Question 392Electricity & Electronics - QMED

70% to pass

The torque-speed and current-speed curves for a three-phase induction motor with a squirrel cage rotor are shown in figures "A" and "B" of the illustration. Which of the following statements is true concerning the depicted curves? Illustration EL-0056

Diagram for USCG Electrical QMED: The torque-speed and current-speed curves for a three-phase induction motor...

AThe starting current is nearly 1.5 times the normal full load current value.

BStarting current is approximately 4.75 times the normal full load current value.

CThe pull-up point on the torque curve is about 20% of the normal full load torque value.

DRated torque and rated current occur at approximately 20% slip.

AI Explanation

The correct answer is B) Starting current is approximately 4.75 times the normal full load current value. This is correct because induction motors typically have a high starting current, often 4-6 times the full load current, in order to overcome the initial torque requirements during startup. The torque-speed curve in figure "A" shows a very high starting torque, which corresponds to the high starting current depicted in figure "B". The other answer choices are incorrect: A) The starting current is typically higher than 1.5 times the full load current. C) The pull-up point is usually around 50-70% of the full load torque, not 20%. D) Rated torque and current typically occur at around 2-4% slip, not 20%.