Test: DC Motor Starting - Electrical Engineering (EE) MCQ

For both the machines the purpose is different.

Due to the slow cut off the resistance the current will be high for a large amount of time and it will cause the machine to burn.

n= log(Ra/Rt)/log(Imin/Imax) ; Rt = Vt/Imax= 250/700 = 0.357 ohms
= log(0.05/0.357)/log(350/700)
= 2.84
= 3 (approx).

All the observations can be seen due to large starting current in dc motor.

Both 3-point and 4-point starters can be used.

The direct-on-line starter can not limit the speed by limiting the current.

A thyristor controlled method is more efficient as it has lesser resistance and losses while operating.

Full load current = 7460/(200*0.85) = 43.88 A
Starting current = 1.5*43.88 = 65.883 A
R = V/I = 200/65.883
= 3.038 ohms
Starting resistance = 3.038 – 0.25 = 2.788 ohms.

Fringing is the effect in which the magnetic flux lines bulge out of the the flux. and it is introduced at the air gaps.

There is no such post effect of armature reaction . The armature reaction phenomena affects the working condition only.