5/29/13 Gulf Electroquip - GE 752 Drilling Motors, AC Generators, Motor Blowers, Bug Blowers, Spark Arrestors
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AC & DC MOTORS 500HP+Large Motors Industrial, Marineand Commercial
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BRUSH/COMMUTATOR WEAR GUIDECommutator Appearance Guide
In addition to the physical appearance of the surface of the commutator, the skin or patina (film) is of equal importance for the good runningof the carbon brushes. Each carbon brush builds a characteristic patina (film) which is affected by operating and ambient conditions. Thepatina (film) consists mainly of copper oxides, graphite deposits and absorbed water, and its appearance is of importance for theassessment of the running behavior of the commutation set. The following pictures are used by carbon brush manufacturers and users ofbrushes as a guide to assist in judging the operation of carbon brushes.
LIGHT FILM: Indicates good brushperformance. Light load, lowhumidity, brush grades with lowfilming rates, or film reducingcontamination can cause lightercolor.
MEDIUM FILM: Is the idealcommutator condition for maximumbrush and commutator life.
HEAVY FILM: Results from highload, light humidity or heavy filmingrate grades. Colors not in the browntones indicate contaminationresulting in high friction and highresistance.
STREAKING: Results from metaltransfer to the brush face. Light loadsand/or light spring pressure are themost common causes.Contamination can also be acontributing factor.
THREADING: Is a furtherdevelopment of the streakingcondition as the metal transferredbecomes work hardened andmachines into the commutatorsurface. This condition can beavoided by increased loads andincreased spring pressure.
GROOVING: May result from anoverly abrasive brush grade. Themore common cause is poorelectrical contact resulting in arcingand the electrical machining of thecommutator surface. Increasedspring pressure reduces thiselectrical wear.
COPPER DRAG: Develops as thecommutator surface becomesoverheated and softened. Vibrationor an abrasive grade causes thecopper to be pulled across the slots.Increased spring pressure willreduce commutator temperature.
BAR EDGE BURNING: Results frompoor commutation. Check 1.) that thebrush grade has adequate voltagedrop, 2.) that the brushes areproperly set on neutral, and 3.) thatthe interpole strength is correct.
SLOT BAR MARKING: Results froma fault in the armature windings. Thepattern relates to the number ofconductors per slot.
Carbon Brush Performance Assessment
Notice the appearance of the brush sliding face. The following pictures show typical brush sliding faces. For easy identification, we suggestyou use the symbols S1, S3 etc. S1, S3 and S5 are satisfactory sliding faces, indicating that there are no mechanical or electrical problems.Depending on the carbon material, the sliding surface appears dense or porous, and shiny, dull or matte. If there is dust in the circulatingair, fine hairlining may occur, as shown in S5.
S1Normal operation
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5/29/13 Gulf Electroquip - GE 752 Drilling Motors, AC Generators, Motor Blowers, Bug Blowers, Spark Arrestors
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S1Dense, shining sliding face
S3Slight porous sliding face
Normal operation
S5Fine hairlining
Normal operation, slight dust influence
S7Hairlining
CAUSES:Underload, influence of dust, oil, orgrease, weak spring pressure
S9Tracking with hairlining and grooves
CAUSES:Like S7, but stronger
S11Ghostmarks, difficult commutation
CAUSES:Commutation problems, e.g., false orincorrect position of the neutral zone orinterpole
S13Burning edge of the leaving or trailing edge
CAUSES:Difficult commutation, heavy sparking,interruption of contact due to out of roundof commutator or insufficient brush holderspring pressure
S15Eroded brush face
CAUSES:Electrical overload, interruption of contact
S17Lamination of sliding face
CAUSES:Burned segments of the sliding face,caused by a winding fault giving voltagesurge during commutation
S19Double facing here for a twin brush
CAUSES:Tilting of the brush in dual directionmachine
S21 CAUSES:
5/29/13 Gulf Electroquip - GE 752 Drilling Motors, AC Generators, Motor Blowers, Bug Blowers, Spark Arrestors
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S21Copper nests
CAUSES:Pick up of copper particles, often followingcopper drag
S23Broken edges
CAUSES:High raised lamination, commutatorseriously out of round, brush chatter bylow load and idle running
Got Wear?
Are you experiencing similar symptoms of brush or commutator damage? If possible, you may take a photo of the damage and email usthe image. This will help us to diagnose the cause and prescribe the solution.
Information courtesy of Helwig Carbon Products www.helwigcp.com
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