Answer / shekar

MNA stands for Magnetic nuetral axis. It is an imaginary
line perpendicular to magnetic lines and passing exactly at
the centre of magnetic field. The emf induced at MNA will
be zero as the conductors will not cut any flux at MNA. At
MNA the conductors will be parallel to magnetic lines.
Hence brushes are located at MNA to collect current. During
armature reaction the MNA shifts in the direction of
rotation of generator. So the brushes should be shifted to
new position of MNA to avoid sparking.

Answer / santosh!

well MNA stands for MAGNETIC NEUTRAL AXIS! and it is very
important as it is the axis for housing brushes where the
arise of sparks is zero! due to armature reaction brushes
tends to move in the direction of rotation, to avoid this
compensation techniques are used!

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