What methods are employed to reduce the starting current of squirrel-cage motors?

Where the starting conditions are light, the starting current can be lessened by some method of reducing the stator voltage when switching on. There are four ways of starting on reduced voltage:

  1. Primary-resistance starting - introducing resistance between the supply and the stator windings.
  2. Primary-reactor starting - introducing a reactor in series with the stator windings, usually connected in the star point.
  3. Star-delta starting - connecting the stator windings in star for starting and in delta for running.
  4. Auto-transformer starting - supplying the stator windings through tappings on an auto-transformer.