Why is a starter necessary to start a DC motor?

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MPPGCL JE Electrical 19 March 2019 Shift 2 Official Paper
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  1. Because it has zero starting torque
  2. Because at start, back EMF is zero
  3. Because it has high starting torque
  4. To restrict high inrush current

Answer (Detailed Solution Below)

Option 4 : To restrict high inrush current
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Starters in DC motors

Starters are used to protect DC motors from damage that can be caused by very high inrush currents and torque during startup.

This is done by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level.

F2 Vinanti Engineering 21.03.23 D4

\(V=E_b+I_aR_a\)

where, V = Terminal voltage

Eb = Back EMF

Ia = Armature Current

Ra = Armature Resistance

As Eb is directly proportional to the speed. So, at the starting speed is zero, hence Eb = 0

At starting:

\(V=0+I_aR_a\)

\(I_a={V\over R_a}\)

Hence, starters are used to limit starting current as the current at the starting of the motor is high.

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