Working principle of DC generator

A DC generator converts mechanical energy into electrical energy using Faraday's law of electromagnetic induction: an emf is induced in a conductor whenever it cuts magnetic flux. The commutator then makes the output direct current.

Working with a single-loop model

            N pole                     S pole
          +---------+               +---------+
          |         |   a ---->     |         |
          |         |  +------+     |         |
          |         |  |      | rot.|         |
          |         |  +------+     |         |
          +---------+   b <----     +---------+
                          |    |
                       [seg1][seg2]  split-ring commutator
                         B1     B2   brushes
                          |_[LOAD]_|

1. A single loop with coil sides a and b is rotated by a prime mover between the N and S poles.
2. Sides a and b cut the flux, so an emf e = B l v sin θ is induced in them. Its direction follows Fleming's right-hand rule.
3. In the first half turn, side a moves under N and side b under S. Current flows out through brush B1 into the load.
4. After half a turn, the sides change places, so the emf in the loop reverses. But the commutator segments also exchange brushes at that instant, so brush B1 always stays connected to the conductor under the N pole.
5. The current in the external circuit therefore keeps one direction (pulsating DC). With many coils and many commutator segments, the output becomes almost steady DC.

Output voltage

E = PΦZN / (60A) volts

Main parts used

• Yoke and poles with field winding: produce the flux.
• Armature core with winding: where the emf is induced.
• Commutator and brushes: rectify and collect the current.