According to the periodic table carbon lies in the list of
semiconductor having valency of 4 thus semiconductors have
the property that with increase in temp. their resistance
decreases. Thus when carbon brushes rub against the commutator
due to friction their temp. increases and resistance falls.
Thus they are used for collection of current in DC machines.
In AC systems slip rings are used.
i wanna know that star point in transformer becomes as a
neutral on secondary side now tell me that how is that
possible?because if joit the all three winding ends with
each other it can b short circuited.dut it doesn't.WHY?pls
Answer me in brief.thanks alot