how does a commutator work in a DC generator?

Answer 1

Principle:
A commutator is an electrical switch that periodically reverses the current in an electric motor or electrical generator. Commutators enable motors to run on, and generators to produce, direct current instead of alternating current. More generally, commutators can be used to convert between direct and alternating current.

Construction and working:
It typically consists of a set of copper contacts, fixed around the circumference of the rotating part of the machine (the rotor), and a set of spring-loaded carbon brushes fixed to the stationary part of the machine (the stator) that complete the electrical circuit from the rotor's windings to the outside of the machine. Friction between the copper contacts and the brushes eventually causes wear to both surfaces. The carbon brushes, being made of a softer material, wear faster and are designed to be replaced easily without dismantling the machine. The copper contacts are usually inaccessible and, on small motors, are not designed to be repaired. On large motors the commutator may be re-surfaced with abrasives. Each segment of the commutator is insulated from the adjacent segments; a large motor may contain hundreds of segments
As the motor rotates, the commutator contacts will turn through 180° and the current flowing in the winding will reverse. However the fixed magnetic field that the rotor is in has also switched polarity relative to the rotor winding, and so rotation continues in the same direction.

Answer 2

Generator Commutator

Answer 3

You are speaking about the nearly imponderable. Truly, any discussion of sparking at commutators will needs be a particle physics discussion and quite frankly Nobody all there is to know about THAT. But the simple answers are the old ones. You don't have to understand what is arcing to stop it. Increase the spring tension is likely a one thing an engineer can do ~ this stops or limits bounce and increase contact area. But this wears out parts faster and decreases efficiency if taken to extremes. Decrease the relative speed between the commutator and brush is a like solution ~ to decrease bounce and increase contact. This increases the size of the parts, and increases initial cost of the equipment as well as storage overheads of both parts and machines in use. But it works to lower sparking somewhat. One can increase the number of brushes in some cases. One can increase the size or width of brushes in some cases. In some cases it's the material chosen for the commutator itself that causes problems ~ it can be either to hard or too soft. Brushes likewise can be too hard or too soft ~ and both commutator and brushes can change in hardness whilst in use especially in harsh chemical environs. So in some cases sealing off the brushes does wonders. But in the old days neither of these solutions would help remove the "itch" cause by being near DC generators and motors, especially in the confines of submarines. No, they weren't actually screening for VD in Das Boat. It was the particle accumulation on ones hair ~ as well as burning from X ray emissions. It would drive some men actually nuts. The fix proved quite simple: carbon. Large carbon resistors would absorb and or stop the creation of these particles. By screening out (dampening) the higher frequency waves, the carbon filters stop arcing in the unuseful frequencies of the electromagnetic spectrum. Nobody knows why. There is some question as to what these resistors actually do, and what the particles actually are. And, if you are going into the rare metal casting feild... well here's a hint: NAW, I'm not going to tell ya. It would take all the fun out of getting a turbine not to crack... And the defense departments I've worked for (but not been paid buy ~ selfish buggers) would shoot me again.

Answer 4

the same way as in an ac generator, but you would then have a rectifier pack to convert to dc.