Electrical Motor Efficiency Study

Overview
The motor efficiency can be calculated from the total losses, which are assumed to be the summation of the following losses.
Losses considered:
The stray losses are difficult to measure with any accuracy. IEEE Standard 112 gives a complicated method. Which is rarely used on shop floor. IS & IEC standards take fixed value as 0.5% of output. It must be remarked that actual value of stray losses is likely to be more. IEEE – 112 specifies values from 0.9 to 1.8%.
Case Study
Overview
- Application: All Induction motor more than 50HP.
- Type of Audit: Motor Efficiency Study.
Motor Efficiency Calculation
| SN | Descriptions | Unit | Value |
|---|---|---|---|
| 1 | No of poles | - | 6 |
| 2 | Winding connection | - | DELTA |
| 3 | Type | - | TEFC |
| 4 | Output | kW | 180 |
| 5 | Voltage | Volts | 415 |
| 6 | Full load current, Ifl | Amp | 311 |
| 7 | Phase current at Full load, Ifl-ph | Amp | 179.6 |
| 8 | Speed | rpm | 990 |
| 9 | Frequency | Hz | 50 |
| 10 | Full load slip | p.u. | 0.010 |
| 11 | Efficiency | % | 90 |
| 12 | Insulation | - | Class F |
| 13 | Full load winding temperature | 0C | 85 |
| -- | No load test | -- | -- |
| 14 | Line voltage, U | Volts | 415.67 |
| 15 | Line Current, Inl | Amp | 118.7 |
| 16 | Phase current, Inl-ph | Amp | 68.5 |
| 17 | No load power input, Pi-nl | Watts | 9183 |
| 18 | Stator phase resistance at cold condition | Ohms | 0.4333 |
| 19 | Stator phase resistance after no load test | Ohms | 0.4333 |
| 20 | Ambient Temperature, Ta | 0C | 30 |
| 21 | Frequency, f | Hz | 50 |
| 22 | Winding resistance at full load Rph-fl | Ohms | 0.5233 |
| -- | Calculation of losses | -- | -- |
| 23 | No load power input, Pi-nl | Watts | 9183.33 |
| 24 | No load stator copper loss at T1 Temp. | Watts | 6102.1 |
| 25 | Iron, friction and windage loss | Watts | 3081.23 |
| 26 | Stator full load copper loss | Watts | 50611.24 |
| 27 | Synchronous speed | - | 1000.0 |
| 28 | Full load slip | - | 0.01 |
| 29 | Rotor Input power | kW | 181.82 |
| 30 | Rotor ohomic loss | kW | 1.8 |
| 31 | Stray loss 1.5% | kW | 2.7 |
| 32 | Total loss | kW | 58.21 |
| 33 | Motor full load input power | kW | 238.2 |
| 34 | Efficiency | % | 75.563 |
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