GENSET SIZING — DETERMINING LOAD CHARACTERISTICS
Three-Phase Induction Motors
Calculate RkW as follows:
If EFF (motor running efficiency) of the motor is not known, refer to Table 5 and use the value corresponding to the motor horsepower.
Calculate RkVA as follows:
If RPF (running power factor) is unknown, refer to Table 5 and use the value corresponding to the motor horsepower.
Calculate SkVA as follows:
1.If the NEMA motor code letter is unknown, refer to Table 4 on previous page and select the SkVA value corresponding to the code letter and the horsepower. The factors used to generate these values are shown in Table 5.
2.If the NEMA motor code letter is unknown, refer to Table 7 on page 25 and select the SkVA value in bold letters that corresponds to the motor horsepower. The bold letters show the values for the NEMA code letters that are typical for standard motors.
3.If the motor is rated greater than 500 HP and the NEMA motor code is known, calculate SkVA as follows:
4.If the motor is rated more than 500 HP and the NEMA motor code is not known, assume a NEMA code letter of G and calculate SkVA as follows:
where 5.9 is the multiplying factor corresponding to NEMA code letter G in Table 5.
NEMA Code Letter Multiplying Factor
Use Table 5 below to calculate the starting kVA. DO NOT confuse the NEMA (National Electrical Manufacturers Association) motor code and design letters.
The code letter refers to the ratio of locked rotor kVA to HP, whereas the design letter refers to the ratio of torque to speed.
Table 5. NEMA Code Letter Multiplying Factor
A | 2.0 |
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B | 3.3 |
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C | 3.8 |
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D | 4.2 |
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E | 4.7 |
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F | 5.3 |
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G | 5.9 |
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H | 6.7 |
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J | 7.5 |
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K | 8.5 |
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L | 9.5 |
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M | 10.6 |
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N | 11.8 |
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P | 13.2 |
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R | 15.0 |
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S | 16.0 |
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T | 19.0 |
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U | 21.2 |
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V | 23.0 |
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INDUSTRIAL GENERATOR SETS — APPLICATION & INSTALLATION MANUAL — REV. #4 (09/07/07) — PAGE 23