Whenever the change in magnetic flux in the coil, the emf is induced in the coil.
Practically the rate at which the conductor is cutting the magnetic field induces emf in that coil.
The total magnetic flux cut by armature conductor = flux per pole × no of poles
= P × Փ
p = Number of poles
Փ = Magnetic flux per pole
N is the speed of the armature conductor in revolution per minute (RPM)
We can take n revolution in one minute or 60 seconds
N number of Revolution = 1 minute = 60 seconds
The time required to take one revolution
1 revolution = 60/N seconds
The emf induced per coil,
Z = Total no of conductors
A = Number of parallel paths
Consider A number of parallel paths in armature and Z number of conductors. So, Z/A gives the number of conductors in each path.
In Lap winding,
Number of parallel paths = Number of poles in dc generator
A=P
Replace A=P
In Wave winding,
Number of parallel paths is always two
For example, 6 pole dc machine having 480 conductors driven at a speed of 1200 rpm and flux per pole is 0.012 wb
case 1
Consider a lap winding
A=P
case 2
Consider Wave winding
Number of parallel paths is always two
A=2
Conclusion
In dc generator emf is generator by converting mechanical energy into electrical energy is the other hand the have to give supply to dc motor in this case emf generator in the armature opposes the supply voltage called as back emf Eb
Comments
Is Back emf Eb equal to generated emf in dc generator?
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