Types of DC Motors

Classification

• Separately Excited DC Motor
• Self Excited DC Motor
  • Series Motor
  • Shunt Motor

Separately Excited DC Motor

• Field winding has an independent supply.
• Separate supply produces the main flux.
• Voltage and current relationship:
  • Vs = E + IaRa
  • E is the back EMF.
  • IaRa is the armature voltage drop.
• Can neglect brush voltage drop: Vs = E + IaRa
• Constant flux motor as flux is dependent on Vf only.

Self Excited DC Motor

Series Motor

• Field winding is in series with the armature.
• Voltage and current relationship:
  • Vs = E + Ia (Ra + Rsc) + Vbrush
  • Ia is same as the current drawn from the supply.
  • Flux is directly proportional to armature current Ia.

Shunt Motor

• Field winding is in parallel with the armature.
• Voltage and current relationship:
  • If = Vs/Rsh
  • Vs = Eb + IaRa + Vbrush
  • Total current I = Ia + If
• Constant flux motor:
  • If is constant if Vs is constant.
  • Flux is directly proportional to If.