Star-delta Starter Consists following units The current in star is one third of the current in delta, so this contactor can be AC3 rated at one third (33%) of the motor rating. The third contactor is the star contactor and that only carries star current while the motor is connected in star. These are AC3 rated at 58% of the current rating of the motor. There are two contactors that are close during run, often referred to as the main contractor and the delta contactor.

They are used in an attempt to reduce the start current applied to the motor during start as a means of reducing the disturbances and interference on the electrical supply. Star/Delta starters are probably the most common reduced voltage starters. Scheme – Working Principle of Star-Delta StarterĪfter a period of time the winding are reconfigured as delta and the motor runs normally. This also reduces the torque by a factor of three. During starting the motor windings are connected in star configuration and this reduces the voltage across each winding 3. Voltage reduction during star-delta starting is achieved by physically reconfiguring the motor windings as illustrated in the figure below. This is the reduced voltage starting method. Two methods used for reduction of starting voltage are: Star delta starting and Auto transformer starting. To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed.

Siemens star delta timer wiring diagram