57
Rev.12/31/97
Commutation is best when the commutator is perfectly smooth and
"seasoned" to a chocolate brown color. The commutators should not be
stoned or ground except when necessary to remove grooves or scoring, and
they should not be turned down in a lathe except when allowed to become
badly out of round or after commutators have been dismantled and rebuilt.
Excessive cutting or grinding should be avoided .
"seasoned" to a chocolate brown color. The commutators should not be
stoned or ground except when necessary to remove grooves or scoring, and
they should not be turned down in a lathe except when allowed to become
badly out of round or after commutators have been dismantled and rebuilt.
Excessive cutting or grinding should be avoided .
Cut barely enough to accomplish
the required result.
When stoning, use the finest grit that will serve the purpose and finish by
polishing with a canvas pad and rouge. Mica between bars must be
undercut after turning and after repeated stoning to keep within the 1/32-
inch depth mentioned above.
polishing with a canvas pad and rouge. Mica between bars must be
undercut after turning and after repeated stoning to keep within the 1/32-
inch depth mentioned above.
New brushes must be carefully fitted to the commutator to ensure good
contact. Place a strip of 00 sandpaper between the commutator and the
brushes with the sanded side against the brushes and draw the sandpaper
contact. Place a strip of 00 sandpaper between the commutator and the
brushes with the sanded side against the brushes and draw the sandpaper
back and forth until the brushes are hollowed to fit the commutator.
Increase the spring tension to its highest point to speed this preliminary
fitting, but the tension must be restored to its original position for the final
fitting. The correct operating pressure is about 2-1/2 pounds per square
fitting, but the tension must be restored to its original position for the final
fitting. The correct operating pressure is about 2-1/2 pounds per square
inch of brush surface area.
For the final fitting of the brushes, pull the sandpaper in one direction only.
When the brush holders are of the reaction (Baylis) type, the sandpaper
must be pulled against the direction of rotation. When the brush holders
are of the radial type, the sandpaper must be pulled in the direction of
rotation.
When the brush holders are of the reaction (Baylis) type, the sandpaper
must be pulled against the direction of rotation. When the brush holders
are of the radial type, the sandpaper must be pulled in the direction of
rotation.
Before starting the motor-generator after sanding the new brushes, be sure
to wipe all sand and carbon dust from the brushes, brush holders, and
commutator. See that each brush makes firm contact with the commutator
and is free in its holder. Clean and tighten all connections in the field
circuit. Clean the rheostat contact points and contact arm, and see that
they make firm contact.
to wipe all sand and carbon dust from the brushes, brush holders, and
commutator. See that each brush makes firm contact with the commutator
and is free in its holder. Clean and tighten all connections in the field
circuit. Clean the rheostat contact points and contact arm, and see that
they make firm contact.
B. Positioning Brushes of Diverter-Pole Generators
B. Positioning Brushes of Diverter-Pole Generators
For best commutation, brushes should be set so that the armature coils
short circuited by the brushes are under the influence of the diverter-pole
flux.
short circuited by the brushes are under the influence of the diverter-pole
flux.
Moving brushes in the direction of rotation may improve commutation but
may reduce compounding action of the diverter poles. Increased strength of
the diverter poles is then necessary to produce the same compounding
action. Increased strength of the diverter poles increases the flux change in
the poles and results in greater curvature of the voltage curve. Best results
may reduce compounding action of the diverter poles. Increased strength of
the diverter poles is then necessary to produce the same compounding
action. Increased strength of the diverter poles increases the flux change in
the poles and results in greater curvature of the voltage curve. Best results
are obtained when this curvature is at a minimum.
Brushes should be set as far back (against direction of rotation) as perfect