š Key Concepts
ā¢ Carefully compare the percent of rated torque and percent of rated current marked at key points on the curves (locked-rotor, pull-up, rated).
ā¢ Relate percent of synchronous speed to slip (slip is highest at standstill and very small at rated speed).
ā¢ Estimate numerical values from the graph (e.g., starting/locked-rotor current and torque) and compare them to the full-load (rated) values.
š Think About
ā¢ On the torque curve (Figure A), where does the pull-up torque sit relative to the dashed rated torque (100%) lineāwell below it, about equal, or well above?
ā¢ On the current curve (Figure B), approximately what percent of rated current is shown at locked-rotor (starting), and how many times the rated current does that represent?
ā¢ At about what percent of synchronous speed does the motor reach rated torque and rated current, and what does that imply about the slip at rated load?
ā
Before You Answer
ā¢ Verify from Figure A whether the pull-up torque is less than, equal to, or greater than 100% of rated torque before judging choice A.
ā¢ Read from Figure B the approximate locked-rotor (starting) current in percent of rated current (it should be several hundred percent) before comparing B and D.
ā¢ Confirm from the horizontal axis that rated torque/current occur very close to 100% synchronous speed, meaning slip is only a few percent, before evaluating statement C.