In this article, we will understand the working principle of a DC generator (Direct Current Generator). But before that let us first know a bit about dc generators.
Introduction to DC Generator
A dc machine that
converts input mechanical energy into output dc electrical energy is known as a
dc generator. It consists of two main parts namely, the field system and
armature. The field system produces the required working flux in the machine,
and the armature is a system of conductors in which emf is induced.
However, the emf
induced in the armature of the dc generator is of an alternating nature.
Therefore, to convert this alternating emf into direct emf, a rotating
mechanical rectifier is used which is called a commutator. In a dc
generator, the commutator is one of the crucial parts.
Now, let us discuss
the working principle of a dc generator.
Working Principle of DC Generator
The operating principle of the dc generator is based on Faraday’s law of electromagnetic induction. According to this law, whenever there is a change in the magnetic flux linkage of a coil, an emf is induced in the coil. The magnitude of this induced emf is given by,
Where, N
is the number of turns in the coil, and Ï•
is the magnetic flux linked to the coil.
In a dc
generator, the magnetic flux is stationary and the armature rotates. Therefore,
the induced emf in the armature of the dc generator is called dynamically
induced emf.
EMF Equation of DC Generator
Now, let us
derive the equation of the emf generated in the armature of a dc generator.
When the armature
coil of the dc generator is rotated by a prime mover (mechanical energy input),
there is a change in the flux linkage of the coil.
If Ï• is the magnetic flux per pole and P is the
total number of poles in the generator. Then, the magnetic flux cut by one
armature conductor in one revolution of the armature is given by,
The time taken by the
armature to complete one revolution is,
Where n is the
speed of armature rotation in RPM.
According to
Faraday’s law of electromagnetic induction, the emf induced per conductor is
given by,
`\E_("per cond.")=(dϕ)/dt`
`\⇒E_("per cond.")=(PÏ•)/((60⁄n) )`
`\⇒E_("per cond.")=(PÏ•n)/60`
If in the
armature of the generator, Z is the total armature conductors, and A
is the number of parallel paths in the armature coil. Therefore, the number of
conductors in series per parallel path is equal to Z/A.
Hence, the total
emf induced in the armature of the dc generator is given by,
E = EMF induced
per conductor × Number of
conductors in series per parallel path
Thus, the emf
equation of the dc generator is,
Also,
For wave winding
of the armature, A = 2, and for lap winding of the armature, A = P.
From the emf
equation of the dc generator, it is clear that the induced emf in the dc
generator is directly proportional to the flux per pole and the speed of
armature rotation.
Direction of Induced EMF in DC Generator
The direction of
the dynamically induced emf in the armature of a dc generator is given by Fleming’s
Right-Hand Rule (FRHR).
Fleming’s right-hand rule states that if the thumb, forefinger, and middle finger of the right hand
are kept mutually perpendicular to each other. If the forefinger points to the
direction of magnetic flux, the thumb points to the direction of motion of the
armature conductor, then the middle finger will point to the direction of the
induced emf in the armature conductor.
The graphical
representation of Fleming’s right-hand rule is illustrated in the following
figure.
Hence, this is all about the working principle of the dc generator. In conclusion, the operation of a dc generator is based on Faraday’s law of electromagnetic induction. The emf induced in the dc generator primarily depends upon the generator construction, speed of armature rotation, and magnetic flux per pole.
