DRIVES & CONTROLS
as tantalum capacitors, use a solid
electrolyte and do not wear out, although
random failure or overvoltage damage are
still possible. However, many inverters use
capacitors with a non-solid electrolyte.
Evaporation of the electrolyte in these
‘wet’ capacitors means that, even under
ideal operating conditions, they have
limited lifetime, and this can be greatly
reduced when operated at elevated
temperatures.
Many inverter breakdowns are
caused by failing capacitors. With proper
maintenance, that can usually be avoided.
Failures may be caused by overheating
due to poor installation, failure of cooling
fans or heat sinks becoming clogged with
dust. If wet capacitors are not changed
within their recommended service period,
they may also simply wear out. Insu cient
power quality can also cause sudden
failure of capacitors, so it is important
that power supplies and fuses are able
to prevent overvoltage conditions from
reaching the inverter.
Incorrectly-speci ed cables, or poor
installation into terminals, is another
common cause of inverter failures. Wires
can become loose, resulting in circuit
breaks; undersized cables can burn out.
Inverters induce electromechanical
“Like most electronic parts, frequency
inverters are a ected by heat and should,
therefore, be installed in a cool and well
ventilated location”
vibrations, and these can lead to friction,
heat, wear and loosening.
As with any electrical device, ingress of
contaminants such as water or dust can
also be a cause of failure.
INSTALLATION AND INSPECTION
Like most electronic parts, frequency
inverters are a ected by heat and should,
therefore, be installed in a cool and well
ventilated location. Dust and other
environmental contaminants should also
be avoided when siting the inverter. It
is also vital that the cables are correctly
speci ed for the required currents and
installed into terminals correctly. Regular
inspections should then be carried out to
ensure that the operating environment is
being correctly maintained and to check
the performance of the inverter.
Environmental checks should look for
any build-up of dust, signs of humidity or
dripping water, and temperature. Checks
for water should include prior traces. The
temperature should be checked both in
the room and inside the inverter cabinet.
The inverter should also be checked
for vibration and noise during operation.
A simple touch-check on the cabinet can
be su cient. If there is any noticeable
vibration, the individual components
should be checked, such as transformers
and fans.
Ideally, operational data should also
be checked. This might include the load
current, voltage and recti er temperature.
At regular intervals, a more in-depth
inspection should be carried out involving
physical checks on components and
cleaning. These will require the power to
be disconnected before they are carried
out. Where applicable, drive parameter
settings should rst be backed up to the
control panel and the service engineer’s
laptop.
Wires and terminals should be visually
inspected for damage and terminal screws
should be checked and tightened if they
are loose, using a torque wrench where
applicable. Insulation tests may also need
to be carried out.
Dust and any other debris should be
cleaned and vacuumed from within the
cabinet and its surroundings. This may
also involve removing cooling fans to
vacuum inside the heat sink. Any air lters
should be cleaned or changed as required.
Components such as cooling fans,
smoothing capacitors and fuses should be
replaced if they show signs of damage or if
they have reached a standard replacement
period, typically of several years.
VOICE OF THE SERVICE PROVIDER
Inverter Drive Systems (IDS) is an approved value provider
for ABB inverters and has been an ABB partner for over 20
years. Blaise Ford, managing director, says: “ABB inverters
are fundamentally reliable electronic devices, especially if
installed correctly and situated in the correct environment.
Inverters need to be kept cool, dry and away from dust and
vibration. If this is done, then an inverter can run for over 20
years.
“This reliability, however, hides a problem. Because ABB
inverters are so reliable, maintenance is often neglected,
which means that some inverters do fail prematurely. ABB
o ers a routine maintenance schedule (available via
www.is.gd/sepexe) for each model. In general, the cooling
fans (the only moving part on an inverter) need replacing
every three to ve years and the capacitors need to be
replaced at around nine years.
“If this is done to schedule, then the inverter will have
a signi cantly longer life. If the inverter is controlling a
critical application, it should be inspected, checked, tested
and cleaned more frequently, usually on an annual basis. If
an inverter fails, there will clearly be the cost of repair or
replacement, but very often it is the downtime that costs
signi cantly more.”
Blaise con des that IDS tends to advise the following
when it comes to repairing inverters: “If it is a small inverter,
replace it. If the inverter is large, we would attend the site to
x it; for inverters on a critical application, we replace it with
a hire inverter while the failed unit is being repaired. But by
far and away the most cost-e ective method is to ensure
the inverters are serviced regularly and maintained.”
IDS speci es, supplies, installs, commissions, repairs,
hires and services inverters with a 24/7 emergency service.
Winter 2021 www.operationsengineer.org.uk 59
/sepexe)
/www.operationsengineer.org.uk