Other Maintenance Operations; Maintenance Of Slip Rings And Brush Gear; Care Of Slip Rings; Standstill Period - ABB AMA Series Manual

7.6.7 Other maintenance operations

***Following chapters for rotor type: Slip rings

7.7 Maintenance of slip rings and brush gear

7.7.1 Care of slip rings

7.7.1.1 Standstill period

7.7.1.2 Wear

7.7.2 Care of brush gear

3BFP 000 050 R0101 REV E
Usually, ABB-made winding are trouble free and in addition to periodical monitoring they
require only occasional cleaning and drying as described above. If extraordinary circumstances
occur and other maintenance is required, it is best to acquire professional help. The ABB After
Sales organization is eager to assist in questions regarding maintenance of electrical machine
winding, for contact information see Chapter 9.1.5 After Sales contact information.
A machine with slip rings will function properly only if the slip rings and the brush gear are
inspected and subjected to maintenance regularly.
The sliding surfaces of the slip rings should be kept smooth and clean. The slip rings should be
inspected and the surfaces of the insulation cleaned. Wearing of brushes produces coal dust that
easily builds up conducting bridges over the insulation surfaces. Electric discharges may take
place between slip rings and a flash might appear, leading to interruption in operation of the
machine. The contact surface of slip rings forms a patina, or skin, together with the brushes. The
patina can be seen as a colored surface, it is normal behavior and in many cases a benefit to
brush operation, so the patina is not be considered as a fault in operation and should not be
cleared away.
When a longer standstill period for the machine begins, the brushes should be lifted up. During
transport, storage, installation or longer interruptions, the sliding surfaces of the slip-rings might
be tarnished or covered with dirt, etc. Before restarting the machine, the sliding surfaces should
be inspected and cleaned.
In case that the slip rings have become coarse or uneven, they should be ground or turned on a
lathe. The asymmetry of the whole ring diameter should be less than 1.0 mm, but for a short
distance, a value of maximum 0.2 mm is allowed. In case of the slip rings are worn out or badly
burned, new rings should be assembled.
Measure the eccentricity of the slip-rings using a dial indicator gage. Let the measuring point lie
on the slip ring or on the outer surface of a brush. The highest and lowest values during one turn
of the shaft are recorded. The difference of the maximum and minimum values should be no
more than 1.0 mm and locally no more than 0.2 mm. The difference of the outer diameters of the
two slip rings shall preferably not be more than 2 mm.
The brush gear should be inspected and the surfaces of the insulation cleaned.
Wearing of brushes produces coal dust that easily builds up conducting bridges over the
insulation surfaces. The coal dust is best removed by vacuum cleaning brush gear.
Manual for Induction Motors and Generators
Maintenance - 85