What is the Principle of DC Generator?

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,

`\e=N (dϕ)/dt`

Where, N is the number of turns in the coil, and ϕ 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 ϕ 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,

`\dϕ=Pϕ`

The time taken by the armature to complete one revolution is,

`\dt=60/n`

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.")=(Pϕ)/((60⁄n) )`

`\⇒E_("per cond.")=(Pϕn)/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

`\∴E=(Pϕn)/60×Z/A`

Thus, the emf equation of the dc generator is,

`\E=(nPϕZ)/60A`

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.