DRIVES & CONTROLS
fMreaiqnutaeinnincgy inverters
Failure modes, inspection and maintenance, diagnostics and
troubleshooting, as well as the general checks for non-specialists: all are
covered in this overview article
FBy Jody Muelaner
requency inverters are critical
components of many drive
systems. A frequency inverter
changes the output voltage
frequency and magnitude to
control the speed, power, and torque
of an induction motor. This is often
carried out under closed-loop control
to respond to changing load conditions.
They are commonly used in applications
including industrial drives, pumps and air
conditioners.
Without any maintenance, inverters
will inevitably fail over time due to the
limited lifetime of electrolytic capacitors,
which must be periodically replaced. If the
inverter is allowed to overheat, electrolyte
evaporation will accelerate the wear of
these components and inverters may fail
prematurely. Other common causes of
failure include inappropriate or poorlyinstalled
cabling, blown fuses, voltage
uctuations, and vibration. As with any
industrial equipment, a preventative
maintenance schedule is advisable. This
not only prolongs the life of inverters, but
more importantly it avoids unplanned
downtime which results in additional costs
such as lost production.
Electrolytic capacitors work by using
an anode which forms an oxide layer; this
oxide then acts as the dielectric to store
the charge. The oxide is covered by a lm
of electrolyte, acting as the cathode.
Electrolytic capacitors are sensitive
to overvoltage conditions and can be
destroyed by an overvoltage of just one
Volt. Failure can result in re or explosion.
‘Dry’ electrolytic capacitors, such
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