ABB DC Machines DMI, Инструкция по эксплуатации и техническому обслуживанию

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1
Poor brush
contact
As mentioned, poor brush contact can cause
sparking and produce burn marks on the
commutator contact surface. The following are
the most likely causes:
Vibrations
Vibrations have a decisive influence on brush
contact. For example, unbalanced couplings or
fans with dirt deposits may lead to imbalance
error. Other causes are poor alignment of the
DC machines and vibration excitation via the
foundation. If the brushes exhibit wedging ef-
fect (lateral wear), this indicates inadmissible
vibrations.
Brushes and commutation
Low load
If the machine is permanently operated at low
load, it is advisable to reduce the number of
brushes. As the ideal current load depends on
the brush grade, ABB should be consulted in
such cases.
Humidity
Humidity is an important factor for the formation
of the patina. If the air is dry and the moisture
content less than 3 g/m
3
, normally no patina
can form. If the humidity exceeds 15 g/m 3 , the
patina becomes too thick.
Corrosive environment
Corrosive gases in the surroundings result in a
deterioration of contact between brushes and
commutator.
The problem can show up in different ways, e.g.
as sparking, high brush wear or scratched
commutator.
The gases that give the greatest problem and
should be avoided are sulphur dioxide, hydro-
gen sulphide, chlorine and ammonia.
These gases, in sufficient concentration, attack
the patina, break through it and attack the com-
mutator.
Caution
If the measured vibration level exceeds 4.5 mm/s
r.m.s. , appropriate measures should be taken to
reduce the level of vibrations.
Jammed brushes or pressure fingers
If one of the brushes does not move freely or
if it is jammed, sparking will normally not be
severe. However, if several brushes are affect-
ed, the remaining ones will be overloaded and
sparking becomes dangerous.
Worn brushes
If worn brushes are not replaced in time, the
commutator contact surface will be damaged
by the brush lead.
Caution
Do not let the brush wear down so much that the
flex attachment embedded in the brush comes
into contact with the rotating surface. This can
have serious consequences.
Oil-contaminated surfaces
The oil forms an insulating film and the current
is transferred by small arcs. In the process the
film is burned, leaving black spots on the
commutator contact surface.
Scratched contact surface
Cement dust or similar hard particles can
scratch the commutator surface. If construction
work is to be done near the machine, it must be
specially protected.