What is the function of carbon brushes in dc machine?

Answer 1

The carbon (graphite) brushes in a generator are used to connect external circuits in the generator to the rotor through the commutator. But you want to know what that means, right? Darn it, we always see these "trick" questions here. Okay, this is the scoop. The rotor in a generator is (usually) a group of windings. These are coils of wire. But they need to be connected to the "outside" or non-moving parts. Each coil has two ends, and these ends are connected to copper segments (sometimes called "lands") on the commutator. The segments are all in a ring around the end of the rotor, and the brush or brush sets ride on them. The other end of the brush(s) is(are) connected to wires to electrically connect them to appropriate places in the non-moving parts of the generator. The brush is conductive (naturally), and it is soft enough to provide a good "wear point" against the copper segments. The brushes do most of the "wearing away" in this application, and it is a fairly easy and straight forward evolution to replace them. In the motors of power tools, some of the units have a way to access the brush holder without taking the housing apart. Particularly the older ones. Anyway, it is said that a picture is worth a thousand words. Use the link below and take a look at the pictures. It's all there.

Answer 2

The carbon brush conducts current from the moving slip rings of the generator to the output lines. As the mechanical energy applied to the generator spins the coils in relation to the magnets surrounding them, electrical current is produced in the copper wires. The brushes conduct this current from where it is generated to where it is needed.

Answer 3

Carbon brushes are electromechanical conducting devices that connect to moving parts to provide an electric current. They are typically used in motors, generators and alternators. Many carbon brush uses exist, but the three basic uses are in household applications that run on alternating current (AC), automotive applications that run on direct current (DC) and industrial applications that run on both AC and DC.

Answer 4

Carbon brushes are there to keep the electrical contact with copper stripes while the armature is in motion.

A current should run through the winding for the armature to rotate (move) within the stator's electromagnetic field. But if it was assembled by soldering the supply inputs to the armature copper stripes, when it rotates the connecting wires will be tangled. To avoid this two carbon brushes are used to maintain the electrical contact while the armature is rotating.

Answer 5

used to pass the generated current from commutator to external circuit

In an AC generator, these are used to get excitation current onto the sliprings to regulate your generated output voltage and energise the rotor poles.

Answer 6

because if we use metallic brush then due to heating the effective resistance increase and voltage drop across the brush is much more but in carbon brush as the temperature increase then resistance is decrease.

Answer 7

The carbon brushes are spring loaded pads of carbon that press against the commutator. The commutator is at the ends of the rotating coil in a DC motor or DC generator. The pads connect the rotating coil to the battery source (for a motor) or the electrical load using the power supplied by the DC generator.

Answer 8

it collects the current from armature winding.