- EMF Definition: Electromotive force (EMF) in a DC generator is defined as the voltage generated by the movement of conductors through a magnetic field.
- Faraday’s Law: This law explains that the induced EMF in a generator’s conductor is proportional to the rate at which it cuts through the magnetic field lines.
- Generator Components: A DC generator consists of conductors, magnetic fields, armature, poles, and winding paths that collectively contribute to EMF production.
- Types of Winding: Wave winding involves fewer parallel paths, generally two, affecting the EMF calculation, whereas lap winding has a parallel path for each pole.
- EMF Equation of DC Generator: The total EMF for the generator is calculated by multiplying the EMF of one conductor by the number of conductors connected in series per path.
The EMF equation of a DC generator is derived in two main steps:
- Induced EMF of one conductor
- Induced EMF of the generator
Derivation for Induced EMF of One Armature Conductor
For one revolution of the conductor,
Let,
Φ = Flux produced by each pole in weber (Wb)
and
P = number of poles in the DC generator.
therefore,
Total flux produced by all the poles
And,
Time taken to complete one revolution
Consider N as the speed of the armature conductor, measured in revolutions per minute (rpm).
Now, according to Faraday’s law of induction, the induced emf of the armature conductor is denoted by “e” which is equal to rate of cutting the flux.
Therefore,
Induced emf of one conductor is
Induced emf of one conductor is
Derivation for Induced EMF for DC Generator
Let us suppose there are Z total numbers of conductor in a generator, and arranged in such a manner that all parallel paths are always in series.
Here,
Z = total numbers of conductor
A = number of parallel paths
Then,
Z/A = number of conductors connected in series
It is important to know that the induced EMF is consistent across each path in the generator.
Therefore,
The induced EMF of the DC generator, denoted as E, is calculated as the EMF of one conductor multiplied by the number of conductors connected in series.
Induced emf of DC generator is
Simple wave wound generator
Numbers of parallel paths are only 2 = A
Therefore,
Induced emf for wave type of winding generator is
Simple lap-wound generator
Here, number of parallel paths is equal to number of conductors in one path
i.e. P = A
Therefore,
Induced emf for lap-wound generator is
