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Motor Starting Analysis

Large motors draw several times full-load current on start, and the resulting voltage dip can stall other motors, drop out contactors and trip protection elsewhere on the network. Motor starting analysis establishes whether a given motor can be started on a given supply, and what starting method is needed if it cannot.

What this covers

  • Voltage dip — magnitude and duration at the motor terminals and across the wider network.
  • Starting current profile — inrush and run-up current against time.
  • Torque analysis — motor torque against load torque throughout run-up, confirming the motor will accelerate.
  • Acceleration time — checked against the motor thermal withstand and locked-rotor limits.
  • Starting method comparison — direct on line, soft starter, star-delta, autotransformer and variable speed drive.
  • Effect on other loads — contactor drop-out, undervoltage tripping and stalling risk on running motors.
  • Generator-supplied cases — starting behaviour where the source is a generator rather than a stiff utility supply.

What you receive

  • Motor starting study report for each motor and starting scenario
  • Voltage dip, current and torque plots against time
  • Starting method recommendation with the reasoning stated
  • Protection setting implications identified for the setting calculations

Standards and references

Studies reference IEEE 399 for analysis method and IEC 60034 for machine characteristics, with acceptable voltage dip assessed against the project specification and IEC 60038.

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Steady-state studies of voltage profile, power distribution and loading across the network.

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Need motor starting analysis scoped?

Work directly with the engineers doing the analysis — clear scoping from the first conversation.

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