PREVENTIVE MAINTENANCE
Put to the test Regular motor checks and inspections form a fundamental part of
predictive maintenance strategies
Although there are technical
By Steed Webzell
di erences between AC
and DC motors, su cient
commonalities exist
between them to indicate
their need for attention by maintenance
teams. “For both types of motor we
generally focus on the condition of
bearings and windings as key health
indicators,” explains Peter Wright, ABB
Motion Services quality & customer
experience manager. “Because windings
carry high currents and are subject to
heating and cooling cycles, their insulation
becomes a classic failure point for motors.
For bearings, problems are usually
mechanical, such as an unbalanced or
misaligned drivetrain, as well as under- or
over-lubrication.”
When focusing on DC motors, a good
sign of correct motor operational health is
brush wear and commutator patina.
“Rapidly wearing brushes can be an
indication of incorrectly-sized brush
gear,” says Wright. “Brushes can also be
damaged by electrical overloading or
under-loading, winding faults, and voltage
surges.”
It is important for motor inspection
activities to focus on the complete
drivetrain. This strategy will help to
pinpoint speci c problems, such as when
the motor is driving an unbalanced fan,
which can cause high levels of vibration
that ultimately lead to bearing failure.
“For this reason, traditional monitoring,
carried out during normal operation
with the motor running, relies largely on
measuring vibration and temperature,
although current and voltage in the
cables feeding the motor may also
be monitored,” says Wright. “It’s now
becoming more common and cost-
e ective to use wireless smart sensors to
gather this kind of data.
“They provide a cost-e ective way
of taking measurements on an hourly
basis, making it possible to spot trends
that might not be captured by monthly
route-based monitoring using handheld
equipment.”
SMART MOTORS
Unfortunately, an electric motor cannot
volunteer the data that indicates its
health, unlike a variable speed drive (VSD).
“That means we rely on smart sensors,
which combine the capability to monitor
vibration, temperature, acoustic signals
and magnetic elds, converting motors
into smart, wirelessly connected devices
that report their own health data,”
says Wright. “However, it’s not just the
collection of data that’s important, it’s
how we make use of it. When data is
analysed and processed by algorithms,
service experts can help customers make
better decisions. They can then draw on
the deep insights they gain into the status
and condition of their assets to take
timely action.”
Predictive maintenance based on
condition-based monitoring allows
engineers can plan and schedule any
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