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AuCom provides comprehensive motor control solutions for both Low Voltage and Medium Voltage applications, including Soft Starters, Drives, and Motor Control Centres.
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Solid-State Soft Starters

Get Your Motor Running White Paper Series

Download Get Your Motor Running Part 4: Solid-State Soft Starters

Part 4 of five. How soft starters control motor acceleration, and why a current rating means little until the starting duty is defined.

An ampere rating means little without the duty. The same starter carries different usable motor ratings depending on starting current, start duration, frequency of starts, ambient temperature and whether it is bypassed during normal running. AC-53 utilisation codes exist to describe that duty. Selecting from a headline current figure without it is how starters end up undersized for the application they are installed in.

Inside:

  • SCR operation, conduction angle and what bypassing changes
  • Open-loop and closed-loop control, from voltage ramp to acceleration control
  • Reading AC-53a and AC-53b codes, and selecting from a ratings table
  • Protection, enclosure cooling, harmonics, semiconductor fuses and isolation

The Get Your Motor Running Series

Five technical papers take you from the fundamentals of motor starting through to the selection and application of soft starters and variable frequency drives.

aucom_gymr_handbook The Complete Series: A Practical Guide to Motor Starting and Control The complete guide to motor starting and control. All five Get Your Motor Running papers in one reference, from what determines starting performance through to selecting and applying soft starters and variable frequency drives. Worked examples and ratings guidance throughout. Read the Handbook aucom_gymr_p1 Reduced-voltage starting of three-phase induction motors What happens when starting current is restricted, and why motor design decides the outcome. Nine four-pole 110 kW motors with similar rated power, speed and efficiency are compared at the same current limit: at 300% FLC the available initial torque ranges from 24% to 65% of full-load torque. Covers locked-rotor current, locked-rotor torque and the speed/torque curve. Read Part 1 aucom_gymr_p2 Starting torque requirements of machines and motor loads What the driven machine requires from the motor during starting. Breakaway torque, work torque, acceleration torque and inertia, with worked examples for a punch press, a centrifugal fan, a compressor and a flywheel, plus the equations for full-load torque, acceleration torque and reflected load inertia. Read Part 2 aucom_gymr_p3 Motor starting solutions The principal methods compared: direct-on-line, primary resistance, auto-transformer, star-delta, soft starter and variable frequency drive. Covers open-transition and closed-transition switching, why the transition point matters more than the initial current reduction, and a side-by-side comparison of all six methods. Read Part 3 aucom_gymr_p4 Solid-state soft starters Controlled starting for fixed-speed applications. Open-loop and closed-loop control methods, from timed voltage ramp through to acceleration control. Also covers SCR thermal duty, AC-53 utilisation codes and ratings tables, motor protection, semiconductor fuse coordination, and power factor correction capacitor switching. Read Part 4 aucom_gymr_p5 Variable frequency drives How a VFD controls speed and torque across the operating range. V/F, sensorless vector and closed-loop vector control, the constant-torque and constant-power regions, load characteristics and energy use, drive and motor selection, harmonics and mitigation, braking methods, and synchronous transfer. Read Part 5