What is speed control?
Factors on which speed control of dc motors lie:
Eb can also be given as,
Eb = V- IaRa
thus, from the above equations
N = Eb 60A/PØ
but, for a DC motor A, P and Z are constants
Therefore, N ∝ K Eb/Ø (where, K=constant)
This shows the speed of a dc motor is directly proportional to the back emf and inversely proportional to the flux per pole.
Speed control methods of dc motor:
Speed control of dc shunt motor:
Speed control of dc shunt motor by flux control method:
Speed control of dc shunt motor by armature control method:
Now by increasing the resistance current decreases.As current decreases back e.m.f Eb decreases. As back e.mf Eb decreases speed of the dc shunt motor decreases.