NEMA Constraints on Voltage and frequency A voltage

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NEMA Constraints on Voltage and frequency • A voltage variation of up to +/-

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

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

Effect on Locked-Rotor Current

Effect on Locked-Rotor Current

Locked-Rotor Impedance (s=1)

Locked-Rotor Impedance (s=1)

Locked-Rotor Current

Locked-Rotor Current

Effect on Locked-Rotor Torque

Effect on Locked-Rotor Torque

Operating 60 -Hz Motors on a 50 -Hz System • Operation below rated frequency

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

Operating 60 -Hz Motors on a 50 -Hz System • General-purpose 3 -phase 60

Operating 60 -Hz Motors on a 50 -Hz System • General-purpose 3 -phase 60 -Hz NEMAdesign 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.