(ET) Reversing Motor

["Rhett T. George" <rtg ee duke edu>]

 - Greetings -

Allan has asked about compensating field windings.  Let's review the 
fields that may be found in a wound-field, D-C, brush-type machine.
There may be a shunt field or a series field, giving the definition
to shunt-wound motor and series-wound motor.  If the motor has both
shunt and series and they add to produce the total field, it is a
cumnulatively-compound motor.  If the series field subtracts from 
the shunt field, it is a differentially-compound motor.  [This one
may not be very stable over a wide torque range.]  The shunt and
the series fields are wound in the same locations in the motor.

Interpoles and/or compensating windings are wound 90 magnetic degrees
away from the main poles.  They are used to keep the reaction field
due to current flowing in the armature winding from shifting the total
field away from the main poles.  This reaction field is negated as 
much as possible by armature current flowing in the compensating/
interpole windings.  Compensating windings are put inot the faces of 
the main poles.  Interpoles are in between the main field poles.

Sorry, I do not know of a sure way of determining the presence of 
compounding or compensation in a simple way without looking inside,
presuming that such info does not come from the manufacturer.

Hope this helps.

                                        Rhett George