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If your plant makes extensive use of AC or
DC drives, it pays to perform regular (scheduled) preventive maintenance
on all drives and controllers. Preventive Maintenance can identify problem
areas of your systems and quite possibly some minor adjustments and upgrades
could prevent major problems and downtime in the future. Properly-trained
technicians will attempt to spot potential problems, and recommend corrective
action before a failure causes unscheduled and costly downtime. Some preventive
maintenance may be done while the equipment is running. Other types of
preventive maintenance requires that the drive be shut down with a proper
lockout-tagout.
During a PM technicians may:
- CLEAN THE DRIVE EQUIPMENT
Dust and other foreign material can create cooling problems, hide damaged
components, cause corrosion, and cause arcing and other damage.
- CHECK MOTOR RESISTANCE AND CONNECTIONS
Motors often exhibit changes in resistance prior to failing.
- VERIFY ALL POWER CONNECTIONS
Power connections can loosen over time due to vibration, and heat related
expansion and contraction. Loose power connections can cause fuse blowing,
breaker tripping, damage to terminal strips, insulation failure and ground faults.
- VERIFY POWER SUPPLIES FOR TOLERANCE
Power supplies can drift out of tolerance due to electronic problems
such as faulty electrolytic caps. These will eventually cause complete
shutdown.
- OBSERVE RELEVANT WAVEFORMS FOR BEST OPERATION
The tech may typically look at the supplies, at the output waveforms,
at the reference signals, and at feedback signals. This often uncovers
otherwise hidden problems.
- VERIFY SIGNAL WIRING, SHIELDING PROPERLY TERMINATED AND TIGHT CONNECTIONS
Improper shielding can cause erratic and intermittent behavior of drive
equipment, and loose signal wiring is a primary cause of drive equipment
downtimes.
AC/DC Drive Preventive Maintenance may also be farmed out
to external contractors. With this service, the contractor may included
a checklist of measurements taken:
DC System Data
- Drive
- Speed Reference
- Armature Voltage
- Armature Amps
- Field Voltage
- Field Amps
- Tachometer Voltage
- Motor R.P.M.
- Oscilloscope test
AC System Data
- Drive
- Speed Reference
- Motor Voltage
- Motor Amps
- Tachometer Voltage
- Motor R.P.M.
- Oscilloscope test
The contracted service will usually check wiring, motors,
blowers and overload circuits. Also they may interview operators to see
if there is any tweaking that may be needed to enhance systems operations.
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