AC and DC Drives: Preventive Maintenance

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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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AC and DC Drives: Spare Parts

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