STAR DELTA STARTER

While starting a motor we usually do the on line starting but it is not applicable for large motors if we do that it will create a disturbance of voltage on the supply lines due to large starting current surges. So, in that case, we could use star delta starter it will be used to reduce the starting current surge. Large induction motors are started by this process it would start at reduced voltage and then it will be reconnected with full supply voltage when they run up to near the rotating speed

A dual starter connects the motor directly to the power supply and thus full voltage will be applied to the motor and this kind of starting process will be done for the motors below 5hp in case of a motor which has more than 5hp and thus we could use delta starter


Mainly three contactors are used to manufacture star delta contactor a timer and a thermal overload the contactors have less size compared to the single contactor which is used in direct on line starter which does the controlling function of winding current. The winding current is 58% of the current in the line this connection amounts to approximately 30% of the delta values thus the starting current is reduced to one-third of the direct starting current


The main contactor and delta contactor they have 58% of the current rating of the motor and third one is star contactor it only carries the star current is one third of Delta during the operation the main and star contactor are closed initially and after some time the star is opened and the delta is closed a timer kit is built into the starter which does the controlling of the contactors there are four states for star and delta process

  • Off state – all of the contactors are open in off state
  • Star state- in this state the main and star is open and the delta contactor is open and then the motor is connected to the star and it will produce one-third of torque and current
  • Open state – in this state the main contactor is closed and the delta and star is open there is no current flow the motor will behave like a generator due to its spinning motor
  • Delta state- in this state the main and delta is closed while star is open the motor is connected to full line voltage thus full power and torque is available