Answer / marimuthu jayaseelan

The direction of rotation of a DC shunt motor can be
reversed by changing the polarity of either the armature
coil or the field coil.

you can reverse the direction by simply reversing the
armature leads. The same can be done with a shunt motor and
a compound motor,

You also can reverse direction by reversing field leads;
however, you run the risk of changing a cumulative compound
motor, which is inherently stable, into a differential
compound motor, which is somewhat unstable.

Answer / nithi

reversing the armature terminal is better & applied in
practice.this is becoz of the following drawbacks in field
reversing method.
* high voltage build-up during reversing the field terminal
which is high enough to puncture the insulation of field
coil.

* high flash-over will occur.

* during reversal, the armature current should be limited
to the rated value,otherwise it will draw twice the time of
starting current.we can insert the external resistance to
limit the current while reversing the armature
terminal.whereas,in field reversal we cannot give any
provision to limit armature over current.

Answer / vijayakrishna

reversing the field terminl is not do in prctice,why????

how the vfd is working ?

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