Relation between brush contact losses & current in d.c. Machines

Q.  The brush contact losses in a d.c. Machine is
- Published on 19 Oct 15

a. Inversely proportional to the square of current
b. Directly proportional to the square of current
c. Inversely proportional to the current
d. Directly proportional to the current

ANSWER: Directly proportional to the current

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    Discussion

  • Jhon Smith   -Posted on 11 Oct 18
    Brush losses are the losses taking place between the commutator and the carbon brushes. It is the power loss at the brush contact point. The brush drop depends upon the brush contact voltage drop and the armature current Ia. It is given by the equation shown below.

    P = V*Ia

    The voltage drop occurring over a large range of armature currents, across a set of brushes is approximately constant If the value of brush voltage drop is not given than it is usually assumed to be about 2 volts. Thus, the brush drop loss is taken as 2Ia.

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