Locked-Rotor In-Rush Current

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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.

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Locked-Rotor In-Rush Current
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Combining the transient and steady-state
components
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Example 5.13

• For the motor whose nameplate is shown, determine
  the expected in-rush current.

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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 lt kVA/hp lt 6.3
  

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Expected Range of Locked-Rotor Current is
Determined from
Lower Limit
Upper Limit
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The expected range of locked-rotor current is
The full-load current rating of the motor is