Sage-Tips

What is the purpose of the brushes in a DC generator?

In dc motors, the carbon brush makes sure the commutation process remains free from sparks. This contact is a sliding contact capable of transmitting electric current from static to the rotating part of a generator or electric motor. A single or several carbon blocks composes a brush.

Where must the brushes of a DC machine be placed and why?

The brushes of a DC machine should be placed on the commutator in the polar axis. However, they should be given a slight shift and placed on the magnetic neutral axis to reduce the effect of armature reaction.

Where will you place the brushes in a DC?

In a DC machine, the carbon brushes are always placed at the magnetic neutral axis. In no load condition, the magnetic neutral axis coincides with the geometrical neutral axis.

What are brushes used for?

It is used for cleaning, grooming hair, make up, painting, surface finishing and for many other purposes. It is one of the most basic and versatile tools in use today, and the average household may contain several dozen varieties.

How do brushes work on a DC motor?

The brushes make physical contact with the commutator. When a DC voltage is applied to the brushes, that voltage is transferred into the commutator which, in turn, powers the windings. This electrical input generates a magnetic field around the armature.

What is the neutral brush position in a DC motor?

zero
Leave the brushes at the position where the induced voltage is zero. This is the neutral point of your DC Motor/Generator. Each time you use the DC Motor/Generator the brushes should be set at the neutral position.

What is the use of brushes in DC machines Mcq?

What is the use of brushes in DC machines? Explanation: Brushes are another important part in the construction of DC machine. They are connected in the lower end of the machine to allow the current flow between the moving parts and stationary wires.

What is MNA and GNA in DC machine?

The geometrical neutral axis (GNA) is the axis that bisects the angle between the centre line of adjacent poles. The magnetic neutral axis (MNA) is the axis drawn perpendicular to the mean direction of the flux passing through the centre of the armature.

Why should brushes used in DC machines be spring loaded?

These brushes must be held against the rotating commutator, and the material eventually wears away and must be replaced. The spring pushes the brush against the commutator, providing good electrical contact as the material slowly wears away.

What is the function of a carbon brush in a generator?

Carbon Brushes are used collect the current due to the induced emf from the armature coils in a DC Generator, as all of us know. When a brush is at any particular commutator segment, it shorts out that particular coil and draws current from the rest of the coils.

Why brushes are always placed along the MNA axis?

Brushes are always placed along the MNA because reversal of current in the armature conductors takes place along this axis. GNA (Geometrical Neutral Axis) may be defined as the axis which is perpendicular to the stator field axis.

How to determine the exact position of the MNA of a generator?

So, due to armature reaction, it is hard to determine the exact position of the MNA For a loaded dc generator, MNA will be shifted in the direction of the rotation. On the other hand, for a loaded dc motor, MNA will be shifted in the direction opposite to that of the rotation.

How does a brush draw current from a coil?

When a brush is at any particular commutator segment, it shorts out that particular coil and draws current from the rest of the coils. If the brush is not exactly at the particular segment, say one half is in one segment and other half is in a different one, then it draws current in that proportion.