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NEMA Constraints on Voltage and frequency

NEMA Constraints on Voltage and frequency. A voltage variation of up to +/- 10% rated voltage while operating at rated frequency A frequency variation of +/- 5% rated frequency while operating at rated voltage

hedy-sanford
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NEMA Constraints on Voltage and frequency

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  1. NEMA Constraints on Voltage and frequency • A voltage variation of up to +/- 10% rated voltage while operating at rated frequency • A frequency variation of +/- 5% rated frequency while operating at rated voltage • A combined variation in voltage and frequency, with the sum of the absolute values of the respective variations not exceeding 10% providing the frequency does not exceed 5% of rated frequency.

  2. Effect of Off-Rated Voltage and Off-Rated Frequency on Induction Motor Performance • Effect on running torque

  3. Effect on Locked-Rotor Current

  4. Locked-Rotor Impedance (s=1)

  5. Locked-Rotor Current

  6. Effect on Locked-Rotor Torque

  7. Operating 60-Hz Motors on a 50-Hz System • Operation below rated frequency causes • a significant decrease in magnetizing reactance XM • an increase in magnetization current • resulting overheating • To prevent overheating, • reduce the applied voltage, keeping the ratio of volts per hertz constant

  8. Operating 60-Hz Motors on a 50-Hz System • General-purpose 3-phase 60-Hz NEMA-design induction motors with 2, 4,6, or 8 poles operate satisfactorily on 50-Hz systems if the horsepower and voltage ratings at 50-Hz are 5/6 of the corresponding ratings at 60-Hz. • The locked-rotor and breakdown torques at 50-Hz will be essentially the same as for 60-Hz operation.

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