Question 392Electricity/Electronics - QMED70% 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
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%.
Related Questions
#390 An open primary coil in a simple potential transformer will be indicated by which of the listed conditions? #391 What would be the source current and transformer current as shown in figure "B" of the illustration, with the secondary tap connected as shown, if the supply voltage at the branch circuit breaker is 440 VAC and the unity power factor load current draw is 50 amps? Illustration EL-0083 #393 In general, what type of starter would be used to connect polyphase induction motors to full line voltage at the instant of start-up? #394 Autotransformer starters, sometimes called starting compensators, are sometimes used with larger polyphase induction motors. What function do they perform? #395 According to the sample sheet of a typical "List of Motors and Controls" as shown in the illustration, which of the following motor applications features a means of keeping the motor windings warm and dry when the motor is idle? Illustration EL-0204