | 344.50 |
(3) Retrof_IE4 | 327.20 | (3) Retrof_IE4 | 129.30 |
(4) Retrof_IE3 | 300.20 | (4) Retrof_IE3 | 115.80 |
(5) IE3 | 255.50 | (5) IE3 | 66.60 |
Method A | NS (US$) | Method A | NS (US$) |
(1) Rew_IE4 | 496.00 | (1) Rew_IE4 | 350.90 |
(2) Rew_IE3 | 432.30 | (2) Rew_IE3 | 319.00 |
(3) Retrof_IE4 | 310.80 | (3) Retrof_IE4 | 121.10 |
(4) Retrof_IE3 | 248.60 | (4) Retrof_IE3 | 90.00 |
(5) IE3 | 176.90 | (5) IE3 | 27.3 |
8000 Operation h/year | |
---|---|
Method B | SE(US$/MWh) |
(1) Retrofit_IE4 | 1.04 |
(2) Retrofit_IE3 | 1.22 |
(3) IE3 | 2.14 |
(5) IE4 | 2.66 |
Method A | SE(US$/MWh) |
(1) Retrofit_IE4 | 1.10 |
(2) Retrofit_IE3 | 1.24 |
(3) IE3 | 2.50 |
(5) IE4 | 3.03 |
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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Aguiar, V.P.B.; Pontes, R.S.T.; Ferreira, F.J.T.E. Technical and Economic Evaluation of Efficiency Improvement after Rewinding in Low-Power Induction Motors: A Brazilian Case. Energies 2018, 11, 1701. https://doi.org/10.3390/en11071701
Aguiar VPB, Pontes RST, Ferreira FJTE. Technical and Economic Evaluation of Efficiency Improvement after Rewinding in Low-Power Induction Motors: A Brazilian Case. Energies. 2018; 11(7):1701. https://doi.org/10.3390/en11071701
Chicago/Turabian StyleAguiar, Victor P. B., Ricardo S. T. Pontes, and Fernando J. T. E. Ferreira. 2018. "Technical and Economic Evaluation of Efficiency Improvement after Rewinding in Low-Power Induction Motors: A Brazilian Case" Energies 11, no. 7: 1701. https://doi.org/10.3390/en11071701