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

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Presentation transcript:

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.

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

Effect on Locked-Rotor Current

Locked-Rotor Impedance (s=1)

Locked-Rotor Current

Effect on Locked-Rotor Torque

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

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.