Aeronautical Engineering Interview Question:

Rotation of dc shunt motor is revers by using 2
methods,which method is best and why?

Submitted by: Administrator

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.
Submitted by: Administrator