USCG Exam PracticeElectrical fundamentals — DC/AC, motors, distribution
A large three-phase induction motor is to be started across the line. The chief concern with this starting method is that the motor will draw approximately how many times its full-load current at startup, and at what power factor?
- A. 2–3 times full-load current at unity power factor.
- ✓ 5–7 times full-load current at a poor (low) power factor.Correct
- C. 10 times full-load current at a high (leading) power factor.
- D. 5–7 times full-load current at a high (unity) power factor.
Why B is correct
At standstill, a squirrel-cage induction motor behaves like a short-circuited transformer, drawing 5–7 times full-load current at a poor power factor. This is why larger motors use reduced-voltage or soft starters. NEETS Mod. 5 §4-1.
Cited:NEETS Mod. 5 §4-1