1. ECE 4411 Locked-Rotor In-Rush Current At locked-rotor, each phase of an induction motor stator looks like a series R-L circuit. Closing the switch causes a current that consists of a transient and a steady-state component. The steady-state component is called the locked rotor in-rush current.

2. ECE 4412 Locked-Rotor In-Rush Current

3. ECE 4413

4. 4

5. 5 Combining the transient and steady-state components

6. ECE 4416 Example 5.13 For the motor whose nameplate is shown, determine the expected in-rush current.

7. ECE 4417 Solution The motor is a NEMA design B machine rated at 150hp at 460-V, 60-Hz. It has a rated current of 163A, a nominal efficiency of 96.2%, and a Code G designation for locked-rotor kVA/hp. Referring to Table 5.9, the expected range of starting kVA/hp for a Code G machine is 5.6 < kVA/hp < 6.3

8. ECE 4418

9. 9 Expected Range of Locked-Rotor Current is Determined from Lower Limit Upper Limit

10. ECE 44110 The expected range of locked-rotor current is The full-load current rating of the motor is