A 3 point started is a device that is used in the starting of DC Shunt and DC Compound wound motors.
Due to a back emf in the motors the motor emf equation becomes
Emotor = Eback + I(armature) R(armature)
Since at the time of starting the value of Eback is negligible hence
Emotor becomes = Ia x Ra
Or Ia = Emotor / Ra
Hence starting current will be very high if the value of Ra is very low so we have to introduce more resistance at the time of starting to limit Ia hence a 3 Point Starter with Variable Resistance is used to start a motor.
Due to a back emf in the motors the motor emf equation becomes
Emotor = Eback + I(armature) R(armature)
Since at the time of starting the value of Eback is negligible hence
Emotor becomes = Ia x Ra
Or Ia = Emotor / Ra
Hence starting current will be very high if the value of Ra is very low so we have to introduce more resistance at the time of starting to limit Ia hence a 3 Point Starter with Variable Resistance is used to start a motor.
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